Slides by: Ms. Shree Jaswal

Introduction

developing the project schedule

Scheduling Charts

logic diagrams and network (AOA,AON)

critical path

calendar scheduling and time based network

management schedule reserve

PDM network,

Resource loading, resource leveling

allocating scarce resources to projects and several projects

Goldratt’s critical chain.

Chapter 4 Slides by: Ms. Shree Jaswal 2

Activity definition

Activity sequencing

Activity duration estimation

Schedule development

Schedule control

Project Management Tools

Gantt Charts

Project Network Diagrams

Activity on the Node (AON), Activity on arrow (AOA)

Critical Path Analysis

Precedence Diagramming Method (PDM)

Simplest and most commonly used scheduling

technique

The chart consists of horizontal scale divided into

time units-days, weeks or months and vertical

scale showing project work elements.

Advantages:

Gives a clear pictorial model of the project.

Simplicity for the planner and the user.

Easy to construct & understand.

Is a means for assessing the status of individual work elements and the project as a whole.

It can be used as Expense Charts

1.for labor planning

2.resource allocation

3.budgeting

Drawbacks:

It does not explicitly show interrelationships

among work elements.

Gantt charts are often maintained manually. This

is easy task in small projects, but is burdensome

and a disadvantage in large projects; it causes

apathy and results in charts becoming outdated.

Activity Start time Duration

13 Chapter 4 Slides by: Ms. Shree Jaswal

0 6 12 18 24 30

Gantt charts

Activitie

Suppose C & D must start only after activity B is

completed.

0 6 12 18 24 30

Gantt charts

Activitie

Gantt charts don’t explicitly show task

relationships

don’t show impact of delays or shifting

resources well

network models clearly show

interdependencies

network of relationships

elements & relationships (sequence)

this is ACTIVITY-ON-NODE

can have ACTIVITY-ON-ARC

research

what’s

been done

research

what needs

doing pick

topic internet

research

write print

Activity on node diagrams

A,6 B,9

Activity on arc or arrow

Activity Duration Immediate Predecessor

D 4 B,C

E 6 B,C

Duration is given in weeks

AON diagram corresponding to data in prev table

Critical path A-B-E:21 weeks

Start A,6

B,9 D,4

C,8 E,6

Finish

Activity on arc or arrow

Same example on AON network

Activity Immediate Predecessors Duration

D B,C 4

F D,E 6

Duration is in days

D B,C 4

F D,E 6

Duration is in days

D B,C 4

F D,E 6

Duration is in days

D B,C 4

F D,E 6

Duration is in days

D B,C 4

F D,E 6

Duration is in days

3-5, 4-5, 7-8,6-8 are dummy activities

Dummy activities are used in AOA diagrams in case a node has more than one immediate predecessor.

In previous example: Activity Immediate Predecessors Duration

D B,C 4

F D,E 6

To represent activities D & F we use dummy activities

ACTIVITY PREDECESSOR IMMEDIATE PRED: REDUNDANT PRED:

D A,B,C B,C A

E A,B,C,D D A,B,C

F A,B,C B,C A

REDUNDANT ACTIVITY

It is only essential to know the immediate

predecessor of a node while constructing a

network.

All the predecessors except the immediate

predecessors of a node are redundant

predecessors( activities).

AON n/ws

There are no dummy activities

They are simpler

They are easier to construct.

AOA n/w’s

AOA method used just as often, probably because it was developed first and is better suited for PERT procedures

The PERT model places emphasis on events and in the AOA method events are specifically designated by nodes.

AOA diagrams use line segments to represent flow of work and time, it is easy to construct schedules that are similar in appearance to Gantt charts but incorporate advantage of networks

Most software packages create AOA n/w’s

that look similar to Gantt charts.

In particular it is best to select one form of

technique., AON or AOA, and stick to it.

The longest path from the origin node to the terminal

Gives the expected project duration (Te)

One project can have more than one CP

Shortening activities on CP (critical activities) will

help reduce the project duration

Shortening activities NOT on CP has no effect on

project duration

Delay in any activities on CP will result in delay of

project completion

Start A,6

B,9 D,4

C,8 E,6

Finish

Critical path A-B-E:21 weeks

Activity,

duratio

predece

D,4 B,C

E,6 B,C

Specifies when at the earliest the activities can be

performed.

ES & EF are computed by taking a FORWARD pass

through the network

When an activity has several predecessors, its ES is

the MAXIMUM of all EF of predecessors

Latest allowable times that the activity can be started

and finished without delaying the completion of the

project.

LS & LF are computed by taking a REVERSE pass

through the network. LS for the last activity (Ts) is

taken same as the EF for that activity (Te); larger value

can be selected if project does not have to be

completed by EF.

