IMPROVING
SITE PRODUCTIVITY
INTHECONSTRUCTION
INDUSTRY
Compiled by ALAN HEAP
34823
International Labour Office
Geneva
Copyright © International Labour Organisation 1987
Publications of the International Labour Office enjoy copyright under Protocol 2
of the Universal Copyright Convention. Nevertheless, short excerpts from them
may be reproduced without authorisation, on condition that the source is
indicated. For rights of reproduction or translation, application should be made to
the Publications Branch (Rights and Permissions), International Labour Office,
CH-1211 Geneva 22, Switzerland. The International Labour Office welcomes
such applications.
ISBN 92-2-105694-5
First published 1987
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Printed ¡n Switzerland
POP
PREFACE
The International Labour Office has a continuing interest in the
development of the construction industry throughout the world.
Specifically, this interest stems from the dual role of
construction not only as a significant source of direct
employment but as a sector which contributes through its wide
range of operations and projects to the growth and development
of virtually all other economic sectors.
Since the output of the industry typically represents onehalf of gross capital formation and 3 to 8 per cent of gross
domestic product, the national benefits that can accrue from
improving the effectiveness of construction operations can be
very significant. At the level of the enterprise, the scope for
improved performance through higher productivity is also
substantial. Furthermore, those local construction businesses
which make themselves genuinely competitive are able to
secure a steady workload and offer continuous employment to a
properly trained labour forcé.
Improvements in productivity depend mostly upon initiatives
by numerous individual construction managers, struggling to
mobilise resources which are frequently inadequate and
inappropriate, and facing a formidable array of constraints and
difficulties. It is to them that this book is both addressed and
dedicated. As is inevitable in a publication addressed to an
international audience, some of the techniques and examples
may strike the reader as unrealistic. But since most readers will
be practical people, we believe that they will discriminate and
test what they read against the lessons taught by their own
experience. Used in this way, the book should equip the reader
to make his or her contribution to improved performance
through more effective working practices.
ACKNOWLEDGEMENTS
Most of the background research on which this book ¡s based
was carried out under projects financed by the Danish
International Development Agency (DANIDA), the Norwegian
Agency for Development (NORAD) and the Swedish
International Development Agency (SIDA). It draws heavily
upon, and can be regarded as a specialist companion volume
to, the ILO publication Introduction to work study, which has
become a basic reference work in this field.1
The original script was prepared by Alan Heap in
collaboration with the ILO Construction Management
Programme, and edited by the successive directors of the
Programme - Angus Austen and Derek Miles.
1
Vil
Introduction to work study, third (revised) edition, Geneva, ILO, 1979.
CONTENTS
P reface v
Acknowledgements vü
1. Introduction 1
Productivity and the standard of living 1
Productivity of the construction enterprise 3
Work study and the construction ¡ndustry 7
The techniques of work study 9
2. Method study 13
Basic procedures 13
Select the work to be studied 14
Obtain and record the facts 17
Examine the facts 29
Develop the new idea 31
Install the new method 32
Maintain the new method 33
Sitelayout 33
3. Work measurement 41
Uses and techniques 41
Time study equipment 43
Making the time study 46
Relaxation allowances 51
Derivation of standard times 54
Excavation and loading of soils by hand 61
Activity sampling 61
Feedback of output data 69
Using the output data 73
4. Work study - the general approach to some major construction
operations 77
Plant utilisation 77
Machine excavation 80
Concreting operations 81
Formwork manufacture, erection, removal, cleaning and salvaging 82
Steel reinforcement 83
Control of materials 86
IX
5. Motivation and incentives 91
Productivity of labour 91
The human factor 91
The competence of site management 91
Motivation of workers 92
Financial incentive schemes 94
Taskwork 100
Advantages and disadvantages of financial incentive schemes 101
Rules to be observed in operating financial incentive schemes 102
6. Organising for work study 103
Stages of a construction project 104
General management structure of the enterprise 104
Role of the work study engineer 105
Work study technicians 106
7. Practical examples 109
Múltiple activity chart - Pouring concrete upper floor slab 109
Gang balance 114
Sitelayout 117
Rated activity sampling 123
X
FIGURES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
XI
The management task 3
Work content of a construction project 4
Workstudy 9
Outline process chart 22
Flow process chart 23
Flowdiagram 23
Flow process chart for worker 24
String diagram 27
Site layout plan 38
Time study top sheet 45
Time study: Fixing precast wall units 55
Time study abstract sheet 56
Standard time summary sheet 57
Tabular recording of standard times 59
Graphic recording of standard times 60
Activity sampling record sheet 67
Activity sampling extract sheet 68
Daily work record sheet 71
Weekly work summary sheet 72
Weekly performance summary sheet 73
Stages of a construction project 103
General management structure of the enterprise 105
Múltiple activity chart 111
Múltiple activity chart: Altemative (a) 113
Múltiple activity chart: Altemative (b) 113
Layout of site for construction of radio transmitter station 118
Blank layout plan 119
Revised layout of site for construction of radio transmitter station 121
Rated activity sampling record sheet 122
Activity sampling extract sheet 123
Calculating the standard time 124
INTRODUCTION
1
productivity and the standard
of living
THE STANDARD OF LIVING
1
What is the connection between site productivity in the
construction industry and the standard of living? The former
may seem to be of merely technical interest to contract
managers and site foremen. The latter is of direct interest to all
of us, since it measures our capacity to provide ourselves and
our families with a wide variety of goods and services that we
need ¡n order to sustain and enjoy life. Some of these are
classified as prívate consumption, such as food, shelter and
clothing, while others are essential services provided by and for
the community, such as safe drinking water, sanitation,
transport, health and education.
Food, clothing and housing are generally things that
individuáis and families have to obtain for themselves. Health
care, security and education are usually provided by the State
or other public authorities, but even these are ultimately paid for
by the individual citizen in the form of taxes. Therefore everyone
needs to earn enough to pay a fair contribution to these
common services, as well as to support himself and his family.
There are two main ways of increasing the amount of goods
and services produced. One is to increase employment; the
other is to increase productivity. Efforts to increase employment
are very important, and should go hand in hand with efforts to
increase the productivity of those already employed, but it is
with the latter task that we are concerned here.
The greater the amount of goods and services an individual
is able to buy, the higher his or her standard of living will be.
One way of achieving a higher standard of living is by
increasing productivity. By increasing productivity people will
earn more. By increasing national productivity ¡n agriculture,
industry, health and security services and education, the goods
and services produced will be more abundant at a relatively
lower cost.
PRODUCTIVITY
This ¡s defined as the ratio of output to input, that ¡s the ratio of
the amount produced (the output) to the amount of any
resources used ¡n the course of production (the input). The
resources may be land, materials, machinery, tools or
manpower. The input is generally a combination of all of them.
Productivity increases if a greater output is achieved for the
same input, or if the same output is achieved for a smaller input.
An increase in production or output does not necessarily
indícate an increase in productivity. If input rises in direct
proportion to output, then productivity will stay the same. And if
input increases by a greater percentage than output, then a
higher output will be achieved at the expense of a reduction in
productivity.
For example, a team of two workers produces 20 concrete
blocks an hour. The productivity is 20H-2=10 blocks per workhour. Owing to demand it is found necessary to increase input.
The team is increased to three men who now produce 27 blocks
an hour. Thus the output has risen, but productivity has fallen to
27-=-3=9 blocks per work-hour. The operation is studied, and
using an improved method, three workers can now produce 39
blocks an hour. Thus, not only has production increased, but
productivity is upto 39-^3= 13 blocks per work-hour.
PRODUCTIVITY AND THE CONSTRUCTION
INDUSTRY
Building houses is entirely a construction activity, but
construction works are also needed in agriculture, industry,
education, health and other service industries. In many
countries, construction activities in one form or another account
for half the annual expenditure on capital goods.
Therefore an increase in the productivity of the construction
sector should not only raise the earnings and profits of those
working in that sector but also contribute to an improvement of
the productivity in other sectors, thereby improving general
standards of living.
2
WORK STUDY
This ¡s a series of techniques which can be used for the
systematic examination and investigaron of every aspect of
human work and the factors that affect efficiency and economy,
in order to bring about improvements. This manual will show
how work study can be used to improve productivity levéis in
construction work.
productivity of the construction
enterprise
~
THE MANAGEMENT TASK
To carry out any given construction project, an individual mix of
resources including land, buildings, materials, mechanical plant,
tools, equipment and manpower have to be mobilised. It is the
task of management to combine these resources to carry out
the project economically and expeditiously.
Figure 1. The management task
In larger enterprises a management team will share the
various specialist activities, such as site management at various
levéis, materials control, plant management, financial control
and so on, but in a small firm all the management activities
might be carried out by one person.
WORK CQNTENT OF A
CONSTRUCTION PROJECT
Experience has shown that there is always room for
improvement in construction project execution. The total time
taken is often well in excess of what it would have been it the
designs, specifications and methods of construction were
properly planned and prepared, and it site management had
implemented them effectively so that there had been no loss of
working time. This is illustrated below.
Figure 2.
Work content of a construction project
- TOTAL ACTUAL T I M E
—
• T O T A L WORK CONTENT-
BASIC WORK CONTENT
This is the absolute mínimum time in which the project or
operation can theoretically be completed. In practice this is
never achieved.
Unnecessary work ¡s added by defects in design and
specification, and by inefficient methods of construction. For
example, in design and specification it is caused by:
changing the design after work has started;
-
over-design, making project or component stronger or
more elabórate than need be;
lack of liaison between design and construction teams, e.g.
specifying precast units that are too heavy to be handled by
existing plant;
-
non-standardisation of components.
Inefficient methods such as the following can cause
unnecessary work:
-
use of unsuitable plant, equipment and tools;
bad layout and working conditions, involving double
handling of materials or unnecessary movements;
bad timing and sequence of operations.
Whereas the construction agency may not be able to do
anything about bad design and specification, inefficient
methods can generally be put right by good management.
INEFFECTIVETIME
This is time when workers and machines are standing idle.
Ineffective time may be due to extraneous reasons beyond the
control of management, or to the shortcomings of management
or labour.
(a) In tropical countries these extraneous reasons are generally
rainfall and flooding, excessive heat and dust storms. In
other countries they could include frost and snow. Other
reasons are materials and fuel shortages, and breakdown
of law and order.
Although these are beyond the control of management,
their effects can be lessened by anticipation and work
scheduling.
(b) Instances of the shortcomings of management are:
5
delays in providing necessary working drawings, or
setting out lines and levéis;
delays in delivery of materials and plant and equipment;
bad planning of work sequences, so that workers and
machines are idle, awaiting work;
-
unbalanced construction teams (e.g. lomes standing ¡dle
waiting to be filled);
-
failure to ensure proper maintenance of plant and
equipment, causing unnecessary stoppages;
-
failure to ensure safe working practices so that time is
lost and damage caused by accidents;
-
failure to motívate the workers.
(c) The shortcomings of labour could be -
taking time off without good cause, lateness, failing to
start work promptly, idleness or delibérate slowdown;
-
careless workmanship, requiring re-doing or resulting in
structural failure;
failure to observe safe working methods causing
accidents;
not maintaining and sharpening tools.
-
In general, ineffective time is more often due to causes
within the control of management rather than to the
shortcomings of workers.
REDUCING THE TOTAL WORK CONTENT
AND INEFFECTIVE TIME
The task of management is to organise and control all the
available resources in order to achieve máximum productivity that is to reduce the work contení to as near to basic as possible
and to elimínate ineffective time. Work study comprises a variety
of systematic techniques which can be applied to help reduce
this waste of time and effort.
WORKERS OR MACHINES?
One direct means of raising productivity is to replace manpower
by the purchase of modern high-capacity plant or equipment.
However, most developing countries are short of money and
have problems of high unemployment, so that to buy such
equipment may be neither possible ñor desirable. Furthermore,
due to lack of adequate maintenance procedures and a
shortage of spare parts, the benefits derived may be short-lived.
The cheapest and most effective way of raising productivity is
by better management.
6
work study and the construction
industry
~
DEVELOPMENT OF WORK STUDY
Work study is the study of methods of working ¡n order to find a
better way of carrying out various activities. Although the term
was first used ¡n the last century, the basic principies have been
practised since ancient times, in the building of the pyramids,
Román roads and aqueducts and castles and cathedrals, where
large-scale systems of equipment and manpower were used.
There is nothing new about the investigation and improvement
of working methods, and managers of outstanding ability have
always existed. What is new is the systematic disciplined
approach to the investigation of working methods and
problems, and to the development of solutions. By using these
systematic procedures, quite ordinary people can achieve
results as good as the less systematic geniuses of the past.
The development of scientific management and work study
techniques originated in the factories established during the
Industrial Revolution of the nineteenth century. Further
development and application of these techniques occurred
during the early part of this century, fostered by the use of
production line and mass production technology. By 1930,
"scientific management" was an integral and necessary part of
the industrial routine in industrialised counthes.
APPLICATION TO THE
"CONSTRUCTION INDUSTRY
7
It was not until the late 1950s that major construction firms
began to appreciate the potential savings that could accrue by
adopting work study techniques and started to appoint work
study engineers to their building and civil engineering
departments. There were respectable reasons for this long
delay, since working conditions in the construction industry are
dramatically different from those in most factories. In a factory
the elements of work are highly repetitive. The nature of the
work and the layout of the workplace remain unchanged over
long periods of time. The climate inside the factory is generally
controlled and steady. On a construction site the various
construction activities are of relatively short duration, and, after
a few days or weeks, a construction operation may be taking
place in a different way at a different location under different
climatic conditions. Furthermore, although construction work
can be repetitive, cycle times are longer, and days may elapse
before a repetition occurs.
On construction projects employing large Ítems of
mechanical equipment, the high cost of work is generally
caused not so much by the low performance of the operatives
as by low equipment utilisation. On a labour-intensive project,
however, high costs are more likely to be due to inefficient
working practices. It is frequently the case that the workers are
working hard, but not very effectively. In such a case, work
study can enable operatives to achieve greater output while
reducing the physical effort that they have to expend.
It remains true that some work study techniques which are
suitable for factory conditions have only limited use on a
construction site. Nevertheless experience has demonstrated
that significant productivity improvements can be achieved if
these techniques are applied sensitively, and their application
helps to incúlcate a productivity-oriented attitude of mind
among everyone concerned.
THE HUMAN FACTOR
The application of work study has a tendency to reveal the
shortcomings of managers, supervisors and workers alike. The
work study specialist will be challenging working methods to
which they have long been accustomed.
In investigating one set of problems the weaknesses of
other related activities will be laid bare. For example,
observation may reveal that the time of a group of workers is
being wasted through having to wait for certain instructions,
decisions or materials. This points to inadequate supervisión or
a need to revise inefficient procedures.
Most people resent change. Workers resent being timed
and fear redundancy, so a tactful approach is necessary.
WORKING CONDITIONS
Often, quite small improvements in working conditions can
produce marked increases in productivity. Untidy sites and
8
stores can cause delays and accidents. Physical conditions
such as ventilation, temperature, Tighting, sanitation and so on
affect the human capacity for work. Bad working conditions are
uneconomic.
For example, to avoid the debilitating influence of various
mosquito- and fly-borne diseases, construction sites should be
kept clean and drained. Properly designated and maintained
latrine áreas and adequate supplies of clean drinking water
should be available on site.
the techniques of work study
Work study has two main components - method study and work
measurement. The method study is usually carried out first,
although some work measurement (time study) techniques such
as activity sampling may be used before a method study to
identify problems. Time studies are also used to compare the
effectiveness of different methods.
Figure 3.
Work study
METHOD STUDY
The objectlves of method study are to:
improve the use of materials, equipment and manpower;
improve processes and procedures;
-
improve workplace layout;
-
improve the design of tools and equipment;
-
reduce unnecessary work;
-
develop a better working environment.
The British Standard Glossary of Terms in Work Study
defines method study as "... the systematic recording and
critical examination of existing and proposed ways of doing
work, as a means of developing and applying easier and more
effective methods of reducing costs".
WORK MEASUREMENT
This involves using time studies to find out how long a job ought
to take. The objectives are to:
-
compare the efficiency of alternative methods;
-
provide information upon which planning, scheduling and
control of work can be based;
balance the work of components of a team;
-
provide information for cost estimates;
set standards of performance as a basis for incentive
schemes.
The British Standard Glossary of Terms in Work Study gives
the definition of work measurement as "... the application of
techniques designed to establish the time for a qualified worker
to carry out a specified job at a defined level of performance".
WASTAGE OF RESOURCES
Table 1 gives examples of wastage of resources, and the work
study technique appropriate to the analysis of the problem.
Table 1.
Wastage of resources and work study techniques appropriate to the analysis of the
problem
Examples of waste
Remedial action
by work study
SPACE
Bad road surfaces, bad layout of
huís, compounds, loading bays,
wrong arrangements of working
spaces, cluttered stores depots,
poor light or heating in confined
places, etc.
Improved layout plans,
use of string diagrams, process
charts and models to pinpoint the
faults, use of questioning
techniques, use of photography to
spotlight the waste áreas.
MATERIALS
Faulty storage, double/treble
handling, faulty welghts and
measures, mistakes ¡n tolerance
design, materials not ¡ncluded in
overall planning, delivery at the
wrong place or time, etc.
Revised layouts of storage áreas,
time and methods studies of
materials handling, frequent
stocktaking, introduction of more
frequent quality and quantity
checks.
MANPOWER
Underutilisation, negligence and
idleness, mistakes at work, faulty
levéis and setting out of
construction work, faulty
management systems, ignorance of
costing site situation, lack of
incentive to work, poor training.
Methods and time studies, activity
sampling, standard data, múltiple
activity charts, introduction of
description and Job specifications
for all company staff, questioning
techniques, suggestion boxes,
analysis of training needs.
PLANT AND
EQUIPMENT
Underutilisation, excessive use with
lack of maintenance, no inspection
of plant by the site supervisors,
plant left on sites to rot when a Job is
finished, drivers not trained,
use by unauthorised people, etc.
Production and time studies, unit
costing of plant operations,
meetings with plant makers,
introduction of daily plant usage
programmes, introduction of preplanned maintenance as site
responsibility, training of
supervisors in plant management,
analysis of training needs of plant
operatives, "in-company" short
plant courses, analysis of plant
suitability and its unit cost potential,
plant selection assisted by prior
work.
11
METHOD STUDY
basic procedures
When a method of working contains an obvious difficulty, the
worker will usually take steps to get around ¡t. But this method
adjustment deals only with that part of the method that attracts
his attention. It does not necessarily improve the whole method.
Planned method ¡mprovement ¡s a system of analysis which
studies the whole method. The basic procedures, which are
considered in detail later, are first given in outline below.
D Select
- the Job or operation that is in need of
¡mprovement, or that is to be set up.
D Record
- obtain and record al I the facts;
- enlist the co-operation of all concerned;
- watch the work being done, and consult
information on previous experiences;
- chart the present method;
- note the snags and difficulties.
D Examine
13
Examine critically every aspect of the Job or
operation:
- What is achieved? Is it necessary? Why?
What else could be done?
- Where is it done? Why there? What other
place would be better?
- When is it done? Why then? What other
time would be better?
- Who does it? Why that person? What other
person would be better?
- How is it done? Why in that way? What
other way would be better?
Consider: safety; quality; design; layout;
equipment; materials.
Note all ideas.
D Develop
- review ¡deas;
- eliminate, simplify, combine, rearrange;
- make the new method safe;
- chart the new method;
- submit the new method for approval, where
appropriate.
D Install
- consider the best time to introduce to the
Job;
- convince all concerned that
method will work;
the new
- train the users.
D Maintain
- check frequently;
- match results;
- correct deviations.
Method study is equally applicable to planning new work
and analysing an ongoing operation.
As work proceeds on a construction site, a range of
different operations are required, each with its own resource
implications. For example, in the erection of a multi-storey
building, certain equipment is needed for excavating and
concreting the foundations and basement. As the structure
rises, different equipment is needed. Initially, locations need to
be worked out for site offices, materials stores and dumps,
concreting plant, cranes and hoists, etc., in order that all
operations on the site will be carried out efficiently, without
interfering with one another and without double handling. In
such cases a method study is done before the work
commences, based on experience gained on earlier projects.
select the work to be studied
Whether it is a new construction operation, or an ongoing
activity, the question of how to select the work to be studied will
depend on the organisational structure of the construction
enterprise, and the nature and stage of the work. If work study is
being introduced for the first time, and ongoing activities are to
be studied, it is better to start with a relatively simple Job that
will permit quick and significant improvement. Economic
14
considerations are important. It is obviously a waste of time to
spend effort on improving a Job ¡f the cost ¡s low or ¡f ¡t is of short
duration.
