Dr. Nabil I. El Sawalhi -...

Planning & Scheduling

Dr. Nabil I. El Sawalhi

Assistant Professor of

Construction Management

Chapter 3

PLanning & Scheduling L31

Planning• Successful Project Management depends on

continues planning.

• The activities of Designers, Manufacturer, Suppliers & Contractors and all their resources have to be organized & integrated to meet the project objectives.

Purpose of Planning:

• To persuade people to perform before delaying other people involved in the project activities.

• To provide a framework for decision making in the event of change.


Activity/Tasks• Activities consume resources (materials, labor,

Time, Equipment) which are the productive aspects of the project.

• Sequence of activities will be linked on a time scale to ensure that priorities are identified.

• It should be expected that a plan will change.

• Plans must be updated quickly and regularly.

• The plan should be simple and flexible to be understood & updated quickly


Six Methods of Scheduling

• Activity On Arrow (AOA)

• Activity On Node (AON)

• GANTT Chart (Bar Chart)

• Line of Balance

• Program Evaluation & Review Technique (PERT)

• Simulation (Mont-Carlo)


Networks

• AON Network

Activity On Node

• AOA Network

Activity On Arrow


Critical path method (CPM)• CPM “critical path method” identifies those chains of

activities in the project that control how long the project will take.

• the critical path can be defined as the longest possible path through the "network" of project activities

There are two variations of CPM

• The traditional technique is called activity-on-arrow (A-on-A), or an arrow diagram, because the activities are represented in the network as arrows or lines.

• The alternative approach is activity-on-node (A-on-N); it’s also called the precedence diagram.


Activity-on-arrow (A-on-A)/activity-on- Node (A-on-N) Diagrams

• Activity-on- Node (A-on-N) Diagram have the following advantages on Arrow diagram:

• Flexibility since logic is defined in two stages.

• Dummy activities are eliminated.

• Revision and introduction of new activities is simple.

• Overlapping and delaying of activities is easily defined.

• Use of pre-printed sheets is possible.


Example 1. Set of Project Activities and

Precedence use AON

Task Predecessor

a --

b --

c a

d b

e b

f c, d

g e


Stage 1 of AON Network


A Completed AON Network


Stage 1 of AOA Network


Stage 2 of AOA Network


A Completed AOA Network


A Completed AOA Network Using a Dummy Task


Example 2. Find the Critical Path and Critical Time

Activity Predecessor Duration

a -- 5 days

b -- 4

c a 3

d a 4

e a 6

f b, c 4

g d 5

h d, e 6

i f 6

j g, h 4


Complete Network


Float

• Float is a period of time that will be used to adjust the timing of activity to obtain best possible use of resources.

• Total Float: is the difference between activities earliest and latest starts or finishes.

• Free Float: is the min difference between the earliest finish time of that activity and the earliest start time of the succeeding activity.

•


Start and finish• Early Start (ES): the earliest time that an activity can

start as determined by the latest of the early finish of all immediately preceding activities.

• Early finish (EF): The earliest time that an activity can finish. It is determined by adding the duration of the activity to the early start of the activity.

• Late Finish(LF): the latest time that an activity can be finished without dealying the project.

• Late Start (LS): the latest time that an activity can start without delaying the project completion. It is determined by subtracting the duration from the late finish of the activity.


Precedent notation

Early Finish (EF)

Total Float (TF)

Early Start(ES)

ActivityName

Late Finish(LF)

Duration(D)Late Start

(LS)


Logical relationships between activities

Four logical relationship do exist:

• Finish to start (FS):the successor task can’t start until the predecessor task finishes.

• Start-to-Finish (SF): the successor task cannot finish until the predecessor task starts.

• Start-to-Start (SS): the successor can’t start until the predecessor starts.

• Finish-to-Finish (FF) : the successor task can’t finish until the predecessor task finishes.


• Activities that have different early and late start times (i.e., ES(i,j) < LS(i,j)) can be scheduled to start anytime between ES(i,j) and LS(i,j)

• The concept of float is to use part or all of this allowable range to schedule an activity without delaying the completion of the project

• if E(i) + Dij < L(j), then some float is available in which to schedule this activity.


• if one activity is allowed to float or change in the schedule, then the amount of float available for other activities may decrease


Example


Example

• Construct a precedence diagram assuming no research restrictions and calculate the minimum duration of project.

• Schedule the earliest and latest start and finish for each activity and show the critical path method.

• If activity F is extended to a duration of 15 days, what is the effect on critical path


Precedence diagram


Traditional Statistics Versus Simulation

• Similarities

– must enumerate alternate paths

• Differences

– simulation does not require assumption of path independence


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