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implementing lean in construction

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Implementing Lean Construction Theory to Construction Processes’ Waste
Management
S. A. Abbasian Hosseini1, A. Nikakhtar2, K. Y. Wong3, A. Zavichi4
1
M.Sc. student, School of Civil Engineering, Iran University of Science and
Technology, Tehran, Iran, email: [email protected]
2
M.Sc. student, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia,
81310 UTM Skudai, Malaysia, email: [email protected]
3
Lecturer, Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310
UTM Skudai, Malaysia, email: [email protected]
4
PhD student, Department of Civil, Environmental, and Construction Engineering,
University of Central Florida, email: [email protected]
Abstract
Waste in the construction industry has been the subject of several research
projects around the world in recent years. Researchers implement different methods
to reduce the amount of waste in construction industry. One of effective methods is
application of lean approach to construction industry. Lean construction is a result of
the introduction of a new form of production management. Although lean
construction is still evolving, the generic principles, techniques and tools of lean
construction can already be applied. Waste reduction in order to improve
performance is one of the basic concepts of lean thinking. In general, project
managers tend to conceptualize “waste” as physical construction waste, but there are
noticeable wastes in the construction processes which are named “non value-adding
activities” by lean construction theory. In this paper, the waste quantity of
construction processes in any format has determined through discrete event
simulation based on lean thinking approach. Furthermore, a case study conducted to
reveal the result of lean thinking application in a real manner. Results show that the
construction processes have the high potential of optimization via implementing lean
construction principles and computer simulation.
1. Introduction
Construction industry has been suffering enormously from a serious drawback,
which is “Waste” (Senaratne and Wijesiri, 2008). All the researches conducted in the
area of construction waste imply the huge volume of waste generated during a
construction project (see Esin and Cosgun, 2007; Wanga et al., 2010). During last
decades, various methods are utilized in order to reduce construction waste and its
effects. One of innovative approachs in this regard is “Lean Construction”, which was
introduced to construction industry in 1990s based on a successful manufacturing
theory, i.e. lean production.
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Actually, Eliminating waste in a process is one of top priorities in lean
construction theory (Mao and Zhang, 2008; Farrar et al., 2004; Dunlop and Smith,
2004; Al-Sudairi, 2007). In general, project managers interpret waste as physical
construction waste, which dominantly includes material losses (Koskela, 1992). In
addition to stressing on the physical waste, lean thinking specifically pay lots of
attentions to the waste produced over a construction process. Waiting time, non valueadding works and material transportations are categorized in this group.
This paper is based on evaluating the quantity of construction process waste
according to lean thinking approach. Therefore, after describing various kinds of
construction process waste, lean construction principles regarding to waste reduction
are explained. To test and examine lean principles (due to waste reduction) in
construction processes, an actual experiment is required; therefore a case study was
conducted to depict the real application of lean principles. In contrast to the actual
experiment which can be time consuming, risky and costly, computer simulation does
not incur huge costs. In addition, Modeling is a powerful tool, which helps us in two
important ways. The first one is revealing shortages related to designing the system
and the other one is highlighting opportunities for improving the system performance
(Sawhney, 1999). After simulating a selected process, the quantity of each kind of
waste is revealed from model and finally, the potential of lean principles to decrease
the process wastes are depicted.
2. Construction Waste Categorization via Lean Thinking Approach
During last decades, many research efforts have been done in order to classify
construction waste according to different attributes such as kind, quantity, etc. In spite
of different classifications, all of them follow the same basic concept. Excess
materials, delays, rework and defects are those waste commonly mentioned by
researchers (Senaratne and Wijesiri, 2008)
Although the term ‘construction and demolition waste’ has been defined as any
kinds of solid waste generated during construction processes, Formoso et al. (2002)
recommended broader definition of waste to include not only material waste but also
waste generated in a construction project such as waiting times, transportation times,
and etc. Actually, this issue (non-physical waste within construction processes), is the
basis of waste concept from lean construction approach. Actually, these kinds of
waste are those wastes that occurred during the construction processes. Koskela
(1992) also states that a systematic attempt for identifying wastes in construction
processes (flow wastes in lean thinking terms) has not been done by the construction
management practitioners until lean construction concept was introduced.