Other factors to be considered in the selection of work to be
studied are as follows:
(a) Where it is necessary to set up a co-ordinated team of
variously skilled workers and machines, in balance with
other related operations.
(b) When the feedback from the project reveáis high
production costs, a work study may be necessary to find
out the reason. Ideally all the sepárate construction
operations on a project should be individually costed as the
work proceeds, with a prompt feedback for comparison
with standard costs or estimates for the same type of work.
(c) When production operations are being held up, such as
by- lorries waiting to be loaded;
- delays in obtaining materials;
- concreting gang held up by steelfixers.
(d) Double handling of materials, such as - materials not delivered near enough to workplace;
- materials store wrongly sited;
- wrong working methods.
(e) Failure to achieve specified quality standards for reasons
such a s - wrong tools;
- wrong materials;
- wrong methods;
- bad workmanship;
- wrong instructions given.
(f) Danger, effort and fatigue: Work study will be more readily
accepted by the workers if the first jobs studied and
improved are those which are dirty, dangerous, difficult or
. strenuous.
(g) Major components of the project: The larger the item, the
greater the opportunity for saving. A small improvement on
an operation which is a major cost item is more profitable
than a big improvement on a small cost item. For example:
15
Example: On a project worth $100,000 one operation accounts for
50 per cent of the cost, while another accounts for only 1 per cent:
A 5 per cent increase in productivity of the major operation saves
50
100,000 x
5
x — = $2,500.
100 100
A 50 per cent increase in productivity of the small Ítem saves only
1
100,000 x
50
x
100
= $500.
100
(h) Activity sampling: Where none of the above pointers are
appropriate, the technique of activity sampling can be used
to identify sectors Of low efficiency. Activity sampling is
described later in this manual. The technique provides
information on:
- the proportion of the working day during which workers
and machines are producing;
- the proportion of the working day used up by delays;
- the relative activity of different workers or machines.
(i) Wastage in any form: This is an indication of a need for
method study. Examples of waste are:
SPACE
- unplanned or untidy storage of construction
materials;
- bad layout of site offices and storage huts;
- uncontrolled activities of subcontractor on
site;
- bad layout of tower cranes, derricks and
heavy plant.
TIME
Standing or waiting time caused by:
- slow deliveries or flow of construction
materials;
- shortage of construction plant, equipment
or tools;
- plant and equipment breaking
through lack of maintenance;
down
- poorly trained drivers of plant or equipment;
-management and supervisión not trained,
resulting in poor company Communications
and lack of instructions for the operatives.
16
EFFORT
- lack of handling equipment;
- unnecessary double handling;
- skilled operatives doing manual work;
- poor administration and working conditions
resulting ¡n non-productive work.
MATERIALS
- through wrong requisitions;
- wrong methods of material handling;
- detective work causing rejects;
- deterioration of materials through poor
supervisión of storage;
- pilferage.
POWER
- wrong use of plant and heavy machinery;
- handling by untrained people;
- lack of choice on use of power;
- heavy plant working below designated
capacity or at low utilisation because of lack
of supervisión, lack of trained operatives
and also lack of work programming.
obtain and record the facts
ONGOING ACTIV1TY
17
The person making the study will come into contact withworkers, foremen and other supervisors. Before starting it is
essential to explain to all concerned the reason for making the
study, pointing out that no criticism of anyone is implied, and
that everyone's co-operation is sought in improving the Job. If a
unión exists, unión representatives should also be consulted. It
is important to explain that no redundancies will occur as a
result of the studies. Failure to give adequate explanations gives
rise to rumours and unrest.
During the course of an investigation, supervisors or
workers may come up with some good ideas, which should be
noted. If these are ultimately incorporated in the new method,
full credit should be given. It should also be remembered that a
person tends to make his own ideas work better than those of
someoneelse.
Before making a record of the Job, the work study person
will first discuss it with the supervisor. He will watch what ¡s
happening until he thoroughly understands the Job, asking
questions of supervisors and workers where necessary. He will
then make notes and sketches regarding the methods used and
performances seen. He will note any obstructions to the smooth
working of operatives or plant engaged on the construction,
recording the information needed to answer such questions as:
-
What is the purpose of the activity?
-
What is the end-product?
-
Is the place of work right? Is the layout right?
-
Is the sequence of work right?
-
Are there any preparations for work which are part of the
job?
-
Are those preparations necessary?
-
What work will follow?
-
Who did the work before? Who does the work now? Who
will follow?
-
What are the main elements of the job? Can they be studied
separately? How many studies will be needed?
-
What ¡s the frequency of repetition of the job?
NEW OPERATION
ln this case it will be necessary to study previous experience of
the kind of job to be set up. The facts should be obtained, i.e.
everything that will affect the operation, such as:
(a) Nature of the work:
- quantity and quality;
-
time available;
-
conditions of contract and specifications;
-
site plan, working drawings;
location;
weather and ground conditions;
-
access;
budget costs.
(b) The resources available:
- materials (availability, alternatives, location, access,
delivery and costs);
18
-
equipment and tools (types and capacity, condition,
maintenance and service, output and running costs);
- labour (availability, skills and experience, output and
costs).
EXAMPLES OF CONSTRUCTION ACT1VITIES
The facts to be collected ¡n studying some typical construction
activities are given below:
EXCAVATOR
- nature of work (site strip, foundations and
bulk excavation);
- suitability and capacity of machine;
- nature and timing of work elements;
-
DISPOSAL
susceptibility to change of method;
disposal of excavated materials;
balance with allied equipment (e.g. tippers);
expertise of operator.
- capacity of vehicles carting soil totip;
- loading (method and timing);
- access to excavator;
- routetotip;
- access to tip;
- method ofdischarge and timing.
19
CONCRETING
- mixer set-up (layout, storage and delivery of
materials, water supply and gang balance);
- transportaron of concrete (cost effectiveness of pumps, conveyors, lifts, crane
skips, dumpers, wheelbarrows and head
pans). Balance with mixing cycle;
- placing and finishing of concrete in
foundations, slabs, walls, columns and
beams at various heights. Balance with
mixing and transportation methods.
FORMWORK
- methods of manufacture, erection, removal,
cleaning and salvaging. Carpenters' shop
layout and movement of raw materials.
Handling and assembly of units. Methods of
fitting and fixing. Rough handling and
damage in removal.
STEEL FIXING
- prepararon and preservaron of bending
schedules.
CEMENT
- deliveries, storing and stacking of steel.
Layout and equipment for cutting, bending
and stacking. Fixing in position.
RECORD ALL THE FACTS
The analysis of the studies is usually done in the office, away
from the heat, dust and bustle of the worksite. Therefore, in
carrying out the site study it is necessary to make a clear and
concise record of the work. The success of the whole
procedure depends on the accuracy with which the facts are
recorded, and the ease with which they can be studied. Apart
from site layout plans, a variety of recording techniques have
been developed for this purpose. These include process charts,
flow diagrams, string diagrams imposed on layout plans and
múltiple activity charts. It is also sometimes useful to take
photographs or make models to assist in the analysis.
In the case of process charts and flow diagrams, the
recording of the movements and activities of workers or
machines (or of what happens to materials) is facilitated by the
use of five standard symbols:
O
Operafon-something is produced or accomplished. An
operation always takes the material, component or service
a stage further toward completion by changing its shape or
composition;
D
= /nspecf/'oo-something is examined for identitication, quantity or quality;
= 7"ransportaft'on-indicating the movement of workers, materials or machines from place to place;
D
V
= Delay-a temporary hold up or delay/obstruction in the Job;
= Storage-a storage occurs when an object is deliberately
kept and protected against unauthorised removal.
Charting conventions
In using the standard symbols, certain conventions are used:
(i) Similar symbols are numbered consecutively. When two
different activities occur together the symbols can be
20
combined, for example, an operation ¡nvolving elements of
inspection would be shown as • .
(i¡) When a material or component ¡s first introduced ¡nto a
process ¡t is shown as an arrow entering from the left.
(¡ii) Rejects are charted thus:
REJECT5 FOR
DESTRÜCTION
RCJECTS FOR
REPROCESS
REPEAT 3 MORE TIMES
(iv) Repeat activities are charted as above;
(v) Notes may be made alongside the activities shown on the
chart to pinpoint difficulties such as:
- awkward or difficult operations;
- distances moved;
- heavy or bulky loads;
21
- unpleasant conditions, i.e. dust, mud or noise;
- hazards.
RECORDING TECHNIQUES
Recording techniques most commonly used are:
(a) Outline process charts
These give an overall picture by recording ¡n sequence only
the main operations and inspections. The outline process
chart is intended to clarify the understanding and interrelationship of the various operations by giving a bird's-eye
view of the work. Each of the activities shown on the chart
could warrant a sepárate more detailed study. However,
even at this stage, the application of the method study
Figure 4.
Outline process chart
MIX
CONCRETE
TRANSPORT |
CONCRETE '
CÜT +
BENP
3TEEÜ
CLEAN
AND I
<?REASE[
FORMS
A5SEM0LE
ANDTIE
STEELf
SETI
UP
FORMSI
TRANSPORT/
STEELV
rrrsTEEii
TOFORMS
POUR,
CONCRETEN
VÍBRATE ,
&ONCRETE>
CUREl
STI?IP FORMSI
MAMUFACTURE OF
REIMFORCED PRECAST
CONCRETE UNITS
CUREl
5TACK
PRECAST (
UNITS
22
questioning technique (described in "Examine the facts")
to the outline process chart could lead to the elimination of
unnecessary work.
Figure 4 gives an example of an outline process chart
describing the manufacture of precast concrete units.
(b) Flow process chart
This gives a fully detailed account of the sequence of every
operation, inspection, delay, and transport or storage
activity occurring in a process or procedure. It contains all
the information considered desirable for analysis, such as
time required and distance moved. The chart can be used
to show either the activities of worker or machine, or what
happens to the material being processed. The chart is
sometimes used in conjunction with a flow diagram. See the
materials-type example shown in figure 5. A flow process
chart for a worker is shown in figure 7.
(c) Flow diagram
The flow diagram is most appropriate for use on
construction sites. The various movements and activities of
worker or machine are recorded on the plan of the worksite
(text continued on p. 26)
Figure 5.
Flow process chart
DELIVERY,
CUTTINq,
BENDINQ,
FABRICARON,
and STORAQE
of STEEL.
V
<H
STORA6.E RACKTOR.
ÜNCLT STEEL
STORASE T T
RAGK^>J
~P-^~^
MOVETO
CUTTINq BENCH
UNLOAD AND
STACK BY
HAND.
CUTTO
LEN(,TH
L_A>
MOVE TO
BENDIN5 BENCH
STACK WAITING
BENDINq
W <^—\
V *^p
MOVE AND STORE
DELIVER n
BY LORRY 1
UNLOAD AMD
STACKBYHAND
S$—t
<
MOVE AND STORE
STRAlQHT BARS
Flow diagram
STEEL DELIVEBED
BY LORRY
\-r¿?
Tyl,.
Figure 6.
GD
BEND ACCORDIN5
TO SCHEDULE
MOVE TO COLUMN
* CAI^E FABRICATION
BENT BARS
m
STACK WAITING
FABRICATOM
Y/
BEr•IDIKq
BE. •iCU
y
ra)
\7
\7
STORE COLUMN
CA^ES
^
\A\
Cii
STORAQE
STRAiqHTBARS
j ) X»
MAKE 0t>
COLUMN CA^BS
MOVE TO
STORE
N
CUTTINq
BENCH
\7
^^''^STORAGE
BENT
BARS
STORAGE
CO LUMMW14ES
A
II \Y( rofS"TEEL
BEN DiNQYARD
Figure 7. Flow process chart for worker
Flow process chart : Tiling to standard bathroom of hotel buildinc as shown on drawing
D50fa;.
Preliminar/ study of ORIGINAL METHOD
Study reference: 137
Dale: 11.11.83
SAieeí No. 1 of 2
Localion: Bathroom to room 105
Details: Lay 7.5 sq m of 15cm x 15 cm tiles to 3 walls of bathroom
Workman: Mushkil Khan
Study by: A Nobservah
Remarks. Time taken at present ¡s considerad to be excessive.
Normal working hours: 0630-0930,1000-1200,1230-1530.
Distance
Time
(metres)
(mins.)
Symbo
V
130
4.20
1.50
D
O
In workers' locker room
Check tools and drawings
Carry tools to workplace
5.50
m
o
D
o
Search for and obtain length of batten
used on previous day
Clean oíd adhesive off batten
Refer to drawing
Set out and fix batten to bottom edges
of tiled área
4.20
o
2.20
•=c>
Set out and mark top and side edges of
tiled área
Travel to stores to collect materials
9.30
2.20
8.20
1.70
10.50
17.50
1.00
2.00
D
O
D
U
<>
D
O
O
4.10
O
3.10
9.30
=!>
O
32.50
O
7.50
5.30
D
O
41.50
2.50
4.50
3.00
8.40
24.60
4.00
D
O
4.20
4.70
7.50
110
110(X3)
90
90
90
90
Operation
110
2.50
5.20
8.60
110
2.30
1 150
256.30
o
=o
o
o
o
oD
D
-O
Remarks/tools/methods
Including uponeflight
stairs
Chisel and rag
Spirit level, pencil,
hammer, nails, steel
rule
Spirit level, pencil,
steel rule
Including down one
flight stairs
Await storekeeper
Make out requisition
Await storekeeper assembling materials
Check and sign for stores issued
Two trips necessary
Carry materials to workplace
Visit latrines
Assemble grouting materials
Including down one
Move to water point
flight stairs
Bucket and short
Mix adhesive grout
batten
Carry grout to work área
Trowel, metal
Apply grout to wall área 1
spreading comb
Lay tiles, including cutting
Tile cutter, hammer,
pincers, spacer strings
Smoke cigarette
QUERY this practice
Scrape bucket clean and empty out of
window
Break for morning meal
Move to water point
As before
Mix adhesive grout
As before
As before
Carry grout to work área
Apply grout to wall área 2
As before
Lay tiles, including cutting
As before
Scrape bucket clean and empty out of
window
Travel to stores for more adhesive
Await storekeeper
Await storekeeper altering previous
QUERY this practice
requisition, obtaining and issuing adhesive
Return to workplace
CARRY FORWARD TO SHEET 2
24
Flow process chart: Tiling to standard bathroom
Study reference: 137
Sheet No. 2 of 2
Distance
(metres)
1150
90
90
Time
(mins.)
256.30
2.50
2.20
5.00
3.00
7.90
20.00
8.70
6.50
35.20
35.10
15.20
90
90
180
Symbo
O
<í>
o
o
o
D
^>
O
D
O
D
3.20 O
2.00 =¡>
5.30 O
2.40
25.20
3.70
o
o
o
9.20 D
6.10 O
15.90
25.70
o
o
20.00
1 690
D
Operation
Remarte/tools /methods
BROUGHT FORWARD FROM SHEET 1
Assemble grouting equipment
As before
Move to water point
As before
Mix adhesive grout
As before
Return to workplace
As before
As before
Apply grout to wall no. 3
Lay tiles, including cutting
As before
Break lor cigarette
Clean buoket and empty out of window As before
Mid-day break
Screwdriver, claw
Remove space strings and battens,
remove surplus adhesive trom joints,
hammer, oíd rags
clean string and wrap for re-use
Foreman arrives for inspection and
discussion
Assemble grouting materials
As before
As before
Move to water point
Mix jointing grout
As before
Return to work point
As before
Plástic grouting tool
Apply grout to walls 1,2,3
Scrape bucket clean and empty out of
window
Smoke cigarette
Fetch water for cleaning off
Bucket
Sponge, clean rags
Clean off tiles
Clean up and assemble tools preparatory
to moving on
Await end-of-day whistle
515.30
Actual worK time
515.30- 60 - 455.30 minutes
SUMMARY
Symbol
No.
Total lime
O
E3
D
23
3
2
=£>
14
D
12
256.10
13.40
8.90
45.30
45.30
186.10
515.30
NOTE:
25
(i)
Distance
1 690
not recorded
1690 +
The chart would normally be handwritten, but is here
printed for clarity.
(ii) The times taken are approximate only, to assist in getting
an overall picture of the Job. Accurate timing techniques
are discussed in Chapter 3.
(iii) The study brings to light certain interesting facts- of the total work time available of 455.30 minutes (approximately 7'A hours), only 3'Á hours are spent in valid
tiling operations. It took over 3A hour to get to the stores.
A good deal of unnecessary travelling (1,690 metres) is
involved. Over 1 % hours (excluding mealbreaks) were
spent doing no work, plus several other breaks which
were too short to be recorded.
- certain malpractices are revealed, viz. throwing waste
out of Windows and the alteration of requisitions by the
storekeeper.
(iv) It should be possible to streamline the Job, cut out wasteful
activities and motívate the worker, so that two bathrooms
are done ¡n one day.
using the standard symbols. The diagram can also be used
to examine the handling and processing of materials as
shown in figure 6.
(d) String diagram
This is a scale drawing or model on which a thread is used
to trace and measure the path of workers, materials or
machines during the course of the particular operation. The
result is to give a picture of the paths taken showing those
most frequently used, so that rearrangement of work points
or storage áreas can be made to reduce excessive
movement. The technique has limited application to
construction work, but is introduced here for completeness.
The technique can sometimes be useful on a construction
site wherethe haphazard build-up of materials, dumps, etc.,
has led to detours, congestión or delay. The work study
specialist will mount a site plan on a hard backing and
sketch in all the dumps, temporary roads, etc., not shown
on the plan. He will then observe and record movements of
site traffic, noting each turning or destination point. At the
end of the day, or when sufficient data have been collected,
he will return to the office and drive pins into the board to
mark each destination or turning point. Using a length of
fine string or cotton, he will retrace each movement
observed and recorded, by winding the thread across the
board from pin to appropriate pin. The build up of thread
will demónstrate the relative density of movements, so that
priority can be given to improving those routes, or
relocating those operations or storage áreas where the
congestión is greatest. The technique can be used to study
the movement of one particular Ítem of equipment, or
several. In the latter case different coloured thread can be
used. The string diagram can also be used to improve the
location of stores, the layout of reinforcement fabricating
shops, movement of workers and machines in precast
concrete yards and the siting of machines in a workshop,
etc. See the example in figure 8.
26
Figure 8.
String diagram
These string diagrams represent the layout and
movement of workers in a woodworking machine shop, and
¡Ilústrate how alternative layouts can be examined to
evalúate the effect on reducing movement and relieving
congestión. Apart from relieving congestión, the proposed
layout shown above has reduced movement (as
represented by the length of string) by 18 per cent.
(e) Múltiple activity chart
This shows the activities of more than one subject (worker
or machine), recorded on a common time-scale to show
their inter-relationship. A simple example is given opposite.
PHOTOGRAPHIC TECHNIQUES
27
An alternative to site studies is to record the work on either
photographic film or video tape, so that the work once recorded
can be studied and re-studied under office, as opposed to site
conditions.
(a) Memo-motion photography
The camera is set up with a view of the whole work to be
studied. Special automatic time-lapse cameras with zoom
lenses are used that can take one photograph at intervals of
between 1 and 4 seconds (or longer intervals) as the
situation demands, instead of at the normal 18 trames per
second. The processed film is then played back and viewed
at normal speed, so that an operation that has taken hours
to perform may be viewed in a matter of minutes. The
movements viewed will appear jerky, but if the time intervals
Example:
Three workers, A, B and C are pouring concrete inte- a column form using two buckets, a rope and
pulley to lift the concrete from the ground to platform level.
A
filis the empty bucket with concrete, taking 15 seconds, and hooks it onto the rope
taking 4 seconds;
B
hauls the full bucket up to the platform (12 seconds) and, after C has unhooked the
full bucket and hooked on the empty bucket, lowers it to the ground (8 seconds),
unhooks it (2 seconds) for A to refill.
C
unhooks the full bucket (3 seconds) hooks on the empty bucket (2 seconds) walks
to the formwork with the full bucket (4 seconds) empties it into the column form (12
seconds) and walks back to the pulley (3 seconds) to await the next bucket.
The múltiple activity chart for the existing method is:
time
¡n
s«cs
orttm»
actuafty
wofking
- T I M E CYCLE 46SECONDS •
_¡_20
30
40
5CL
o
One way of improving the operation is to use 3 buckets instead of 2, so that A can be
filling the 3rd bucket whilst B is hauling up. Also B does not then have to wait whilst A is
filling the bucket.
