Estimation pdf

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Estimation
Rate Analysis | Factors affecting rate of an item
Rate analysis :
Rate analysis is the study of principal role played by various constituents, elements of
construction such as equipments, cost of labor, number of equipments etc.
Rate of an item = Cost of material (A) + Cost of Labor (B) + Cost of scaffolding (C)+ Cost
of water charges (D) + Cost of sundries (E)*
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Sundries mean cost of all small items which cannot be accounted separately.
Factors affecting rate of an item :
1.
2.
3.
4.
5.
Locality and situation.
Size and extent of work.
Nature of project.
Height/Level of work at which it is being executed.
Environmental and climatic conditions.
Critical path method | CPM Logic Network
Critical path method (CPM)
CPM is a project scheduling method where activities are arranged based
on interrelationships and the longest time path through the network called the critical
path is determined.
The critical path method focuses the relationship between the critical activities. It is an
activity relationship representation of the project. Critical tasks which control the project
duration are determined. Because of the size and complexity of major construction
projects, the CPM is most often applied using a computer software program.
The CPM calls attention to which activities must be completed before other activities can
begin.
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CPM calculation define a time window within which an activity can be performed
without delaying the project.
Requirements of Using CPM
Using the CPM to develop a schedule requires detailed investigation into all identifiable
tasks that makeup a project. This means that manager must visualize the project from
start to finish, and must estimate time and resource requirements of each task. It is good
practice to also obtain information from superintendents and sub-contractors.
CPM Logic Network of Logic Diagram
The most important feature of the CPM is the logic diagram.
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The logic diagram graphically portrays the relationship between project activities.
With this, it is easier to plan, schedule, and control the project.
Reduces the risk of overlooking essential tasks and provide a blueprint for long-range
planning and coordination of the project.
Generates information about the project so that the manager can make timely decisions if
complications develop during the progression of work.
Enable the manager to easily determine what resources are needed to accomplish the
project.
Allows the manager to determine what additional resources will be needed if the project
must be completed earlier than originally planned.
Critical path and critical activities
The critical path through a schedule network is the longest time duration path through
the network.
It establishes the minimum overall project time duration. All activities on the critical path
are critical activities. A critical activity may be determined by applying either of following
rules :
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the early start and the late start times for a particular activity are the same.
the early finish and late finish times for a particular activity are the same.
Calculation of Forward Pass | Early start/Early finish time
Forward Pass
Forward pass is a schedule calculation that determines the earliest start and early
finish time of the activities and the minimum project duration.
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A forward pass through the logic network will yield this information:
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The earliest time each activity in the network can start and finish.
The minimum overall duration of the project.
In performing forward pass calculation, all successor activities are started as early as
possible. And Each activity is postulated to finish as soon as possible. This finish
requirement yields the following equation:
Early finish of nth activity = Early start of nth activity + Duration of nth activity
Early start/Early finish time
Early start time (ES) of an activity is the earliest point in time, that an activity may start.
The starting point for performing a forward pass is the first activity in the network. In the
case of first activity of the project, the earliest time they may start is zero ( the end of day
0 or beginning of day 1).
Calculation of early start/early finish
If only one precedence arrow leads into an activity, then that activity’s early start time is
the same as the previous activity’s early finish time. It means the early start time of the
next activity will be the same as that of the early finish of the previous activity.
To determine the early start time, when more than one arrow leads in to its node. Select
the largest early finish time of all activities at the tail of arrows. Logically, an activity cannot
be start until all previous activities are completed. In this case, the equation of early start
will be:
Early start of nth activity = Maximum early finish of all previous activities
Early finish time
The early finish time is the earliest time the activity may finish.
Add the duration of each activity to the early start time to compute early finish time.
Using this systematic procedure, compute all the early start and early finish times from
the beginning activities to the finish of the project. This sequence will complete the forward
pass.
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Overall duration of the project
The overall duration of the project is the Early Finish (EF) of the last activity in the
network.
Calculation of backward pass | Late start/Late finish time
Backward pass
Backward pass is a schedule calculation that determines the late start and late finish
times of the activities under the condition that the project’s minimum duration be
maintained.
A backward computational sequence through the logic network will produce
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the last point in time that each network activity can start and finish, and still maintain the
minimum overall project duration.
Calculation of backward pass
The backward pass calculation starts with the last activity in the network. This last activity
is assigned a late finish time equal to its early finish time as calculated by the forward
pass.
Late finish/Late start
The late finish time of an activity is the last point in time that an activity may be finish.
To calculate late finish time and late start time of an activity, follow the precedence arrows
backward through the logic diagram.
The late finish time of an activity is the latest point in time, that an activity may be finish
without delaying the project.
Calculation of Late start/Late finish
To compute the late start time of an activity we have to subtract the activity’s duration
from its late finish time.
The late start time is the latest time the activity may start without delaying the entire
project.
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Late start (LS) = Late Finish ( LF) – Duration
The preceding activity’s late finish time is the succeeding activity’s late start time. To
determine the activity’s late finish time when more than one arrow tail leads away from
its node, choose the smallest late start time of all the activities at the arrow’s heads.
Logically an activity must be finish before all following activities may begin.
Using this backward systematic process, work through the entire logic diagram against
the arrows. Compute all the late finish and late start times. This movement back through
the logic diagram is known as backward pass. The late start time of the first activity must
be zero.
Float | Total Float | Free and Interfering float
Float
Float is an additional time available to complete an activity beyond the activity’s work
duration.
For example having 6 days available to do 4 days worth of work. Activities on the critical
path have no float.
Total Float
Total float is the amount of time that an activity can be delayed without delaying the
project’s estimated completion time.
Total float assumes that
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all preceding activities are finished as early as possible.
All succeeding activities are started as late as possible.
Total float for an activity can be determined either :
Total float activity n = Late start activity n – Early start activity n
Total float activity n = Late finish activity n – Early finish activity n
Where n denotes the nth activity.
Both equation will yield the same answer.
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Free float
Free float is the duration of time, that an activity can be delayed without delaying the
project’s estimated completion time and without delaying the start of any succeeding
activity.
Free float is the property of an activity not a network path. Free float can be determined
by :
Free float n = Minimum early start of all successor activities – Early finish n
Where n denotes the nth activity.
Interfering float
Interfering float is the time available to delay an activity without delaying the project’s
estimated completion time, but delaying an activity into interfering float will delay the start
of one or more following non-critical activities.
Interfering float n = late finish n – Smallest early start of succeeding activity
The aggregate of free float and interfering float is equal to the total float.
Total float n = Free float n + interfering float n
Type of Construction contract | Lump sum contract
Lump sum contract
Lump sum contract is typically used in building construction projects in which quantities
are exactly measured.
Typically used with Design-Bid-Build method of project procurement.
A lump sum contract, sometimes called stipulated sum, is the most basic form
of agreement between a supplier of services and a customer. The contractor agrees
to provide specified services for a specific price. The customer agrees to pay the price
upon
completion of the work. Or the customer will pay according the schedule of payment. In
developing a lump sum bid, the builder will estimate the costs of labor and materials. Then
add to it a standard amount of overhead and a normal amount of profit.
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Most of the builders add their profit 12%-16% of the total project cost. This amount of
profit may be enhanced according to builder assessment of risk. If the actual cost of the
project increases than the estimated amount, then builder’s profit will be reduced. If the
actual costs decreases, the builder gets more profit. The cost to the owner will be the
same in both cases. But In actual practice, the costs that exceed the estimated amount,
results in the disputes between the client and the builder. Or the builder will use the low
grade materials to complete the work in the same profit.
The lump sum contract may contain a section that contains unit price of items. Unit Price
is often used for those items that have indefinite quantities, such as pier depth. A fixed
price is established for each unit of work.
Following are some of the features of the lump sum contract.
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Builder is free to use any resources and processes to complete work.
Contractor or builder is responsible for proper work performance.
Work must be very well defined at bid time..
Owner’s financial risk should be low and fixed at outset.
Builder has greater chances of more profit.
Requirements of lump sum contract
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Good project definition is required for lump sum contract.
Lump sum contract requires complete plans and specifications setting and directions in
enough detail to enable a contractor to carry them out.
Stable project conditions are necessary.
Effective competition is necessary when bidding.
There should be much longer time to bid and to award lump sum type of project.
Advantages of lump sum contract
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Low financial risk to Owner.
High financial risk to Contractor.
Know cost at outset.
Minimum Owner supervision related to quality and schedule.
Contractor should assign best personnel due to maximum financial motivation to achieve
early completion and superior performance.
Contractor selection is relatively easy.
Disadvantages of lump sum contract
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Changes in lump sum contract are difficult and costly.
Early project start is not possible because of need to complete design before bidding.
Contractor is free to choose lowest cost means, methods, and materials consistent with the
specifications. Only minimum specifications will be provided.
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If the owner is not able to write the desired specification, then he should expect that the
contractor will use the lowest suitable grade materials. This will increase the profit of the
contractor.
Hard to build relationship. Each lump sum project is unique.
Bidding is expensive and lengthy in lump sum contract.
Contractor may include high uncertainty within each Schedule of Value item.
Definition of Estimate | Estimation | Need for an estimate
Estimate
An estimate is an anticipated or probable amount of construction which is usually made
beforethe execution of the actual construction work.
Estimation
Estimation is the scientific way of working out the appropriate amount of engineering
project prior to the execution of work.
It is important to note that estimated amount may be different from the actual cost of the
project. Estimated amount should not be differ than 5% to 10% of the actual cost of the
project.
Estimation requires thorough knowledge of construction procedure, labor and material. It
requires knowledge of drawing specifications and prevailing market rates.
Need for an estimate
The main purpose of an estimate is to know the probable amount before the work is
executed.
The actual cost is always obtained after the completion of project. If the estimate is carried
out with lot of accuracy. Then the actual cost will be near to the estimated amount. That
is the reason why experienced person is employed for this purpose.
Estimate of a project will help us in following ways.
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It tells whether the project is suitable or not by considering the cost comparison.
The quantity of major components of the project like cement, bricks, steel, sand etc and
their cost to be entered by considering the prevailing market rates.
It helps to invite tenders.
It helps to monitor the contractor payment record.
We can also check the contractor work being executed.
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It helps to experience the details of work to be executed.
It helps to foresee the minor and major components of the project.
Estimate will serve as the basis for developing job costing system.
It will help to build construction schedule before execution.
Job costing system compares actual cost of project at specific time for particular
item of estimate. This date tells which item needs more cost control during construction
process.
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It helps to find out duration of work of various activities for construction schedule.
Duration of work = magnitude of work / standard output
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The essence of an estimate consists of forecasting future events in construction process.
Then placing currency value on those events. Many additional factors can also affect the
future events of construction.For example
1. labor production
2. material availability
3. financial markets
4. weather conditions
5. construct ability issues
6. equipment availability
7. contract types
8. ethics
9. quality issues
10. project control system
11. management ability
Qualities of a good estimator
Qualities of a good estimator
Estimator must have the following qualities:
1.
2.
3.
4.
5.
6.
7.
8.
Estimator has ability to read and interpret drawings and specifications.
Estimator should have good communication skills.
He should have knowledge of basic mathematics.
He should have patience.
Estimator should have good understandings of fields operations and procedure.
He should have ability to visualize three dimensional projects by looking at the drawing.
He should have ability to interpret the risks and then neutralize as much as possible.
He should have good organizational ability. So that he can communicate his estimate in
logical and clear presentation to the client.
9. He should have ability to prepare construction schedule.
10. He should have ability to anticipate all construction steps in building projects.
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11. He should have good understanding of labor productivity and equipment performance.
12. He should have ability to use the construction company’s job costing system.
13. He should have ability to think alternate methods of construction.
14. Estimator should have ability to develop strategy for being successful in bidding and
negotiation phase of the project.
15. Estimator should have ability to meet deadlines and still remains calm.
16. He should have a solid load of ethics.
17. Estimator should have understanding of contractual relationship.
Types and Methods of Rough cost estimate
Types of Rough cost estimate
Rough cost estimates are of the following types.
1.
2.
3.
4.
Preliminary/approximate/rough cost estimate
plinth area estimate
cube rate estimate
approximate quantity method estimate
Preliminary/approximate/rough cost estimate
Estimate of cost before the construction, from the line planes of architectural drawings
when detail and structural drawings are not prepared.
Objective of rough cost estimate
These estimates are used for obtaining administrative approval from the concerning
authority.
Method
Average unit cost is worked out for projects of similar nature like the project under
consideration. In this method average unit cost is multiplied by total quantity of present
work in the same unit.
Average unit cost like:
1.
2.
3.
4.
building cost per person
hospital cost per bed
student hostel cost per student
hostels cost per person
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Plinth area method
Covered area by building is worked out and unit obtained is square feet. For cost per
square feet of the covered area, plinth area method is usually used. This method is
practical and usual method of obtaining rough cost estimate.
Cube rate estimate
In cube rate estimate, third dimension height is also considered. Height is multiplied with
the covered area. Cube rate is established in this method.
The covered area is first calculated and then multiplied with the ceiling height. For each
floor level, different cube rate estimate is obtained.
Approximate quantity method estimate
In this method, a linear length is used for estimation. Therefore, the total length of the
object is calculated in running foot. This length is then multiplied with the running cost per
running foot of the object to get the cost of the wall.
In this method, the structure is divided into sub-structure and super structure. This method
is used in roads, railways, bridges, streets etc.
By using this method, cost may be found in following ways.
1. For roads and railways, cost/km or cost/miles
2. for streets, cost per 100 feet or cost per 30 meters
3. for bridges, cost per foot or cost per meter of the clear span. Clear span is the clear distance
between the supports of the bridges.
Types of Detailed cost estimate for construction
Types of Detailed cost estimate
Types of detailed cost estimate are following:
1.
2.
3.
4.
5.
Detailed/item rate estimate.
Revised estimate.
Supplementary estimate.
Supplementary revised estimate.
Annual repair and maintenance estimate.
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Detailed cost estimates
Detailed cost estimates are prepared carefully. These calculate in detail the cost of
various items work that constitutes the whole project. Detailed estimates are done when
the detailed working drawings are prepared along with specifications. If there is any
mistake in rough cost estimate, then it will eliminate in detailed cost estimates.
These are then submit to the competent authority for obtaining technical sanction. The
whole project is divided into different items of work or activities. The quantity of each item
will be calculated from drawing as accurately as possible. This procedure is known
as taking out quantities or quantities take off.
Hand mixing of Cement Concrete
Following points must be kept in mind for hand mixing of cement concrete.
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Hand mixing of cement concrete should be done in masonry platform or iron sheet.
For example if we are making concrete of ratio 1:2:4 proportion by hand, first two
boxes of sand and one bag of cement should be mixed dry.
Mixing of sand and cement should be dry thoroughly.
Then this dry mix should be placed over a stack of 4 boxes of stone aggregate.
Then this whole mixed dry should be turn at least three times to have uniform mix.
Water can be added then gradually with a water-can to the required quantity 25 to
30 litres (5 to 6 gallons) per bag of cement.
This water quantity will give the mix required work-ability and water cement ratio.
Machine mixing and slump of cement concrete
Machine mixing of cement concrete
Following points must be kept in mind for machine mixing of cement concrete.
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Stone ballast, sand and cement to be pour into the cement concrete mixer.
For example, for concrete of ratio 1:2:4 first four boxes of stone ballast, then two boxes of
sand and then one bag of cement should be put into the cement concrete mixer.
The machine then revolve to mix dry materials.
Then water should be added to the required quantity, 25 to 30 litres (5 to 6) gallons per bag