Innovative waste categorization, which is considered lean thinking concept, is
illustrated in Fig. 1. In fact, lean construction thinking pay special attention to
“construction process waste”, which itself can be devided into two main categories:
waste due to the nature of processes and waste due to non value-adding work. It
should be noted that each of waste mentioned in construction process category, is not
wholly due to nature of process or due to non value-adding works, but since one
categorie’s features predominates, it will be categorized in each subdivision.
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Waste
related to
Construction
Site
•
•
•
•
•
Waste due to wait periods
Waste due to design errors
Equipment wear and tear
Resting time
Excess materials on site
External
Factors
•
•
•
Excess materials
Safety costs
Clarification needs
Lean thinking
emphasizes
Due to nature
of operations
•
•
•
Defects
Rework
Over production
Non valueadding work
•
•
•
•
Transport/handling time
Waiting
Unnecessary inventories
improper choice of methods
Construction
Processes
Figure 1. Waste categorization considering lean thinking approach
3. How Lean Construction Principles Reduce Processes’ Waste
Koskela (2000) believed that construction is mainly managed based on
transformation concept, and principles related to the flow and value
generation concepts as the basis of lean thinking are largely neglected. In
order to apply flow and value views to construction processes, researchers
enumerate various principles. Explanation of all the lean principles is not in
the scope of this paper; therefore, three basic concepts applied to the case
study (conducted in this paper) are explained in following paragraphs.
Value generation through flow production of processes. Lean thinking divides the
activities that are flow in a process into value adding and non-value adding activities.
Value-adding activities are those that directly affect on producing the final product
and considered as a value by the customer, while non-value activities do not. Koskela
(1993) believed that while all activities expend cost and consume time, only value
adding activities add value to the material or piece of information being transformed
into a product. Therefore, lean thinking attempts to re-design the processes in order to
achieve two goals: (1) Omit or at least minimize the share of non value-adding
activities; and (2) Enhancing the labor’s time consumed on value-adding activities.
Implementing concept of pulling (just-in-time delivery of materials). One of the usual
problems in construction industry is related to delivering materials (Thomas et al.,
2002). Equipment and labors are often kept waiting because delays occurred in
supplying materials and in finishing prerequisite works. This problem decreases the
productivity and extends the project duration (Tommelein, 1998). On the other hand,
supplying the downstream’s requirements sooner than they need, generates
unnecessary inventories and it may cause extra cost. “Pulling” is another basic lean
production principle that ensures just-in-time coordination between upstream and
downstream tasks. It is based on that the upstream should not produce a
product/service until the downstream request it (Womack and Jones, 1996).
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Mistake-proofing of processes. Research shows that estimated costs of defects in
construction project have been reported to be 5% of total project price (Mills et al.,
2009). Therefore, construction defects are always the key concern of the construction
industry. In this regard, lean thinking attempts to prevent occurring mistake through
simple way of mistake-proofing. This concept, in the production industry of Japan, is
called Poka-yoke. Mistake-proofing’s objective was to eliminate or minimize the
requirement for inspection (which is believed as waste in lean philosophy) by
eliminating errors before they occur rather than detecting and mending activities
which simply make it fall under unfavorable category of “rework”.
4. A Case Study
To test and evaluate the waste reduction due to lean principles implementation
in construction processes, an actual experiment is required. Therefore, this study
conducted a case study by focusing on reinforcement operations of a six-floor building
construction. Reinforcement operation is a repetitive process, which contains several
activities, labors and resources that interrelates to each other. Hence, it seems to be
appropriate process for testing and evaluating lean principles application.
To do the experiment, a safe and standard trend for simulation was regarded. As
can be seen in Figure 2, data collection, model development and validaition constitutes
the main parts of the trend.
Observing the
process
Collecting data
for activities
Model
development
Validating the
model
Applying lean
concepts
Analyzing the
results
Figure 2. Standard trend of simulation model development
Data were collected through precisely observing reinforcement operations of
the first floor. Afterwards, various continuous distribution functions were tested
against the collected data, and the most promising ones according the goodness-of-fit
tests were selected. It should be noted that each activity repeated several times during
each cycle of reinforcing, therefore the number of durations were recorded for each of
activity of reinforcement operations is enough for statistical analysis.
After finding the best fitting distribution of activities, it is time to develop
simulation model of chosen process (reinforcement operations). The distribution’s
parameters and actual behavior observations were used to accurately model the
conventional reinforcement process via ARENA simulation software. To do so,
various kinds of modules in ARENA were implemented to close the model to what
happened in actual process. Figure 3 illustrated the simulated model for the
reinforcement process. It should be noted that some extra modules or linkages were
also used to meet the logical aspects of the way that process done.