The new chart would be:
¡ - • T I M E CYCLE 3 1 SECONDSi
A =hookt
Nhook^ —
1
on
B
C
haul up
^ ^
1
fill
on
Vold
= j
lomar un Üook
1=1
hook off o nwalk
W
1
fill
ha ul up
E=
empty \#»l k
To 13 lower un nook
E= - = 3
hook off onwalk
empty
61
87
F 77
Improved method using 3 buckets-time eyele 31 seconds
Thus, the introduction of an extra bucket has improved productivity by nearly 50 per
cent.
The workload could be shared more equally by giving over the Job of hooking off the
empty bucket from B to A.
between trames were not too great, no information ¡s lost,
and flow diagrams and activity charts can be drawn up ¡f
needed. Also the work can be studied ¡n great detail, trame
by trame.
(b) Micro-motion photography
This ¡s not so applicable to construction work, but more to
high-speed factory assembly operations. In memo-motion
photography the film technique is used to speed up the
action. Micro-motion photography slows it down so that
very rapid movements of the hands, for instance, can be
studied in detail.
MODELS AND CUT-OUTS
Models and cut-outs representing the plan views of plant or
temporary site buildings, made to the same scale as the plan,
are useful for deciding the best way to set up the site before
work commences. Site layout ¡s discussed later in the chapter.
examine the facís
QUESTIONING TECHNIQUE
Once the operation has been recorded, each activity is
subjected to a systematic and progressive series of questions,
which examine:
The purpose
place
sequence
person
means
for which
at which
in which - the activities are ur
by whom
by which j
eliminating
combining
With a view to •
rearranging
simplifying
those activites
The technique can be presented and applied in tabular
form:
PRIMARY QUESTIONS
SECONDARY QUESTIONS
PURPOSE
What is done?
Is it necessary?
PLACE
Why there?
SEQUENCE
Where ¡s it
done?
When is it done?
PERSON
Who does it?
Why him?
MEANS
How is it done?
Why that way?
What else could
be done?
Where else could
it be done?
When else could
it be done?
Who else could
doit?
How else could it
be done?
Why then?
What should be
done?
Where should it
be done?
When should it
be done?
Who should do it?
How should it
be done? •
ln questioning the existing method, ¡t is important to:
examine the activities as they are, and not as they should
be or might be;
avoid being influenced by previously conceived ideas since
this may exelude other solutions;
avoid hasty judgement;
note all "hunches" as they oceur, but return immediately to
the ordered procedure of challenging;
eliminate all unsafe and undersirable features of the existing
method;
start with the DO activities, i.e. the operations and
inspections;
in questioning the supervisors and workmen involved ¡n the
operation it is necessary to be diplomatic. People dislike
any suggestion that the way they are doing things is wrong,
and resist change.
ALTERNATIVE METHODS
The secondary questions seek to determine and analyse
possible alternatives of place, sequence, person and means of
doing the Job. The following are some of the matters to take into
consideraron:
WORKPLACE
LAYOUT
- relocate storage points for ease of handling,
reduction of movement and elimination of
double handling;
- gravity feed of aggregatesetc;
- avoid mutual interference of trades or
equipment;
- improve ground conditions.
MATERIALS
- substitution of less expensive materials;
30
- revisión of the specification to use
alternative materials;
- modification of size/shape to improve
handling;
- preforming of the materials at some other
place;
- alternative feed to work point.
EQUIPMENT
- use of more appropriate machines;
- making idletime more productive;
- reorganisation of set-up;
- machine runs and interference or hazard;
- machine runs and ground conditions.
WORKERS
- useof more(or less) skilled personnel;
- alternative tools;
- training needs;
- unnecessary or dangerous motions;
- alternative, simpler sequences.
develop the new idea
REVIEW THE IDEAS
All the posslble alternatives and ideas noted during the
questioning process are now reviewed to arrive at the best
method. The concepts of elimínate, simplify, combine and
rearrange are applied in order to decide what, where, when,
who and how shouldW be done. The solution may be influenced
by considerations of time, safety and the relative cost of
alternative possibilities.
SAFETY
Check that the new method includes no unsafe practices.
CHART THE NEW METHOD
31
This will be useful when informing supervisors and workers, or
submitting the method for approval. In setting up a new
worksite, the layout plan showing locations of offices, stores,
workshops and equipment is essential. Operational and control
procedures will have to be deflned.
SUBMIT FOR APPROVAL
Once drawn up, the new method may have to be submltted to
sénior management for approval, and also to gain the
acceptance of supervisors and workers. Their acceptance is
made easier if they have been involved and their co-operatlon
sought from the start. The considerations that mlght be stressed
to gain approval and acceptance include:
-
safety;
-
cost saving;
-
time saving;
-
higherearnings;
easier work;
-
less wastage of materials.
install the new method
Once all concerned have been convinced of the effectiveness of
the new method, it will be introduced on the worksite.
TIMING
The correct time to install the new method will depend upon the
nature and complexity of the operation. For a new operation to
be started on site, the timing will depend upon the overall
programme and progress of the construction project as a
whole. If supervisors or workers require training, some
convenient period will be chosen, causing a mínimum of
interference with other related operations.
PILOTTRIALS
It may be advisable to try the new method out on a small section
of the works in order to iron out unforeseen snags;
test the effectiveness of operational and control
procedures;
32
-
train supervisors who will introduce the method elsewhere;
-
convince the workforce of the merits of the method.
THE HUMAN ELEMENT
This needs attention when change ¡s ¡ntroduced (a) Since ¡t takes time to get into the swing of a new method,
early criticism of the method may be expected.
(b) The following check-list is to ensure that people have been
properly prepared:
- Have all necessary operational and control procedures
been drawn up?
-
Have all personnel remotely concerned, from sénior
management down to labourers, been fully briefed as to
methods and procedures, duties, controls and
incentives, if any? Do they understand what is expected
of them? Are they going to co-operate willingly?
-
What training is necessary? Has adequate training been
given?
-
Are all the necessary equipment and tools available in
sufficient quantity and in good condition?
Are all the necessary materials available in the right
place and in sufficient quantity?
-
maintain the new method
Once the new method is installed, it should be checked
frequently and the results evaluated in order to:
identify and deal with unforeseen problems;
-
check any tendency to drift back to the oíd method;
-
identify further opportunities for improvement.
site layout
~ THE PROBLEMS
33
Failure to plan the site layout in advance is a prime cause of
operational inefficiency, and can increase the overall cost of a
project substantially. In the absence of a precise site layout
plan, neither the site manager ñor his subordinates will have a
clear ¡ndication of where various hutments, items of plant, etc.,
should be located, and the following problems may occur:
(a) Material stacks wrongly located
Materials arriving on site are off-loaded into what someone
guesses to be the correct location. This practice may
subsequently involve double or treble handling of materials
to another place because - they have been stacked over a drainage run, in the way
of the scaffolding, or too near the edge of an excavation;
-
they are too far away from the part of the works where
they are to be incorporated;
-
they are too remote from the hoist, or not within the
radius of the crane needed to place them in position;
-
they impede the smooth flow of work traffic across the
site, causing deviations;
-
they are too near works-traffic routes and may get
damagedorsoiled;
-
their delivery was wrongly phased and they are not
needed until much later in the project;
-
they are fragüe, and in their present location they are
likely to get damaged or pilfered.
(b) Plant and equipment wrongly located, for example:
-
the mixer is inaccessible for the delivery of materials; not
enough room for the storage of aggregates; cement
store too far away; equipment wrongly located for ease
of delivery of mixed concrete;
- fixed cranes are unable to reach all parts of the works;
insufficient capacity in relation to loads to be handled at
various radii;
-
hoists have insufficient capacity or height in relation to
the loads to be handled or the nature of the building, or
are badly located in relation to the floor layout of the
building.
(c) Inadequate space allowed
Where inadequate space is allowed for the stacking of
materials or ancillary activities such as steel storage, cutting
and bending and formwork manufacture:
-
materials may be stacked too high or may intrude into
roadways or other áreas, presenting hazards and
causing breakages;
34
- working áreas may become too cramped for efficiency,
or additional áreas may have to be allocated, with the
consequent waste of time caused by having to travel
between them.
(d) Site huts wrongly located in relation to their effective use
and convenience, such as:
-
site office located too near noisy activities such as a
mixer or carpenters' shop; too near site or other roads in
dusty conditions; too remote, not giving a sufficient
overview of the site;
-
stores having inadequate access for loading and
unloading, or being badly located with regard to
security;
-
latrines located up-wind of office; or in badly drained
áreas.
Therefore, before moving on to a site it ¡s necessary to
prepare a detailed site plan, showing the positions to be taken
by every Ítem of equipment, accommodation, ancillary work
áreas and materials storage áreas.
GENERAL CONSIDERATIONS
35
The layout of a construction site will depend upon the methods
and sequence of operations to be employed in carrying out the
work, and on the space available. The methods and sequences
will themselves depend upon the space available, the time
allowed for construction, the relative costs of different methods
and the availability of equipment and materials. All of these
aspects will have been considered earlier at the time of
tendering for the works, and should be known before the site
plan is prepared. For a building on a restricted city site, the área
available will díctate the equipment to be used and the methods
to be employed. The tighter the space, the more critical the
layout. In such circumstances it may be necessary to fabrícate
formwork and reinforcíng steel off the site, and to have the
concrete delivered reády mixed.
Generally, the site will have to accommodate a varíety of
temporary buildíngs, materials and supplíes and plant and
equipment at different times during construction, and schedules
will be needed giving their respective times on and off the site.
Such Ítems must be located for ease of access and operation, to
ensure smooth work flow and avoid interference with
construction activities. The procedure ¡s to list all the ítems and
storage áreas that will be needed on the site, and to indícate
their positions on a site plan.
Table 2.
Considerations affecting site layout
ítem
1. Buildings
Offices for site manager, assistants and support staff
Stores (lock up for small Ítems)
Mess room, canteen, toilets, latrines
Gatekeepers' and watchmen's huts
Ancillary shops (carpenters, steel benders,
blockmaker)
2. Plant and equipment
Cranes
Consideraron affecting location
Avoidance of noise, dust, good view of site
Security
Clear of the works
Good visibility
Adjacent to appropriate store (or mixer)within crane radius
Generator
Circular saw
Power bender
Block maker
Máximum anticipated lift. Capacity in relation
to radius. Anchorages
Location in relation to building and anticipated
loads
Adjacent to aggregates and hoist. Within
crane radius
Isolated
Adjacent timber store
Adjacent steel store
Adjacent mixer set-up
3. Materials store
Cement
Aggregates
Timber
Steel
Bricks, blocks
Doors, Windows and frames
Earthenware and sanitary fittings, glass
Fuel
Formwork
Under cover. Security. Adjacent to mixer
Possibility of gravity feed to mixer
Within crane radius/adjacent access road
Within crane radius/adjacent access road
Adjacent to hoist, adjacent access road
Safe storage área, easily damaged
Safe storage área, easily damaged
Isolate — fire hazard
Fabrication, cleaning, within crane radius
Hoists
Mixer
4. Access roads
Site entrance
Temporary site roads
5. Hoardings and fencing
Safety. Traffic control
Ground conditions. Deliveries and unloading
Parking áreas
Safety of site personnel and general public
security
LIST OF ÍTEMS TO BE
ACCOMMODATED ON SITE
Table 2 lists some of these ítems, viz., temporary buildings,
ancillary shops, plant and equipment, materials stores, etc., to
be accommodated on site, together with some considerations
affecting their siting. The list will also state the size of the área
taken up, or to be allowed, and the dates at which the ¡tem or
área will be required on site.
ÁREA ALLOWED FOR ANCILLARY
ACTIVITIES
Often the área to be allocated will be known from previous
experience, but in any case the área needed can be determined
by carrying out a method study. In the case of steel storage and
cutting and bending, ¡t will first be necessary to assemble all the
relevant information concerning quantities, sizes and lengths of
delivered bars, method of delivery and off-loading, steelbending schedules, required rate of working, place of assembly
and storage of cut and bent bars. For instance, such bars may
be transferred at once to their point of assembly in the building,
or, as in the case of column cages, assembled and stored in the
steel working área. When all this information is known, a flow
diagram such as that shown in figure 6 on page 23 can be
drawn up to ensure that the área allocated is adequate.
MATERIALS SUPPLY AND STORAGE
37
The stage of construction that the building has reached will
affect not only the need for materials but also the space
available for their storage. Once the underground foundations,
drainage and services have been constructed and backfilled,
further space becomes available. It may also be possible to use
the space inside the partially completed building.
The time for delivery and storage of materials on site will be
affected by the availability and reliability of supplies, and the
distance of the work from the supply base. Other considerations
affecting the size of the stock held will be: the anticipated
weather conditions; the vulnerability of the materials to damage,
deterioration and pilferage; and the extra cost of ordering and
stacking supplies of materials too far in advance of the time they
will be needed.
A study of the construction programme and the materials
delivery schedules will indícate the quantities, methods and
phasing of materials deliveries and their rate of use. This
information will indícate the optimum quantities to be held on
the site, and consequently the áreas needed for storage.
SITE PLAN
A detailed site plan is required to a scale of at least 1:100 (or 8
feet to 1 inch). The plan will show the extent of the works,
including details of underground drainage and service runs,
extent of foundations, etc. The best position of the various Ítems
to be accommodated on site can be derived by trial and error,
using either pencil and rubber, clear plástic overlay and crayon
or cut-out models. The models would be the plan of the Ítem of
accommodation, plant or storage área, cut out of cardboard to
the same scale as the site plan.
Figure 9.
Site layout plan
The example shown in figure 9 ¡llustrates the site layout for
the construction of a three-storey, concrete-framed, brick-clad
bank and office block in a city centre. The layout has been
superimposed on a foundation plan of the works. The site itself
is congested, so that some compromise is necessary in locating
Ítems.
The following points can be noted:
(a) Access - this is restricted to the side street only. The
footway crossings at the gate will require reinforcing to
avoid damage to the pavement and the services
underneath. The área available for site offices, etc., is
ultimately to be used as a car park. After constructing the
drains this área can be stripped and hardcore laid, before
laying out the site facilities. The limits of the scaffolding are
defined in order to keep hutments, etc., clear.
(b) Services - water is run to the mixer and ablutions block.
The electricity supply runs overhead to a distribution panel
fixed to the ablutions block.
(c) Temporary buildings - these are from the builder's stock of
re-usable prefabricated sectional buildings, and are
assembled on site.
(d) Mixer - adjacent to the street for ease of deliveries.
(e) Tower crane - the whole site is within the crane radius. The
jib clears adjacent buildings. At máximum radius the load
capacity is adequate for lifting the concrete skip containing
a full batch of concrete. The crane is dismantled after
pouring the roof.
(f) Hoist - this is used for cladding and internal finishes. The
brick stack and mortar-mixing área are adjacent to the
hoist.
(g) Steel and formwork - previous experience or a preliminary
method study will decide the áreas to be set aside. The
nature and extent of cover provided will depend upon
anticipated weather conditions. Some of the work can be
done inside the building once the ground floor has been
cast.
(h) Windows, doors and internal fixtures - these will be stored
inside the building, as space becomes available.
39
WORKERS' ACCOMMODATION
The construction of major projects in remote áreas may
necessitate the provisión of accommodation for the workforce.
The cost of such accommodation would be a proper charge
against the works, whether ¡t is built by direct labour (forcé
account) or by contract. In the case of contract works, the client
authority should not only specify the mínimum requirements of
shelter, amenities and sanitary facilities but should also include
an Ítem in the Bill of Quantities against which the contractor can
price.
Accommodation for the workforce will normally lie adjacent
to, but outside the boundaries of the worksite.
SUBSITES
In cases where the works are spread over a considerable área,
such as irrigation projects or new road construction, it may be
necessary to set up a series of subdepots for construction
bridges, concreting or asphalt plants, equipment harbours and
workshops, etc. The location of each subsite will depend on the
nature of the work and the proximity of materials sources, gravel
pits, quarries or bridge locations. However, the same general
considerations will apply for the layout of each site.
A practical example of site layout ¡s included in Chapter 7 of
this manual.
WORK MEASUREMENT
3
uses and techniques
INTRODUCTION
41
The construction of any project must be controlled to ensure
that the best methods are used, that the work flows easily
without delays, that ¡t ¡s completed on time to correct quality
standards and within the (correctly) estimated costs. This in turn
requires that the right materials, plant, equipment, workers
(skilled and unskilled) are employed at the right times and in the
right numbers. In order to control the works, planning and
programming are essential. To plan, programme and control
requires accurate knowledge of the work capacity of both
workers and machines and the cost per unit of work.
There are two ways of obtaining these output figures: one is
by the feedback of output data from previous construction
works, and the other is by work measurement, sometimes
known as time study.
The feedback of output data from construction sites gives a
purely hlstorical record of output and costs. The data are
derived by dividing the output by the time taken to achieve it.
However, these data will include the effects of ineffective time.
They do not show what output and costs could be achieved if
the job was properly managed and the workers or equipment
operators properly motivated to give of their best. Scientific
work measurement uses a series of techniques to identify
ineffective time and set sound time standards for the work.
This chapter covers the establishment of time standards
derived both by work measurement techniques and by
feedback.
DEFINITIONS
(a) Work measurement is the application of techniques
designed to establish the time for a qualified worker to carry
out a specified job at a defined level of performance.
(b) A qualified worker ¡s physically fit, and has the required
level of education, ¡ntelligence, skill and knowledge that the
job demands.
(c) The defined level of performance ¡s the brlsk rate of worklng
of a well-motlvated qualified worker.
USES OF WORK MEASUREMENT
Work measurement is used to develop time standards for -
planning and scheduling of construction operations;
-
estimates for tenders, quotations and completion dates;
setting output standards for workers and machines which
can be used both for control, and as a basis for incentive
schemes;
-
balancing the work of workers or machines to form a
composite team (gang balance).
STAGES IN THE APPLICATION OF
WORK MEASUREMENT
(a) Select the work to be studied.
(b) Record all the relevant data, the methods and elements of
the job.
(c) Examine the recorded data and detailed breakdown to
ensure that the most effective methods are being used and
that the productive elements are recorded separately from
the unproductive.
(d) Measure the quantity of work in each element in terms of
time.
(e) Compile the standard time for the operation as a whole,
which will include time allowances for relaxation, personal
needs, contingencies, etc.
(f) Define the method and issue the standard time.
42
TECHNIQUES USED
The principal techniques of work measurement in construction
work are:
-
time study;
activity sampling;
-
feedback of output data;
-
synthesis from standard data or estimates.
"THE HUMAN FACTOR
Workers generally may resent being timed and studied at their
work, both because of the implied criticism and on account of
suspicion that some may lose their Jobs and the remainder will
have to work harder as a result. The reasons for, and the
methods used in the time study should be explained to
supervisor and workers alike. On no account should the work
study specialist resort to secret timing as the practice is
invariably found out, and leads to serious and understandable
labour unrest.
time study equipment
Basic time study equipment comprises a watch, a study board,
pencils and time study forms.
WATCH
A regular stop watch is best, although an ordinary wrist watch
with a legibile second hand can be acceptable for some
operations. On construction sites, most operations are of fairly
long duration, so that timing to the nearest five seconds is
generally accurate enough. A suitable specialist stop watch is
illustrated below.
CENTI-MINUTE FLYBACK
STOP WATCH
The maín scale is graduaUd
¡ n V\oo minutes
43
minute hand
To opérate: Button A winds up, starts and stops the watch.
With the watch running, pointers a and b go round together.
The first touch on button B stops pointer b, allowing the time to
be read off and recorded whilst pointer a is still moving. The
second touch on button B causes pointer b to rejoin pointer a.
Having stopped the watch (button A), one touch on button C
causes pointers a and b to fly back to zero.
STUDY BOARD
This is a fíat plywood board, large enough to hold the study
sheets. Provisión is made for clipping on the watch, so that the
watch, study sheet and the actual job can be taken in at a single
glance.
di
Wabcli
4-''
PENCILS
Two or three sharpened pencils are carried to avoid
interruptions to the study if the point breaks. Pencils are
preferred to ink - in wet weather or if the hands are sweaty, the
ink will run or smear.
TIME STUDY FORMS
An example of a typical time study form is reproduced in
figure 10.
44
Figure 10. Time study top sheet
PROJECT
STUDY No.
SHEET
OPERATION
TIME STARTED
TIMEFINISHED
ELAPSEDTIME
OPERATIVES
TOTAL O.T.
TOTAL I.T.