of cement to have the required water cement ratio.
The mixing should be proper to have a plastic mix of uniform color.
It requires 1.5 to 2 minutes rotation for proper mixing.
Mixed concrete shall be unloaded on a masonry platform or on a iron sheet.
Output of concrete mixer is 15 to 20 mix per hour.
Slump of cement concrete
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Slump test is carried out to control the addition of water into the cement concrete.
It is carried out to maintain the required consistency.
A slump of 7.5 cm to 10 cm (3 inch to 4 inch) is required for building work.
For road work it may be 3 to 4 cm (1.5 inch to 2 inch).
How to calculate quantity of mortar and its materials
Below is the step by step process of calculating quantity of mortar required for cementing.
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Area of the surface multiply with the thickness gives the quantity of mortar for uniform
thickness.
This quantity is increased by 30% for filling the joints and to make up uniform surface of
wall. It will give wet mixed mortar.
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This mortar quantity is further increased by 25% to get the dry volume of the
ingredients.
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Quantity of each material of the mortar may be found by dividing the dry volume of
mortar by the sum of numerals of the proportions and multiplying the answer with
the individual numeral.
For example
Materials for 12 mm or half inch thick plastering in wall for 100 square
meter
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First of all, we have to multiply 100 square meter surface with 12 mm.
100 square meter x 0.012 m = 1.2 cubic meter. (12 mm can also be written as 0.012)
1.2 cubic meter is wet mixed mortar for uniform thickness.
Add 30% in this value to fill up joints, uneven surfaces, etc., the quantity of mortar comes
out 1.2 + 0.36 = 1.56 cubic meter.
Increasing by 25% the total dry volume will be 1.2+0.36+0.39 = 1.95 cubic meter or 2 cubic
meter.
For cement sand mortar, cement = dry volume / ( sum of ratios) x numeral of cement.
For 1:4 cement sand mortar, cement will be 2/5 x 1 = 0.4 cubic meter.
For 1:4 cement sand mortar, sand will be 2/5 x 4 = 1.6 cubic meter.
In this way you can calculate the dry volume of any ratio of mortar ingredients.
Weight of steel bars per meter – Weight of steel bars formula
Here is a list of mild steel bars weight.
Diameter of bars in millimeter
6 mm
Weight of bars in kilogram
0.22 kg/meter
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10 mm
0.62 kg/meter
12 mm
0.89 kg/meter
16 mm
1.58 kg/meter
20 mm
2.469 kg/meter
25 mm
3.858 kg/meter
Weight of steel bars formula
To calculate weight of steel bars, there is a formula used to calculate weight.
W=(D^2 x L)/162
In the above formula:
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D is in millimeter.
L is the total length of steel bars of which weight is to be calculated.
For example: if we have to calculate the weight of 10 mm steel bars, then we will
proceed as follow:
W=10^2/ 162
W=0.617 kg/meter
In this way we will get steel bars weight per meter. After that multiply unit weight with
the total length of steel bars of which weight is to be calculated.
Weight of steel bars per foot in kg
Diameter of bars
Weight of bars
#2 bars (diameter 2/8 inch)
0.075 kg/ft
#3 bars (diameter 3/8 inch)
0.170 kg/ft
#4 bars (diameter ½ inch)
0.30 kg/ft
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#5 bars (diameter 5/8 inch)
0.473 kg/ft
#6 bars (diameter 6/8 inch)
0.68 kg/ft
#8 bars (diameter 1 inch)
1.21 kg/ft
How to Calculate The Quantity of Cement And
Sand in Mortar
Mortar is a mixture of cement, sand, and water. More specifically it is
called cement mortar.
Cement mortar is used in almost all types of masonry work in civil construction.
Such as brickwork, plasterwork, tiles work etc.
Although there is dry ready mix mortar available in the market, we often prepare
mortar manually in our construction projects.
The main ingredients of mortar are cement and sand.
In a building project, when we want to start any types of masonry work, we need
to stack cement and sand in the project.
For stacking cement and sand in the project, we often need to calculate the
required quantity of cement and sand for the masonry work. So, let’s see how we
can calculate the quantity of cement and sand in the mortar.
The quantity of sand and cement in mortar can be calculated in two ways. One is
by weight and another is by volume.
The easy way to calculate the quantity of cement and sand in mortar is by volume
and we often use this method. So, I’ll explain how to calculate cement and sand
quantity in the mortar by volume.
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First of all, you need to know the required quantity of mortar for your masonry
work. Then you need to know the proportion of the cement and sand in the
mortar.
Let’s assume out required mortar quantity is 100 cubic feet and the ratio of
cement and sand in the mortar is 1:4.
When we say the cement-sand ratio is 1:4, we mean that the mortar contains one
part of cement and four parts of sand.
But when we get or buy cement and sand, we get those in dry condition. After
adding water in the cement-sand mix, the volume of sand is reduced.
So, when we calculate the quantity of cement and sand in the mortar, we need to
consider the reduced volume of the sand.
Considering all these things lets calculate the quantity of cement and sandin the
mortar.
Get The Required Quantity of Mortar
Getting the quantity of mortar for plaster work is easy. You just need to get the
plastering area and the thickness of plaster. Then multiply the area with
thickness. The result is the quantity of mortar for the plasterwork.
Get calculating mortar quantity for masonry wall is a little bit tricky.
However, for our calculating purpose let’s assume we need 100 cubic feet mortar.
Get The Dry Volume of Mortar
As we get the sand and cement in the dry condition we need to get the mortar
quantity in the dry state. But when we calculate mortar for any masonry work, we
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get the wet quantity of mortar. So, we need to convert the wet quantity into dry
quantity.
To get the dry quantity of mortar, we multiply the wet quantity of mortar
with 1.27. That means,
The dry quantity of mortar = wet quantity of mortar x 1.27
So, the dry quantity of 100 cubic feet of wet mortar is,
= 100 x 1.27
= 127 cubic feet.
Get The Cement And Sand Quantity in The Mortar
Now it’s time to calculate the quantity of cement and sand in the mortar. For this,
we need to know the proportion of cement and sand in the mortar.
Different proportion of cement and sand is used in mortar for different types of
masonry work. For our calculating purpose, let’s assume we’ll use 1:4.
That means, we’ll mix one part of cement with four parts of sand to prepare our
mortar. The total part of ingredients is,
= 1+4
=5
Calculating The Quantity of Cement
So, the quantity of cement is,
= 127 ÷ 5 × 1
= 25.40 cubic feet
But cement is sold in bags. So, we need to convert the volume of cement into
bags. The volume of a 50-kilo bag of cement is 1.25 cubic feet.
So, the bag of cement is,
=25.40 ÷ 1.25
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=20.32 bags
Say, 21 bags.
Calculating The Sand Quantity
The quantity of sand is,
=127 ÷ 5 × 4
=101.60 cubic feet.
Say, 102 cubic feet
Summary
Wet mortar volume = 100 Cubic feet
Cement-Sand ratio = 1:4
The Quantity of cement = 21 bags
The quantity of Sand = 102 cubic feet.
How to Calculate Concrete Quantity for Neck
Column
Either you are going to use ready-mix concrete or on-site machine mix concrete,
you need to calculate the concrete quantity of neck columns for ordering readymix concrete or purchasing concrete ingredients.
It is our common practice. We often calculate concrete quantity before going to
cast any concreting members. There are many things which depend on the
concrete volume. Such as required manpower, the tentative cost for the
concreting work, etc.
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The main reason, we calculate concrete quantity for, is to know the volume of
concrete or concrete ingredients.
In this post, I’ll discuss the manual calculating process for the concrete quantity of
neck columns of a building project.
What is Neck Column?
Neck column is the most bottom part of a column. Saying more specifically, neck
column is the part of a column which is buried below ground. The portion
between footing and grade beam is normally called neck column. Neck column is
also called short column.
So, after casting footings of a building project, the next step is to cast neck
columns. When we plan to cast neck columns, we need to calculate the concrete
quantity for that.
How to Calculate Concrete Quantity for Neck Column
Calculating concrete quantity for neck column of a building construction project is
actually easy. You can do this within a short period of time. Just follow the steps
below –
Step 1: Get The Total Number of Columns in The Project
A building can have many columns of different sizes. There must be some
columns with the same size. The first step is to summarize the number of
different sizes column. For this, you’ll need column layout and column
schedule drawing sheet.
You’ll get those drawing sheets in the structural drawing book. Sometimes you’ll
find both column layout and column schedule in a single drawing sheet.
Sometimes you’ll get two separate sheets.
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Column layout drawing is that where the column placements for the building are
shown. And the column schedule is where size, symbol, and reinforcement details
of columns are shown.
Columns are normally specified as C1, C2, C3, etc. For estimating neck column
concrete you need to find out the total number of different types of columns
from the column layout drawing sheet.
Summarize the all different types of columns which will look like, for example,
below:
C1 – 5 numbers
C2 – 10 numbers
C3 – 7 numbers, etc.
Step 2: Get The Size of Neck Column
You’ll get the column size and shape form the column schedule drawing sheet.
The commonly used shape of columns is round and rectangular/square.
Here I would like to explain a most important thing…
From my personal experience, I found that the size of neck columns are
sometimes not specified in the column schedule drawing separately. Only the size
of ground floor columns is shown.
But the size of neck column should be bigger than the size of ground floor
column. Because the concrete clear cover should be more for neck column as it is
built under the ground.
In that case, you’ll find the concrete cover for neck column in the general
notes sheet of the structural drawing.
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For example, the concrete clear cover for neck column is specified in the general
notes sheet as 2½″and the size of C1 column in ground floor level is shown in the
column schedule as 30″x 12″.
In this case, the size of neck column (C1) will be 32″ x 14″.
Most of the time a separate schedule for neck column is shown in the column
schedule drawing. In that case, you don’t have to think about anything. You can
proceed to calculate the column area.
Suppose, you get the size of the column from the column schedule as below –
C1 – 32″x 14″
C2 – 42″x 14″
C3 – 15″x 14″
From these sizes, you can just calculate the column area. But to get the quantity
of neck columns’ concrete, you need the third dimension too. That is the height of
neck columns.
Step 3: Getting Height of Neck columns
Getting the height of neck column is a little bit tricky. You need to get the gap
between the top of footing and bottom of the grade beam.
There may all the footings top isn’t on the same level. And grade beam may not
be at the same level too. Then how do you get the height of neck columns?
If you already cast footings, you can take measurement practically from the field.
That is the most accurate way. I often do this in my project.
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But sometimes you need to calculate neck column concrete before casting
footing. In that case, you need to depend on the drawings.
Most of the time you’ll get the data from footing section and grade beam
layout drawing.
From the footing section drawing sheet, you’ll get the depth of the ground the
footing placed on. It is normally shown from road level (土0). For example, I
assume that this level is shown in the footing section as -5′. That means the
bottom of the footing is place 5′ below the ground.
We also need the top level of grade beam which you’ll get from either footing
section or grade beam layout drawing. For example, it is specified in the drawing
as +3′.
Now let’s calculate the height of the neck column.
The height of neck column is,
= Bottom level of footing + top level of grade beam – the thickness of footing –
the thickness of grade beam
= 5′ + 3′ – 1′ – 1′ (the thickness of footing and grade beam 1’ – assumed)
= 6′
So, The height of neck column is 6′.
Now we can calculate the concrete quantity for neck columns.
Step 4: Calculating Concrete Quantity for Neck Columns
We know, the formula for getting volume is area x height.
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For square and rectangular size, the area is length x width. But if the column is
round shape then the formula for getting the area is πr² (π = 3.14 and r = radius of
the column).
So, let’s calculate the concrete volume for neck columns which we found in step
1.
C1 – 5 x 32″ x 14″ = 5 x 2.67 x 1.17 = 15.62 ft3 (12″ = 1 feet, ft3= cubic feet)
C2 – 10 x 42″ x 14″ = 10 x 3.5 x 1.17 = 40.95 ft3
C3 – 7 x 52″ x 14″ = 7 x 4.33 x 1.17 = 35.46 ft3
Total concrete quantity is
= 15.62 + 40.95 + 35.46
=92.03 ft3
This is the exactly required concrete quantity for our neck columns. If you plan to
cast the neck columns with ready-mix concrete then you can order for this
concrete volume. But if you want to use on-site machine mix concrete then you
need to calculate the concrete ingredients. I’ve talked about this before in “how
to calculate concrete ingredients”.
Conclusion
Calculating concrete volume for neck columns is actually easy. You just need to
get the total numbers of different sizes columns and the size and height of the
columns from drawing. And then multiply and sum them up for getting the total
concrete volume.
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How to Easily Estimate Shuttering Materials
for Footing
Before estimating shuttering materials for footing you need to check the
availability of shuttering materials in your project. If you built any other building
before you may have some shuttering materials there which you can use in your
current project. The purpose of this is to reduce costs as this is the major concern
in building construction.
As footing is built on the farm base of the ground, so you don’t need to make
special formworks for this purpose like column, beam, and slab. Whichever
shutter materials are available to you can be used for making formwork of
footing.
There are various types of formwork materials can be used for footings. You can
use plywood, wooden plank or even steel shutter. In my case, if I have any steel
shutter in my previous project, I try to use them first.
There must be also some shutter material renting company in your area. You can
hire shutter from them.
The purpose is to reduce cost as the shutter materials for footing is one-time use.
Those shutters need to be reassembled for using later. So, it is better to focus on
reducing cost in this respect. Whichever shuttering material you have currently
try to use those first then calculate rest of the required quantity of materials.
As footing shutters are used one time only, it is better not to make new steel
shutters for the footing as it is costly. Whichever materials are cheap and
available in your area, use those for making formwork of the footing.
Mostly used shutter materials for footing is wooden planks, plywood or wooden
board as those are cheap and widely available.
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Estimating shuttering materials for footing is easy. Even a non-technical guy can
estimate these.
We estimate the shuttering materials for the purpose of purchasing it. Wood and
plywood have many uses in a building construction project. So if you purchase
some more materials that wouldn’t be a big deal.
The purpose of this post is to make the estimating process of shutter materials for
footing easy. So that anyone can estimate the materials. So I’m not going to deep
technical details as most of them can be ignored.
How to Easily Estimate Shuttering Materials for Footing
A building has many footings. Not all the footings are different. There must be
same types of footings. First of all, summarise the same type of footings.
Summarizing footings
Footings are normally marked as F1, F2, F3… etc.
Suppose, you have 10 numbers of F1 type footing, 6 numbers of F2 type footing,
and 8 numbers of F3 type footing, etc.
Summarise them all.
For summarising similar types of footings you’ll need the footing layout drawing
sheet. You’ll find the footing layout drawing in the structural drawing book.
There is a problem when summarizing footings. That is you’ll forget which footing
you counted from the drawing and which isn’t. To overcome this problem take a
pencil and start marking the footing one after another once counted.
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After counting all types of footings check the footing layout drawing to find out if
there is any unmarked footing. If you found any count that too.
After finishing this step, you’ll have the numbers of all types of footing.
Now count the total number of footings in the footing layout drawing by marking
one by one with the pencil. Cross check the total number of footing you found are
correct with the counted number.
This is not a thumb rule. I just apply this when counting the numbers of footings
in a building. If you know any better way you can apply that. The purpose is just to
get the exact numbers of different types of footing.
Deciding How Many Formworks You’ll Need
You don’t need to make formwork for all footings. For example, you
have 10 numbers of F1 type footings. All these footing sizes are same. If you just
make one formwork for this type, you can reuse that for all 10 footings.
This is done for cost saving. You can buy shuttering materials for all 10footings.
But that isn’t cost effective.
If you are in the tight project schedule and need to finish the project on a short
period of time you may need to make formwork for all footings.
There are also many things involve deciding how many formworks you need to
make for one type of footing. Such as manpower – if you have enough workers,
you need to have enough formwork. So that they all can work together.
Considering all these things you need to make a decision for how many
formworks you’ll make for the footings.
If you want to save costs you may make one formwork for three footings and plan
for making sufficient formwork for different types of footing. So that, all the
workers can work at a time and no workers need to be idle. After casting one set
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of footings, you can remove the formworks and reuse them in the next set of
footings.
Estimating Shuttering Materials for Footings
It is better to use wooden shutter materials for footing. I won’t recommend
making new steel shutter for footings. Because it’s costly.
However, you don’t need to estimate exact quantity of wood or plywood for the
footings of your building project. If you buy some access wooden plank or some
less, that would not make a big difference.
You can use the access wooden shutter materials later in some other works. Such
as lintel, staircase, etc. If you buy some less quantity of wooden plank, that won’t
hamper your project progress. Because if you don’t make a formwork that
wouldn’t hamper your project’s progress.
Below I’ll show you a simple process to estimate wooden shutter materials for the
footing of a building project. Even a non-technical guy can estimate the shuttering
materials for footings easily. Follow the steps below –
Step 1: Calculate the Periphery Length of Footing
Suppose, the size of the F1 footing is, 4′ x 6′ x 1′.
So, the periphery length of this footing is,
= (4′+6′) x 2
= 20′
Step 2: Calculating The Periphery Area of The Footing
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The periphery area of the F1 footing is,
=20′ x 1′ (the height of the footing is 1′)
= 20 square feet (sft)
Step 3: Calculating Shuttering Materials
What materials do you need to make formwork for footing? You’ll need –
Wooden plank or plywood (which is available in your area): The periphery area
of the F1 footing is the exactly required area of wooden plank or plywood which
is 20 square feet. You need to add 5% extra when ordering wooden plank or
plywood. So, required wooden plank or plywood for our footing is, 21 sft.
Wooden batten: We normally use 3″x 2″ wooden batten for the formwork of
footings. The easiest way to estimate wooden batten is to use a thumb rule which
is 2 rft (running feet) per shuttering area. So, required wooden batten for our
example footing is,
= 2 x 21
= 42 rft (running feet)
Nail: the easiest way to estimate nail for formwork is to use a thumb rule which
is 0.02 kg for one square foot of shuttering area.
So, the required nail for our example footing is,
=0.02 x 21
=0.42 kg (kilogram).
We have got the required shuttering materials for one formwork of F1 type
footing. Based on how many formworks you need for F1 type footing, multiply the
shuttering materials we’ve got above with that number.
For example, you’ve 10 numbers of F1 type footing and you’ve decided to
make 3 numbers of formwork for this type footing. So, required shuttering
materials for 3 numbers of formwork for F1 type footings are,

