CONSTRUCTION SCHEDULING PROCEDURES
Various scheduling procedures are discussed below.
Construction Schedule
This schedule consists of the duration of construction of
various components of the work. Based on the availability of the following
data, the construction schedule can be made:
(i) Number of activities
(ii) Quantity of various items of works
(iii) Labour contribution and number of field workers
(iv) Machinery required
(v) Stages of activities to be executed
Labour Schedule
Under this schedule, one can know in advance the type of
labour and the numbers required from time to time. This is needed to recruit
the persons (both skilled and unskilled labour) needed so as to have a
continuous flow of work without any disruption.
Material Schedule
This is an important schedule by which one will be in a
position to know the requirement of various construction materials well ahead.
This helps to start the work and continue without any dearth of materials at
any stage. If adequate funds and storage facilities are available, materials that
can not be spoiled with time may be stored to some extent.
Equipment Schedule
The success of any project depends to a large extent on
the proper use of construction equipment. Properly maintained equipment and
application in construction can bring down construction time and cost. Further
proper deployment of equipment judiciously yields economical results without a heavy financial burden on the project. Thus project management should properly
plan the judicious deployment of equipment.
Expenditure Schedule
The project engineer and his team have to primarily
judge to give the most economical construction. Thus it is essential to review
the financial position of the project at regular intervals so as to ensure the
following:
(i)
The annual expenditure, if any, of the project has to be kept within the
allotment.
(ii)
A properly balanced expenditure will result in early completion of work.
CONSTRUCTION SCHEDULING TECHNIQUES
In any project, the sequence through which the project is
to develop should be decided. The requirement is met in a systematic manner by
scheduling techniques. The project scheduling techniques are concerned with resource time. One of the objectives of project management is to optimise
the use of resources. Scheduling techniques offer solutions to the optimisation of
project time.
Technical scheduling can be done by different methods
depending on the size of the project. The methods used are as follows:
1. Bar
charts
2. Milestone
charts
3. Network
analysis
Bar Charts
1. Principle
of Bar Chart
In dealing with complex
projects, a pictorial representation showing the various jobs to be done and
the time and money they involve are generally helpful. One such pictorial chart,
also known as the bar chart, was developed by Henry Gantt around 1900. Bar the chart is also referred to as the Gantt chart.
A bar chart consists of two
coordinate axes, viz., one representing the time elapsed and the other
representing the job or activities to be performed. The jobs are represented in
the form of bars as shown in Fig below
Bar chart
The beginning and end of each
bar represent the time of start and time of finish of that activity. The length
of the bar represents the time required for the completion of the job or
activity.
In any project, there may be
some activities which are to be taken up simultaneously but may take different
lengths of time for their completion (e.g., Activities A and C) and some
activities have to be taken up only after the completion of some other activity
(e.g., Activities A and B). There may also be some activities that are
independent of all other activities (e.g., Activities D and E).
2. Example
Let us consider the steps involved in the construction
of a factory shed. Major activities identified in the construction of a
factory shed where machines are to be erected are presented in the Table below. The
activities have been identified and arranged in a logical sequence. At the
factory site, no water is available and is not feasible to get water from the surrounding. Hence, a bore well has to be sunk before starting the actual
construction. Hence, excavation of the foundation and sinking of the bore well may be
started simultaneously. That is, at the end of one week, water will be
available.
Activities of construction of factory shed
Activity no. |
Activities |
Time required (weeks) |
1. |
Excavation
for foundation |
4 |
2. |
Sinking
of tube well |
1 |
3. |
Base
concrete and placing of column reinforcement |
2 |
4. |
Shuttering
and construction of columns |
4 |
5. |
Fabrication
of truss at site |
1 |
6. |
Erection
of trusses |
4 |
7. |
Construction
of entrance and all round walls |
4 |
8. |
Roofing |
2 |
9. |
Doors,
Windows and Shutters |
2 |
10. |
Plastering |
1 |
11. |
Construction
of machine blocks |
2 |
12. |
Electrification |
1 |
13. |
Flooring |
1 |
14. |
Painting |
2 |
Other activities succeed one after the other. These
activities are shown in a bar chart in Fig below, with the given data and given
precedence/succedent relationships.
As seen from the bar chart, the total time required for
completion of the factory shed project is about 30 weeks.
3. Limitations
of Bar Chart
Following are the limitations of a bar chart:
1. A bar chart can be successfully used only for small
projects.