MACHINES
OBSERVER
DATE
REMARKS
ELEMENT
DESCRIPTION
R - Rating
45
WR
WR = Watch Reading
OT
BT
ELEMENT
DESCRIPTION
OT = Observed Time
BT - Basic Time
WR
OT
IT - IdleTime
BT
making the time study
SELECTING THE JOB TO BE STUDIED
Some possible reasons for selecting a particular Job are:
-
to study a new job, or a Job for which no reliable output
figures exist;
-
tostudy achangeof method;
-
to investígate workers' complaints that the time allowed for
a particular job is too tight;
-
to investígate delays;
-
to ascertain correct gang balance;
-
as a preliminary to introducing an incentive scheme;
-
when the cost of a particular job seems excessive.
TIME STUDY PROCEDURE
-
observe the job as a whole without any timing;
decide on the breakdown of the job into elements of work;
-
establish the break points;
-
record the elements and break points on the time study
sheets;
observe, rate, time and record the observations;
add in relaxation and contingency allowances;
-
develop the standard time for the job.
OBSERVE THE JOB
The first step is to study the job without timing, watching a few
repeats of the work cycle until it is thoroughly understood and
obtaining explanations from the supervisor or workers as
necessary. The next task is to break the job down into elements
of work and record them on the time study sheet.
BREAK DOWN INTO ELEMENTS
An element is a basic, distinct part of the job selected for
convenience of observation, measurement and analysis. For
instance, in the case of mixing concrete the work cycle can be
46
broken down into the elements of loading the mixer hopper with
aggregate and cement, discharging into the drum, adding
water, mixing and discharging the mix. Where a more detailed
analysis is needed, these elements can be broken down still
further. In the case of loading this could be:
-
labourers fill the gauge box with sand;
labourers grasp the handles of the gauge box;
labourers lift the gauge box and move it to the hopper;
-
labourers empty the gauge box into the hopper;
labourers return to the sand-pile and set the gauge box on
theground.
BREAK POINTS
For ease and accuracy of identification each element will have a
distinctive start and finish known as break points. These should
be easily recognised by eye or ear, such as:
-
labourers' hands grasp the handles of the gauge box;
labourer's hand grasps the first brick;
-
crane's hook touches precast wall unit;
-
engine roars as driver prepares to move off;
-
dragline bucket comes to rest.
The break point should be entered on the study sheet to ensure
the clear identification of the beginning and end of the element.
TIMING THE ELEMENTS
(a) Cumulative timing - The watch or stop watch will run
continuously over the whole period of the study. The watch
is started (or the time is noted) at the beginning of the first
element of the first cycle to be timed. It is not stopped until
the whole study is completed. Whenever a break point
occurs and an element is completed, the watch reading is
recorded. The individual element times are obtained by
subtraction after the study is completed. The subtracted
times are called the observed times.
47
(b) Flyback timing- In this method a stop watch is used and at
the end of each element of work observed the hands of the
stop watch are returned to zero (flyback). The watch then
automatically recommences the timing of the next element.
(c) Time reconciliation - As a check, the time of day when the
timing began and ended should be recorded. This allows
for a comparison between the sum of all "flybacks" and the
actual duration of the study. If the timing error is greater
than 5 per cent, the results should be scrapped and the
study redone.
RATING
It will be appreciated that timing alone does not produce a fair
assessment of the working ability or efficiency of a worker, or
whether he is working hard or going slowly. Also, many of the
labouring tasks on construction sites are carried out not just by
men in their prime, but also by older men, women and young
boys, who through undernourishment, etc., may not be 100 per
cent fit. It would be incorrect to time the work of the strongest,
best and fittest workers, and make that the standard for the
whole workforce. A system of rating has been derived so that
not only the timing but also the performance of the worker can
be measured.
Table 3.
Rate
Various rates of working
Description
Comparable walking
rate
m ph
kph
Noactivity
0
0
50
Very slow, clumsy, fumbling movements. Worker appears half asleep with no interest in the Job
2
3.2
75
Steady, delibérate, unhurried performance, as of worker
not on piecework, but under proper supervisión; looks
slow, but time is not being intentionally wasted while
under observation
3
4.8
100
(standard
rating)
Brisk, business-like performance as of an average qualified worker on piecework; necessary standard of quality
and accuracy achieved with confidence
4
6.4
125
Very fast; operator exhibits a high degree of assurance, 5
dexterity and co-ordination of movement, well above that
of an average trained worker
8.0
150
Exceptionally fast; requires intense effort and concen6
tration and is unlikely to be kept up for long periods; a
virtuoso performance only achieved by a few outstanding
workers
9.6
0
At the same time as the study specialist records the time of
each element, he will also assess and record the rate of working
(that is, the speed and effectiveness with which the work is
being done). In order to assess the performance or rate of
working, a rating scale has been drawn up, on which the valué
of 100 is given to the desirable rate at which the worker should
consistently work. This standard performance of 100 is defined
as the rate of output which the qualified worker will naturally
achieve over the working day or shift, without overexertion,
provided he knows and sticks to the proper method, and
provided he is motivated (by bonus payments, piecework) to
apply himself to the work. Table 3 gives examples of various
ratesof working.
(a) Qualified worker: The standard performance relates to a
"qualified worker" who has the necessary physical
attributes, possesses the required intelligence and
education, and has acquired the necessary skill and
knowledge to carry out the work to satisfactory standards of
safety, quantity and quality.
(b) Factors affecting rating are the effectiveness and speed of
the operators.
(i) Effectiveness - this means the application of acquired
skill given to the work by the worker. It implies
keenness, alertness and applied intelligence. The signs
of good application are:
- shortest path of movement - no detour;
- keeping consistently to the best method;
- sureness of touch and sequence;
- avoiding unnecessary actions or flourishes;
- effective use of both hands (or feet);
- intelligent anticipation of movements and events;
- tidiness and systematic arrangement of tools and
materials.
(ii) Speed (industrious application to the job) - this means
diligence, steadiness and continuity. The signs are:
- rhythm and consistency of movement;
- speed of movement;
- steady effort - no frequent small pauses;
- making the job look easy.
49
In general, workers under study tend to improve their
performance, simply as a result of the unaccustomed attention
they are receiving. This temporary rise of performance drops as
soon as the study specialist departs. On the other hand, ¡f the
workers know the study is to be the basis for an incentive
scheme, they may put up a premeditated slow performance, in
the hope that this will result in easier bonus targets. Skilful rating
will detect both these deviations.
Unless the supervisión and motivation of the workers is
exceptional, a standard performance will rarely be sustained for
long if a bonus is not paid. Without such incentives the normal
pace of work will normally lie between 50 and 75 per cent of the
standard performance.
The rating code of 100 represents standard performance.
The work study specialist will evalúate the observed
performance in relation to this (e.g. 75, 90, 110, 120) during the
course of the element being timed. If the element is of relatively
short duration, one evaluation will suffice. For an element of
longer duration the performance of the worker may vary, so that
more than one assessment of rating may be needed to obtain a
fair average.
BASIC TIME
This is the time for carrying out an element of work at standard
rating. The basic times are calculated by the following formula:
Basic time = Observed time x
Observed rating
Standard rating
Thus, if a qualified worker, working at a steady rate of 100, performs
a certain element of work in 15 minutes without any rest pauses, then
the basic time for that element of work is100
15 x
= 15 minutes.
100
If his rate of working was 125, then the task would only take 12 minutes, but the basic time is still12 x
125
15 minutes.
100
With a slower rate of working of 75, the element of work would take
20 minutes, but the basic time will still be75
20 x
= 15 minutes.
100
An example of a time study form, used for evaluating basic
times, is given in figure 10.
50
relaxation allowances
The basic time makes allowances for the speed and
effectiveness of each operator, but not for time needed for
recovery from fatigue. For example:
a worker breaks up a concrete slab with a 7-kilogram
hammer. After striking say 15 blows in one minute, he will
be compelled to rest for a similar length of time before he
can resume;
a painter may paint for ten minutes without a pause, but he
will then need a rest for half a minute or so, to flex his
fingers, etc., before proceeding.
To allow for these needs, a relaxation allowance is added to
the basic time. Relaxation allowances are usually expressed as
percentages of basic time, and are applied as appropriate to
each sepárate element. In practice, a labour work unit of one
hour and one shift is never composed of continuous,
uninterrupted work. Relaxation periods of a few seconds or
minutes occur throughout the working period, as the worker
feels the demands made on his body. The time taken up by
these relaxation breaks may be 10 to 30 per cent of the working
time, depending on the nature of the work. On particularly
arduous Jobs carried out under severe climatic conditions, the
relaxation necessary could total more than 40 per cent of the
working time. Brief periods of relaxation are needed for the
following reasons:
(a) standard - e.g. to drink water, urinate, etc.;
(b) posture - to give relief from the discomfort arising from
working in an unnatural and uncomfortable position;
(c) attention - to give relief from the strain of concentrating on
dials, precisión work, calculations, etc.;
(d) conditions - excessive heat, cold, wetness and poor
lighting;
(e) effort - to allow periods of rest from heavy physical work;
(f) monotony-to give relief from boredom or isolation.
51
The mix and magnitude of these breaks will depend upon
the type of work. Office workers in an air-conditioned office
might need only 10 per cent of work time made up chiefly of (a),
(c)anó (f). A labourer doing heavy manual work during the heat
of the day may need 40 per cent made up chiefly of (a), (d) and
(e). The worker himself will decide on the rate of working and on
the breaks demanded by that rate. One hour of working time
Table 4.
Relaxation allowances
Nature
Description
Allowance
expressed
as percentage of
basic time
Standard
Personal needs (toilet, drinking, washing) plus basic fatigue
8
Posture
Standing
Awkward bending
Very awkward (lying, stretching up)
2
2-7
2-7
Attention
Fairly fine to very exacting visual work
Fairly to very complex mental process or span of attention
0—5
0-8
Conditions
Lighting: fair to inadequate
Ventilation: fair to dust or fumes to extreme conditions
Noise: quiet to intermittent or high pitched
Heat: températe to 35 °C at 95 per cent humidity
0-5
0-5-10
0-5
0-70
Effort
Light: up to 5 kg lifts
Médium: up to 20 kg lifts
Heavy: up to 40 kg lifts
Very heavy: up to 50 kg lifts
1
1-10
10-30
30-50
Monotony
Mental
Physical: tedious to very tedious
0-^4
0-5
may include 50 minutes of slow, steady continuous working
with only 10 minutes of relaxation, but a faster rate of working
would need longer rest breaks. The rate of working will depend
on the physical condition of the worker, and the degree to which
he is supervised and motivated.
Table 4 gives typical examples of relaxation allowances
which are allowed as a percentage of basic times.
It should be noted that where the nature of the work is
varied, this variation itself would provide some measure of
relaxation.
RELAXATION ALLOWANCES IN HOT
ANDHUMIDCLIMATES
The relaxation allowance necessary to cover the conditions
encountered in hot and humid climates can be very large, and is
worthy of special comment.
When a human being does physical work, heat is generated
which is dissipated mainly by the evaporation of perspiration.
The rate at which heat is lost depends on the surrounding air
52
Table 5.
Relaxation allowances ¡n hot and humid climates
Dry bulb temperature
in °C (°F)
Additional time
allowance for relaxation %
26 (79)
28(82)
30 (86)
32 (90)
34(93)
0
10
20
40
70
temperature, the humidity and wind speed. Human work
capacity is generally not affected at temperatures below 24
degrees centigrade (75 degrees Fahrenheit) but this capacity
decreases as the temperature rises, depending on the
metabolism and degree of acclimatisation of the individual.
Assessment of the relaxation time to be allowed is extremely
difficult since not only is there a scarcity of data on this topic but
there also may be a considerable variation in temperature,
humidity and wind speed during the course of the day's work.
Studies undertaken in the Philippines by the Food and
Agriculture Organisation of the United Nations (FAO) give some
idea of the relaxation allowances that may be necessary for
forest workers, working in the shade, with a relative humidity of
90 per cent or more and a wind speed of 0.5 metres per second.
This indicates clearly that not only to maintain high
productivity, but also in the interests of the workers' well-being,
it is necessary to avoid working in the heat of the day. Ideally, in
hot and humid climates, work should start as near first light as
possible, and continué until conditions become severe enough
to reduce productivity significantly. Work could resume later
when the day has cooled off, and continué until dusk.
NOTE:
- Where an operation requires a relaxation allowance of 40 per
cent or more, it should automatically be subject to a method
study to make the Job less exacting. It is often possible to
introduce some minor device to make the Job easier.
- Calculations of relaxation allowances are done in the office,
not on site. The allowance is calculated separately for each
element of work and for each relaxation factor, as shown on
the study sheet.
CONTINGENCY ALLOWANCE
53
There are many necessary elements of work and occasional
delays which occur during a working day but which are random
and of short duration. For instance, a joiner has to sharpen his
tools; materials may occasionally not be to the exact dimensions
and may need correction; work may be held up while
¡nstructions are received or problems discussed. It ¡s usual to
make a contingency allowance to cover such eventualities. An
allowance of 5 per cent ¡s normally adequate for most
construction Jobs.
derivation of standard times
DEF1N1TION
Standard time ¡s the total time in which a Job should be done at
standard performance, and is the sum of the basic times to
which the appropriate relaxation allowances have been added,
plus any other extra allowances for contingencies, interference,
etc. Figure 13 illustrates a form used in deriving standard times.
- Standard time can be
represented as:
sum of basic times =
puré work
- In practice the relaxation
breaks will be scattered through
the Job, thus:
y ^
fe^=l
relaxation and
other
allowances
N ^ y
- A worker can achieve a standard |
|
performance in different
|
rate
of
puré
working
plus
S 0W
ways, e.g.:
less relaxation
^ B
|
fast rate of working with more
relaxation
CALCULATION OF STANDARD TIMES
When the recording of the construction operation is completed,
the work study specialist will return to the office to prepare
summaries of the site studies. For every hour of site study, two
or three hours of calculations are ¡nvolved. First the study
reconciles differences between the stop watch time and the
elapsed dock time. The discrepancy should not exceed 5 per
54
Figure 11. Time study: Fixing precast wall units
PROJECT SMJtfUSS f(Mfá ak fredviUe.
STUÜYNo.,¿g3
OPERATION ftX PWOJJT UIHl UHITS. 67» HOOK..
OPÉRATIVES &>rt4 <¿Wt»ék. ¿ X I M / C * » * * , áUf&inSB)''
<u*á toe e»«¿ttk5.
MACHINES Uiffiuy hower CKCU*e Aí$.
REMARKS W e a t K j e ^ / á i K - .
ELEMENT
DESCRIPTION
WR
TIMESTARTED 09 10
TIME FINISHED (Q-S?
ELAPSED TIME I • Zg
j wc
= z*
TOTAL O.T.
TOTAL I.T.
í^-33
f-W
OBSERVER M
DATE¿/7/g7
30°C.ítigfW'^feí€.
OT
BT
ELEMENT
DESCRIPTION
OSO0-55 ( P
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roo
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uo
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100
zoo 2 00
100
0 * 0 OW
90
100
no
!•*> l-ÍO
210 2 * 1
30
95
110 f-o*
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K>0
íOO
R - Rating
55
IÜSL
WR - Watch Reading
OT = Observed Time
9?
«X>
35
100
BT = Basic Time
IT - Idle Time
¿4
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Figure 13. Standard time summary sheet
STUDY No. 2 - 9 3
STANDARD TIME SUMMARY SHEET
OPERATION
REF. No.
fix WHJUUHÍBto(fafústr —Sneigrass fiaJts-
DATE 2 / 7 / J 7
DESCRIPTION
t/t ók&ar o} use. en. ?kte*ix (aw-touder. f\b fuvsy \jvaHk koU uñfk pfOtas eu^i. bdtfc©#I0K> o u n e
hdéiyy. Team of .'— <7F: ¿aguama*! ¿utd ¿«73 <6iv€K/¿5Ttnj& c^^áJb^/é^pi^v-:
supervise*
(mi stx etecAcrs . 72»^ u # /Zm^ WvjeMítt/ sien; /¿m.
ELEMENTS
% RELAXATION
%
S
0-60
8
5
(3
•6*
/•T3
$
5
n
202-
{í)úfMe¿t crtxjftS- k> (Juail UH¿t
P
A
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E
M
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Zanuní. (JpertltarJ
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(D \)¡SC6lw¿ct anxneEclMxQ
@)$ou\y\$ OUrtU) per mxk u*úb-
S-97
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202.
TOTAL BASIC TIME
S - Standard
E = Eftort
TOTAL
BASIC
TIME
%
Q
UNIT
S.T.
/
•6S
S.T.
z-oz
/
S
5
S
1* Z95
/
z-93
S
3
5
5
lé
6-91
/
/
é93>
236
f
Z&,
n
i
IZ SI
P - Position
M - Monotony
Con
TOTAL STANDARD TIME
A = Attention
Con - Contingency
C - Conditions
0 - Quantity
5A^
IG06
IÍOO\
ST - Standard Time
Relaxation and contingency allowances are added on to the average basic times to derive the standard times for each element, and by
addition the total standard time for the whole operation.
cent. Next all elements of work are extracted and the times
extended to find the standard times, e.g. observed time x rating
+ relaxation and contingency allowances. To obtain a truly
representative time, the average of a number of studies is
required. Examples of the forms used are given in figures 11
to13.
RECORDS
A copy of the summary of every standards study will be filed
away for future reference, so that a reference library of standard
times can be built up for the use of all concerned, i.e. cost
estimating, planning, resource scheduling, control, and as a
basis for task work or incentive schemes. In setting targets, it is
necessary to define clearly the method of working so that the
people concerned, workers, supervisors and estimators,
understand the exact work content involved. The definition will
include details of workers, tools, equipment needed and quality
standards required.
Standard times can be recorded in tabular or graphical
fashion, depending on their nature. Alternative methods of
presentation are given in figures 14 and 15.
PRACTICAL DERIVATION OF
STANDARD TIMES
It has been stated above that difficulties may be encountered in
deriving standard times because of lack of experience and
confidence in rating and assessing relaxation allowances. The
explanations given are not so much intended to develop
expertise as to créate an awareness of the factors affecting
human work capacity, and an understanding of the scientific
method of assessing it. Most standard times will be arrived at
by studying the performance of daily rated labour. The
explanations above will enable these assessments to be made
with greater confidence. Even with a limited experience of these
methods it is possible to make a reasonably fair assessment.
Some organisations, experiencing significant seasonal and
other variations in working conditions, prefer to keep a record
library of basic, as opposed to standard, times and build in
relaxation and contingency allowances appropriate to each
individual site.
Figure 14. Tabular recording of standard times
CODE ¿X Z$
STANDARD OUTPUT DATA
OPERATION éX&WXhe
DESCRIPTION Kw6
1
Z
5
•
#
3
<f
UNIT of MEASURE
/•/* /•/í)
fádjpMtowM
"•ÓW
/•05
(•27
(•69
2«"
/-IFT 0S-lóv^ehes
MS (OS izo 110 /•OS I-2J
M l-HO l?5 f-fl W i<tc
flíAI
iba HS 2-JO z-7fl z*J 2-^0
*7¿
1-20 110
/
2-
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0$
lio
Ofc M* M5 *p 1-0* l«)
i£
1 % /•£ |-20
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i^S 1-70 (-60 /•75 /•70 | - «
2$¡> ¿ « W 27* 2-tf 2-7S 2U 27/)
/
3
k
\*k>
é* MWfr 4*"fa¿ &¿ftú v*r ui&tovfriwia. W*&
sb&fy,) fic/OMeZjOrtfrSIpaj&j
EQUIPMENT
VLT\&
<*"d ItmA b$ hOM¿
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170 í 65 170 \n
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115 VIS
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342
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59
As the results of new studies come in, they will be entered in the appropriate
column, and the mean figure adjusted as necessary. When sufficient data is
obtained, missing figures can be interpolated. The above information can also be
ptotted graphically as shown in figure 15.
Figure 15. Graphic recording of standard times
STANDARD OUTPUT DATA
CODE
OPERATION
UNIT of MEASURE
DESCRIPTION
EQUIPMENT
4T
UJ
or
\~
LÜ
O
CO
3--
r>
o
ce
UJ
a
2--
Oí
LOADINQ
HEIQHT
IN METRES
rs
o
X
I
z<
1 --
0
2
3
SOILTYPE
NOTE:
The data shown in tabular form in figure 14 are here reproduced .
graphically. See table 6 for soil classification chart.
60
excavation and loading of
soils by hand
SOIL CLASSIFICATION
Productivity is related to the soil type. The following table gives
a rule-of-thumb classification for easy ¡dentification of soil types
on site.
Table 6.