When an activity with multiple paths leading back,

backward path with MINIMUM of all LS is selected.

activity duration__predecessor

A requirements analysis 3 weeks -

B programming 7 weeks A

C get hardware 1 week A

D train users 3 weeks B, C

Critical path is: A-B-D 13 weeks

Total slack= LS-ES or LF-EF

Total slack of all activities along critical path

is zero.

Hence delaying any of these activities will

delay the project.

Free Slack= ES( earliest successor)- EF

In the eg, activity C has a free slack of 6

weeks( 10-4=6)

Free slack indicated the amount by which

activity can be delayed without affecting the

start of its successor activity.

can have more than one critical path

activity duration predecessor

A requirements analysis 3 weeks -

B programming 7 weeks A

C get hardware 7 weeks A

D train users 3 weeks B, C

critical paths A-B-D

both with duration of 13 weeks

Need for PDM: “Predecessor - Sucessor” type of networks

assume a “strict” sequential relationship between activities

They do not provide for tasks that can be started when their predecessors are only “partially” complete

PDM allows multiple relationships between activities Finish-to-Start (FS)

Start-to-Start (SS)

Start-to-Finish (SF)

Finish-to-Finish (FF)

Finish-to-Start (FS)

The start of the Activity B can occur n days, at the earliest after the finish of Activity A

Start-to-Start (SS)

The start of Activity B can occur n days, at the earliest after the start of Activity A

Start-to-Finish (SF)

The finish of Activity B must occur n days,

at the latest after the start of Activity A

Finish-to-Finish (FF)

The finish of Activity B will occur in n

days, at the latest after Activity A finishes

PDM: Relationships A 15

Plaster Wall

B 10 Tear-down scaffolding

A 15 Furniture move in

B 10 People

move in SS=5

A 15 Test

new system

B 10 Phase out old system

A 15 Lay

asphalt

B 10 Paint

parking lines FF=5

52 Chapter 4 Slides by: Ms.

Shree Jaswal

The two most commonly used methods for project planning and scheduling are:

Program Evaluation and Review Technique (PERT)

Critical Path method (CPM)

Program Evaluation & Review Technique (PERT)

The Framework for PERT and CPM

There are six steps which are common to both

1. Define the Project and all of it’s significant activities or tasks.

2. Develop the relationships among the activities. Decide which activities must precede and which must follow others.

3. Draw the "Network" connecting all the activities. Each Activity should have unique event numbers. Dummy arrows are used where required to avoid giving the same numbering to two activities

4.Assign time and/or cost estimates to each activity

5. Compute the longest time path through the network. This is called the critical path.

6.Use the Network to help plan, schedule, monitor and control the project.

PERT was developed for application in projects where there is uncertainty associated with the duration and nature of activities.

reflects PROBABILISTIC nature of durations

assumes BETA distribution

same as CPM except THREE duration estimates

optimistic

most likely

pessimistic

Three time estimates :

The Optimistic (a) The minimum time in which the activity can be

completed

The Most Likely (m) Completion time having the highest probability

(normal time to complete the job)

The Pessimistic (b)

The longest time an activity could take to complete

a = optimistic duration estimate m = most likely duration estimate b = pessimistic duration estimate Mean or expected time for completion of an

activity , te is given by te = (a + 4m + b)/6 Variance, V is given by V = sqr((b-a)/6)

The expected time Te , represents the point on distribution where there is a 50-50 chance that the activity will be completed earlier or later than it.

a=3,b=5,c=13

Te= (3+4(5)+13)/6= 6 days

Variance is the measure of variability in the activity completion time:

V=sqr((13-3)/6)=sqr(1.67)= 2.78

The larger V, the less reliable Te, and the higher the likelihood that the activity will be completed much earlier or much later than Te.

More dispersed the distribution and greater the chance that the actual time will be significantly different from the expected time Te

Probability of finishing by a target completion

The expected duration of a project - Te, is the

sum of expected activity times along the

critical path.

Te = ∑ te

The variation in the project duration

distribution is computed as the sum of the

variances of the activity durations along the

critical path

Vp = ∑ V

Putting too much emphasis on the critical

path can lead managers to ignore other paths

that are near-critical or have large variances,

and which themselves could easily become

critical

Need to have considerable amount of

historical data to make time estimates

PERT gives overly optimistic results.

Beta distribution gives large errors in

estimating Te.

Most of the errors in Te come from faulty

time estimates not Beta distribution.

Although PERT and CPM employ networks and use the concept of critical path, the methods have two points of divergence.

CPM is a deterministic approach. CPM includes a mathematical procedure

for estimating the trade-off between project duration and cost.