Wooden plank or plywood = 3 x 21 = 63 sft
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

Wooden batten (3″x2″) = 3 x 42 = 126 rft
Nail = 0.42 x 3 = 1.26 kg.
Similarly calculate the shuttering materials for all different types of footing for
your building project and summarize them all.
conclusion
Estimating shuttering materials for footings is actually easy. You just need to
decide how many formworks you’ll make for different types of footing. And then
calculate wooden plank or plywood, wooden batten, and nail for all the formwork
you required.
How to Calculate The Concrete Volume for
Footings of a Building
When you plan to cast footings of a building, you need to calculate concrete
volume. Either you use ready mix concrete or plan to cast the footings manually
you need to know the exact concrete volume. So that you won’t have excess
materials after complete footing casting or you won’t run out of concrete
ingredients before completing footing casting.
If you plan to use on-site machine-mix-concrete than you have some flexibility.
Because if you order for excess concrete ingredients you can use those in some
other concreting works. Yet, you need to calculate required concrete volume. So
that you won’t run short of concrete ingredients before casting the footing.
If you plan to use ready mix concrete to cast the footings, you need to know the
exact required concrete volume for ordering concrete.
Over-ordering ready-mix-concrete will cost you more. Because ready-mix supplier
won’t take ordered concrete back. You will need to pay for excess concrete.
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As cost is a major issue in construction, you need to control cost by not over
ordering ready-mix concrete or over mixing concrete. So, calculate the exactly
required concrete volume for the footings before going to cast.
In this post, I’ll show you how to calculate the concrete volume for footings of a
building easily.
How to Calculate Concrete Volume for Footings of a
Building Construction Project
Calculating concrete volume for footings is easy. You just need to get the volume
of different sizes of footings by applying some geometric formula.
Let’s see how we can do that.
Summarising Similar Types of Footings
A building has different types and sizes of footings. They are marked
as F1, F2, F3…etc.
The first thing you need to do is to summarize them all.
For example, The building has 5 numbers of F1 footing, 6 numbers
of F2footing, 4 numbers of F3 footing etc.
Counting numbers of the same type of footings from the drawing is a little bit
tidy. Because you’ll forget which footing you have counted and which you didn’t.
The best way to do this is to mark the footing after counting.
Take a pencil and mark one after one when counted.
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After counting all the footings in this way, check the footing layout drawing if any
footing is not marked. Unmarked footing means you didn’t count that footing. If
you found any footing unmarked, count that too.
After summarizing all types of footings, now calculate the concrete volume for
each type.
Calculating Concrete Volume
For calculating concrete volume, you just need to get the volume of
some 3D shapes.
The shapes can be square, rectangle and trapezoidal.
For example, the F1 footing is a square size footing and the dimension is 4′ x 4′ x
1′.
So, the concrete volume for this footing is 16 cubic feet.
As we have 5 numbers of footings of this type, so the total concrete volume
for F1 type is,
= 5 x 16
= 80 cubic feet.
Again, the F2 footing is a rectangular shape footing and the dimension is 4′ x 6′ x
1′.
So, the concrete volume for one footing of this type is 24 cubic feet.
As we have 6 numbers of F2 type footing, so the total volume for this type of
footing is
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= 6 x 24
= 144 cubic feet.
Again, for example, F3 type footing is a trapezoidal shape and the calculated
concrete volume for one footing of this type is 30 cubic feet (assumed).
As we have 4 numbers of F3 type footing. So, the total concrete volume
for F3 type footing is,
= 4 x 30
= 120 cubic feet.
Concrete Volume of Footings of a Building Construction
Project
You may have other types of footings in your building construction project.
Calculate concrete volume for all the different types of footings.
For keeping this post easy to read and easily understandable, I’ve just shown
three types of footing.
So, the total concrete volume in footings for our example building project is,
= F1 + F2 + F3
= 80+144+120
= 344 cubic feet.
This is the exactly required concrete volume for footings of the building project.
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One Dispute Regarding Concrete Volume
There is a dispute regarding concrete volume. That is, do we need to deduct
reinforcement volume from concrete volume?
I didn’t find any written instruction anywhere about this.
Some say we should deduct reinforcement volume and some say we shouldn’t.
In my experience, I found that if we deduct reinforcement volume from the total
concrete volume, we run short of concrete during casting.
So, my recommendation is not to deduct concrete volume from the total volume
to find the exact volume.
So, how much concrete volume we found in the above calculation for the footings
of our example building is the concrete volume we exactly require.
Conclusion
To calculate concrete volumes for footings you just need to get the volume of
some 3D shapes. It is not hard if you know some geometrical formulas. After
getting volume for all the different shapes, just grand total them.
How to Calculate Quantity of Steel in Footing
We often need to calculate steel quantity of different RCC members in a
construction project before ordering for purchase. We often do this manually in
the project.
We actually need to calculate steels for different RCC members when we need
that. Because over-purchasing steels (MS Bar) can block a huge amount of money
as it is highly priced material.
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You also can’t order less quantity than the required quantity. Because it will
hamper your project’s workflow.
So, at different stages of construction of a building project, we need to calculate
the steel for different RCC members to know the required quantity.
In this post, we will see how to calculate the steel quantity in footings.
What is a footing?
I think you all know about this. A footing is the most bottom part of a building.
And it is a part of the substructure. There are many types of footing used for a
building. It depends on the structural design of the building.
In this post, I’ll discuss how to estimate reinforcement or steel quantity of a
footing
How to Calculate Steel Quantity of a Footing
Calculating steel quantity of footing is easy. You just need to find out the length of
steel bars and then convert the total length of bars into kilogram as steel is sold
in Kilograms or Tons (1 Ton=1000 kilogram).
The process to calculate steel quantity is same for different types of footings.
Once you’ve learned to estimate steel quantity for one type of footing, you’ll be
able to estimate steel quantity for any type of footings.
So, I’ll show you how to calculate steel quantity for an Isolated footing.
What is an Isolated Footing?
An isolated footing is normally used to support a single column. It can be a square
or rectangular shape.
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If you know how to calculate the quantity of steel for an isolated footing, you’ll be
able to calculate steels for other types of footings.
So, let’s see how to calculate steel quantity for an isolated footing.
How to Calculate Steel for an Isolated Footings
You’ll need structural drawing sheets of footings for calculating steel.
Things you’ll require for estimating steel quantity of footings –


Size of footings
Reinforcement details of footings
In structural drawings, you will find all the details required to calculate steel and it
is somehow shown in the drawing as shown in the image below.
From the above image, the size of the footing is 4′ x 6′ x 1′
And,
The reinforcement details are,