Soil classification chart
Cohesive soils
Non-cohesive soils
Description
Site recognition test
Description
Site recognition test
Soft
Easily moulded in the
fingers
Can be moulded in the
fingers by strong pressure
Cannot be moulded in the
fingers
Brittle or tough. Crowbar
required for hand digging
Difficult to dig by hand
even with a crowbar
Very loóse
Easily excavated with Í
shovel
Can be dug with a
shovel only
Pick or swung tool
needed to loosen
Crowbar required for
hand digging
Difficult to dig by hand
even with a crowbar
Firm
Stiff
Very stiff
Hard
Loóse
Compact
Dense
Very dense
activity sampling
Activity sampling can be used to assess the degree of activity on
the various sections of a construction site, to check the amount
of time wasted and the reasons, and to check the balance of a
gang. It may also be used for developing standard times,
especially of gang work.
DEFINITION
61
Activity sampling is a technique in which a large number of
instantaneous observations are made over a period of time, on a
group of machines, operations or workers. Each observation
records what is happening at that instant. The percentage of
observations recorded for a particular activity or delay is a
measure of the percentage of time during which the activity or
delay occurs.
If ¡t were possible to look down on the whole construction
site continuously throughout the day or week, and record every
stoppage of worker or machine, a complete picture of effective
and ineffective time could be obtained. However, to do this.
would take up too much time and staff. Instead a series of tours
of the site are made at irregular intervals. Each time the
observer notes what a particular worker or machine is doing at
the instant he or it is observed. If a sufficiently large number of
observations are made, the percentage of readings that show a
worker or machine as working will tend to equal the percentage
of time that they actually were working.
It is important to make the observations at irregular
intervals, to avoid observing the activities at the same point in
the work cycle each time.
DEGREE OF ACTIVITY ON SITE
During the site inspection, each worker or machine is noted
simply as working or not working. Since a work period is
normally made up of active work interspersed with short
relaxation breaks, the average derived from several counts will
never show 100 per cent activity. On construction works it will
normally be 60-80 per cent depending on the heaviness of the
work and climatic conditions, etc. Where lower figures than
these are observed there is something wrong on site and further
investigation is needed. On a large site employing a large labour
forcé, this technique is useful for identifying weak spots where
more supervisión, or a more detailed study may be needed.
DETAILEDANALYSIS
For a more detailed analysis of activities, instead of recording
just "working/not working", the observer could use a code
letter to describe what the worker or machine is doing at the
time of observation, such as:
Machine excavating
E
Worker working W
Machine travelling
T
Worker resting
R
Machine breakdown
Machine maintenance
Machine refuelling
BD
M
F
Worker absent
A
62
These could be recorded on the form ¡llustrated below:
ACTIVITY _f
SAMPLE u
Machine
or
Worker
1
j
Tour of Inspection N°
1
2
3
4
5
6
7
/
9
8
10 11 12
y
CHECKING GANG BALANCE
An example of how the technique may be used for checking the
balance of a concreting gang is shown later.
ACCURACY
The larger the sample, Le. the greater the number of ¡nspections
or observations, the nearer the data will be to presenting a true
picture of the facts. There is a formula which glves an
approximate valué of the accuracy of the results of the sample.
It can be wrltten ¡n two ways:
either N =
4(1 - P)
2
SP
orS=
V
4(1 ~ p;
pN
where N = number of observations
S = degree of accuracy, expressed as a decimal (e.g. 5%=0.05)
P = extent of activity being observed, expressed as a decimal (e.g.
40% of time = 0.40)
63
EXAMPLE OF ACTIVITY SAMPLING
TO DETERMINE INACTIVE TIME
Four scrapers are working on an earth-moving operation. It ¡s required to assess on average the proportion of the working time that
the machines are stopped. Over a period of two days 120 observations are made of each of the four machines, the results being:
machine working
machine stopped
192occasions
288occasions
(a) Ouery
These observations indícate that on average the machines are idle288
x 100 = 60 per cent of the time.
120 x 4
How accurate is this figure likely to be?
Solution:
UsingS= -y /
/4(1 - p)
where p = 0.6 and N = 480
Then S = .075 or 7.5 per cent
Degree of accuracy is 60 ± 7.5 per cent,
or the average inactivity of the machines is 52.5 to 67.5 per cent of
the time
(b) Query
If a degree of accuracy of ± 5 per cent is required, how many more
observations would be needed?
Solution:
4(1 - p)
Using N =
where S = .05 and p is approximately 0.6
S2P
ThenN = 1067
Since there are four machines, the number of observations to be
made is
1067
•• 2 8 7 , that is,
4
an additional 167 observations are needed.
64
EXAMPLE OF USE OF ACTIVITY CHART
IN CHECKING GANG BALANCE
A concrete slab ¡s being poured. The activities and labour forcé
are as follows:
Activity
Labour
1.
2.
Load aggregate into mixer
Load cement
3.
Add water. Discharge mixed concrete
on to the ground
1 operator
4.
Load the concrete into wheelbarrows
3 labourers
5.
Barrow the concrete away, and deposit
in slab forms
Spread the concrete
Tamp the concrete
6 labourers
4 labourers
2 labourers
6.
7.
3 labourers
1 labourer
8.
Float the concrete
1 masón
During the course of the day, the Job ¡s inspected 80 times,
and the activities of every worker are noted. The summary is as
follows:
65
Activity
Total no. of occasions worker
seen working
1.
2.
3.
4.
5.
6.
7.
8.
120
56
64
216
336
136
128
64
Load aggregate
Load cement
Empty mixer
Loadbarrows
Barrow away
Spread concrete
Tamp concrete
Float concrete
The analysis of the results is:
2
4
5
6
7
3
Load Empty Load Wheel Spread Tamp
cement mixer barrow barrow
1
Load
agg.
No. of workers engaged
in each activity
Total no. of workers
observed
(80xno. of workers)
1
3
1
8
Float
3
6
4
2
1
240
80
80
240
480
320
160
80
No. of workers observed
as working
120
56
64
216
336
136
128
64
Average percentage of
lime working
70
80
90
70
80
80
50
42.5
It will be seen that labourers on activities 1 and 6 are
underworked, while those on activity 4 appear to have
insufficient relaxation from the heavy Job of loading wet
concrete into wheelbarrows. A better balance is had by moving
one labourer from activity 1 to activity 4, and by taking two
labourers off activity 6 and finding them another job elsewhere
on site.
The new percentages of effective working time would then
be:
Activity
1. Load agg regate
2. Load wheelbarrows
3. Spread concrete
No. of labourers
Percentage of time working
Previous
Revised
Previous
Anticipated
3
3
4
2
4
2
50
90
42.5
50 x% = 75
90x3/4 = 68
42.5x4/2 = 85
USE OF ACTIVITY SAMPLING FOR
DEVELOPING STANDARD TIMES
Activity sampling is especially appropriate for developing
standard times for gang work where there are too many workers
or machines for easy observation by normal stop watch time
study. Before starting the activity study, it should be ascertained
as far as possible that the method and gang balance are right,
though the study itself may reveal problems. In the study each
member of the gang is observed at regular one-minute intervals.
66
A code letter ¡s used to indícate what each worker is doing at
the time of observation, and his rate of working is also noted (to
the nearest five units). The study continúes until sufficient
observations have been made, or until a particular work cycle is
completed, whichever takes the longest. Then, the number of
observations of each activity or element of work is taken to be
equal to the number of minutes taken up by that element during
the period of observation. It follows that the basic times for each
element of work will be the minutes observed times the
percentage rating.
Figure 16. Activity sampling record sheet
PROJECT
STUDY NO.
OPERATION
TIME STARTED
TIME FINISHED
ELAPSEDTIME
TOTAL O.T.
SHEET
TOTAL
ELEMENT CODE
O.T. = Observed Time
ELEMENT DESCRIPTION
B.T. = Basic Time
QUANTITY
O.T.
B.T.
Rated Activity Sampling - Record Sheet
Since observations are made every minute only, there ¡s a
chance that ele.ments of work lasting less than one minute may
be missed. The method is obviously not as accurate as a normal
time study, but provided that sufficient observations are made, it
is sufficiently accurate for most purposes of construction work.
The methods of recording and evaluation are shown in
figures 16 and 17.
Figure 17. Activity sampling extract sheet
PROJECT
STUDY No.
SHEET
ACTIVITY SAMPLE EXTRACT
ELEMENT CODE LETTER
Total BT
Total
Total BT
Total
Total BT
Total
Total BT
Total
Total BT
Total
Total BT
Total
Total
Total BT
Total
No.
of
Obs.
Total BT
Observed
Rating
A
ACTIVITY SAMPLING EXTRACT SHEET
Regardless of which worker performs the element of work,
elements are abstracted from the rated activity sampling record
sheet ¡nto the appropriate element column, and opposite the
approphate rating. An example is shown ¡n figure 17.
Having derived the basic times for each element of work in
the whole operation, standard times can be derived by
summation after adding in appropriate relaxation and
contingency allowances.
An example of the use of this technique is given in
Chapter 7.
feedback of output data
One way of obtaining performance data is by feeding back
details of the actual output from ongoing construction projects.
This data will not be as accurate as that obtained by detailed
time studies, but should provide reasonably reliable information
upon which estimating, planning or bonusing can be based.
Caution is necessary in analysing the data collected since no
formal rating of the workers' performances will have been
carried out. The feedback of output data can form part of a
project cost control system. To be effective such a control
system should feed back information from the works to the site
management as soon as possible after a particular operation
has been started on site. This enables identification of
deviations from the estimated costs, outputs or progress to be
made ¡n time for matters to be corrected before the situation
gets out of hand. Apart from providing material for building up a
reference library of output data, the feedback system will also
point out those áreas of inefficiency where work study is needed
to analyse and remedy a problem.
DETAILREQUIRED
69
The benefits derived from the system will be balanced against
the cost of running it. It will be necessary to decide upon the
nature and frequency of the data required. Generally, feedback
is necessary from all major cost Ítems, and Ítems where prompt
completion is critical to progress as a whole. Feedback may
also be called for from those items on which information is
lacking, either to fill a gap in the record library, or for bonus
target setting. It is generally adequate to analyse feedback
information weekly, but occasions will arise when a daily
analysis ¡s required. It will also be necessary to decide upon the
amount of detall required. For ¡nstance, ¡n pouring a concrete
floor slab, the cost and productlvlty of the concreting gang as a
whole can be measured, or else the breakdown details of
mlxlng, transportlng, placlng and flnishlng. The more detalled
information would be useful for syntheslslng the times of
dlfferent but similar operations. It ¡s ¡mportant that feedback
information includes comprehenslve details of the condltlons
under which the work was carrled out, not only the physical and
technical details, but also ground and weather condltions, type
of worker and method of payment; ¡n fact, everythlng that could
¡nfluence productlvity.
COLLECTION OF DATA
The work carried out by men and machines will be shown on a
daily work record sheet. The actual work done may be shown
on the same sheet or it may be measured and recorded
separately. The two are brought together on a summary sheet
(generally weekly) where the analysis is made. In some
countrles some of the data may be recorded by the foreman or
ganger in charge of each particular operation, depending on the
complexlty. However, it is usually more satlsfactory to appoint a
production control technician both to collect the data and make
and present the analysis to the site management. Examples of
the forms used for data collectlon are given in figures 18-20. It is
usual to give each construction activity a code number, to
facilítate filing and retrieval of information.
Output rates calculated on the weekly work summary sheet
can be presented to site management on the sheet showing the
summary of weekly performances for all operations. This may
show both output rates and costs. Records kept of feedback
data will normally be output figures rather than costs, since cost
of labour and plant hire vary with time, and would require
frequent updating. Against each operation is shown both the
output for the week under revlew, and the cumulative figures to
date. Site management can then compare the achievement with
the original targets, and also observe the trends. If on any
particular operation the weekly achievement deviates
significantly from the target figure, the figure can be entered in
70
red ¡nk to draw the site manager's attention to ¡t. The site
manager can then study the operation and decide what action
to take. This could result in either improving an inefficient
method, or correcting an inaccurate target figure.
Figure 18. Daily work record sheet
DAILY WORK RECORD
PROJECT
REF:
GANG
FOREMAN
DATE
WORKFORCE
ÑAME
IDLE
TIME
OPERATION No.
TOTAL
HOURS
No. 3RAFT
TOTALS
REMARKS
LU
PLANT
CE
O
ú
3
<
O
ce
O
5
ti
LU
CO
3
<
LU
OC
O
O
i
W ce
3
< O
O
LU
l
3
<
O
TOTAL TOTAL TOTAL
WORK IDLE HOURS
HOURS TIME
TOTALS
PREPARED
BY
REMARKS
IDLE TIME
M = Maintenance
B = Breakdown
R = Repairs
COMPARISON WITH EST1MATES
The above paragraph describes a method whereby site
management can compare the output achieved with that
originally estimated. These target estimates may nave been
based on work study data from other sources or on rates that
the organisation's cost estimator has built up. In the latter case,
to enable effective site comparisons to be made, the breakdown
of estimates into the sepárate elements of labour, plant and
materials must be available to site management. The greater the
detail, the greater the potential for control in identifying the
precise cause of deviations from the target. For example, major
Figure 19. Weekly work summary sheet
WEEKLY WORK SUMMARY
REF:
PROJECT
DATE
OPERATION
HOURSWORKED
No.
M
DESCRIPTION
T
W
Th
F
S
Sun rOTAL
F
S
Sun TOTAL
LABOUR
CRAFT
PLANT
WORK
COMPLETED
OUTPUT
RATES
LABOUR
PLANT
REMARKS
OPERATION
HOURSWORKED
No.
M
DESCRIPTION
T
W
Th
LABOUR
CRAFT
PLANT
WORK COMPLETED
OUTPUT
RATES
LABOUR
PLANT
REMARKS
OPERATION
HOURS WORKED
concrete formwork operations would be broken down into
elements of materials, manufacture, erection, stripping, cleaning
and repairing.
Figure 20. Weekly performance summary sheet
SUMMARY OF WEEKLY PERFORMANCES
TARGETS
Output
Quantity
Cost
Output
OUTPUT
RATE
Cost
COST
Quantity
DESCRIPTION
3
2
Date
Quantity
No.
1
W E E K No.
Cost
TOTAL
ESTIMATED
QUANTITY
Output
OPERATION
PROJECT
WEEKLY
CUMULATIVE
WEEKLY
CUMULATIVE
WEEKLY
CUMULATIVE
WEEKLY
CUMULATIVE
WEEKLY
CUMULATIVE
Note.
Any deviations from target should be entered in red.
using the output data
The library of output data can be used for a variety of purposes
such as estimating and costing, planning and controlling,
incentive schemes and synthesis of data for new operations.
PERFORMANCE
73
It should be remembered that standard times derived by work
study represent a performance rating of 100, whereas those
derived from feedback have no scientific measure of
performance assessment rating built in. In applying output data
it will be necessary to forecast the expected performance of the
workforce. This will depend on the quality of labour in the
locality of the works, the quality of the site management and
supervisión, and whether any incentive schemes are to be used
on the project. A very approximate indication of the performance that might be expected from the labour forcé is:
Payment method
Management quality
Piecework
Task work
Daily rated
Daily rated
Good
Good
Good
Poor
Performance
'
100+
75+
75
40-
The decisión as to what performance figures to allow for
both labour and plant will be a matter of experience, and can be
assisted by comparing feedback with work study data.
PLANT AND EQUIPMENT
ln the case of plant and equipment, performance is affected
more by the ability of site management to reduce standing time
than by operator skill and efficiency. Standing time may be due
to breakdowns and/or poor planning and organisation.
Especially in the case of earth-moving equipment, output
will be affected by the nature of the soil and ground conditions.
ln the absence of locally obtained output data on plant
performances, the productivity data given in the manufacturer's
handbook may be used. However, it is necessary to bear in
mind that these figures will be difficult to achieve, and
performances ranging from 50 to 80 per cent of those stated are
more likely, depending on incentives and management on the
project site.
SYNTHESIS
From time to time, especially early on, there will be some work
operations for which no output data are available. ln these
cases it will be necessary to synthesise the data required.
Although the operation is a new one, it will probably contain
elements of other jobs carried out previously, details of which
have already been fed into the library.
The new operation is therefore broken down into its
component elements and, where they exist, the appropriate
elemental times are selected from the library. Where no
corresponding time exists, then the elemental time must be
estimated either by modifying the nearest appropriate time, or
74
by skilled judgement. This estimation may be made using the
judgement of an experienced foreman or reliable craftsman, by
simulating and timing the movements ¡nvolved or by reference
to data lists from textbooks or makers' handbooks.
The time for the new Job will be obtained by summing up
the elemental times. When assessing the times for the new job,
the anticipated working conditions will be borne in mind to
ensure the validity of any relaxation or contingency allowances
incorporated, and to forecast performance.
75
WORK STUDY
4
THE GENERAL APPROACH
TO SOME MAJOR
CONSTRUCTION OPERATIONS
plant utilisation
77
Where mechanical equipment ¡s used extensively on a project, it
will form a major part of costs, and its effective management
and operation are critical to profitability. In selection and
purchase of plant there are conflicts of interest. Sénior
management ¡s preoccupied with capital costs and availability of
back-up services and spare parts. Site management is
preoccupied with problems of suitability for the job in hand and
true operatlng costs. Work study is necessary to evalúate
suitability and operating costs, and in the general absence of
such studies and feedback data, considerations of capital cost
will predomínate, so that the most effective Ítems of plant may
not be acquired.
Operator efficiency will affect operating costs. Plant
operators are either direct employees of the construction
organisation, or may be seconded to the site by plant hire firms.
Direct employees are generally self taught, having first
understudied a regular operator on the site. Though such
operators are keen and acquire a high level of dexterity, they
may pick up bad habits and their lack of formal training means a
lack of knowledge about the mechanics of the machine, metal
technology and safety. This may result in negligence, misuse,
serious breakdown and accidents, leading to excessive
standing time and overhead costs. Operators from plant hire
companies are more likely to have had formal operator training,
but present different, supervisory problems. Their principáis are
preoccupied with the long life of their machines and continuity
of hire, so that the operators are required to nurse their
machines rather than achieve record-breaking outputs, and
productívity will therefore be less than it could be.
In both circumstances, time assessment of potential outputs
can only come about as a result of studies of operation and
performance.
The work study approach will therefore consider not just
the selection of plant but also every aspect of its operation. Thus
in the case of eartfi-moving plant, the following factors are
examined in detail to arrive at the true potential output of the
machine:
-
selection of plant (e.g. excavator or scraper);
-
location and direction of working;
-
suitability of attachments;
requirements, availability, suitability and balance of support
labour and equipment;
operator handling;
-
routes travelled to tip, full and empty;
tipping and cleaning-out times;
refuelling methods and times;
-
routine maintenance and servicing;
fuel and lubricant consumption;
-
inactive or down time, and reasons for this.
INEFFECTIVE WORKING TIME
The best output is achieved by a steady, even pace of work
throughout the whole day rather than by sporadic outbursts of
high activity. In general, the utilisation of construction plant
seldom rises above 33 per cent of the available working time.
Work study analyses indícate that the most common causes of
low plant utilisation are:
-
insufficient maintenance of plant, leading to breakdowns;
plant operatives not properly trained;
-
too frequent changes of plant operatives;
-
shortage of spare parts;
wrong type of plant in relation to site conditions;
-
lack of planning leading to hurried plant requisitions which
in turn lead to delayed deliveries or having to accept inferior
alternatives;
78
-
lack of daily supervisory programme planning, resulting ¡n
work interruptions caused by plant operators seeking
instructions;
-
wrong balance of plant, due to lack of measurement and
assessment of work content;
long waiting periods due to lack of Une and levéis;
poor layout or lack of approach roads on the site;
poor supervisión;
-
delayedinspections and approvals of completed sections
by resident engineers, etc.
SCOPE FOR SITE STUD1ES
A library of output data should be established based on studies
of all of the organisation's own plant plus that of hired plant on
site for long periods.
(a) Excavations - Data are needed for selecting not only the
right type of equipment but also the right balance of
supporting transport. Normal procedure is to establish the
potential output and unit cost of the excavator itself, and to
follow up with an investigation of all ancillary plant such as
lorries, bulldozers, graders, etc. In every case the work
study will establish the actual and potential output of the
ancillary plant, and then calcúlate the numbers of that plant
required to keep the excavator fully utilised. In every case
all possible alternatives will be evaluated before the final
recommendation is made to site management.
(b) Lifting equipment- The tower cranes are amongst the most
important Ítems of plant on a construction site. Their
efficiency should be a main concern of site supervisión and
work study staff. Work study data are used to prepare
detailed advance lifting programmes for the cranes. The
programme should be designed to allow all site trades to
share the lifting equipment without any need for costly
queueing. A crane must also be assured of continuity of
lifting work. Daily or weekly loads or packages needing to
be lifted should be prepared in advance.
