With the advancement of technology and the speed of construction, the traditional bar charts planning approach has become inadequate to tackle the modern complex construction projects. The bar charts provide very little information about the inter-relationship of the voluminous interdependent tasks. This traditional bar charts approach carry risk of schedule slippage’s, time over-runs, improper decisions and contractual complications.
The network analysis techniques developed in sixties,
is being effectively used as a management tool for planning and then scheduling
of complex projects involving interlinking activities.
Project Networks analysis is a generic term that
covers all network techniques used for planning scheduling and controlling of
projects. The three commonly used techniques in this family are Critical Path
Method (CPM), Program Evaluation and Review Technique (PERT) and the Precedence
Network Analysis (PNA) Technique. The common features of these techniques are
that they make use of network model for depicting time-plan of the project,
apply critical path concept for determining project duration and identifying
critical activities, and employ network analysis techniques for controlling
project time objectives But each technique has a distinct model and its field
of application varies.
Network
analysis procedure
The
modeling and analysis of a network involves the following steps:
·
Defining scope of
network
·
Determining
activities
·
Developing
network logic diagram
·
Structuring model
·
Incorporating
activity durations
·
Numbering
events / activity
·
Computing
critical path
·
Validating Network
Illustrations
Some time analysed CPM, PERT and Precedence networks, given below are in
Exhibits shown against each;
·
CPM Network of
Pumping Station Project
·
PERT Network of
Pumping Station Project
·
Precedence
Network of four rafts foundation construction
·
Summary
Precedence Network of Primary School
·
Precedence
Network of a group of similar Education Buildings
·
Precedence
Network of Raw Water Clarifier Tank
Criteria
for selection of network technique Experience shows that:
·
CPM is best
suited for developing sub-project/task/work package sub-networks having
activities with deterministic single-time duration.
·
PERT is useful
for work packages, tasks or sub-projects involving uncertainties. In such
cases, probabilistic approach of three-times (or a mathematical time-related
function) is used for assessing activity duration.
·
Precedence
Network is the most commonly used technique for time planning of construction
sub-projects and projects.
·
Networks
containing 200 to 300 activities/work packages are manageable, and those having
activities/work packages greater than 300 are difficult to comprehend.
A project schedule
can be depicted by a bar chart, time-scale network or other pictorial displays.
The 2000 Housing Units summary schedule of work as a bar chart is shown in
Exhibit.
It is not
necessary to draw networks for all projects/sub-projects, as some projects like
repetitive type buildings can be better planned using Line-of-Balance technique.