16 mm∅ [email protected]″c/c along the long side, and
20 mm∅ [email protected]″ c/c along the short side.
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That means you’ll need to place 16mm dia bar at 4″ center-to-center (c/c)
distance along the long side and 20mm dia bar at 4″ center-to-center (c/c)
distance along the short side of the footing.
So, let’s calculate the steel quantity for the footing.
To calculate the steel quantity, we first need to calculate the required number of
bars for both directions. Then we need to find the length of one bar. If you
multiply the number of required bars with the length of one bar then you will find
the total length of bars. Once you found the total length of bars, you need to
convert that length into kilograms or Tons.
So, let’s see how we can calculate the steel quantity for our example footing.
A formula for Calculating The Number of Bars
To find out the required number of bars for a footing, use the following formula,
Number of bars = {(length or width of footing – concrete cover for both sides) ÷
spacing} +1
For our example footing,
Number of bars along the short side of the footing,
= {(6′ – 3″ x 2) ÷ 4″} + 1 [Concrete clear cover for footing is 3″]
= {(6′ – 6″) ÷ 4″} + 1
= (5½′ ÷ 4″) +1
= 17.67
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Say, 18 Nos.
Number of bars along the long side of the footing,
= {(4′- 3″ x 2) ÷ 4″}+1
= {3½′ ÷4″} + 1
= 11.61
Say, 12 Nos.
A formula for calculating the length of a steel bar
To find out the length of a steel bar use the following formula.
Length of a bar = length or width of footing – concrete cover for both sides + 2 x
length of a bend
For our example footing,
Length of a steel bar along the width of the footing,
= 4′ – 2 x 3″ + 2 x 6″
= 4½ feet.
Length of a steel bar along the long side of the footing is,
= 6′ – 2 x 3″ + 2 x 6″
= 6½ feet.
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Finding total length of bars in the footing
The total length of bars along the short side of the footing is,
= number of bars x length of a bar
= 18 x 4½′
= 81 feet (20mmØ bar).
The total length of bars along the long side of the footing is,
= number of bars x length of a bar
= 12 x 6½′
= 78 feet (16mmØ bar).
If the same size of bars is used in both directions then you can sum up both
quantity of the bars. But, in our example footing, we used different size of bars.
So, we will calculate the steel quantity for different diameter bars separately. For
purchasing the steel, we need to convert the required length of steel into
kilogram.
From the above calculation, we found –
Required 16mmØ bar for our example footing is,
= 81 feet
= 38.88 kilograms
And, Required 20mmØ bar is,
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= 78 feet
= 58.50 kilograms
In our example footing, we use a single reinforcing net. But, in your building
project, you may find some footings with the double reinforcing net. In that case,
you need to follow the same procedure again to calculate the steel quantity for
another reinforcing net too.
So far, we calculated the quantity of steel for a footing. Now let’s see how we can
calculate footing’s steel quantity for a building project.
How to Calculate The Steel Quantity in Footing for a
Building Project
A building has many footings with different sizes and shapes. You’ll need to
calculate the steel quantity for those footings too.
For making the steel calculating process easy for footings of a building
construction project,



first, summarise the similar type of footings
Secondly, calculate the steel quantity for each type of footing separately and
Finally, multiply the calculated steel quantity by the number of each type of
footings.
For example, you have 10 numbers of footing for F1 type and 5 numbers of
footings for F2 type and so on.
For calculating the steel quantity for F1 type footing, you just need to calculate
the required steel quantity for one footing of that type and then multiply that
quantity by 10.
Similarly, for F2 type footing, calculate the steel quantity for one number of
footing than multiply that quantity by 5. And so on.
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After calculating steel quantity for the footings of the building project, add the
steel quantity for short columns before purchasing. Because you will need the
short columns’ steel for completing the footings’ reinforcement works.
Conclusion
Calculating steel quantity for footings is easy. You just need to get the total
required length of the steel bars of different sizes and then convert that length
into Kilograms or Tons before purchasing.
What Should Be the Standard Door Frame
Width?
You should understand the standard door frame width properly as it is
related to door shutter width.
Let’s understand some terms first related to this issue for better
understanding the standard door frame width.
Door shutter width: This is somehow the clear opening of a door. That
means, it is the inner width of a door frame.
Door frame width: Door frame width is the outer width of a door
frame.
Door rough opening width: Door rough opening is the opening we keep
on a wall to fix a door frame. So, the width of opening in a masonry wall
to be fixed a door frame is the width of door rough opening.
Now let’s take a look at a door frame.
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Anatomy of a door frame
A door frame consists of three parts. Two Jambs and one Head.
Jamb: Jamb is a vertical part of a door frame. A door frame has two
Jambs.
The length of a jamb is normally 84“. And the cross-sectional dimension
of a jamb is normally 6” x 2½”.
But if you plan to fix tiles in a wall then the cross-sectional dimension of
a Jamb should be 6½” x 2½”. For example, bathroom wall and kitchen
wall.
Head: Head is the horizontal part of a door frame. A door frame has
one head.
The length of a head should be same as the width of a door frame. And
the cross-sectional dimension of a head should be same as the crosssectional dimension of jamb for the particular door frame.
As you now know about the door frame particularly, let’s move on to
understanding Standard door frame width.
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What should be the standard door frame width
In architectural drawing, we commonly see the door width as below –
For Bedrooms – 40”
For Kitchen – 36”
For Bathrooms – 30”, etc.
Let’s take a bathroom door for the sake of our example which
is 30” width.
So the width of the door frame for the bathroom will be 30”.
Let’s see what will be the door shutter opening width for the door.
Jamb thickness = 2 x 2½“ = 5”
Bit thickness for fixing door shutter in both Jambs = 2 x ½” = 1”.
So, the door shutter opening width will be,
= 30” – 5” + 1”
= 26”
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The available door shutter size in the market is 24”, 27”, 30”, 33”, 36”,
etc.
So, if you keep the door shutter opening 26”, you won’t face any
problem fixing 27” width door shutter. Because, if the door shutter
opening is increased for some reason (straightening, sandpapering, etc)
and the door shutter width is reduced for some reason (straightening,
etc.), you will be able to fix the door shutter in the door shutter
opening.
But there is a problem with 40” wide door. The bedroom doors are
often shown in the architectural drawing as 40”.
Let’s calculate the required door shutter width for the 40” wide door.
Required door shutter width for the 40” wide door frame is,
= door frame width – 2 x jamb thickness + 2 x bit thickness.
= 40” – 2 x 2½“ + 2 x ½“
= 36”.
The available door shutter width in the market for the door is 36”.
But, if you take some portion from Jambs and some portion from door
shutter for straightening and sand papering purpose, you won’t be able
to fix the 36” wide door shutter in the opening.
So, although the door width is shown in the architectural drawing
as 40”, you should use the 39” width door frame for bedrooms.
So, the standard door frame width depends on the available door
shutter width in the market.
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When we talk about the standard door frame width, we actually talk
about the standard door width.
Although some codes are discussed on the standard door size, I’m not
talking about those codes.
But, we normally use standard door width for various types of rooms in
an apartment as following –
For,
main entrance door – 45”
Bedroom Door- 39”
Bathroom – 30”
Kitchen – 36”
Kitchen veranda and servant toilet etc – 25”.
Keep in mind that you will also find a readymade door in the market
which is combined with the door frame and door shutter. Thus you
don’t need to calculate all these things.
However, standard door frame width depends on the width of door
shutter. So, whatever door size is shown on the drawing doesn’t
matter, you should check which door shutter width you will be able to
provide.
How to Estimate Concrete Volume for
Staircase?
Estimating concrete volume for staircase is a little bit tidy as it is
inclined and has geometrical shapes. But we can do that easily using
some formulas.
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Let’s first know deeply about a staircase.
Staircase and Its Parts
A staircase is an essential part of a building which is provided to make a
path between two floors.
A staircase has mainly two parts – Step and Landing.
Step: A step is normally a triangular shaped part of a staircase which
sits on an inclined slab (Waist slab). A step also has two parts
– Riser and Tread.
Riser: Riser is the vertical portion of steps. Normally, the height of a
riser is 6 inches.
Tread: It is the horizontal part of a step. The width of a tread is
normally kept 10 inches.
Landing: It is a horizontal slab which is provided in between the flights
of a staircase. It is mainly provided for changing moving direction of a
stair. It also gives users comport to climb.
Flight: A staircase normally has two flights. One is below the landing
and another is above the landing.
The flight below the landing is called first flight and the flight above the
landing is called 2nd flight.
This is somehow an anatomy of a staircase.
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To estimate concrete volume for a staircase, you need to calculate all
these parts of a staircase.
Let’s see how we can do that.
How to Estimate Concrete Volume for a Staircase?
Estimating concrete volume for a staircase, you need to calculate the
concrete volume for,



Steps and waist slab of 1st flight
Steps and waist slab of 2nd flight, and
Landing.
See the image below. In the image, we have a plan of a staircase.
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Now Let’s calculate the concrete volume for the staircase.
Concrete volume for 1st flight of the staircase
From the above two images –
Riser = 6 inches
Tread = 10 inches
Length of a step = 4 feet
Number of steps = 9
Thickness of waist slab = 6”
Concrete volume for the waist slab
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To know the concrete volume for the waist slab, we need to calculate
the inclined length of the waist slab.
Inclined length of waist slab isn’t normally shown in the drawing. But
we can calculate that from the architectural plan.
let’s calculate.
Horizontal length of a waist slab is,
=number of steps x tread
= 9 x 10”
= 7′-6”.
The height of the landing top from floor is,
= number of riser x height of riser
= 10 x 6″ [number of riser = number of steps = 1]
= 5 feet.
So the inclined length of the waist slab is,
=√{(horizontal length)2 + (Height)2}
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= (7’-6”)2 + (5’)2
= 9’ (round up)
So, the concrete volume for the waist slab is,
= inclined length of waist slab x width of waist slab (width of a step) x
thickness of waist slab
= 9’ x 4’ x 6”
= 18 cubic feet
Concrete volume for steps
As steps are triangular shape so the volume of a step is,
= ½ x tread x riser x length of step
= ½ x 10” x 6” x 4
= 0.84 cubic feet
As we have 9 numbers of steps in a flight, so the concrete volume for
the steps of first flight is,
= 9 x 0.84
= 7.56 cubic feet
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So the total concrete volume for the 1st flight of the staircase is,
= Waist slab concrete + steps concrete
= 18 + 7.56
= 25.56 cubic feet
Concrete volume for 2nd flight of the staircase
As the 1st flight and 2nd flight are same in our example drawing (above
image) so the concrete volume will be same. That is,
= 25.56 cubic feet
Now, we need to calculate the concrete volume for landing.
Concrete volume for the stair landing
From our example drawing,
Length of landing = 8’-6”
Width of landing = 4’-6”
Thickness of landing = 6”
So, the concrete volume for the landing is,
= 8’-6” x 4’-6” x 6”
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= 19.12 cubic feet
So, total concrete volume for the staircase is,
= 1st flight concrete + 2nd flight concrete + landing concrete
= 25.56 + 25.56 + 19.12
= 70.24 cubic feet
Estimating concrete volume for a staircase isn’t so difficult. We just
need to apply some geometric formula.
Nowadays, getting concrete volume for any shape of a structure is just
a matter of few clicks in AutoCAD.
But, in a construction project, we don’t always have access to
computers. So, often we need to do it manually.
How to Calculate Wooden Formwork for Grade Beam?
Most of the time we use wooden formwork for constructing grade
beam. In this post, we’ll see, how to calculate the wooden formwork for
grade beam.
First we need to know what is grade Beam?
Grade beam is a sub-structure of any structure which is normally built
on short column. Grade beam is also called tie beam.
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You can use different types of shutter materials for the foomwork of
grade beam. Such as steel shutter materials and wooden shutter
materials.
When shutter materials are used to make a concrete form than it is
called concrete formwork.
How to Calculate Wooden Formwork for Grade Beam?
Before calculating the wooden formwork, you need to know how the
grade beam will be constructed?
Grade beam can be constructed directly on the ground or above from
the ground.
If the grade beam is constructed directly on the ground then you don’t
need to calculate the shutter materials for the bottom of the beam. In
that case, a brick flat soling is done on the compacted soil and then
the formwork is fixed with the brick flat soling for constructing the
grade beam.
But, if the grade beam is constructed above the ground then you need
to calculate the shutter materials for bottom side of the beam.
We will calculate the formwork for both case.
So, let’s begin calculating the wooden formwork for a grade beam. The
details of the grade beam is given below.
Grade beam details:
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

Size – 10″ x 12″
Length – 14′
Required shutter materials for the formwork of the grade
beam:


1½” thick wooden plank
2″ x 3″ wooden button
So, we need to calculate the above two shutter materials for the
formwork of grade beam.
Calculating wooden plank:
Required 1½” wooden plank for one side of the grade beam –


Length of grade beam: 14′
Height of grade beam: 1′
So, Volume of wooden plank for the formwork of one side of the grade
beam is,
= 14′-0″ x 1′-1″ (1″ extra height for jointing) x 1½”
= 1.90 cubic feet.
For another side of the grade beam, you’ll require the same quantity of
wooden plank. That is, 1.90 cubic feet.
Total required volume of 1½” wooden plank is,
= 1.90 x 2
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= 3.80 cubic feet.
If the grade beam is built directly on the ground then you’ll need
this quantity of 1½” wooden plank for the formwork of the beam.
But, if you want to build the grade beam above the ground then
you’ll require more wooden plank for the formwork of the bottom
side of grade beam.
So, let’s calculate the shutter materials for the formwork of grade beam
bottom.


Length of grade beam: 14′-0″
Width of grade beam: 10″
So, required wooden plank for the bottom of grade beam is,
= 14′-0″ x 10″ x 1½”
= 1.46 cubic feet.
In this case, total required wooden plank for the formwork of grade
beam is,
= 3.80 + 1.46
= 5.26 cubic feet.
Now let’s calculate 2″ x 3″ wooden button.
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Calculating 2″ x 3″ wooden button for the formwork of the
grade beam
Wooden button is placed 2′ center to centre distance.
As our grade beam is 14′ long, so the required number of wooden
button for one side of the beam is,
= 14/2 + 1
= 8 nos
The length of a wooden button is 1½’ as our beam is 1′ hight.
So, volume of 2″ x 3″ wooden button for one side of the grade beam is,
= 8 x 1½’ x 2″ x 3″
= 0.50 cubic feet.
For both side of the grade beam, required button is,
= 2 x 0.50 = 1.0 cft.
If your grade beam will be built above ground, then you’ll also need
wooden button for the bottom side of the beam.
So, required wooden button for the bottom side of the grade beam is,
= 8 x 1½’ x 2″ x 3″
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= 0.50 cubic feet.
Summary:
If the grade beam is built on ground –


1½” wooden plank: 3.80 cubic feet
2″ x 3″ wooden button: 1.0 cubic feet
If the grade beam is built above ground (shutter for bottom side of the
beam will be added) –


1½” wooden plank: 5.26 cubic feet
2″ x 3″ wooden button: 1.50 cubic feet
Conclusion:
If you don’t use wooden button for supporting the grade beam, then
only the above calculated wooden shutter materials will be required for
the formwork of the beam. But, if you want to use wooden button for
supporting purpose also then you need to calculate those for
the formwork of the grade beam.
When you order for wooden shutter materials, always add extra 5%
with the calculated quantity.
What Should Be Standard Size of Rooms in
Residential Building?
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I’ve been asked this question many times by my relatives as well as by
my clients. That is, what should be the standard room size for a
residential building?
In this post I’ll answer this question from my experience which I gained
from last 14 years of time working with several architects and clients.
Before knowing standard room size, we need to know what types of
room we may have in a residential building.
Type of rooms in a residential building
Although type of rooms depend on the personal preference, here are
some common types of room we normally build in a residential
building:












Living room
Master bed room
Child bed room
Guest Bed Room
Dining room
Kitchen
Bath room
Dressing room
Foyer
Store Room
Pantry
Office room, etc.
You can also include some other type of rooms in your residential
building. For example, you may want to include a “study room” in your
residential building.
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Now we’ll talk about these various type of rooms-How they can
be locatedand what are the standard size of those rooms in a residential
building?
Standard size of rooms in a residential building
Once I worked with a client, who built his living room such big that we
can make a whole apartment in his living room, if we take standard
room size. So, when I’m asked about the standard size of rooms in a
residential building by my relatives or clients then I always confused
that what I should say.
Because, when I tell them standard size of a room, they replied, this is
too small or this is big!
So, size of a room in a residential building completely depends on your
personal preference.
However, everything has a standard, if you like it or not. So, let’s talk
about the standard size of various type of rooms in a residential
building.
Living room:
We all know about this room. It is used for sitting and gossiping
purpose with guest or friends. It is also called drawing room.
Location of living room: During locate living room in your apartment,
keep the following things in mind –

Locate the living room near main door.
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

Locate the living room near the dining room. Sometimes, living
room is used as dining room. In that case, living room should
be bigger than standard size.
Try to locate the living room in the middle of your apartment’s
front side.
Standard size of living room: the standard size of a living room should
be as below –
Small: 12′ x 18′ (3600mm x 5400mm)
Medium: 16′ x 20′ (4800mm x 6000mm)
Large: 22′ x 28′ (6600mm x 8400mm)
Master Bed Room:
Master bed room is the main bed room of an apartment.
Location of master bed room: keep the following things in mind during
locating master bed room in your apartment –





Master bed room should be well ventilated. So, locate this bed
room in such a way that it can get enough ventilation.
Try to keep at least one wall of master bed room expose to outer
for sufficient ventilation.
Locate your master bed in the side of the building where natural
view is visible.
Locate the master bed in such a way that it provides privacy.
Locate the master bed room in such a way that it receives enough
sunlight in the morning.
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Standard size of master bed room: Master bed room should be bigger
in size than other bed room. The standard size is,
Small: 12′ x 14′ (3600mm x 4200mm)
Medium: 14′ x 20′ (4200mm x 6000mm)
Large: 16′ x 24′ (4800mm x 7200mm)
Child bed room:
Child bed room is made for children. This room is like any other bed
room.
Location of child bed room: During locate the child bed room, consider
the things which we considered during locating the master bed room.
Most of the time it is not possible to give all the facility of master bed
room to child bed room. In that case, you need to deduct some facility.
Okay, no problem, children will understand that.
Size of child bed room: Child bed room is not as big as master bed
room. The size of child bed room is as the size of normal bed room.
However, the standard size is,
Small: 10′ x 12′ (3000mm x 3600mm)
Medium: 12′ x 14′ (3600mm x 4200mm)
Large: 14′ x 16′ (4200mm x 4800mm)
Guest bed room:
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Guest bed room is as normal bed room and it is made for guest. It can
also be called common bed room.
Location of common bed room: To locate the guest bed room, consider
the following things –



If possible try to locate this bed room in a well lighted and
ventilated place.
During locating guest bed room, consider the privacy of family
members. Because guest bed room will be used by guest. So, it is
essential to disconnect this room from rest of the rooms of the
apartment.
Guest room should be located in the front of the apartment and
beside the living room.
Standard size of guest bed room: The standard size of guest bed room
is,
Small: 10′ x 12′ (3000mm x 3600mm)
Medium: 12′ x 14′ (3600mm x 4200mm)
Large: 14′ x 16′ (4200mm x 4800mm)
Dining room:
We all know about the dining room. We sit and take our food here.
Location of dining room: Consider the following things during locating
dining room in your apartment –
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

Dining room should be located near the kitchen room and back
side of living room.
In the modern apartment, dining and living room are
combined together to get a big room for family occasion like
birthday party. So, you can do the same too.
Standard size of dining room: If you want to separate your dining room
from living room then the standard size of dining room is,
Small: 10′ x 12′ (3000mm x 3600mm)
Medium: 12′ x 14′ (3600mm x 4200mm)
Large: 14′ x16′ (4200mm x 4800mm)
Kitchen
We know this room very well. It is the room to cook food for our family.
Location of kitchen room: Considering things during placing kitchen
room in a residential building –



Kitchen room should be located near the dining room.
At least one wall of kitchen room should beexposed to outer for
escaping smoke.
It should be placed in such a way so that it has enough sunlight and
air circulation.
Standard size of kitchen room: Although some prefer to make a big
kitchen room, the standardsize of it is,
Small: 5′ x 10′ (1500mm x 3000mm)
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Medium: 8′ x 13′ (2500mm x 3900mm)
Large: 10′ x 12′ (3000mm x 3600mm)
Bathroom:
There are two type of bathrooms can have in an apartment of a
residential building. One is master bathroom and another is common
bathroom.
Master bathroom is generally attached with master bedroom. We can
also have an attached bathroom with child bedroom. But, the guest
room doesn’t need to have attached bathroom. For this purpose, it is
better to have a common bath room for guest.
Standard size of bathroom: Although the size of master bathroom
depends on the personal preference, the standard size of a master bath
is,
Small: 6′ x 9′ (1800mm x 2700mm)
Medium: 7′ x 10′ (2100mm x 3000mm)
Large: 8′ x 12′ (2500mm x 3600mm)
Standard size of common bathroom,
Small: 5′ x 9′ (1500mm x 2700mm)
Medium: 6′ x 10′ (1800mm x 3000mm)
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Large: 7′ x 12′ (2100mm x 3600mm)
Dressing room:
Dressing room is provided in front of Master bathroom. It
doesn’t need to provide dressing room with any other bathroom. But it
depends on you.
standard size of dressing room: The standard size of dressing room is,
Small: 4′ x 4′ (1200mm x 1200mm)
Medium: 5′ x 5′ (1500mm x 1500mm)
Large: 6′ x 6′ (1800mm x 1800mm)
Foyer:
Foyer is a lobby or corridor used in an apartment of a residential
building to separate the entrance from living room. But some prefer to
omit the foyer and use the living room as an entrance of the apartment.
The standard size of foyer:
Small: 5′ wide (1500mm)
Medium: 6′ wide (1800mm)
Large: 8′ wide (2500mm)
Store room:
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Store room is used for storing the kitchen goods. It should be placed
near the kitchen room. And it should have sufficient rack to store
materials.
Standard size of Store room: The standard size of a Store room is,
Small: 6′ x 6′ (1800mm x 1800mm)
Medium: 8′ x 10′ (2500mm x 3000mm)
Large: 10′ x 10′ (3000mm x 3000mm)
Pantry
Although kitchen serves the purpose of pantry, someone prefer to have
a pantry adjacent to kitchen. Pantry is a small room where cooked
foods are kept. It should have sufficient rack and cupboard.
Standard Size of pantry: The standard size of pantry is,
Small: 2′ x 2′ (600mm x 600mm)
Medium: 3′ x 4′ (900mm x 1200mm)
Large: 4′ x 6′ (1200mm x 1800mm)
Office Room:
You can use the guest room as an office room. Because, guest room
isn’t always used. But some prefer to have a separate office room in an
apartment.
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The location of office room should be in front of apartment like guest
bed.
Standard size of office room: Although the size of office room depends
on personal preference, the standard size of the room is,
Small: 8′ x 10′ (2500mm x 3000mm)
Medium: 10′ x 12′ (3000mm x 3600mm)
Large: 12′ x 14′ (3600mm x 4200mm)
You don’t have to build the rooms in your apartment as standard sizes.
You should define the size of rooms as your personal requirement. So
increase or decrease the size of rooms that best suites you.
How to Estimate Beam Reinforcement
An ordinary person can estimate reinforcement as lumsum. I see many
people estimate reinforcement as a percentage of concrete volume.
Such as 2% or 1.5% of concrete volume.
But as a construction professional you shouldn’t estimate rebar
quantity as percent of concrete volume. You should estimate that as
shown in the structural drawing.
Estimating rebar quantity is easy. All you have to get the cutting length
for each type of bar in the beam.
Let’s start estimating. We’ll use the following image as a structural
drawing of beam.
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Process of Estimating Beam Reinforcement
From the image above we have found –






Top longitudinal bar, T – 3D20
Bottom longitudinal bar, B – 3D20
Extra top bar on support1, Et1 – 2D20
Extra top bar on support2, Et2 – 2D20
Extra bottom Bar, Eb – 2D20
Stirrup, S1 – D10 @ 4″ c/c
If you don’t know the name of bar on different location in a beam then
read the following post.
You will also need the following data to estimate the beam
reinforcement –



Clear cover for reinforcement
Lap length
Bend length
You’ll get this data from the general notes sheet of structural drawing.
That’s fine.
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We have enough data to estimate the beam reinforcement. Let’s
estimate.
Top Longitudinal Bar (T)
Apply the following formula to get the cutting length of top longitudinal
bar.
Cutting Length of top longitudinal bar is,
= Length of beam – 2 x clear cover + 2 x bend length – 2 x bend
deduction length + lap length
Length of beam: 20″ + (22′-8″) + 20″ + (8′-4″) + 20″ = 36′ (from above
image)
Clear cover: 1½”
Bend length: 12D = 12 x 20 = 240 mm, say 9½”
Bend deduction length: Bend deduction length for 90° bend is equal to
two times of bar dia = 2 x 20 mm = 40mm = 1½”
So, the cutting length of the top longitudinal bar is,
= 36′ – 2 x 1½” + 2 x 9½ – 2 x 1½” + 0
= 37′-1″.
There are 3 numbers of top longitudinal bar in the above image. So the
total length of top longitudinal bar is,
= 3 x (37′-1″)
= 111′-3″.
We know the full length of a reinforcing bar is about 40′. The length of a
top longitudinal bar, we are estimating, doesn’t exceed the length of a
full bar. So you don’t have to add lap length.
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Bottom Longitudinal Bar (B)
The formula for calculating the cutting length of bottom longitudinal
baris same as the formula for top longitudinal bar. So the length is also
same as T1 . That is 37′-1″.
So the total length of B1 bar is,
= number of B1 bar x cutting length of a B1 bar
= 3 x (37′-1″)
=111′-3″.
Extra Top Bar on Support1 (Et1)
Calculating cutting length of extra top bar follow the following formula
–
Cutting length of Et1 = extended length from support + width of
support – clear cover + bend length – bend deduction length
Extended length from support: 7′-5″
Width of support: 20″
Clear cover: 1½”
Bend length: 9½”
Bend deduction length: 1½”
So the cutting length of Et1 is,
= (7′-5″) + 20″ – 1½” + 9½” – 1½”
= 9′-7½”
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There are 2 number of Et1 bar shown in drawing (image above). So the
total length of Et1 is,
=2 x (9′-7½”)
= 19′-3″
Extra Top Bar on Support2 (Et2)
Extended length fron support: 7′-5″
Width of support: width of support for Et2 should be the width
of support2 + distance between support2 and support3 + width of
support3 = 20″ + (8′-4″) + 20″ = 11′-8″
Clear cover: 1½”
Bend length: 9½”
Bend deduction length: 1½”
So, cutting length of Et2 = (7′-5″) + (11′-8″) – 1½” + 9½” – 1½”
= 19′-7½”
Total length of Et2 = 2 x (19′-7½”)
= 39′-3″
Extra bottom bar (Eb)
Cutting length of extra bottom bar is,
=Distance between support – 2 x distance between extra bottom
bar and nearest support
= (22′-8″) – 2 x (2′-10″)
= 17′
Total length of extra bottom bar is,
= 2 x 17′ (there are 2 bar for Eb shown in the image above)
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= 34′
Stirrup (S1)
For estimating stirrup you have to calculate the required number of
stirrup for the beam and cutting length of bar for a stirrup.
Number of stirrup:
Required number of stirrup for 1st span,
= (22′-8″)/4″ +1 = 69 + 1 = 70 nos.
Required number of stirrup for 2nd span,
= (8′-4″)/4″ + 1 = 25 + 1 = 26 nos.
Total number of stirrups = 70 + 26 = 96 nos.
Formula for calculating cutting length of a stirrup’s bar is,
= 2 x (a+b) + 24D (for 135° hook)
Where,
a = length of stirrup’s long side
b = length of stirrup’s short side
D = dia of stirrup bar
So cutting length of the bar is,
= 2 x (21″+9″) + 24 x 10mm
= 69½” (240 mm = 9½”)
= 5′-9½”
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Total length of bars for all stirrups,
= 96 x (5′-9½”)
= 556′
Summary:
Total reinforcing bar we have estimated for the beam so far –
20 mm ø bar –
T = 111′-3″
B = 111′-3″
Et1 = 19′-3″
Et2 = 19′-7½”
Eb = 34′
So total 20 mm ø bar is,
= 111′-3″ + 111′-3″ + 19′-3″ + 19′-7½” + 34′ = 296′.
10 mm ø bar,
S1 = 556′
But steel reinforcing bars are measured in kg in the market. So you
have to convert the bar length to kilogram.
Unit weight of 10 mm ø bar is 0.188 kg/ft and 20 mm ø bar is 0.75 kg/ft.
Read the following post to know how to calculate unit weight of
reinforcing bar.
So reinforcement required for our example beam,