79
-
To programme the utilisation, data are needed on:
loading and unloading times for different materials;
lifting and slewing times for different loads;
-
variations due to different weights, heights and reaches.
With an adequate library of data, ¡t will be possible to build
up the cumulative crane time required to prepare a schedule of
lifts.
(c) Concreting plant - The concreting operation involves
several work Ítems and trades which must all be balanced.
The work study procedure will involve the listing of all items
of work directly or indirectly involved in the concreting
operation, and the detailed study and analysis of each.
In general, on construction sites the slowest Ítem of plant
controls the rate of progress of the whole Job. In preparing any
work programme it is necessary to identify the slowest items,
and to investígate alternatives before fínalisíng the programme.
machine excavation
STUDY OF THE EXCAVATING MACHINE
The work study specialist focuses his attentíon not on the
machine driver, but on the machine itself so as to find out
whether the machine is the right one for the particular type of
operation. Very often it is either too small or too large. He must
establish the elements contained in the work, and the capacity
of the bucket (allowing for bulking). He must also time the
working elements and, from their duration, decide which can be
reduced by changes of method. He must find out from his
studies the potential output per hour of the excavator, and then
ascertain the factors affecting the utilisation of this machine. It is
unusual for an excavator to work in isolation. Usually the
machine loads the spoil into tipper trucks, which take it away to
the disposal point or tip. One of the most common causes of
high excavation costs is that the excavating machine has either
too few trucks or too many. If there are too few, the excavator
must wait for them and lose potential ouput, while if there are
too many, the trucks must queue for long periods to be loaded.
It will be appreciated that whether a machine works or not, it
must be paid for.
STUDY OF THE VEHICLES REMOVING
THE SPOIL TO THE TIP
The study of the excavator transport vehicles will commence
with a method and time study of a truck being loaded by an
80
excavator. Elements of work under consideration will be the
positioning of the truck towards the excavator; measurement of
the actual load taken; the effectiveness of the loading method
(this will overlap with the studies taken of the excavatlng
machine); the method, time and route of the loaded truck from
the loading-place to the place of discharge. To make sensible
observations and recommendations the work study specialist
must travel with the driver of the vehicle under observation. It is
usual to make as many as three trips ¡n order to obtaln a true
reading of the situatlon. The full cycle of study will also include a
study at the tip. Here the approaches to the tipping áreas will be
analysed and the tipping times recorded. Finally, the work study
specialist will travel back to the excavating point in the empty
truck.
The above information will be summahsed and analysed for
possible improvement of methods. The information obtained will
also be used for calculating the number of lorries to be allocated
to the excavator. The excavation supervisors appreciate this
kind of service, and requests from them for studies of
excavations are quite common in construction companies with
work study services. See Chapter 7 for an example.
concreting operations
There are several distinct but inter-related activities to be
studied:
(a) Mixer set-up - layout of machinery, delivery and storage of
cement, delivery and storage of aggregates and supply of
water.
(b) Transportation - of the concrete from mixer to placingpoint. Comparison of the effectiveness and costs of lifts;
crane skips; conveyor belts; concrete pumps; dumpers;
wheelbarrows and head-pans. Ready-mixed concrete
delivery may also be studied for comparison.
(c) Placing concrete - most effective methods of placing
concrete to slabs, walls, columns, beams, pile caps, etc. At
every floor level the transportation conditions may change,
and the method of work may be different to those used on
the level below.
81
(d) Curing the concrete granolithic, mosaic, etc.
or special finishes such as
For an effective study of concreting and related formwork
and reinforcement operations, the full support of the supervisor
¡n charge isessential.
formwork manufacture, erection,
removal, cleaning and salvagiñg"
Before commencing any studies, the work study specialist will
collect all costing data connected with the manufacture and
fixing of site formwork. If the company is using ready-made
formwork there is no need to study manufacturing processes.
On the other hand, if a company is using timber formwork which
is manufactured on the site, there is always scope to improve
the manufacturing process.
CARPENTERS' SHOP
The work study specialist will usually commence by making a
sketch of the carpenters' shop layout. This will be shown on the
site plan layout. All movements of raw materials and completed
formwork will be studied and recorded in the shop and on the
site.
Possible savings in the movement of men, materials or the
finished product will be sought. The potential cost of every
alternative will be worked out and the cheapest method will be
discussed with the shop supervisor as a possible new method. If
a supervisor is against the recommended method and supports
his rejection by a constructive criticism, the work study
specialist must find and try another alternative. If no alternative
is acceptable, the chances are that the existing site method is
the best one.
FORMWORK ERECTION
The method study of these operations should be done jointly
with a work measurement study. If method study is separated
from work measurement, the element of comparison between
methods is not effective. The erection of formwork always offers
a good opportunity for method and cost improvement.
82
" REMOVAL OF FORMWORK
There is a tendency amongst operatives to take formwork from
walls or ceilings in large strips and drop them down to the
ground, often from considerable heights. After this treatment
more than 60 per cent of the formwork ¡s damaged beyond
repair and has to be replaced by completely new units. By doing
this, the operatives hope to save a considerable amount of time,
and thus achieve a higher weekly bonus payment. From the
employer's point of view, the loss is double — the cost of new
formwork plus the cost of an incentive which was not really
earned.
When fixing incentive targets, a work study specialist must
be aware of this type of "short cut" and must design an
appropriate defence system.
CLEANING AND SALVAGING
OF FORMWORK
Whether the formwork used on the site is made of timber or
metal, it always gets contaminated by lumps of concrete and
must be cleaned before it can be used again. Where detailed
site costing is used, it is not unusual to discover that cleaning
costs are inordinately high. This is because the operation is
considered too simple to warrant much supervisión and
analysis, but in fact there is generally scope for savings.
steel reinforcement
Variations in design, shape, size and weight of reinforcing bars
make the planning and control of steel fixing very complicated.
Any work study may spread over the whole duration of the
construction work. The high cost of steel fixing may also be due
to shortage of supplies - if steelfixers notice that steel is in short
supply, they may go slow to make the Job last longer and so
avoid lay-off.
There are a number of related studies which may be carried
out at different times and places for particular steel-fixing
operations. These are:
83
the study of all costs connected with the fixing of concrete
steel reinforcement;
the study of bilis of quantities and detail drawings, with
particular reference to the design of steel reinforcement;
-
the study of the deliveries of steel reinforcement to the site;
-
studies of the general layout of steel reinforcement on the
site;
-
observation and study of all elements connected with
transporting steel reinforcement on the site;
-
studies of the steel-cutting shop and of steel-cuttlng
operations;
-
studies of steel bending;
-
studies of actual fixing of steel for concrete structures.
Sepárate studies must be done to cover floor slabs,
reinforced walls, reinforced columns and reinforced pile caps.
On all of them there will be substantial design differences to
cope with varying heights from floor to floor and from one
structuretoanother.
GENERAL LAYOUT AND SITE STORAGE
OF REINFORCED STEEL
The work study specialist needs to equip himself with a site plan
made to a reasonably large scale. A sketch should then be
superimposed on this plan, showing the exact position and
detailed layout of the steel stacking points, cutting shop and
cutting and bending benches. The movements of the steel
fixers, benders and/or cutters must be recorded and then a
string diagram or a flow process chart drawn to analyse the
methods.
From this analysis, an improved layout of the steel storage
system can be prepared and discussed with everybody
concerned. The recommendations will then be prepared and
presented to management for consideration and approval. If the
trial run of the new method confirms its superiority over the oíd
one, management will take the appropriate steps to have it
implemented on the site.
TRANSPORTING STEEL
The elements to be studied are:
walking or travelling empty towards a steel stack;
-
selecting the required length of steel rod;
loading the steel rodson toa vehicle ora cranewinch;
84
-
swinging the crane jib towards the waiting transport;
-
depositing a bunch of steel on the transport vehicle;
-
returning the empty jib to the stack and repeating the
operation;
-
vehicles travelling to the cutting área;
unloading the steel at the cutting shop;
returning the empty vehicle to the stacking point and
repeating the operation as required.
Whether the steel is handled by workers or machines, the
elements will be similar. No studies of more than two workers
should be attempted at the same time. If the work is carried out
by a gang consisting of several people, each person should be
studied separately.
STEEL CUTTING
The work study specialist should study only one worker at a
time cutting one specific gauge of steel. Sometimes, in the case
of heavy and long rods, two workers are used - one for holding
the steel and the other for operating the cutting equipment. The
usual work study breakdown of elements is as follows:
-
setting the bench and the nail marker;
-
selecting steel from the stack and dragging it to the cutting
bench;
-
cutting steel to the required length - the study specialist
records length and time taken per cut. As cutting times are
short, a stop watch is needed. Alternatively, the time taken
to make several cuts can be measured and divided by the
number of cuts to obtain the average individual times.
STEEL-BENDING STUDIES
85
When bending a specific gauge of steel the work study
specialist studies only one worker at a time. If several different
gauge sizes are used on site, each gauge should be studied
separately. The time taken for a changeover from one gauge to
another will also be recorded. On some sites the steel is
prefabricated weeks or months before fixing takes place. In
these circumstances, the cutting and bending becomes a
continuous operation and the change of gauge may occur only
periodically. On some other sites cutting and bending may be
carried out as dictated by the progress of the Job. The work
study specialist will need to adjust his observations and
recording methods to suit the site conditions and the
requirements of management and supervisión.
The usual elements observed in steel bending are:
-
collection of steel bars from the cutting place and
transportation to the bending bench;
-
adjustment of the bench for the new gauge and design of
steel and the nailing of the markers;
-
bending the length of every bar; the number of bends made
will be recorded and a three-dimensional sketch made of
the particular design being studied;
-
placing bent steel on to a stack (in some cases it may be
built into a prefabricated reinforcement cage);
-
delivering bent units to the fixing position (this may take
place on a different occasion).
STUDY OF STEEL FIXING
Before commencing the steel-fixing study, a careful survey will
be made of the fixing place. If steel fixers work on a scaffolding,
its erection may also be included in the study. As steel fixing
consists of placing and tying together different gauges of steel,
every time the pattern of fixing is changed a note will be made
regarding the diameters and the length of the bars bound
together.
The typical elements of steel fixing are:
walking or climbing to the place of fixing;
preparation of a scaffold (if any) and/or location of ladders,
walking boards, tools, etc.;
-
collection and transportation of reinforcement from the
bending shop. On some sites this might be only a few
metres from the fixing spot, but it could be a sepárate
operation if the stacking point is at a different level of the
building or at a distant part of the site.
control of materials
One of the responsibilities of site management is the control and
storage of construction materials. There is always some
wastage of materials: indeed studies indícate that it is not
unusual for wastage to amount to as much as 10 per cent of
86
materials used. On some projects materials can make up twothirds of the total construction cost so that wastage of materials
¡s a significant factor affecting the profitability of a construction
project.
MATERIALS AT RISK
Apart from tools and small ítems of equipment, the main group
of construction materials in danger of wastage or loss can be
classified as follows:
basic materials, e.g. bricks, sand, aggregate, cement,
structural and reinforcement steel, piles, drainage ware,
construction timber, stone and precast units, roofing
materials, etc.;
-
-
built-in components, e.g. Windows, doors, trames, washbasins and sanitary ware, electrical components, heating
appliances, timber fitments, etc.;
equipment, e.g. refrigerators, air conditioners, ovens,
miscellaneous electrical appliances, etc.;
finishing materials, e.g. bitumen, felt, glues, paints,
varnishes, wallpapers, tiles, mosaics, cladding, etc.
CAUSES OF WASTAGE AND LOSS
The main causes of wastage and loss are:
faulty workmanship or bad quality control, resulting in
demolition and rebuilding of substandard work;
setting-out errors due to human error or faulty instruments
so that works are not to true line and level, resulting in
demolition and rebuilding, or making up to true levéis;
-
87
-
faulty orders as to quality, quantity or sizes;
excessive use of concrete (e.g. in bedding and haunching
pipes); shallow rubble under slabs resulting in excessive
making-upto level;
faulty concrete weighbatcher producing mixes that are too
rich;
substandard materials, e.g. poor quality or faulty tolerances
resulting in excessive rejects;
breakages, e.g. in loading, transit or off-loading, faulty
handling and incorrect methods of assembly;
faulty storage resulting in site or weather damage;
-
short deliveries;
-
wilful damage due to malice;
-
pilferage, theft and corruption.
IDENTIFICATION OF WASTAGE AND LOSS
It is not always obvious that certain materials are being wasted
or lost, so a series of checks are necessary to find out the true
situation. These can take various forms -
visual: a systematic survey of the site and site stores would
reveal instances of damage and deterioration of materials;
-
documentary: reconciliation between orders, receipts,
issues and uses and remaining stocks. The materials
purchased to date should equal the sum of materials built in
plus materials on site;
-
measurement of work done, calculation of materials used
and reconciliation with the materials component of the
estimators' breakdown.
"RESPONSIBILITY FOR MATERIALS
"ECONOMY
It will be necessary to appoint someone to be responsible for
carrying out the checks, either to report back when
discrepancies are found, or to make further investigations to
find out the cause of the discrepancies. Such work could fall to
the work study specialist, since work study techniques,
particularly method study, may be used in researching causes,
modifying methods or improving controls to elimínate the
losses. In appointing such a person the procedures would be
to-
define responsibilities, powers and limitations;
provide appropriate training (e.g. ordering and accounting
procedures, analysis of estimates, etc.);
instruct site managers and supervisors to give the support
necessary to ensure effectiveness.
ADMINISTRATIVE PROCEDURES
It is not possible effectively to control the use of materials unless
the organisation has a proper system for materials accounting,
which should include -
88
89
-
materials schedules abstracted from the project master
plan showing the nature, quantity and timing of materials
requirements;
-
procedures and documentation for orderlng and receiving
materials on site;
-
stores control procedures and documentation for orders,
receipts, issues and control of stock balances.
MOTIVATION AND
INCENTIVES
productivíty of labour
On any construction site the contractor's financial gain is
dependent, amongst other things, on completion of the work ¡n
good time and at the least cost, and the productivity of labour
has a direct bearing on this being achieved. The factors
affecting the performance of labour generally fall into three
categories (a) the human capacity for work;
(b) the competence of site management;
(c) the motivation of the workers.
the human factor
The human capacity for work has already been discussed in
Chapter 3. The factors affecting it are summarised in table 7,
together with comments and suggestions for improvements.
the competence of site
management
91
The various measures that may be taken to improve the physical
work capacity or to motívate the workers will not be effective if
site management is substandard. It is essential for the workers
to have confidence in their supervisors. If the workers observe
that site management is poor, unfair or corrupt, their morale,
motivation and consequent productivity will be reduced.
Examples of management shortcomings which reduce
efficiency and productivity in this way include -
delayed, unclear or ¡nadequate instructions;
delays ¡n delivery of materials, tools or equipment;
provisión of poor tools and equipment;
unbalanced work gangs;
use of wrong methods;
bad advance planning or allocation of work tasks;
failure to delégate authority from sénior to lower-level
supervisors.
motivation of workers
Workers are motivated in their work by a variety of methods, all
of which may be present in varying degrees. They include-
fear;'
-
discipline;
-
jobsatisfaction;
-
financial incentives.
Table 7.
Factors affecting the human capacity for work
Factor
Explanation
Comments and suggestions for improving
the capacity
Age
Peak capacity for physical work is
generally reached between the
ages of 20 to 35.
Capacity is related to calorie and
protein contení of food.
In older persons, especially in skilled
Jobs, experience and efficiency
compénsate for lower work capacity.
Establish project canteens to provide
balanced meáis. Arrange talks on
nutrition.
Start work at first light and avoid
working during the heat of the day.
Nutrition
Temperatura,
humidity
Health
Acclimatisation,
adaptation,
learning
Affect the rate at which heat can
be dissipated from the human
body by radiation, convection and
evaporation of sweat. Heat and
humidity increase dangers of heat
stroke and reduce work capacity.
Resistance to disease is affected
by diet. Good hygiene and
sanitation is essential to avoid
occurrence of debilitating
intestinal parasites.
New workers, or workers given
new tasks, need time for their
bodies and muscles to adapt to
the work.
Enforce strict site hygiene. Arrange
talks on hygiene and sanitation.
Unpractised workers would initially
have a lower productivity, which
would improve as they become
acclimatised to the work, and are
instructed in the best methods of
working.
FEAR
This ¡ncludes fear of the supervisor and fear of losing a Job and
being out of work and destitute, especially ¡n a country where
no form of social security exists. This is a negative and
unsatisfactory form of incentive.
DISCIPLINE
This is exemplified by punctuality, lack of absenteeism, good
standards of workmanship and the observance of site
cleanliness and hygiene. When discipline is lacking, site morale
is generally low and productivity is unsatisfactory.
Ways of achieving site discipline include:
-
site rules drawn up and explained to all workers by their
supervisors;
-
supervisors, by personal example, setting a high standard
in self-discipline;
-
workers encouraged to feel that they are working with,
rather than under, the supervisor (but at the same time the
supervisor should leave no doubt in their minds that he is
the leader);
-
retribution should be a matter of inevitability rather than
severity. No breach of discipline should go unchecked;
developing self-discipline through pride in achievement.
Good work should always be praised;
-
taking a personal interest in the worker, discussing
problems fairly, never showing favouritism;
-
disciplinary action should be taken as soon after an
infringement as possible.
JOB SATISFACTION
93
Apart from work providing the means of satisfying the workers'
basic needs as to food, clothing and shelter, Job satisfaction is
obtained when the higher psychological needs of the worker,
e.g. self-respect and personal dignity, are met. Individuáis have
a need to belong and for their usefulness to be apparent. Job
satisfaction is obtained through a sense of achievement as to
quality, output or other contributions, particularly if that
achievement is recognised and acknowledged. Pride in craft
and skill and a sense of responsibility are to be encouraged, and
rewarded with opportunities for advancement and promotion.
Negative aspects which detract from job satisfaction and
morale, and which consequently affect productivity, are to be
avoided. These are generally aspects which imply that the
worker is held in low esteem by management and include:
-
poor working conditions and terms of employment;
-
poor or subservient relations with supervisors.
FINANCIAL INCENTIVES
Incentive schemes of this nature are widely used in
industrialised countries, but are often a source of contention
and dispute between management and workforce. The schemes
enable workers to earn bonuses over and above the normal rate
of pay for achieving a rate of output at or above a
predetermined standard. It is not always easy to work out what
this standard performance should be, so that the output targets
set by management on which the bonus earnings depend are
often inaccurate. Different schemes are discussed below.
financial incentive schemes
BONUS TARGETS
Targets are set before the work starts, usually in the form of:
-
piecework targets, i.e. payment based on the amount of
work done;
time targets, i.e. a target time is set for completing a specific
task. If the task is completed in less time, the bonus paid is
based on the time saved.
BASIS FOR SETTING TARGETS
(a) Work measurement. This is the best method as targets are
more likely to be accurate. Depending on policy, it is usual
to offer a bonus over and above the basic wage for a
standard performance of 100.
(b) The estímate. Where a bilí of quantities has been prepared,
and the estimated labour cost component of each operation
is known, this can be used as a basis for target setting.
94
(c) Feedback. The records of output figures fed back from
previous projects are used as a basis for both estimating
and setting bonus targets.
PIECEWORK
Piecework
The price
equivalent
that would
is the payment of a fixed price per unit of work done.
is fixed so that a 75 performance would earn the
of the basic daily wage, and any output in excess of
provide the bonus.
133/3
25
50
75
100
PERFORMANCE AS % STANDARD
Example: Casual labour is to be employed to break stones for use as
40 mm aggregate. Stones when broken are stacked for ease of
measurement in standard heaps 0.5 metre high on level ground, the
mean volume of stone per heap being Va cubic metre. If a standard
performance over an 8-hour day is 0.75 cubic metre, and the basic
daily wage is $2.00, what is a fair piecework price per heap of
stones?
Solution
A 100 performance of 0.75 m3 per day earns 33V3 per cent bonus,
i.e. $2.66
Therefore 1 m3 earns 2.66 x
1
= $3.55
0.75
95
3.55
Therefore Va m3 earns
= $0.45
8
Thus, a fair piecework rate is $0.45 per pile.
The cost of breaking per m3 is $3.55
The piecework system ¡s particularly applicable to repetitive
work, or to the manufacture or preparation of materials.