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Figure 3. Simulated model for the reinforcement process
Simulating an accurate model is completely dependent on the development of the
model that certainly shows the actual various tasks and their interrelationships (AlSudairi, 2007). Therefore, before experimenting with simulation to evaluate the effect
of lean principles, it is necessary to validate the model. One of the appropriate factors
to show how actual process and simulated process are alike is cycle time which is
used for validation by many researchers (see Al-Sudairi, 2007; Hassan and Gruber,
2008). After each testing, necessary modifications were done to close the simulated
model to the actual process. As can be seen in the results of last validation in Table 1,
variation between actual and model outputs is 1.5%, which is acceptable.
After construction and validation the base model, it is time to apply the
aforementioned lean thinking concepts. Flow considering of a construction process is
one of basic principles of lean construction. In the observed reinforcement process, in
each workstation, all the rebars delivered to the next workstation together. To flow
the entities in whole the process concurrently, first, the batch size delivered in each
step is decreased and then the labors are allocated to all the operations depend on
their abilities. In fact, the labors do not move from a workstation to another and just
deliver entities to the next station. By this work, all the operations in a reinforcement
cycle performing together and the problem of overstuffing and waiting time became
minimum.
Table 1. Final results of validation based on 10 replications of the model
Replication
Cycle
Time
(min)
1
2
3
4
5
6
7
8
9
10
Actual 589 595 591 535 564 572 581 589 582 602
Simulated
601 561 569 577 556 574 575 576 556 561
model
St. Dv.
Average
Variation
Cycle time
(%)
19.2
583
13.4
571.11
1.5
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Being late in hauling rebars from a workstation to next one cause waiting time
and therefore it increase cycle time directly. On the other hand, providing rebars
sooner than needed generate the unnecessary storages of rebars which can increase
double handling and distance to working area. Furthermore, extra accumulations of
materials increase the probability of making mistake through tiring worker’s mind.
To implement the concept of pulling in the reinforcement operations, upstream
workstations such as “cutting” can be model in the way that produce and send the
products (rebars) to the downstream stations such as “tightening” only in the right
amount and at right time.
The general practice of mistake-proofing is to find a defect and problem in
current process of working and find the ways not to let the problems happen again.
For example, one of the most important mistakes in reinforcement operations is to
deliver, cut or bending the rebars with wrong size. To prevent this kind of mistakes,
one of mistaking-proofing method is coloring the end of bundled bars in to avoid
misuses. Totally, defective rebars in reinforcement operations includes 5% of all the
rebars. It is predicted that the defective entities can be reduced to almost 1% with
implemeting the mistake-proofing devices.
To evaluate the effect of lean construction principles application on the waste
reduction, the menntioned construction processes’ waste calculated in both conventional and
lean model and the results are summarized in Table 2.
Table 2. Process waste generation between the conventional and lean model
Conventional
process
Type of waste (in each cycle)
Number of defects
Labor time on rework (min)
Number of over produced rebars at the end
Transport/handling time (min)
Total waiting time (hrs)
Lean
process
Improvement
(%)
18
4.2
76.667
40.13
15
160.45
4.95
7.81
1.2
64.1
4.95
80.53
92
60.04
-4.84
Note : The quantities is the average of 20 replications for both conventional and lean model.
5. conclusion
The research contained in this paper presents a systematic approach for the
application of lean production principles to construction process emphasizing on
construction processes’ waste reduction. Results of the study affirmed the great
potentiality of such principles in improving construction processes and also reducing
waste generated during the processes.
Although, the construction industry witnesses noticeable share of waste in
construction process, an effective practices for reducing them are performed rarely.
However, lean construction thinking, through considering integrated view of
production, attempts to show the importance of neglected concepts in designing and
engineering of the construction processes. Actually, high share of non value-adding
works in the construction processes brings about excellent opportunities of lean
principles application. Sometimes, changes or modifications in the construction
operations may have to be made in order to better apply these principles. However,
costs of these modifications always will be considerably less than the benefits made by
lean principles.
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Finally, it should be concluded, while this study is just dedicated to one of many
operations in a construction project, it can be predicted that the construction operations
have high potential of optimizing through application of lean principles and simulation
which finally lead to a drastic promotion in construction industry.
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