20 mm ø bar = 296′ x 0.75 = 222 kg
10 mm ø bar = 556 x 0.188 = 105 kg
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That’s it.
When you want to purchase reinforcing bar for the beam you should
add 5% more with your estimated quantity as wastage.
4 Terms to Understand to Truly Estimate
Rebar Quantity
Estimating Reinforcement is easy. All you have to get the cutting length
of bar and convert them to weight.
When estimating rebar for a rcc member you have to understand few
terms clearly regarding reinforcement.
4 Terms to understand to truly estimate rebar quantity
Below are 4 terms you should understand clearly to truly estimate the
rebar quantity –
1. True length of bar
2. Cutting length of bar
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3. Bending length of bar
4. Bend deduction length
1. True Length of Bar
For estimating rebar quantity we just calculate the length of some
leaner shapes of bar.
For example, take a top longitudinal bar of a beam. The shape of the
bar will look like the image below.
For estimating purpose we just get the length of the bar and convert it
to the weight of bar.
Let’s calculate the bar in the image above. The length of that bar is,
=A+B+C
Suppose, A is = 20′, B is = 1′ and C is = 1′
So the length of the bar is,
= 20′ + 1′ + 1′
=22′
This is the true length of bar.
2. Cutting Length of Bar
As we know steel is ductile and subjected to elongation. When it bends
it is increased in length.
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So if you we cut the bar as its true length and bend it we won’t get the
desired shape after bend. To get the desired shape, the bar should be
cut lesser than the true length.
The required length to get the desired shape of the bar is calledcutting
length of bar.
3. Bending Length of Bar
Now the question is how much a reinforcing bar is increased in length
when it is bent?
It depend on the size of bar and angle of the bend.
The increased length for specific diameter of bar for specific angle is
called bending length of the bar.
4. Bend Deduction Length
It is confusing. Because bend deduction length conflicts with the
bending length.
Actually both the terms are same. Then why the engineering world
using both terms to confuse the fresher? This question is mine.
The purpose for writing this post is to eliminate the confusion between
these two terms.
Don’t be confused. Both terms are same. When we deduct the bending
length from the true length of a bar then it is calledbend deduction
length.
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Mostly used bend angle in civil construction world are 45° and 90°
bend.
For 45° bend, Bend deduction length is equal to dia of bar.
and
For 90° bend, bend deduction length is equal to two times of bar dia.
Bend deduction length is actually used for calculating the cutting length
of bar in construction.
Let’s calculate the cutting length of the bar shown in the image above.
Cutting length = true length of bar – (2 x dia of bar) x number of bend.
= 22′ – 2 x ¾” x 2 (20 mm = ¾”)
= 21′-9″
For estimating purpose only, you don’t have to deduct the bend
deduction length form the true length of bar. It is required when you
are cutting bar or making bar bending schedule for placing
reinforcement in the rcc member.
How to Calculate the Unit Weight of Steel
Bars
There is a formula to calculate the unit weight of steel bars. I’ll come
that point later.
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Why do we need to know the unit weight of steel bars?
When we estimate the steel bars for a Reinforced Concrete member we
get the length of that as a result. For example, 1000 feet 20mm ø bar or
500 feet 16mm ø bar, etc (ø – symbol of diameter).
But steel bar suppliers measure the steel bars as weight. So we have to
order them in weight for purchasing. The weight of steel bars can be
expressed in kg or quintal or ton.
1 quintal = 100 kg
1 ton = 1000 kg or 10 quintal
Now come to the point.
How to Calculate the Weight of Steel Bars
We often use a formula for Calculating the weight of Steel Bars.
The formula just converts the length of steel bars to weight. We can
also use this formula to know the unit weight of steel bars of different
diameter.
The Formula: D²L/162
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Where,
D = Diameter of steel bar in millimeter
L = Length of steel bars in meter
Understanding the Formula
We know, the weight of a material is,
= Cross sectional area of the material x Length of the material x Density
of the material
For steel bar this is also same.
Weight of steel bars= Cross sectional area of steel bar x Length of steel
bar x Density of steel bar.
That means,
W=AxLxρ
Where,
A = Area = πD²/4
π (pai) = 3.14
D = Diameter of steel bar in millimeter
L = Length of steel bar in meter
ρ (Rho) = Density of steel bar = 7850 kg/m³
Therefore,
W = 3.14 x D²/4 x L x 7850
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But there are two conflicting unit in the formula. Those are millimeter
for D and m for ρ (Rho).
We have to convert either D or ρ to same unit.
Let’s convert D from millimeter to meter.
1 millimeter = 1/1000 meter
Lets implement this to the formula,
W= 3.14 x D²/(4x1000x1000) x L x 7850
= D²L/162
Using this formula we can calculate the weight of steel bars.
Calculating Weight of Steel Bars When Length is in meter
Keep in mind that you always use D as millimeter and L as meter in this
formula.
Lets see some example.
Example-1:
How to calculate the weight of 100 meter long 16mm ø bar?
In this example,
D= 16mm
L = 100 m
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So,
W = D²L/162
= 16² x 100/162
= 158 kg (approx)
Answer: Weight of the 100 meter long 16mm ø bar is 158 kg.
Example-2
How to calculate the weight of 100 m long 20mm ø bar?
In this example,
D = 20mm
L = 100 m
So,
W = D²L/162
= 20² x 100/162
= 247 kg (approx)
Answer: Weight of the 100 meter long 20mm ø bar is 247 kg.
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Unit Weight of Steel Bar When Length is in Meter
If you put 1 meter length for each diameter of steel bar in the formula
then you’ll get the unit weight.
Let’s see.
W = D²L/162
Unit weight of,





10mm ø bar = 10² x 1/162 = 0.617 kg/m
12mm ø bar = 12² x 1/162 = 0.888 kg/m
16mm ø bar = 16² x 1/162 = 1.580 kg/m
20mm ø bar = 20² x 1/162 = 2.469 kg/m
25mm ø bar = 25² x 1/162 = 3.858 kg/m
If you multiply the length of estimated bars with this unit weight you’ll
get the total weight of steel bars for your reinforced concrete member.
For example, total weight of 1000 meter long 25mm ø steel bar is,
1000 x 3.858 = 3858 kg.
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So far we have seen the unit weight for each diameter of steel bar in
meter basis. That means weight of bar per meter.
But what if you estimate the steel bar length in foot. What will be the
formula to calculate the steel bar’s weight if the length of bar is in foot?
Calculating Weight of Steel Bars When Length is in Foot
Again,
Weight = A x L x ρ
= 3.14 x D²/(4 x 304.80 x 304.80) x 222
= D²L/533
Where,
D = Diameter of bar in mm (1 foot = 304.80 mm)
ρ (Rho) = 7850 kg/m³ = 222 kg/ft³ (actually it is 222.287 kg/ft³)
Keep in mind that you always should use D as millimeter and L as feet in
this formula.
Unit Weight of Steel Bar When Length is in Foot
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If you calculate 1 foot length of any diameter of steel bar you will get
the following result and that will be the unit weight of steel bars per
foot length.
Unit weight of,





10mm ø bar = 10² x 1/533 = 0.188 kg/ft
12mm ø bar = 12² x 1/533 = 0.270 kg/ft
16mm ø bar = 16² x 1/533 = 0.480 kg/ft
20mm ø bar = 20² x 1/533 = 0.750 kg/ft
25mm ø bar = 25² x 1/533 = 1.172 kg/ft
If you multiply the estimated length of steel bars with these unit
weights you’ll get the total weight of steel bars.
For example,
Weight of 1000 feet long 10mm ø bar is,
1000 x 0.188 = 188 kg.
How to Estimate Materials for Isolated
Footing
Companies often use Software for estimating the project cost. They
more often do this for biding purpose.
But we are construction professionals and working on field level. So we
can’t always use software for estimating materials for the small part of
a building. Sometimes it is impossible to construct the whole part of a
building at a time because of the critical condition of the project.
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Let me clear this.
Suppose, there are 30 numbers of isolated footing in a building.
Whatever the reason, sometimes we can not make the all 30 numbers
of footing ready for casting at a time. At that situation, we just make 3
or 4 numbers of footing ready for the casting. And it is not economical
to cast this small quantity of concrete with readymix. So we always
prefer machine mix concrete for this purpose.
For constructing footing of a building you have to have plan before
starting the task. You have to estimate the materials for footing. You
have to make purchase requisition for materials and ensure the
required materials are available on the project.
The question is, what is isolated footing and what are the materials
required for a isolated footing?
Isolated footing is a shallow type footing. It normally holds one column
on it. To know more about the types of footing read the following post
–
Materials Required for Isolated Footing
For constructing a isolated footing following materials are required –





Shutter Material
MS Rod
Binding Wire
Cover Block and Chair
Concrete
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Shutter Material for Isolated Footing
Most of the time wooden shutter materials are used for the isolated
footing. Sometimes steel shutter materials are also used. We will use
wooden shutter for this purpose, at least in this post.
How to Estimate Wood for Shuttering Isolated Footing?
See the above picture. The length of footing is 5 feet, width is 4 feet
and height is 1 feet. To make the shutter for side-A of the footing you’ll
need 4 feet long and 15 inches height wooden plank.
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Our footing height is 1 feet. Then why we use 15 inches height wooden
plank? Because we will fix the shutter below 3 inches from the bottom
of footing.
Then the required wooden shutter for side-A is,
4′ x 15″ = 5 sft (12″ = 1 feet, sft= square feet)
We’ll use 1.5″ thick wooden plank.
So the volume of the wood is,
5 sft x 1.5″ = 0.63 cft (cft= cubic feet)
Wood is always measured as cubic feet.
For the side-C we’ll require the same quantity of wood as side-A.
Now, lets calculate the wood for side-B.
Length of wood for side-B is, 5′-3″. But our footing length is 5 feet then
why we’ll require 5′-3″ long shutter? Because we’ll join this shutter with
the side-A’s and side-C’s shutter. The thickness of side-A and Side-C
shutter is,
1.5″ + 1.5″ = 3″
Therefore,
Length of side-B shutter is 5′-3″ or 63″
Width of side-B shutter is 1′-3″ or 15″
Thickness of shutter is 1.5″
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Then,
volume of side-B shutter is,
63″ x 15″ x 1.5″ = 0.82 cft (cft= cubic feet).
Side-D also require the same quantity of wood as side-B.
So far, we have found –
Required wood
For side-A = 0.63 cft
For side-B = 0.82 cft
For side-C=side-A=0.63 cft
For side-D=side-B=0.82 cft
Total wood= A+B+C+D= 2.92 cft
We will require 2.92 cft wood for making shutter for the isolated
footing. If you don’t find required size of wood then you’ll need some
2″ x 1.5″ size wooden plank for making shutter.
We estimated required wood for one isolated footing. If you have 30
isolated footing of different sizes calculate the required wood for each
one using same technique we applied here. Total them all and make
purchase requisition for the required wood.
Now we’ll estimate the MS rod for the isolated footing.
How to Estimate MS Rod for Isolated Footing?
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See the above picture. There is a instruction for rod placement. That is
12mmØ[email protected]″c/c both way.
It means 12mm diameter bar should be placed at the distance of 4″
centre to centre.
The length of our isolated footing is 5 feet. The clear cover of
reinforcement is 3 inches for one side. For both side it is 6 inches. So we
have to place rod for 5′ – 6″=4.5′.
Requires number of rods are, 4.5′ divided by 4″.
That means
4.5’/4″= 13.63 numbers.
Say 14 nos.
You have to add one more number of rod for starting point.
So total required number of rod is 14+1= 15 nos.
Now we have to calculate the length of rod. We’ll place the rod along
short-side (4′ side).
So the length will be
4′ – clear cover of both side + hook (90 degree bend) length of both
side.
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= 4′ – 2×3″ + 2×6″
= 4′ – 6″ + 12″ (12″ = 1 feet)
= 4.5′
So total length of all 15 numbers of bar is
15 x 4.5′
= 67.5 feet
Now we’ll calculate the rod for long-side of the isolated footing.
By following the above method,
Number of rods,
= 3.5’/4″ + 1
=11.61
Say 12 nos
Length of rod,
= 4.5′ + 1′
= 5.5′
Total length of rods for long-side of isolated footing,
= 5.5′ x 12
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= 66 feet
Total rods for the isolated footing = 67.5′ + 66′
= 133.5 feet.
Say 134 feet
You have to add 10% more rod with the estimated rod during ordering
for purchase.
You may not order rod as running feet. So you have to convert them in
kilogram or ton.
Oh. One more thing, you have to order rod for short column also.
Because rebar of short column should be placed before casting footing.
Summary of MS Rod Calculation
For rods along short-side
Numbers of rod= 4.5’/4″ +1= 14.64 say, 15 nos.
Length of rod= 4′ – 6″ + 1’= 4.5′
Length of total rods=15 x 4.5=67.5′.
For rods along long-side
Numbers of rod= 3.5’/4″ + 1= 11.61 say, 12 nos.
Length of rod=5′ – 6″ + 1′ = 5.5′.
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Length of total rods=12 x 5.5=66′
Total rod for the footing= 67.5′ + 66’=133.5′
You’ll need a 10mm Ø bar for binding the main rod of the footing. The
length of the binder is,
2 x 4.5 + 2x 3.5= 16′.
So, total required rod is,


10mm Ø bar= 16′, and
12mm Ø bar= 133.5′
Binding Wire for Isolated Footing
For binding rods you need binding wire. We need 9 kg to 13 kg binding
wire for 1 ton of rod. You can estimate average 10 kg binding wire per
ton of rod. So estimate total binding wire depending on required rod.
Cover Block and Chair for Isolated Footing
To keep the rod in place and maintaining concrete clear cover you
should provide either cover block or chair for bottom and cover block
for side. Cover block should be placed at 2 feet distance.
You’ll need 8 numbers of cover block for sides and 5 numbers of cover
block/chair for bottom of the Isolated footing.
Concrete for Isolated Footing
The size of our isolated footing,
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Length – 5 feet
Width – 4 feet
Height – 1 feet.
Volume of concrete for the footing is,
5x4x1
= 20 cubic feet.
If you want to estimate ingredients for the footing first know the ratio
of concrete suggested in the structural drawing. Then read the
following post.
I’ve just shown the estimating technique for one isolated footing here.
You may have many footings of different sizes in your project.
Follow the same technique to estimate materials for all the isolated
footings of your project and sum up them to order materials for
purchase.
Some symbols and terms I used here in this post
‘– Foot symbol
“ – Inch symbol
Ø – Diameter symbol
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1′ = 12″
Sft – Square feet
Cft – Cubic feet
Nos – Numbers
How to Estimate Concrete Volume for
Grade Beam
Grade beam is normally constructed on neck column and It connects
two or more column together.
In another word, grade beam carries the load from ground floor slab
and transfer to column.
Grade beam is normally constructed on ground.
Purpose of this post is not to define what the grade beam is. I just
giving some idea about grade beam so that newbie can understand the
grade beam well.
The purpose of this post is to show you how to estimate the concrete
volume of grade beam.
So let’s do this.
Estimating Concrete Volume for Grade Beam
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For estimating the concrete volume for grade beam you’ll need
following structural drawing sheets.