Piecework rates can also be expressed ¡n time units, by
giving the worker a target time to complete a certain task. If a
target of five hours is given and the Job is completed in four
hours, the worker is still paid five times the hourly rate, earning a
bonus of 25 per cent. He then moves on to the next Job. This
system requires the work to be pre-measured in order to set the
target.
Example: Several shallow manholes are to be constructed on the
drainage system of a construction project. A bricklayer is engaged to
raise the brickwork off prepared bases, to form the benching and to
set the covers to the required levéis. The amount of work and standard times per manhole are:
Work
Standard
performance
Standard
time
Lay 770 bricks
Extra for cutting round pipes
Form benching
Bed and set cover
70 bricks per hour
11.00
00.10
00.60
00.25
11.95
hours
hours
hours
hours
hours
Round off at a standard time of 12 hours per manhole
If the normal rate of pay for an 8-hour day is $4.00, and a standard
performance is to earn a bonus of 3316 per cent, then the time
allowed per manhole would b e -
12x
133%
= 16 hours
100
so that no matter how long each manhole took, the bricklayer would
earn 16 hours' or two days' pay, and $8.00 would be the wages cost
of each manhole.
If the bricklayer's performance was only 75, then each manhole
would take h i m 100
12 x — = 16 hours or 2 days to complete.
75
He would receive $8.00, which is the same as if he had been daily
rated ( 2 x 4 = 8.00). Thus, as long as his performance is greater
than 75, he will earn a bonus. For a performance lower than 75, his
earnings would be less than if he had been daily rated.
96
GUARANTEED DAILY WAGE
PLUS BONUS
ln most countries a mínimum daily wage is ¡n forcé. Also, on
construction projects where motivation is low and particularly
where workers are new to the Job, the performance of labour
can be lower than 50 per cent of the standard. A scheme paying
a bonus only after a 75 performance is reached may offer no
incentive to the workforce, who may remain content to receive
the mínimum wage for their very low performance. Therefore it
may be of benefit to start bonus payments at a lower level of
performance that all workers can reach, at the same time
guaranteeing the basic daily wage.
25
50
15
\00
PERFORMANCE AS % STANDARP
The table below shows a comparison of the earnings for
different performances under piecework and a 50 per cent
bonus scheme, expressed as a percentage of the daily wage.
Performance
97
50
75
100
125
Earnings as % ot basic daily rate
Piecework
50% bonus scheme
66%
100
1331/3
166%
100
116%
133%
150
Example of target time for the whole operation: The work content of a
particular task is 120 standard hours. It is proposed that a 100 performance shall earn a 33Ms per cent bonus.
(1) What target times should be set if the bonus is to be:
(a) 100 per cent of time saved?
(b) 50 per cent of time saved?
(2) What will the bonus payments for various other performances
under each scheme be?
Solution 1: Target times
(a) 100 per cent scheme: target set will be 120 x
133'/3
= 160hrs.
100
Thus a standard performance (120 hours) saves 40 hours. The
workers are paid 100 per cent of this saving, so they receive
120 + 40 = 160 hours' pay for 120 hours' work, i.e. a 33% per
cent bonus.
166%
(b) 50 per cent scheme: target set will be 120 x
=200 hrs.
100
Thus a standard performance (120 hours) saves 80 hours. The
workers are paid 50 per cent of this saving (= 40) so they
receive 120 + 40 = 160 hours' pay for 120 hours' work, i.e. a
33'A per cent bonus.
Solution 2: Bonus payments for various performances
100 per cent scheme: target set for 160 hours.
Performance
120
100
75
50
Time
taken in
hours
Time
saved in
hours
Bonus paid
100
120
160
240
60
40
0
0
60
40
0
0
Hours
Per cent
60
Labour cost
of the task
in hours
160
160
160
240
33'/ 3
0
0
50 per cent scheme: target set for 200 hours
Performance
120
100
75
50
Time
taken in
hours
Time
saved in
hours
Bonus paid
100
120
160
240
100
80
40
0
50
40
20
0
Hours
Per cent
50
33 y3
16%
0
Labour cost
of the task
in hours
150
160
180
240
PRESENTATION OF TARGETS
TIME-SAVED METHOD
The bonus targets must be presented to the workers ¡n a form
that they can understand. A scheme which ¡s readily
understood, and which approximates to the payment lines
shown ¡n the previous paragraph, is a time-saved scheme ¡n
which the workers are set a target time and paid perhaps 100
per cent or 50 per cent of the time saved against the target. The
target set will depend upon the size of the bonus to be offered,
and the percentage of time saved to be paid. In the case of one
easily identifiable and distinctive operation of sufficiently long
duration, such as fixing the reinforcement of a large floor slab, a
target time can be given for the whole operation. Where this is
not possible, unit target rates can be set for each of the different
activities.
EXAMPLE OF USE OF TARGET RATES
A gang comprising one foreman carpenter, three carpenters
and two labourers is engaged in erecting formwork. The
quantities of work done during the week, the unit target rates,
and the hours worked are given below. The basic wage is $1.00
per hour and the bonus paid is 50 per cent of the time saved.
The bonus is shared out in a ratio of foreman 1 V¿ parts,
carpenters 1 VA parts, labourers 1 part.
The bonus earnings for the week are calculated below:
Table 8.
Total time worked
Descriplion
ofwork
Unit of
measure
Unit
target
time
(hours)
Ouantity
ofwork
(m2)
Total
target
time
(hours)
Actual hours worked
M
Tu
Strip formwork
towalls
m2
0.5
84
42
24
4
Clean and repair
wallforms
m2
Fix beam formwork
m2
Fix wall formwork
m2
84
36
24
100
21
90
48
120
8
m2
0.25
2.50
2.00
1.20
8
Fix column formwork
Make beam
formwork
m2
1.50
64
96
16
Total target time: 417 hours
W
Th
Fr
S
Total
28
16
16
24
16
16
8
16
16
12
8
16
8
8
16
Total hours worked: 256
16
48
32
72
60
Table 9.
Worker
Foreman
Carpenter 1
Carpenter 2
Carpenter 3
Labourer 1
Labourer 2
Total bonus earned
Hours worked
M
T
8
8
8
8
8
8
8
8
8
8
8
8
w
Th
8
8
8
8
8
8
8
8
8
8
8
-
Bonus
shares
Bonus
earned
No.
$
Fr
s
Total
8
8
8
8
8
8
4
4
4
4
4
4
44
44
44
44
44
36
66
55
55
55
44
36
17.07
14.24
14.24
14.24
11.40
9.31
256
311
80.50
Totals
The bonus shares are calculated from tables 8 and 9.
Total time saved = 417-256 = 161 hours
Total bonus = 50 per cent of 161 @ $1.00 = $80.5
ce
Bonus shares - Foreman
x 80.50
311
- Carpenter
x 80.5
311
44
- Labourer
311
36
x 80.5 and — x 80.5 are as tabulated.
311
task work
This ¡s another form of incentive, though not as effective as
financial incentives. The incentive is to finish a task early and go
home, but be paid for the full day's work. The task set requires
pre-measurement, such as excavating a given length of
roadside ditch, or completing a specified concrete pour. The
task will generally equate to a 75 performance over a full eighthour day. Thus if the worker's rate of working is 100, he will
finish h i s t a s k i n 75
-X8 = 6 hours,
100
giving a time saving of two hours.
advantages and disadvantages of
financial incentive schemes
These are summarised as follows:
ADVANTAGES
- the worker ¡s given an opportunity to
earn more than the basic wage as a
reward for higher output;
- the worker's output will be higher, so that
the Job should be completed ¡n less time,
with a more predictable performance
and at lower cost;
- the systems encourage self-discipline,
and supervisión can concéntrate on
quality rather than output;
- the worker himself will try to improve the
efficiency of the method. Where a gang
is bonused, it will organise itself for
máximum efficiency, and the better
workers will encourage the inexperienced or less hard-working members;
- the operation of the scheme should keep
site management on its toes, since the
workers will protest against any delays
or mismanagement that reduce their
opportunity to earn bonuses.
DISADVANTAGES - in striving for higher output, quality and
safety may be neglected;
- if bonus rates are too low, the incentive
to work hard may be destroyed;
- differences in earnings between good
and poor workers, or due to inaccurate
bonus rates, may give rise to bad feeling
and labour problems on the site;
- bonus systems are more complicated to
opérate, and require special staffing and
organisational procedures.
101
rules to be observed in operating
financial incentive schemes
(a) When it ¡s proposed to introduce a bonus system on a
project site, the project manager should first discuss and
agree the principies and operation of the scheme with
workers' representatives.
(b) The method of payment and the targets for the work set
should be understood by the workers before starting any
particular item of work. The system should be simple and
easy to opérate.
(c) Once a particular item of work has started, the bonus rate
should not be changed unless it is found to be too low to
offer any incentive, and then only after investigation and
agreement with the workers. If the rates are found to be too
high, they should not be reduced during the duration of the
particular task for which they were set.
(d) The rates set should be high enough for an average worker
who does a good day's work without over-exertion to be
able to earn a reasonable bonus above the ordinary daily
rate.
(e) The workers should not be penalised for matters outside
their control (e.g. delays), and where workers are required
to work a full normal day they should never receive less
than the daily rate for a normal day's work.
(f) The bonus rate should be offered to individuáis or small
groups of workers rather than to large groups, so that
individual earnings do not become dependent on the efforts
of other workers.
(g) Dangerous work should not be offered on a bonus work
basis.
(h) Since bonus schemes can lead to substandard work,
penalties for such work must be enforced. Very high-quality
work should only be offered on a bonus work basis if the
supervisión is adequate to ensure no loss of quality.
(i) Any dispute about earnings should always be investigated
fairly and at once.
(i) Care should be exercised when setting bonus work rates
for raw, unpractised workers.
ORGANISING FOR
WORK STUDY
6
This section identifies the contribution of the construction
enterprise to the overall construction process, and outlines the
management structure of such an organisation and the role of
work study within this general framework.
Figure 21. Stages of a construction project
Stage
BRIEFING
DESIGNING
TENDERING
(CONSTRUCTING)
(COMMISSIONING>
103
Description
Client briets designer.
Analysis of user
requirements.
Outline investigation,
planning, design,
approvals, costs.
Technical investigations.
Detailed design, working
drawings, planning and
approvals.
Bills of quantity and
estimates.
Involvement of construction
enterprise
Nil
{
Except in the case of large
organisations having both a
design and construction capacity
}
Nil
Issue of invitations,
preparation and
submission of tenders.
Award of contract.
Obtain information on special
techniques or materials.
Obtain quotations from subcontractors.
Assess alternative
construction methods.
Devise construction programme.
Prepare and submit tender.
Construction of the works
to design and
specif ¡catión.
Appoint site staff and workforce.
Prepare construction programme.
Prepare site layout.
Prepare materials, plant and
manpower schedules.
Appoint subcontractors and
procure materials.
Prepare cash flow budget and
forecast.
Direct and co-ordinate
construction work, subcontractors and deliveries.
Completion and handover formalities.
Start up and adjust mechanical
and other systems.
Train operating/maintenance
personnel.
Provide as-built records.
Correct defects.
Formal hand-over.
Prepare and agree final accounts.
stages of a construction
project
There are five major stages ¡n a construction project - briefing,
designing, tendering, construction and commissioning. These
are outlined in figure 21, which also indicates the involvement of
the construction enterprise, which does not usually start until
the tender stage.
Work study has a role to play at the tender stage in
providing general output and cost data, and in the analysis and
cost comparisons of alternative construction techniques and
methods. At the construction stage, work study is involved in
site layout, preparing the construction programme, plant and
manpower scheduling, and in setting up, monitoring and
controlling all the various construction operations on site.
general management structure
of the enterprise
A variety of management functions are involved in a
construction enterprise. In a small firm most of these functions
will be undertaken by the owner with maybe one or two
assistants. In larger enterprises, it is necessary to set up
sepárate departments to carry out the specialist functions.
These are tabulated in figure 22, but the way in which they are
grouped together and organised will vary from one enterprise to
another. A prime task of the general management is to ensure
that there is adequate co-ordination and co-operation between
specialist departments.
Within the organisation, the work study section will act in a
purely advisory capacity, and will have no command authority.
Its recommendations and findings will be made available to
contract managers or site managers who will be responsible for
their implementation, and also to estimators, designers or
planners. The effectiveness and authority of the work study
section will derive from its own proven competence and the
support accorded by general management.
104
Figure 22. General management structure of the enterprise
GENERAL MANAGER
ACCOUNTS and
ADMINISTRATION
CONSTRUCTION
MANAGEMENT
Wages and salaries.
Bookkeeping.
Statulory accounts.
Cash flow.
Legal matters.
Personnel management.
Training.
Health and safety.
Public relations.
Plant and equipment.
Construction work
on various sites.
SERVICES
Purchasing.
Estimating and tendering.
Cost control.
Design of temporary
works.
Planning.
Work study.
SECONDED STAFF
SITE STAFF
SECONDED STAFF
Office managers.
Wages/stores
clerks.
Typists.
Security.
etc.
Site managers.
Site engineers.
Supervisors.
Operators.
Craftsmen.
Labourers.
Assistant quantity
surveyors.
Work study/production
control /planning
assistants.
Draughtsmen.
SITE
LEVEL
PRODUCTION PLANNING AND CONTROL
The work study section ¡s concerned with methods and times,
workloads and work cycles, all of which are vital inputs to the
overall planning and.control of construction work. There is a
very cióse relationship between work study and planning. In
some organisations the two functions are combined into one
production control section. The work study engineer should
have a good knowledge of production planning and control
techniques.
role of the work study engineer
105
This will vary with the size and nature of the enterprise, and will
develop as the individual begins to demónstrate a beneficial
effect on operational performance. Where a work study
discipline is being introduced into a construction organisation
for the first time, the initial step will be to appoint a suitably
qualified person as a staff specialist. A suitable background
would be that of a construction engineer with additional work
study qualifications. In addition to formal qualifications, essential
qualities are a keen and inquiring mind and a pleasing and
diplomatic personality. The latter is important, since in seeking
for better ways of doing a Job existing conventions and longestablished practices may be challenged, giving rise to
resentment and hostility. The role will cover the following
aspects:
(a) Trouble-shooting
Sorting out problems on the worksite as they arise.
(b) Advisory service
To provide an advisory service on request to all levéis of
management, and on the various worksites.
(c) Training
To provide introductory and/or training courses to selected
personnel at all appropriate levéis with the objectives of -
developing attitudes and the climate for improvement
throughout the organisation;
-
building up the work study section in order to respond to
needs and demands.
(d) Methods improvement
To keep constantly under review, study and analyse
construction activities within the enterprise, and make
recommendations for improvement where appropriate.
(e) Library of output data
To establish procedures for measurement, feedback,
storage and retrieval of output and performance data
relevant to the activities of the enterprise.
(f)
Incentive schemes
To draw up proposals and design procedures for
introducing incentive schemes, and assist in their
implementation.
(g) New techniques
To keep abreast of new developments in the construction
sector, and the effect of new materials, equipment and
methods on the enterprise's activities, and to make
recommendations where appropriate.
work study technicians
One objective of the training outlined above would be to develop
a cadre of work study technicians to attach to the various
worksites. Such a technician would answer executively to the
106
site manager, and functionally to the work study engineer at
central office. Duties would ¡nclude:
familiarisation with the construction project and the site
manager's plans and policies;
-
following the progress of all activities on site regarding
resource utilisation, methods and costs;
-
analysis of unit cost returns and, in consultation with the
site manager, investigation of unsatisfactory operations with
a view to improving them;
-
in consultation with the approphate supervisor, the carrying
out of triáis of improved methods, and assistance in
installation and follow-up of viable improvements;
-
studies to provide feedback data for inclusión in the
enterprise's library oí production data;
spot-costing of site operations as requested by the site
manager;
-
assistance to the site manager in providing the data
necessary for forward planning;
studies necessary for fixing bonus targets;
identifying opportunities for effecting improvements, and
discussing them with the site manager.
PRACTICAL EXAMPLES
7
múltiple activity chart: pouring
concrete upper floor slab
The flow diagram (materials type) outlines the methods used.
1
Sand and gravel are loaded into the mixer hopper by two labourers using shovels
and a 1 cubic foot gauge box. Four boxes of gravel and two of sand are needed
per batch of concrete.
One bag of cement ¡s loaded Into the hopper per batch of concrete by the mixer
operator.
The operator uses a graduated bucket to add water to the mix.
O
5
6
Concrete ¡s mixed ¡n a 10/7 mixer, 4:2:1 volume per batch of 5 cubic feet.
The mixed concrete is discharged into a wheelbarrow by the operator, one
barrowman wheels the loaded barrow onto the hoist, and raises the hoist to the
upper floor level. When the full barrow has been removed and replaced with an
empty one, he lowers the hoist and returns to the mixer with the empty barrow for
more concrete.
A second barrowman at the upper floor level removes the loaded barrow, replaces ¡t with an empty one, wheels the barrow to the working point, empties the
concrete, and returns the empty barrow to the hoist to await the next full barrow.
©
At the working point, one masón spreads, tamps and floats the concrete smooth.
Details of equipment: 10/7 mixer; wheelbarrow, capacity 2 cubic feet; gauge
box, capacity 1 cubic toot; hoist, máximum safety load 1 ton.
Working time: An eight-hour day is worked. Effective time is 80 per cent.
The output using this method is too low, and a study is
carried out in order to effect improvements. As a first step the
various activities are timed and the following standard times
derived.
Element
Labour
Load gauge box
Empty box ¡nto hopper
Empty cement bag into hopper
Discharge hopper to drum
Mixing time
Lower hopper
Add water to mix
Discharge to empty mixer
completely (5 cubic feet)
Discharge concrete to
wheelbarrow (2 cubic feet max.)
Wheel full barrow to hoist
Manoeuvre full barrow on to hoist
Opérate hoist up
Manoeuvre full barrow off hoist
Wheel empty barrow on to hoist
Opérate hoist down
Wheel empty barrow off hoist
Wheel empty barrow to mixer
Wheel full barrow from hoist
to workpoint
Empty full wheelbarrow
Return empty wheelbarrow to hoist
Spread, tamp and float one batch
of concrete (5 cubic feet)
2 labourers
2 labourers
Operator
Operator
Mixer
Operator
Operator
Standard
minutes
.2Ülrepeated
.20/ 6 times
.40
.20
2.00
.20
.40
Operator
.50
Operator
Barrowman 1
Barrowman 1
Barrowman 1
Barrowman 2
Barrowman 2
Barrowman 1
Barrowman 1
Barrowman 1
.30
.30
.10
.20
.10
.10
.10
.10
.20
Barrowman 2
Barrowman 2
Barrowman 2
.40
.10
.20
Masón
3.00
Daily operating costs: Mixer $20.00; hoist $25.00; labourer and
barrowman $4.00; masón $6.00; mixer operator $5.00.
NOTE:
For the purposes of simplifying this example, the times have
been rounded off to the nearest tenth of a minute.
110
The múltiple activity chart is plotted in figure 23. The chart
highlights the main cause of the low productivity. It takes three
trips with the wheelbarrow to empty the mixer, taking 3.50
minutes as opposed to the best possible emptying time of 0.50
minutes. Figures 24 and 25 show how productivity can be
improved.
Figure 23. Múltiple activity chart
LABOURER
1and2
MIXER
OPERATOR
42
llfH
37
ú W
54
BARROW
MAM
HOIST
B ARROW
MAN 2
load, up
msnouvrtffüU
füllo»
wh«tf¡
wtr«vl
bHIti
mixtp
68
dewry un load
42
impty «
Egiwfct1
47
tamp,
ftoat
53
Operation: Mixing and delivering and spreading concrete to upper floor slab.
Original method: 10/7 mixer; 1 ton hoist; two 2 cubic foot barrows; 1 masón; 1 mixer operator;
4 labourers.
Cycle time: 5.70 minutes.
60 x 8
80
Daily output:
x 5 x — = 331 cubic feet = 12.3 cubic yards.
5.7
100
Operating costs per day = 20 + 25 + (4 x 4) + 6 + 5 = $72.
Cost per cubic yard: $5.85.
IMPROVED METHODS
lf the operation is subjected to the work study questioning
technique, several alternatives present themselves. These
alternatives can be analysed, costed and compared to select the
most appropriate. Examples are:
m
(a) Use larger wheelbarrows.
(b) Discharge the full mix on to the ground, and engage
additional labour to shovel the concrete into the
wheelbarrows.
(c) Discharge the full mix into a small hopper, from which it will
discharge into the wheelbarrows. This assumes that
sufficient height is available at the mixer.
(d) Move the mixer nearer to the hoist.
(e) Move the mixer nearer to the hoist and use a concrete hoist
with a 5 cubic foot skip.
