OPSM 639, C. Akkan

Resource Planning

• Resources affect the schedule, cost and performance of a project.

• Resources are– Individual people, departments/teams, machines/tools, material.

– There could be many of these, how do we know which ones to plan for?

• Resource planning covers:– Assigning resources to activities;

– Understanding the effects of limited resources on the project schedule.

– Seeing the contribution of resource costs to the overall cost.

OPSM 639, C. Akkan

Resource Planning

• Almost always there are more project proposals than can be handled by the available resources.

• Schedules created without taking resource limitations into account are bound to be wrong.

• There is always a need to determine the impact of starting a new project on the availability of resources.

OPSM 639, C. Akkan

Resource Planning

• A useful tool for assigning specific project responsibilities to personnel is the project responsibility matrix

Tasks R.B. D.A. K.A. L.Q. E.R.Identify target customers R S SDevelop draft questionaire R S SPilot-test questionaire R SFinalize questionaire R S S SPrint questionaire RPrepare mailing labels RMail questionaires RReceive & monitor returned questionaires R SInput response data RAnalyze results R S SPrepare draft of report S R S SPrepare final report R S

Project Team

OPSM 639, C. Akkan

Resource Planning

• In more complicated projects R.M. can have more detail.– In addition to Responsible and Support, as above, there

could be Consult, Notify, Approval.

• Thus, R.M.s outline, responsibility, authority and communication within the organization.

OPSM 639, C. Akkan

Cost Planning

• Types of costs in a project:– Direct costs: labor, materials, equipment, etc.

• chargeable to a work package.

• Represent actual cash outflows that are paid as the project progresses.

• These are costs of resources. The cost of an activity (work package) the sum of the costs of resources it uses.

– Project overhead costs• Cannot be tied to any specific deliverable but serve the entire

project.

• Examples: project manager, consultants, training, travel.

OPSM 639, C. Akkan

Scheduling Resources

• Time estimates for work packages (thus the entire project) is done by the implicit assumption that resources would be available.

A

B

C D

A B

C

D

A BC D

OPSM 639, C. Akkan

Scheduling Resources

• The scheduling problem of the project can be formulated in two different ways:– Minimize the duration of the project subject to resource

constraints that can not be violated. (a resource-constrained project model)

– Minimize the resource use subject to an imposed due-date constraint. (a time-constrained project model)

OPSM 639, C. Akkan

Scheduling Resources

• Some simplifying assumptions to tackle the resource scheduling problem.– Activities can not be split (no preemption).

– Level of resource used by an activity is given and cannot be changed.

OPSM 639, C. Akkan

Scheduling Resources

• For a time-constrained project a common scheduling objective is resource leveling.– Reducing peaks and valleys of resource requirement to

obtain a more or less even resource use throughout the project.

– The general approach• Create an early-start schedule

• Delay some activities to even out the resource use.

– Drawback: loss of flexibility due to reduction in slack.

OPSM 639, C. Akkan

Scheduling Resources

• Consider the following example where there is only a single resource. Given resource requirement is per period. Project deadline is 12.

Legend:Act. (dur’n, res. req)

A(2,2)

B(6,2)

C(4,2)

D(2,1)

E(2,1)

F(4,1)G(2,1)

OPSM 639, C. Akkan

Scheduling Resources• Early-start schedule and resource profile

Act RES ES LF TS 1 2 3 4 5 6 7 8 9 10 11 12

A 2 0 2 2 2

B 2 2 10 2 2 2 2 2 2

C 2 2 6 2 2 2 2

D 1 2 10 1 1

E 1 6 10 1 1

F 1 6 10 1 1 1 1

G 1 10 12 1 1Total Resource Load 2 2 5 5 4 4 4 4 1 1 1 1

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10 11 12

OPSM 639, C. Akkan

Scheduling Resources

• Levelled resource schedule (any other alternative?)– maximum resource requirement down to 4 from 5 (20% decrease)– resource utilization increased to 34/(12*4)=71% from 34/*12*5)=57%

Act RES ES LF TS 1 2 3 4 5 6 7 8 9 10 11 12

A 2 0 2 2 2

B 2 2 10 2 2 2 2 2 2

C 2 2 6 2 2 2 2

D 1 2 10 1 1

E 1 6 10 1 1

F 1 6 10 1 1 1 1

G 1 10 12 1 1Total Resource Load 2 2 3 3 4 4 4 4 3 3 1 1

OPSM 639, C. Akkan

Scheduling Resources

• For the previous example, let’s assume there are only 3 units of the resource available.– To obtain a schedule for which maximum resource

requirement is less than or equal to 3 for all time periods, we will have to accept a delayed project.