Grade beam layout
Cross-sectional dimension of grade beam
Column layout
Cross-sectional dimension of column
Grade Beam Layout: This sheet of structural drawing shows how to
place grade beam on column.
See the image below.
In the above image, the grade beam layout just shows the grade beam
number (GB1, GB2, etc.). It also shows the cross-sectional dimension
that is 12″ x 20″. So you don’t need to look out for cross-sectional
dimension of grade beam. You’ll get it from here.
Column Layout: The grade beam layout we have in the above image
doesn’t show the length of beam. If you want to calculate concrete
volume of grade beam you’ll need it. So you’ll need to go to column
layout for the length of beam.
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See the image below.
The above image is a column layout sheet of structural drawing.
To get the grade beam length you have to calculate the distance
between columns.
I told before that you’ll also need the cross-sectional dimension of
column for calculating concrete volume of grade beam. See the above
image you’ll get this from there. Such as C1 (15″ x 45″), C2 (20″ x 45″),
C3 (20″ x 35″), etc. So you don’t need any further cross-sectional
dimension sheet for column.
Are you still here? Then let’s estimate the concrete volume for grade
beam.
We’ll estimate concrete volume for GB1 shown in the 1st image.
For estimating concrete volume of GB1 you’ll need following data –


Cross sectional dimension of grade beam (GB1)
Length of grade beam (GB1)
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

Cross sectional dimension of column (C1, C2 and C3)
Height of column
Cross Sectional Dimension of Grade Beam (GB1)
From the grade beam layout sheet (1st image) you’ll find the cross
sectional dimension of GB1. That is,
12″ x 20″.
Length of Grade Beam
Length of grade beam shows nowhere in grade beam layout sheet (1st
image). sometimes it’s shown on the reinforcement detailing layout
sheet of grade beam in structural drawing.
You can also calculate the length of grade beam from column layout
drawing sheet (2nd image).
For finding the length of grade beam (GB1) you have to find the
distance between C1 and C2 as well as the distance between C2and C3.
Distance Between Column C1 and C2:
For finding distance between column C1 and C2 you have to find the
gap between grid-1 and grid-2. Then you have to deduct column
portion inside the grid-lines. Let’s do this.
Gap between grid line 1 and 2 is 24′-1″.
Column portion inside grid-line1 and grid-line2:
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C1 = 7½”
C2 = 10″
So the distance between c1 and c2 is,
= (24′-1″) – 7½” – 10″
= 22′-7½”
Applying same process you can find the distance between c2 and c3.
That is,
= (18′-3″) + (5′-10″) – 10″ – 12½”
=22′-2½”
So the length of the grade beam (GB1) is,
= 22′-7½” + 22′-2½”
= 44′-10″
Therefore, the volume of grade beam is,
= 44′-10″ x 12″ x 20″
= 74.87 cubic feet.
Wait, we are not finished yet.
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To get the concrete volume of grade beam you also have to estimate
the concrete volume for column head.
Column head is the portion of column which intersect with beam.
Estimating Concrete for column head:
In the 2nd image you’ll find three column heads connecting by the
grade beam (GB1).
So you have to estimate the concrete volume for these column heads
also.
Let’s do this.
Cross Sectional Dimension of Column
C1 – 15″ x 45″
C2 – 20″ x 45″
C3 – 20″ x 35″
So the area of the those three column heads are,
(15″ x 45″) + (20″ x 45″) + (20″ x 35″)
= 15.80 sft.
Height of Column
The height of all three column heads are same as height of the grade
beam. That is 20″.
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So the volume of column heads are,
= 15.80 x 1.67 (20″= 1.67′)
= 26.39 cft (cubic feet).
So total concrete volume for the grade beam (GB1) is,
= 74.87 + 26.39
= 101.26 cft.
Following this process you can estimate the concrete for all grade
beams of your project.
If you want to cast the grade beams manually by mixture machine then
you have to calculate required concrete ingredients for the volume of
concrete. Read the following post to know how to calculate concrete
ingredients.
Summary

Concrete volume for grade beam (GB1) only= Length x width x
height
= (22′-7½” + 22′-2½”) x 12″ x 20″
= 74.87 cft
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
Concrete volume for column heads = Area of column heads x
height of column head
= 15.80 sft x 20″
= 26.39 cft