CPM features analysis of reallocation of resources from one job to another to achieve the greatest reduction in project duration for the least cost.

Tn- how long the activity will take under normal work conditions.

Also associated with normal pace is the normal cost, Cn, the price of doing the activity in normal time.

Usually normal pace is assumed to be the most efficient and thus least costly pace.

When maximum effort is applied, the duration so that activity can be completed in the shortest possible time, the activity is said to be crashed.

In our example, cost slope for the activity

is $3K per week.

Thus, for each week the activity duration

is reduced( sped up) from the normal

time of 8 weeks, the additional cost will

be $3K.

Completing the project 1 week earlier i.e.

7 weeks, would increase the project cost

by ($9K +$3K=$12K)

Basic rules:

Reducing the duration of an activity,

increases the cost by the cost-slope.

Increasing the cost of activity, reduces the

duration of the activity

Reduce the duration of activity with min

value of cost slope.

Activity Normal Crash Cost Slope

Tn Cn Tc Cc_____________

A 9 10 6 16 2

B 8 9 5 18 3

C 5 7 4 8 1

D 8 9 6 19 5

E 7 7 3 15 2

F 5 5 5 5 _

G 5 8 2 23 5

$55K $104K

Activity Normal Crush Cost Slope

Tn Cn Tc Cc_____________

A 9 10 6 16 2

B 8 9 5 18 3

C 5 7 4 8 1

D 8 9 6 19 5

E 7 7 3 15 2

F 5 5 5 5 _

G 5 8 2 23 5

$55K $104K

CCPM was introduced in 1997 by Eliyahu

Goldratt.

CCPM is based on the idea that people often

inflate or add cushioning to their time

estimate in order to give themselves a form

of “safety” to compensate for uncertainty.

There are 3 basic reasons for inflating:

If your work is dependent upon the work of

someone else

Because of pessimism arising from a previous

experience where things did not go as planned

To guard against the cut which the project

sponsor or customer may put

Added safety does not ensure timely

completion of projects due to following

reasons:

1. Student’s syndrome

2. Parkinson’s law

3. Resource contention

CCPM follows a completely different

assumption: instead of adding safety to each

task, put that safety in the form of buffers

where needed the most.

This would be in the form of feeding buffers,

resource buffers & a buffer at the end of the

project

CCPM begins by asking each person or team

assigned to a task to provide an estimate that

would have a 50 % chance of being completed

Critical chain is different from the critical path

in that it also takes into account resource

contention. Chapter 4 Slides by: Ms. Shree Jaswal 81

A,10 B,10 C,10 E,10

A,5 B,5 C,5 E,5

Buffer

Feeder buffer

Project schedule with safety in each task

Critical chain project schedule

Chapter 4 Slides by: Ms. Shree

Jaswal 83

In earlier slides, it was assumed that the

resources are available (may be at a cost) in

abundance

In reality, some resources may be scarce or

shared

Resource loading refers to the amount of

resource required to conduct a project

Note: resource loading keeps changing

throughout a project because the amount of

resources needed for individual activities differs

Resource leveling refers to scheduling activities in a

manner such that the resource loading is somewhat

“balanced” (or “smoothed”)

SMOOTHING: “flatten” as much as possible

Smoothed: Manpower

Equipment Requirement(!Erratic!)

LEVELING: flatten with reference to available resource

Leveled: Manpower

Activities must be scheduled so that the allocation of a particular resource to project activities does not exceed a specified maximum

Attention is given to maximum availability of resource

Most project management scheduling software use heuristics (procedure based upon a simple rule) for making the decisions

The heuristic rule for determining the scheduling priority are:

The critical path length is 9 weeks and the

constrained-resource level is of 10 workers

a. As soon as possible: activities that can be started sooner are

given priority over those that must be started later

As Soon As Possible

b. As late as possible: activities that can be finished

later are given lower priority than those that must

be finished earlier

As Late As Possible

c. Most resources : activities requiring more resources

are given priority over those requiring fewer

resources

Most Resources

d. Shortest Task Time: activities of shorter duration

are given priority over those of longer duration

Shortest Task First

e. Least Slack: activities with less slack time are given

priority over those with more slack time (critical

path activities are given highest priority)

Least Slack time

• All these rules are subordinate to precedence

requirements, which means whatever the rule, the

resulting schedule will not violate the necessary

predecessor-successor relationship.

• Other ways to account for resource constraints in project

scheduling include:

• Reduce the level of resources per activity

• Split activities

• Alter the network: use PDM, convert FS to SS

relationships

Slides by: Ms. Shree Jaswal - Shree Jaswal | Assistant...

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