Alternatives (a) and (b) are examined in greater detail
below.
ALTERNATIVE (a)
Use larger wheelbarrows. Using barrows of larger capacity (2.5 cubic
feet or more), the mixer can be emptied in two barrow loads instead
of three. The revised múltiple activity chart (figure 24) shows the daily
output raised from 12.3 to 17.3 cubic yards, and a reduction in
operating costs from $5.85 to $4.16 per cubic yard.
ALTERNATIVE (b)
Discharge the full mix and hand load concrete into wheelbarrows. For
this method, one additional labourer and a spare wheelbarrow are
needed. The concrete is discharged from the mixer on to a raised
platform from which one labourer can shovel 5 cubic feet of concrete
into wheelbarrows in 3.00 minutes. A time of 0.1 minute is allowed for
changing barrows. Thus, the various time cycles become:
Element
Fill mixer hopper
Fill mixer, mix, discharge
Fill wheelbarrows
Barrow to hoist and return with
empty
Barrow, hoist to workpoint and
return
Spread, tamp and float
Hoisting time, loading and
unloading
Labour
2 labourers
Operator+mixer
1 labourer
Standard
Minutes
2.4
2.7
3.3
1 barrowman
3.9
1 barrowman
1 masón
2.7
3.0
2.4
This arrangement, which is shown on the múltiple activity chart (figure 25) would give a revised time cycle of 3.90 minutes, a daily output of 18.2 cubic yards at a unit operating cost of $4.17 per cubic
yard. The time cycle is restricted to 3.9 minutes by the barrowman at
ground level, and could be reduced further still by employing an additional barrowman.
Note that barrowman 2 has spare time, which will allow for a change
of workplace at the upper level.
112
Figure 24. Múltiple activity chart: Alternative (a)
1.AB0URER
•Und2
MLL HOPPIK
WKER
OPERATOR
íht
59
FILL HOPPCR
a|° j-
Ui
BARROW
MANÍ
44
68
63
\¡ta&
hímlar
39
load, i
BARROW
MAN 2
44
73
«pTNd, Ump, flo»t
Operation: Mixing and delivering and spreading concrete to upper floor slab.
Improved method: Using larger (2Ví> cu ft+) wheelbarrows
Cycle time: 4.10 minutes
60 x 8
80
Daily output
x 5x
= 467 cubic feet = 17.3 cubic yards
4.1
100
Operating costs per day: $72.
Cost per cubic yard: $4.16.
Figure 25. Múltiple activity chart: Alternative (b)
TIME IN
MINUTES
1
2
3
4
5
LAB0URER
1ind2
MIXER
OPERATOR
62
JflI
empty
??
43
empty
69
LA80URCT
77
3
BARROW
MANH
: loparanc
wSMIto
mutr
load, up
100
62
down ofF
BARROW
MAN 2
rAASON
69
Spñ3¿,
tsmp «nd
77
Operation: Mixing and delivering and spreading concrete to upper floor slab.
improved method: Discharging mixer to platform and hand loading concrete into wheelbarrows.
Cycle time: 3.90 minutes.
60 x 8
5
80
x — x — = 18.2 cubic yards.
Daily output: —
3.9
27
100
Operating costs per day: $76.
Cost per cubic yard: $ 4.17.
gang balance
Where a construction operatíon ¡s carried out by a team of
workers and/or machines whose work ¡s interdependent then
the output of the gang will be restricted by the performance of
the slowest or least productive member. It ¡s ¡mportant that the
gang should be properly balanced so that each member of the
team can achieve full potential output.
EXAMPLE 1. EXCÁVATE AND CART TO TIP
An excavator equipped with a 1 m 3 skid shovel has to excávate
9,175 m 3 of soft soil to formation level. The soil is oaded into tipper
lorries of capacity 2.5 m 3 (allowing for bulking) and is hauled to a tip
4.5 km distant. Two lorries are provided. A 44-hou week is worked.
Output and cost data are:
Standard excavator output per working hour
23 m 3
Anticipated ineffective time:
Preparation, heat up, refuel
Late arrivals from meáis, early closing
Local average lost time due bad weather
Total
Lorry haul time, including loading and unloading
Hire rate per hour:
Excavator + operator
Lorry + driver
11%
6%
13%
30%
29.5 minutes
US$16.00
US$10.00
Analysis
Effective utilisation of excavator and lorries is
70
44 X — = 30.8 hours/week
100
Effective output of excavator ¡s 30.8 x 23 = 708 m3/week
60
Average number of lorry trips = — = 2.03 trips/hour
29.5
Average number of trips per week = 30.8 x 2.03 = 62.6 trips/week
Average output of lorry is 62.6 x 2.5 = 156.5 m3/week
Average output of 2 lorries is 156.5 x 2 = 313 m3/week
Since the excavator cannot dig more than the lorries can cart away, the excavator is restricted to the capacity of lorries, viz. 313 m3 per week.
114
313
The excavator is therefore only — x 100 = 44 per cent effective
708
Weekly costs are: Excavator 16 x 44
Lorries 2 x 10 x 44
Total
Duration of Job ¡s
9,175
= 704
= 880
$í ,584
= 29.3, say 30 weeks
313
Total cost is 30 X 1,584 = $47,520
47,520
Unit cost ¡s
= $5.18 per m 3
9,175
Balancing the Gang
To balance the gang it will be necessary to ¡ncrease the number of lorries to
match the potential output of the excavator.
Excavator weekly potential is 708 m3 per week
Potential output of 1 lorry is 156.5 m 3 per week
Therefore number of lorries needed is
708
. = 4.5
156.5
So that either four or five lorries are needed. The two alternatives are compared below:
Potential output
Using 4 lorries
Using 5 lorries
156.5 x 4 = 626 mVweek
1 5 6 . 5 x 5 = 782.5m 3 /week
(But restricted to 708 by output of
excavator)
9,175
9,175
Duration of Job
= 14.65, say 15 weeks
626
Total weekly cost
4 X 10 X 4 4 = 1,760
16 X 44 = 704
$2,464
Total cost
2,464 X 15 = $36,975
Unit cost
12.95, say 13 weeks
708
36,975/gl75 =
5 X 10 x 44 = 2,200
16 X 44 = 704
$2,904
2,904 X 13 = $37,752
$4.03/m
3
3 7 , 7 5 2 / Q 1 7 5 = $4.1 f/m3
Within the margins of error, there is little to choose between the
costs of the two methods. If it is decided to save two weeks by
using five lorries, the comparison with the original method
shows:
Original method (2 lorries)
New method (5 lorries)
Savings
Time
Total cost
Unit cost
30 weeks
13 weeks
17 weeks
$47,520
$37,752
$9,786
$5.18
$4.11
$1.07
EXAMPLE 2. REGRAVELLING OF
FEEDER ROAD
On a labour-intensive feeder road construction project ¡t ¡s required to excávate, load
and haul gravel to the road site where ¡t is tipped and then spread by hand. The haulage
is by tractor and hydraulic tipping trailers. Standard output data (100 per cent performance) is:
Tractor speed (loaded and unloaded)
Trailer capacity (compacted measure)
Manoeuvre and unhitch empty trailer
Manceuvre and hitch on loaded trailer
Manoeuvre and tip loaded trailer
Daily lost tractor time
Excávate loóse gravel (soil type 2) and load
(loading height 1.25 metres)
Spread loóse gravel in layers of 100 millimetres (compacted)
15 km/hour
2.5 m3
2.0 minutes
3.5 minutes
3.0 minutes
10 per cent
1.7 work-hours/m3
0.5 work-hour/m3
The haulage distance is 2 km, the Job is carried out on a daywork basis and the anticipated performance is 75 per cent of standard. The normal working day is eight hours.
Using one tractor only, how many trailers and labourers are required, and what will be
the daily output?
Solution:
1. Cycle time for tractor/trailer2x2
Haulage time — — x 60 =
15
Hitch on/off + tipping = 8.5 minutes at 75 performance =
Total
16.00 minutes
11.33 minutes
27.33 minutes
2. Daily outputActual working time 90 per cent of 8 hours = 7.2 hours
7.2 x 60
No. of trips per day =
= 15.81, say 16
27.33
Daily output = 16 x 2.5 = 40 m3
3. Labour force(a) Excávate and load: work-hours needed at 75 performance are
40 x 1.7 x
100
= 90.6
75
90.6
No. of labourers required is
= 11.33, say 12
8
(b) Spreading gravel: work-hours needed at 75 performance are
100
40 x 0.5 x
= 26.7
75
No. of labourers spreading is
26.7
= 3.3, say 4
Summary: The gang would be working a tractor and two trailers (one being hauled whilst
the other is loaded); 12 labourers excavating and loading; four labourers spreading. The
daily output should be 40 m3.
site layout
The plan ¡n figure 26 illustrates the site layout for the
construction of a radio transmitter station on a remote site in
open country.
Question 1: What are your criticisms of the present site
layout (see figure 26)? Tabúlate these criticisms and then
compare them with the list given below and on page 120.
Question 2: Assuming you were the engineer in charge of
the construction works, where would you have located various
Ítems of equipment, storage, work áreas, etc., at the very start of
the job?
A blank layout plan is provided in figure 27. There are
several acceptable alternative site layouts, one of which is
illustrated in figure 28.
CRITICISM OF EXISTING SITE
LAYOUT FOR THE CONSTRUCTION OF
RADIO TRANSMITTER STATION
(a) In general, the working área is too spread out, making
control more difficult and increasing non-productive
travelling time about the site.
(b) Site latrines and canteen are too far away, causing loss of
time due to unnecessary travelling. There is no apparent
supply of drinking water on site.
117
(c) No security fencing is shown. Is it unnecessary?
(d) Temporary access road should follow the line of the
proposed station access road to avoid duplication of work.
(e) Water supply is a problem. More storage space should be
provided. Can the construction of a borehold be advanced?
Figure 26.
Layout of site for construction of radio transmitter station
TO QUARRY
9ITE
E l HOIST
2 STOREY O F F I C E ANDTRANSMITTER
GjBWERATOR
HO0S6
BUlLDINQ: R. C. F R A M E a n d FLOORS
an¿ ROOF, S L O C K W O R K I N T E R N A L
WALLS, DRESSED STONE O U T E R
SEALEDCOMTAINERS HOLPINq
SEMERAToRS^SWITCH^EAR AMD
TRANSMnTER COMPONENTE.
^
I^TACKof
D a
a a
¡ PYLON B^O
.QIRDERSB D
j
•
IAVWUTÍUCV
I
^ERECTIOM
S T E E L L A I 0 AT R A N D O M
ONGROUÑD'.^
AWDCJTIN
^ \ ^
171
.SITU
FA3RICATI0N AND STACKIMq
BENDIN^ BENCH
T I M B E S STORAQE
I NEW, U S E P A N D
ISCRAPTIM8ER
Nj
14
SANITARY FITTINqS+PIPES
-J
METAL D 0 O R +
WINDOW FRAUES
, UNE
3EWER
R.C. PYLON
BASES
a
CENTrtLlNE
O F PROPOSED
STATION ACCESS
ROAD
WATCHMANfe
HUT
WCJRKERS'QUARTE RS
C A N T E E » a n d LATRINES
I
ú
_
•
SEPTIC
TAKIK
200 meh-es DISTANT
LEQEND I
i .
ALLSITE TRANSPORTATION M A N U A L O R BY WHEELBARROW.
2.
ALLTECWNICAIEOUIPMEHTWASDEUVEREOBEFORE BUILDIUq FOUNDATIOMS
WERE COMPLETE. A L L O T H E R F n T l N q ALSO DEUVERED(DOoRS, SANITAH^etc).
3 . QEWERATORHOUSE COMPLETED AND WATERTl^nT. COMCRETINq OF Ai* '
FLOOR O r T R A N S M I T r E R BUIL.DIN1, IN PRoqRESS. HOIST W A S NOT
AVAILABLE AT CCMMENCEHENT ANO HAS OHL-C JUST BEEN DELIVERED.
4 . NEAREST PURÉ WATER IS IN T H E TOWN í O K m A W A Y . WATER DELIVERED
BYTANKER A N D S T O R 6 D I N 6
20CH-ITRE DRUMS.
5 . PYLON BASES A N D S E W 6 R / S E F T I C T A N K NOT YET STARTEO.
6 . AGENTS OFFICE IS S I T E D T O C A T C H T H E P R E V A l L I N q B R E E Z E A N D ENJOY
T H E BEST V I E W I T IS S I T E P M E A R SMALL STORES A M D C B M E N T
S T O R E FOR SETCURlTY.
7 . S O R E H 0 l £ FOR WATER SUPPWBY SEPÁRATE A<5ENCY NOT Y E T S T A R T 6 D .
TO MAJOR
'~l*\
H I Q H W A Y , . ^ ^
SCALE
NEAREST T O W N
2 0 Km DI9TANT
10
%0
METRES
30
AO
Figure 27. Blank layout plan
TRANSMITrER
D D
O D
BUlLDINCj
qEHERXTOR
HOUSE
R.C.PVLON
BASES
UNE
of
SEWER
o a
o a
a D
a a
CEMTRE LlrJE
OF PROPOJED
STATION ACCESS
ROAD
1SEPTIC
J
TANK
SCALE
40
20
METRES
30
(f) Surplus excavation should nave been led directly to the
erosión nullah to avoid double handling.
(g) Pylon girders have been stacked over foundation bases,
necessitating double handling.
(h) Stonemason's yard interíeres with the movement and
handling of technical equipment from the sealed containers.
(i) Site office is badly sited. As the building rises the view of the
site is completely blocked.
Q) Cement store is too far from the mixer.
(k) Concrete aggregates are tipped haphazardly, causing
waste and impurities. Access by lorry is also difficult.
(I) Hoist is on the wrong side of the building, too far from the
(m)
(n)
(o)
(p)
(q)
work áreas.
Mortar-mixing and block-making áreas are too far from the
building.
Temporary buildings and storage áreas are sited over the
line of the sewer. The sewer should be constructed early, to
freetheground.
Steel is laid haphazardly on the ground and not stacked in
an orderly manner. Bending and fabrication benches are
wrongly placed.
Timber storage área appears disorganised.
Sanitary fittings, pipes and trames are stacked too near to
the access road for their safety.
Figure 28. Revised layout of site for construction of radio transmitter station
. To
QUARRY
MASONS
TRANSWUTTER
MOIST •
QENERATOR
HOUSE
BUILDINIq
I I RAMP
SEALED
CONTAINERS
.MIXERS-. ,<<.*•
BIOCKS
D D
D D
n
°nf
TIMBER STORE
AMD CARPENTERS'
SHOP
a a
R.C.PVLON
8ASE9
D
D
SURPLUS EXCAVATION
CONSTRUCT SEWER
EARLV BEFORE ERECTIOM
OFCARPENTERS'WORK ÁREA
CARTED DIRECTlY ^
TONULLAH
M>YLOig
SIRDERS
E
SITE I
'Frica!
| STORES |
LIME
of
•SEWER
: i i
a o
D D
a a
a a
CENTRE UNE
OF PROPOSEP
STATION ACCESS
FtOAD
D
LATRINES
I SEPTIC
TANK
1
I
SITE ACCESS RD
,'
SCALE
JO
2o
METRES
30
40
Figure 29.
Rated activity sampling record sheet
PROJECT &HA<<
JUWK
srwf tfutfréKS
OPERATION U i J 4M.I Mgü** I5Ú ÍHIVN
ELEMENT CODE
|
n
STUDYNO.P62 SHEET |
^
TIME STARTED OW>
TIME FINISHED USO
ELAPSEDTIME V " > s >M *»*•'•
ta
TOTAL O.T. * • * f 5 * 1*3 »* TOTAL
ELEMENT DESCRIPTION
QUANTITY
O.T.
bOm
27
60>\
241
B.T.
2T
<&M$ u/*H\tepsse*to(eueC af u4í»^<le ofpiptí.
5
<p
5^€^<)u^lCo€ÍI?0m^a^í<5W>€^te(tfcífp6it£v4.
ÍOn*60m
II2J2¿)
éOm
60n<\
(7S
Z2-Í
"73
7S
|»UPrp>etAa/ivvSíyu¿tvJKt<iA^.
No.ol
observation
mase*
1
UMUrC*'
2
3*?
DETAILS OF WORKER
' • f c a t u c r lAhauurr
3
24-7
Í00é>
191-7
/6Í-7
5
4
6
7
8
Code Rate Code Rate Code Rate Code Rate Code Rate Code Rate Code Rate Code Rate
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
<?
<?
Q
<?
<*
L
L
L
LíU
P
iL.
U
U
<?
t>
0
<?
P
<?
L. IfO t_
<?
«
Q
<?
<?
$
<?
(00 u 100 0
u 30
too u 90 u 50 u 90
100 U 9o u fo
u «0
90 u ¡00
u to p
100
100 U
(06 L
100 L30 L 90
90 /W
L- 90
100 L (00
100 L. (OS
110
1(0 L
IM
(10 U
D
f)
u too
u 100
u 50
u
u
p
4
110
110
1(0
<?
90
90
9í>
u 10 u 90
u so
u
u tfO i» 90
p
u to
IA 90
p í)0
U
U
U
P
<?
90 u
90 u 90
70
D
D
<?
U (10 L.
r 90 0 * 0
L 1(0 U
T 30 T
D
1>
r 90 T r>
0
D
r 90 r r>
l>
T 90 T ?o
í>
*
D
<*
<*
S so S 90 T 100 r 90
O.T. = Observed Time
NOTE:
0
L-
<?
4
«
B.T. = Basic Time
<?
<
?
p
T
VO
T
r>
3o
T
r 90
T 90
T to
Rated Activity Sampling Record Sheet
The following record sheets are not shown.
rated activity sampling
Figures 28-30, which are self-explanatory, give an example of
the way rated activity sampling (see figure 16) can be used to
derive the standard times for the various work elements involved
in laying drainage pipes.
Having obtained basic times, relaxation and contingency
allowances are added in the usual way. Standard times are then
divided by quantities to obtain the unit of standard time.
Figure 30.
PROJECTgHAft
Activity sampling extract sheet
3UMIQR STrtfF
<W@e5
S T U D Y N o . p 6 2 - SHEET
(
. ACTIVITY SAMPLE EXTRACT
ELEMENT CODE LETTER
u
II
Q
No.
of
obs.
SO
55
60
WfWt
6«S
70
7«5
lili
un n
urUH
«0
SS
I» II
I00 « *
«II
9»
9?
W
HO
*TI1HI
(MMf
ii
ntim
Itfl'll
UHIHW
9-Oí* ni
75 «Mtt
M
UHM
uno*
nri
la""
JM1IMI
1-2 5ÜÍP I? H II _
i^nrwt 12-7$
UHUf
,H«IM
'0 7-0 £
mi*»
<f t í . U M Í *
2SS*
UHM
IHIWI
« mu»
irv
tNáv
«atl
2
3
12 7*
10 55
21
IZ
s-edl
120
s
rK
wKO
25 JM
M»i« 20
S
i
7 (0
n
H-1
%
imvnm
• 4 » un JO
lUMnfti 10 95
(0 9-S
¡Üfwr 17 ñÑW IS iüfwr
11 ufl.
15 inri" í i l<
« i?
II5
/20
1*5
130
¡V>
m UM
o.« www
2KIIW Hl
fíítwiwi
"5 lili
«o II
uMini
M UMIM
«riw
2V
15Q
Tefal ns-45 | n
TohUBT 2.7-y
123
21
24-7
itt
100 t
SO
Mt-7
73
171
197-5
75
Figure 31. Calculating the standard time
ELEMENT
5étta>etpeg$
Unt«U
TrwvtolfiAJel
BASIC
TIME
(mins.)
ll*t
w
KXM
(&£M!tetá$&K,W-7
% RELAXATION
c E M
s Z / - - % 2- - - 1 % 2 / - 2 % 2 / - Id S
p
TOTAL
%
A
^•7 % £ 2 - Z ^Kvwk¿we^ *7"S % Z / - 10 ¿Ajjpwtó
%
CONT
s
/£>
5
lí.
STANDARD
TIME
(mins.)
'?
fí?
s
2¿
**>
/$
<T
26
UNIT STANDARD TIME
V- 60**
*9 60»
S
5
OUANTITY
2
?0«
O 9u*rtk***//«>*
o-flfwnKtairi/KXW
Ó07WW*JÍ(M*S/IH
ío^
200 ío^
tu
• *
O-OhJO&UúnfiHi»
66*w Otfuioto&a}»**
1%
Comparing 856 standard time with actual time taken of 948 minutes gives
the average performance of the gang as 90 per cent.