Total volume of concrete for grade beam (GB1) is,
= 74.87 + 26.39
= 101.26 cft.
Symbol and notation used in this post
sft – square feet
cft – cubic feet
‘ – foot
” – inch
C1, C2, C3 – column symbol
GB1, GB2, GB3 -grade beam symbol
4 Easy Steps for Making Column Stirrup
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A rcc column has two types of bar. One is longitudinal bar and another
ishorizontal bar.
As horizontal bar we use stirrups and ties in column. Stirrup also has
some other name in construction sector. Such as ring, shear
reinforcement, etc.
For making stirrup for column you have to calculate the cutting length
of bar for stirrup, you have to calculate the number of stirrups and you
have to determine the size of stirrup.
You can do this in 4 easy steps.
4 Easy Steps for Making Column Stirrup
Making column’s stirrup involves following 4 steps of work.
1.
2.
3.
4.
Determine the size of stirrup
Calculating cutting bar length for stirrup
Calculating the number of stirrups
Bending the bar in stirrup’s shape
1. Determine the Size of Stirrup
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See the above image. The column size is 20″ x 40″. We know the
concrete clear cover for reinforcement of column is 1½”.
So the length of stirrup will be 40″-2×1½”=37″ and width will be 20″2×1½”=17″.
So the size of the stirrup is 37″x17″.
2. Calculating Cutting-Bar-Length for Stirrup
Before cutting the bar you have to calculate the cutting bar length for
the stirrup.
There are two terms – actual bar length and cutting bar length.
The actual bar length of stirrup is,
2 x length + 2 x width + 2 x hook’s length
= 2 x 37″ + 2 x 17″ + 2 x 3″
= 114″ or 9.5′.
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Let’s discuss a little about hook length.
Hook length is calculated by a formula that is 6db (diameter of bar).
So the hook length for 10mmø bar is,
6 x 10 = 60 mm.
But length of hook should not be less than 75mm (as per code).
So the hook length for the stirrup is 3″ (75mm = 3″).
The actual bar length of the stirrup is 9.5′. But the cutting bar
length will be less than the actual bar length.
See the above image. That is our stirrup. The stirrup has three 90° bend
and two 135° hook.
For each bend, the length of bar will be reduced. There is a certain
formula to calculate the reduced length for bend.
Below I’m giving a chart for reduced length for a 90° bend for different
diameter of bar.
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10 mmø bar – 1″
12 mmø bar – 1¼”
16 mmø bar – 1½”
Since, we are using 10 mmø bar for our stirrup so the cutting bar
length will be,
9.5′ – 3 x 1″ (bend deduction is ignored for 135° bend).
= 9′-2″
So, you have to cut 9′-2″ length of 10mmø bar.
That means, cutting bar length for the stirrup is 9′-2″.
3. Calculating the Number of Stirrups
See the image above. There are two types of spacing for stirrups. One is
S1 and another is S2. S1 is spaced 4″ c/c and S2 is spaced 8″ c/c.
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S1 is provided in the bottom ¼th portion and top ¼th portion of clear
column’s length. S2 is provided in the middle half portion of clear
column’s length.
Clear column’s length means the height of column between the top of
floor to bottom of beam.
You also should provide 2 numbers of stirrup for column into beamcolumn joint.
Now let’s calculate the numbers of stirrups for column.
The floor height is 10′.
Beam height is 2′
Clear height of column is,
= floor height – beam height
= 10′ – 2′
=8′
Number of stirrups are,
= 4’/4″ + 4’/8″ + 2 + 1 (1 bar should be added for getting the correct
number of stirrups.)
= 21 nos.
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4. Bending the Bar in Stirrup’s Shape
You can use stirrup-making-machine for large project where vast
quantity of stirrups are required.
But, we often make stirrups by hand in our project.
For making stirrups by hand you need a stand and a handle.
See the above image. That is a hand-made stand and a handle. You can
make stirrup with these tools.
Just place the rod in the stand and bend the rod with the handle. You
have to go for trial and error method to get the desired size of stirrup.
Also don’t forget to make the hook angle at 135°.
Symbol used in this post
“ – inch
‘ – foot
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° – degree
db – diameter of bar
nos – numbers
ø – diameter
c/c – center to center distance
Estimate the Neck Column’s Reinforcement
With these 8 Easy Steps
For complete estimating and costing solution of a construction project
we always use computer aided software like Contractor’s office. It is
time-saving and accurately deliver us what we want.
But for our day to day construction activities, we always do this
manually on the project to find the required materials for our tasks.
In this post I’ll show how you can estimate the required reinforcement
for neck column in 8 easy steps.
As we know a neck column has two types of bars. One is longitudinal
bar and another is stirrup.
Longitudinal bars are those which are vertically places in column and
stirrup are those which are horizontally provided around longitudinal
bars.
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So we’ll estimate both types of bars in following 8 easy steps.
8 Easy Steps to Estimate Neck Column’s Reinforcement
Let’s start with the longitudinal bar first.
1. Determining the Number of Longitudinal Bar
Summarise the numbers of same diameter bar separately.
See the image below. There are different diameter of bars in the
column section.
Neck Column: Not scaled and designed
From this image we have found
25mmø bar – 4 nos
20mmø bar – 6 nos
2. Determine the Length of a Longitudinal Bar
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It is not practical to place the longitudinal bar more than 20′ long.
Another thing to consider is that the full length of a bar is about 40 feet.
If you cut them at middle you’ll get 20 feet long bar.
So the length of longitudinal bar for the neck column is 20′.
3. Calculating total length of Longitudinal bars
To find the total length of longitudinal bars multiply the length of each
bar with the total number of bars of same diameter.
Total number of 25mmø bar = 4 nos
Total numbers of 20mmø bar = 6 nos
Length of each longitudinal bar= 20′
Total length of longitudinal bars
25mmø bar= 4 x 20′ = 80′
20mmø bar= 6 x 20′ = 120′
4. Calculating the Weight of Longitudinal Bar
To calculate the weight of bar you should know the unit weight of
different diameter bar.
Read the following post to know how to calculate the unit weight of
steel reinforcement.
From the above post, we found the unit weight of,
25mmø bar = 1.172 kg/ft, and
20mmø bar = 0.750 kg/ft.
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Now multiply the total length of bar with unit weight to find the total
weight of bar.
25mmø bar = 80 x 1.172 = 93.76 kg. Say, 94 kg.
20mmø bar =120 x 0.750 = 90 kg.
Now let’s move for estimating stirrups of neck column.
5. Determining the Number of Stirrup
To find the number of stirrup you need to know the length of neck
column and the spacing of stirrups.
The length of neck column is the distance between the top face of
footing and the bottom face of grade beam. Let’s assume, neck column
length is 5′.
We can find the stirrups specification from the above image. That is
10mmø [email protected]″c/c.
Now divide the neck column’s length with the stirrup’s spacing.
That means,
=5’/4″+1 (1 additional number should be added)
=16 nos
6. Determine the Length of a Stirrup’s Bar
The neck column size we found from the above image is 43″ x 23″.
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That means, the length of column is 43″ and width of column is 23″.
If we deduct the concrete clear cover from both side, the length of
stirrup will be 43″-6″= 37″ and width is 23″-6″=17″.
The length of bar for a stirrup is,
2 x length of stirrup + 2 x width of stirrups + 2 x hook’s length.
= 2 x 37″ + 2 x 17″ + 2 x 3″
= 114″ [12″=1′]
=9.5′
7. Calculating Total Length of Bars for Stirrups
To calculate the total length of bars multiply the numbers of stirrups
with the bar length of a stirrup.
Total numbers of stirrup = 16 nos
Bar length for a stirrup= 9.5′
Total length of bars = 16 x 9.5 = 152′
8. Calculating the Weight of stirrups
To calculate the weight of stirrup’s bar just multiply the unit weight of
10mmø bar with the total length of stirrup’s bar.
Unit weight of 10mmø bar = 0.188 kg/ft
Total length of stirrup’s bar= 152′
Weight of stirrups bar= 152 x 0.188=28.58 kg, say 29 kg.
So, the required steel reinforcement for the neck column is,
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“25mmø bar = 94 kg
20mmø bar = 90 kg
10mmø bar = 29 kg”
Symbol I used in this post
ø – diameter of bar
c/c – center to center distance
‘ – foot
” – inch
ft – foot
kg – kilogram
nos – numbers
How to Estimate Ingredients for 3″ Brick
Masonry Wall?
Masonry wall is the most common item in building construction. We
use bricks for making masonry wall. The common size of brick is
9½”x4½”x2¾” inch.
Most commonly used wall thickness in building construction are 3″, 5″
and 10″. We generally use cement-mortar for jointing bricks with one
another. The ratio of cement-mortar, we use, for 3″ and 5″ thick wall is
1:4 and for 10″ thick brick wall is 1:6.
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The ingredients or materials needed for making brick masonry wall are
cement, sand and bricks. So, we have to estimate those materials.
To estimate materials for brick masonry wall we need to know the
thickness of mortar joint. We put half inch thickness of mortar between
bricks for jointing. So our brick size with mortar thickness will be
10″x5″x3″.
Now lets estimate the materials.
Materials for 100 square feet 3 inch thick brick masonry
wall –
Area of one brick with mortar = 10″x5″ =0.83’x0.42′ = 0.35 square feet
(as our wall is 3″ thick, so we’ll ignore the 3″ side of bricks for
estimating bricks).
Bricks needed for 100 sq.ft masonry wall are = 100/0.35 = 285.71
numbers,
say, 286 numbers.
If we take 5% wastage of bricks, then total bricks needed for 100 sq.ft
3″ thick masonry wall are = 285.74 + 5% = 300 numbers.
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Now lets calculate the mortar volume –
volume of 1 number of brick with mortar is = 10″x5″x3″=
0.83’x0.42’x0.25′ = 0.09 cubic feet (cu.ft).
Without mortar volume of one number of brick is = 9½” x 4½” x 2¾”=
0.79′ x 0.38′ x 0.23’= 0.07 cu.ft.
For 100 square feet (sq.ft) brick wall brick needed 286 nos excluding
wastage.
So, mortar volume for 100 sq.ft brick wall is = 286 x (0.09-0.07) = 5.72
cu.ft.
Dry volume of mortar is 5.72×1.54 = 8.81 cu.ft,
Including 5% wastage dry volume of mortar will be 9.25 cu.ft.
As we use 1:4 cement-sand ratio for 3″ brick wall, so cement will be –
cement = 9.25/5 = 1.85 cu.ft.
1 bag cement volume is = 1.25 cu.ft.
So, cement needed 1.85/1.25 = 1.48 bag,
say, 1½ bag.
Sand will be needed for 100 sq.ft 3″ thick brick wall is =9.25/5 x 4= 7.40
cu.ft.
Say, 8 cu.ft.
Summary:
Materials needed for 100 square feet 3″ thick brick wall are –
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Brick – 300 numbers,
Cement – 1½ bag, and
Sand – 8 cu.ft.
Practical estimation:
The above estimation of 100 sq.ft 3″ thick brick wall is correct. But
practically I found that the required sand quantity is 10 cu.ft. So, it’ll be
better to calculate the required materials for 100 sq.ft 3″ thick brick
wall by following manner –
Cement – 1½ bag,
Sand – 10 cu.ft, and
Brick – 300 NOS.
How to estimate materials for different quantity of 3″ thick
brick wall?
Suppose you need to calculate the required materials for “Y” sq.ft 3″
thick brick wall. You can do this by following way –
Cement – Y x 0.015,
Sand – Y x 0.10, and
Brick – Y x 3.
How to calculate materials for differentratio concrete
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Stone chips
Now-a-days, most of the modern construction company use computer
aided software like priosoft for their complete estimating and costing
solution. But for on-site job execution we often estimate materials
ourselves.
Mix design is commonly referred by mix proportion in a selective zone
where same materials are used in concrete. Suppose, in Bangladesh,
most of the structural designers refer concrete mix design as ratio in
drawing. Because materials of same properties are used in all over the
Bangladesh.
The question is,
How Do We Estimate Materials for Different Ratio
Concrete?
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The most common ratio referred here in Bangladesh for column
concrete 1:1.5:3 and for slab 1:2:4. When we mix cement, sand and
stone chips at 1:1.5:3 ratio, the concrete strength of 28 days cube test’s
result comes around 3500 psi. If we mix cement, sand and brick chips at
1:2:4 ratio the 28 days cube test result will come around 3000 psi,
which is referred for slab concrete.
I will estimate materials for 1:1.5:3 ratio concrete. After learning this
process you will be able to estimate materials for any concrete ratio.
Now lets estimate the required materials for the volume of 100 cft
concrete of 1:1.5:3 ratio:
Wet volume of concrete = 100 cft.
Dry volume of concrete= 100 x 1.54 = 154 cft.
Sum of ratio 1:1.5:3, 1 + 1.5 + 3 = 5.5.
So, Cement content in concrete = (154/5.5) x 1=28 cft.
Sand content= (154 / 5.5) x 1.5 = 42 cft.
Stone chips = (154/5.5) x 3 = 84 cft.
As we know, Cement is available as 50 kg bag in the market. The
volume of 50 kg cement bag is 1.25 cft. So the required cement is 28
divided by 1.25 equal to 22.4 bag.
Summary:
Cement : 22.4 bag,
Sand : 42 cft,
Stone chips: 84 cft.
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In this estimation, we use cubic feet as our concrete unit. If you want to
use cubic meter, same method can be applied. But that will be timeconsuming. The easiest way to estimate concrete materials for different
unit is, apply the above result as percentage. That
means, Cement content for 100 unit of 1:1.5:3 ratio concrete is 28%
(unit will be as concrete unit), Sand is 42% and Stone chips is 84%.
Now lets calculate the water content of concrete. Suppose, watercement ratio for concrete is specified 0.45. That means, water/cement
= 0.45, or W/C = 0.45.
for 1 bag cement, water is, = 0.45 x 1.25 (as we know, 1 bag cement
equal to 1.25 cft),
Water = 0.5625 cft.
We know 1 cubic feet water is equal to 28.31685 litre,
So we can write, water = 0.5625 x 28.31685 = 15.92 litre, say, 16 litre.
So One bag cement needs 16 liter of water for 0.45 W/C ratio.
That’s it.
Here, one thing should be cleared that someone assume the dry
volume of concrete is equal to one and half times of wet volume. But it
is better to use 1.54 for calculating dry volume.
How to Estimate Materials for 5″ Thick
Brick Wall
Brick wall is used to separate a floor in a different usable space. Such as
bed room, living room, toilet, kitchen, store etc.
We use different thickness of brick walls for this purpose. The
thickness can be 3 inch, 5 inch and 10 inch. We normally make 10 inch
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thick brick wall at periphery and 5 inch thick brick wall as internal
partition wall.
Whatever you are, a house owner, a civil engineer, a construction
supervisor, a civil contractor or a builder, you should estimate the
required raw materials for the brick walls which you plan to build.
In this post i’ll show you how to estimate the required raw materials for
5 inch thick brick wall. The raw materials we use to make brick wall are
brick, cement and sand.
Lets take a 10 feet long and 10 feet high brick wall for our estimation
project. Then, area of our wall is,
10′ x 10’= 100 square feet.
As our wall thickness is 5 inch, so the wall’s volume is,
100 sft x 5 inch =41.67 cft (5″ = 0.42)
As we know, we make the masonry brick wall with cement-sand
mortar. The ratio of the mortar we use for 5 inch thick brick wall is 1:4.
You should read the following posts to know more about this –
The brick size we use to make brick wall is 9.5″ x 4.5″ x 2.75″ which will
be 10″ x 5″ x 3″ after jointing with mortar.
Volume of one brick with mortar is, 10″ x 5″ x 3″ =0.08715 cft. (1 inch =
0.08 feet)
So, the required bricks for our wall are,
wall volume divide by one brick volume.
That is,
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41.67/0.08715 =478 nos. These are required bricks for our wall.
Now, we’ll estimate required mortar. If we deduct the volume
of unmortared brick from our wall volume, that is our mortar volume.
Lets see –
Wall volume is 41.67 cft,
Total brick volume (excluding mortar) is,
478 x 9.5″ x 4.5″ x 2.75″ =32.52 cft.
So, the mortar volume is,
41.67-32.52 =9.15 cft.
This is the wet volume of mortar. The dry volume of mortar is,
9.15 x 1.50 = 13.73 cft.
As we know, cement-sand ratio is 1:4, then cement content in dry
mortar is,
13.73 /(1+4) x 1 = 2.75 cft
As cement is measured by bag and we know 1 bag contains1.25 cft
cement so,
2.75 cft cement equal to 2.75/1.25= 2.20 bag cement.
If we deduct cement volume from dry mortar volume then we will get
sand volume.
That means,
13.73 – 2.75= 10.98 cft.
Required materials for 10′ x 10′ brick wall, we found –
Brick – 478 nos, we can assume this 500 nos.
Cement – 2.16 bag, we can assume this 2 bag.
Sand – 10.98 cft, we can assume this 11 cft.
That’s it.
Here is full calculation process,
Wall volume,
10′ x 10′ x 5″=41.67 cft (5″ = 0.42, cft means cubic feet).
One brick volume with mortar,
10″ x 5″ x 3″ =0.08715 cft. (1 inch = 0.08 feet)
Required brick,
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41.67/0.08715 =478 nos,
Total brick volume (excluding mortar) is,
478 x 9.5″ x 4.5″ x 2.75″ =32.66 cft.
Wet volume of required mortar is,
41.67-32.52 =9.15 cft.
Dry volume of mortar is,
9.15 x 1.50 = 13.73 cft.
cement content in dry mortar is,
13.73 /(1+4) x 1 = 2.75 cft
2.75/1.25=2.20 bag cement.
Sand volume,
13.73 – 2.75= 10.98 cft.
Types of Estimates in Building Construction
Estimation determines the probable construction cost of a project.
Estimating can be done at various stages of project duration depending
on the purpose of estimation. First estimation is done before
construction starts for the purpose of making budget of the project or
bidding the project as a contractor. There are various types of
estimation can be done depending on project manual and drawing
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provided and the purpose of using estimated data.
Types of Estimates in Building Construction
Followings are common types of estimate –
* Detail Estimate
* Unit Based Estimate
* Model Estimate
* Comparison Estimate
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* Parametric Estimate
Detail Estimate – This type of estimate includes everything that needs
to complete the project as well as overhead and contractor’s profit. For
this type of estimate, an estimator needs complete set of drawing and
instruction manual of the project. This estimate shows required
materials, labor, time to complete the project, complete cost details
and overhead and also contractor profit. It also includes insurance,
bond, equipment and other necessary things that need to complete the
project. Estimator for this type of estimating should be experienced
person because complete project budget, time duration and contractor
profit depends on his visualization.
Unit Based Estimate – This type of estimate is prepared by calculating
building area and then multiplying area by predefined unit cost. And
then adjusted the cost by considering building height, length, width and
other necessary building components. Required documents for
preparing this type of estimate is a simple floor plan with measurement
and key elevation of the building. This type of estimation is used to
check whether the project was designed within owner’s budget.
Model Estimate – This type of estimate is prepared based on a model
project estimate which is developed before. Preparing this type of
estimate needs answering several key questions depending on model
project. Such as length and width of building, number of base, size of
base, floor height, number of bath etc. Keep in mind that proposed
project should be similar to model project. this type of estimate may
prepare a details estimate of whole project or a part of project
depending on the model project.
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Project Comparison Estimate – In this method, an estimator prepares
estimate of proposed project by comparing similar completed project.
After preparing the comparison estimate, estimator makes adjustment
for variation of proposed project with the completed project.
Parametric Estimate – In this type of estimate, an estimator uses
equations to prepare the estimate. This equation is the relationship
between “parameters” and “cost” of a building project. This estimate is
like unit based estimate but more complex than unit based estimate.
This type of estimate is done for getting concept of proposed project
cost.
There are some other methods are used to determine the project cost
in the different location of the world. Nowadays, there are many
computer programs available in the market to make the estimation
process easy and quick.
Estimation, Costing & Quantity Surveying
What is Check measurement book
Check measurement book is maintained by the sub-divisional officer with the sole
purpose of checking at least 25% of the measurements made by junior engineer.
Main items of work involved in construction
Main items of work involved in construction are :
(a) Earth work
(b) R.C.C. and R. B. work
(c) Flooring
(i) Ground floor
(ii) Upper floor
(d) Roof
(e) Plastering and Pointing
(f) Doors and windows
(i) Frame work
(ii) Levers and shutters for doors or windows
(g) Iron work
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(h) White washing or Distempering
(i) Painting
What is Measurement book
Measurement book is a note-book in which measured entries regarding the work
done or supplies made are recorded. It is then used for the purpose of making
payments to the contractor. This is one of the most important book and is
maintained by the junior engineer.
What is Standard measurement book
Standard measurement book is a measurement book of permanent nature. In it
detailed measurements of a building are correctly recorded on its completion so as
to facilitate preparation of estimates for periodic repairs. For annual white washing,
painting etc. payment to the contractor is made on the basis of this book after
preparing the bills.
Tools and plants (T and P) :
In big project a percentage of 1% to 1 1/2% of the estimated cost is provided for
the purchase of tools and plants which is required for the execution of the work.
Explain Estimation and its Objectives
Estimation :
An estimation is a record of computation of the quantities of materials and items of
work required and expenditure likely to be incurred in the construction of building,
road, dam etc.
Objectives of Estimating :
1. To find probable cost of the work.
2. To find the quantity of various materials and labour required.
3. To have an idea about the time of completion of the work.
4. To help in controlling of the expenditure during execution.
5. To help checking the work done by contractors.
6. To help in completion of departmental formalities such as inviting tenders,
technical sanction etc.
7. To help in the fixation of standard rent, sale price of flats and valuation of
properties.
Materials For Different Works
Materials For Different Works :
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Describe Specification
Specifications describe the nature and the class of work materials to be
used in the work standard of workmanship desired etc. specification should
be clear and there should not be any scope for ambiguity.
(a) General specifications : These give the nature and class of work in
general terms to be used in the various parts of the work. from the
foundation to the super structure.
(b) Detailed specifications : Detailed specifications of an item of work
specify the quality and quantity of material, the proportions of mortar, the
method of preparation and execution, workmanship etc. Detailed
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specifications are written to express the requirements clearly in a concise
form avoiding repetition and ambiguity. These usually form a part of
contract.
Task Work or Out-Turn
Task Work or Out-Turn
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Types of Estimate
Various types of estimates are
1. Rough cost estimate : It is prepared to decide the financial policy matter. It is
prepared on the basis of practical knowledge and cost of similar works. The
competent sanctioning authority accords 'Administrative approval'.
2. Plinth area estimate : It is prepared on the basis of plinth area of a building
multiplied by plinth area rate prevalent in the region. Plinth area rates are fixed
from the cost of similar buildings constructed in the locality having similar finishing
and amenities.
3. Cubical content estimate : This estimate is worked out on the basis of the
cubical contents of the proposed building to be constructed and then applying to it
the rate per cubic metre. This is more accurate than plinth area estimate. The cubic
content rates are deduced from the cost of similar buildings constructed in the
same locality.
4. Detailed or Item rate estimate : This estimate is an accurate one and is
based on the plan and sanctions of the building. The quantity of items under each
sub-head of work are calculated from the dimensions taken from drawing and then
total cost is worked out in a form called abstract of cost.
5. Revised estimate : It is also a detailed estimate and is prepared a fresh when
the original sanctioned detailed estimate exceeds by 10% or more, either due to
the rates being found insufficient or due to some other reasons.
6. Supplementary estimate : This is a fresh detailed estimate of the additional
work in addition to the original one and is prepared when additional work is
required to supplement the original work.
7. Repair and maintenance estimate : In order to keep the structure, roads etc.
in proper condition annual repairs are carried out annually for which an estimate is
prepared. The estimated amount should not be more than 1.5% of the capital cost
of the work.
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