CONSTRUCTION SCHEDULING PROCEDURES | CONSTRUCTION SCHEDULING TECHNIQUES | DETAILS | TYPES | LCETED -lceted LCETED INSTITUTE FOR CIVIL ENGINEERS

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Aug 30, 2021

CONSTRUCTION SCHEDULING PROCEDURES | CONSTRUCTION SCHEDULING TECHNIQUES | DETAILS | TYPES | LCETED

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


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

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


Conventional bar chart

 

Milestone 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



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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