– Resource-constrained project scheduling problem is a combinatorial problem. Hence, even medium-sized problems have too many feasible solutions.

– Algorithms to find optimum schedules exist but are very technical and can solve problems with around 50 activities.

OPSM 639, C. Akkan

Scheduling Resources

– A common approach for solving such complicated problems is to use heuristics (algorithms that generally give good solutions, but not necessarily the optimum).

– One heuristic type for resource scheduling is “forward scheduling”.

• Define: an activity is startable if all its predecessors are complete.

• Idea: Schedule startable activities as early as possible without resulting in a resource constraint violation.

• Problem: If there is a set of startable activities which cannot all be started without violating the resource constraint, at least one of them must be delayed. Question: which one(s)?

OPSM 639, C. Akkan

Scheduling Resources

• The answer to the above question is the use of priorities.

– Some scheduling priorities• Minimum slack

• Shortest duration

• Lowest activity identification number

– If there is a tie in one priority, the next one is used to break the tie.

OPSM 639, C. Akkan

Scheduling Resources

A(2,2)

B(6,2)

C(4,2)

D(2,1)

E(2,1)

F(4,1)G(2,1)

2 2

Startable tasks: A

Act RES ES LF TS 1 2 3 4 5 6 7 8 9 10 11 12

A 2 0 2

B 2 2 10

C 2 2 6

D 1 2 10

E 1 6 10

F 1 6 10

G 1 10 12Total Resource LoadResource available 3 3 3 3 3 3 3 3 3 3 3 3

OPSM 639, C. Akkan

Scheduling Resources

A(2,2)

B(6,2)

C(4,2)

D(2,1)

E(2,1)

F(4,1)G(2,1)

Time = end of period 2Startable tasks: B; C; DSlacks: (10 – 8) = 2; (6 – 6) = 0; (4 – 4) = 0

2 2

Act RES ES LF TS 1 2 3 4 5 6 7 8 9 10 11 12

A 2 0 2

B 2 2 10

C 2 2 6

D 1 2 10

E 1 6 10

F 1 6 10

G 1 10 12Total Resource LoadResource available 3 3 3 3 3 3 3 3 3 3 3 3

OPSM 639, C. Akkan

Scheduling Resources

A(2,2)

B(6,2)

C(4,2)

D(2,1)

E(2,1)

F(4,1)G(2,1)

Time = Startable tasks: Slacks:

2 2

Act RES ES LF TS 1 2 3 4 5 6 7 8 9 10 11 12

A 2 0 2

B 2 2 10

C 2 2 6

D 1 2 10

E 1 6 10

F 1 6 10

G 1 10 12Total Resource LoadResource available 3 3 3 3 3 3 3 3 3 3 3 3

OPSM 639, C. Akkan

Scheduling Resources

A(2,2)

B(6,2)

C(4,2)

D(2,1)

E(2,1)

F(4,1)G(2,1)

Time = Startable tasks: Slacks:

2 2

Act RES ES LF TS 1 2 3 4 5 6 7 8 9 10 11 12

A 2 0 2

B 2 2 10

C 2 2 6

D 1 2 10

E 1 6 10

F 1 6 10

G 1 10 12Total Resource LoadResource available 3 3 3 3 3 3 3 3 3 3 3 3

OPSM 639, C. Akkan

Critical Chain Approach

• Eliyahu Goldratt’s approach (the author of The Goal)

• People have a tendency to overestimate the time required for an activity. They usually report 80 to 90th percentile to increase their chances of on-time completion.

• Paradox: Then why are so many projects late?

OPSM 639, C. Akkan

Critical Chain Approach

• Goldratt’s claims the reasons to be: – Work fills available time.

– Organizational disincentives for reporting activities finished early.

– Early finished activities may not lead to early start of successors because resources (people etc.) may not be available for an early start.

– Excessive multi-tasking delays the completion of individual activities.

OPSM 639, C. Akkan

Critical Chain Approach• Goldratt’s solution

– make sure people use the 50th percentile as activity time estimates.

– Insert “time buffers” (or safety time) at parts of the schedule where there might be problems.

– Three types of time buffers are recommended:• Project time buffer: to deal with the delay of the activities on

the critical path.• Merge time buffer: added where non-critical paths merge the

critical path.• Resource time buffer: to account for the delay of an activity due

to a scarce resource required not being available.

OPSM 639, C. Akkan

Critical Chain Approach

Schedule A (with 50th percentile durations)

Schedule B (after inserting buffers to Schedule A)

resource buffer merge buffer project buffer

Schedule C (50th percentile durations inflated by approx. 30% to 40%)