2. Bar charts can not be updated when there are many
changes.
3. The progress of the project can not be assessed at
different stages scientifically.
4. Bar charts do not equate time with cost. That is
time-cost relationship can not be derived.
Bar chart for factory shed
5. Delay in the work can not be deducted.
6. It does not clearly show the interdependencies
between the various activities in the project.
7. It does not reflect the critical activities of the
project.
8. Bar charts do not provide methods for optimising the allocation of resources.
Milestone Charts
1. Principle
of Milestone Chart
The shortcomings or the inadequacies of the bar chart
have been modified to some extent in the milestone chart. In every activity, there
are certain key events that are to be carried out for the completion of the
activity. Such key events are called milestones and they are represented by a
square or circle. These events are those which can be easily identified over
the main bar representing the activity.
It has been observed in a long time activity the details
will be lacking. If the activity is broken into a number of sub-activities or
key events each one can be recognised during the progress of the project. In
such cases controlling can be done easily and some inter-relationships may be
established between the activities. In a milestone chart, the events are in
chronological, but in a logical sequence. The figures below show the conventional
bar chart and milestone chart.
Conventional bar chart
Milestone chart
2. Limitations
of Milestone Chart
Following are the limitations of a milestone chart:
(i) This method has one great deficiency, that is, it
does not clearly show the interde- pendencies between events.
(ii) Here the events are in chronological order but not
in a logical and sequential order.
Network Analysis
1. Principle
of Network Analysis
The network analysis techniques, developed between 1950s
and 1960s, have now come to be used as an effective management tool for
planning, scheduling and controlling of complex projects.
The term project network analysis is a general term
covers all the network techniques used for planning, scheduling and controlling
of projects. The three techniques commonly used are as follows:
(i) Critical Path Method (CPM)
(ii) Program Evaluation and Review Technique (PERT) and
(iii) Precedence Diagramming Method (PDM) or Precedence
Network Analysis (PNA).
These network techniques produce time-oriented diagrams
having activities organised into a logical order.
2. Network
Diagram
Network Diagram is a
graphical flow plan of the activities that are to be accomplished for
completing the project. The precedence and succedent relationships between
activities are identified first.
Sequencing activities
refers to finding out the logical relationships among the activities of a
project and arranging them accordingly. By studying the project features the
different activities involved in a project the concerned officer-in-change of
the project establishes the precedence-succedent relationships between the
activities.
While deciding the logical
relationships between the different activities, activities which are mandatory
to be operated before some of the activities to be taken up have to be identified. In addition, there may be certain activities that may not be mandatory
dependencies (such activities are called discretionary dependencies) are to be
identified. After finalising all the activities and finding their
characteristics the network diagram for the project can be drawn.
Activities of construction
of a building are given in Table below and shown as network diagram in Fig. below
Activities
of construction of a building
Activity |
Description |
Immediate
predecessors |
A |
Plan approval |
– |
B |
Site preparation |
– |
C |
Arranging foundation materials |
A |
D |
Excavation for foundation |
B |
E |
Carpentry work for Doors and Windows for
main supporting frames |
A |
F |
Laying foundation |
C, D |
G |
Raising wall from foundation to sill |
F |
H |
Raising wall from sill to lintel level |
E, G |
I |
Casting of lintels |
H |
J |
Raising wall above lintel up to roof base |
I |
K |
Electrical wiring |
I, J |
L |
Casting of roof |
J |
M |
Fixing frames of doors and windows |
L |
N |
Making of shutters |
J |
O |
Plumbing works |
L |
P |
Plastering |
O |
Q |
Making ready shutters to Doors and Windows |
P |
R |
White washing and painting |
Q |
S |
Fitting Electrical and plumbing parts |
R |
T |
Clearing the site before handing over |
S |
Network diagram for construction
activity
3. Definitions
of Network Techniques
(i) Critical Path Method
(CPM)
In a network the sequence
of activities arranged in each path will have a different duration. The path that
has the longest duration is called critical paths.
(ii) Program Evaluation and
Review Technique (PERT)
It uses three times, viz.,
optimistic time estimate, pessimistic time estimate and most likely time
estimate.
(iii) Precedence Network
Here each activity is
represented by a rectangular or square box. The time duration of the activity
is incorporated inside the modal box.
SOURCE: BUILDING CONSTRUCTION MATERIALS AND TECHNIQUES | P. PURUSHOTHAMA RAJ
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