Resource analysis

Project management(lecture + seminar)

Introduction• Sometimes one or more resources (especially

skilled workers) are equally or more important than time. According to priority, there are:– time-limited and – resource-limited

projects. Priority can change over time but it is not wise to have double priorities.

• Basic tools came from production engineering: loading (resource allocation)

Resources• Definition: anything that is scarce and required for any activity

in the project. Resources are constraints for the project.• Resources can be:

– Non-storable: has to be renewed for each periode.g. work

– Storable: depleted only by usage (remains available if not used)e.g. money

• The most common resource typology, the 4Ms:– Men– Machines– Money (cost)– Material – Other

Loading (resource allocation)• The assignment of work to an worker, machine

or unit (generally: to a workstation) in time.• A workstation can be:

– underloaded (load < capacity)– fully loaded (load = capacity)– overloaded (load > capacity)

• Fully loading is nearly impossible to reach except in flow production.

• Underloading is the most common, because it respects time. Overloading leads to be late.

Defining resources for projects• SOW• WBS• Task list

– Resource needs given in resource-hours (e.g. man-hour, machine-hour)

– Two forms of resource specification:• Rate-constant (can be changed to a constant

function/pattern): constant usage rate defines the duration, too

• Total constant: to finish the activity

What to do with non-linear duration-resource functions?

• Use a computer• Focus on quasi-linear parts of the functions

Capacity

• Be realistic:– Usual efficiency– Estimated absenteeism, sickness, holidays– Existing commitments– Ancillary tasks and their resource needs– Any additional constraints (like methodology) and

limitations (like work contracts)

• Also calculate with the possibilities (cost, time, trade-offs) to increase capacity

Optimum seeking procedures• Constraints:

– Resource-limited projects– Time-limited projects– Resource-limited AND time-limited projects

(question of priority)

• Methods:– Linear programming– Levelling– Allocation – Smoothing

Linear programming

• Successful only for small networks (up to about 200 activities)

• Need for precise data

Levelling (simplest technique)

• Need for a previously produced starting schedule.

• Attempts to level out peaks and valleys in resource requirements by rescheduling some activities.

• Difficulty of interactions between activities.

Allocation (for resource limited cases)• Allocation resources • ‘Splitting’ an activity: stopping an activity, which

is currently in progress, by the removal of its resources for use on an activity of higher priority.

• Two procedures for allocation: – Serial: if only a few activities are splitable – Parallel: if many activities are splitable; more

complicated method that needs more time and data

Allocation when resources are limited

• Serial procedure:1. All activities in the project are ranked using constant priority rule.

The most frequently used rule: ascending order of the LSTs with a tiebreaker of the ascending order of total floats (a kind of ‘urgency’).

2. Activities are scheduled in the above order at the earliest possible point in time consistent with the availability of resources and the precedence requirements.

• Step-by-step process:– Draw the network diagram for the logical connections– Compute the activity times and total floats– Plot a Gantt or time-scaled network in tandem with a resource-

histogram

Allocation when resources are limited

• Parallel procedure:Activities are considered sequentially (sub-lists). Unscheduled activities are retained and ranked in the next period with new activities.

START

a

b

c

d

g

f

e

hk

j

i

l FINISH

The time-limited case

• Balancing the S-curve with milestones:Forcing early activities to start sooner

Smoothing (time limited)• Aim is to produce a feasible schedule within the

time constraints & provide as smooth a resource requirement profile as possible.

• Informational needs of smoothing:– Start time and timeframe (TPT or deadline)– Priority order of the resources required

• Prioritising activities and selecting them in order for scheduling (critical activities have supreme priority).

• Finding the best place for the activity (placing). • Repeat the process with the next activity.

Prioritising activitiesConsiderables:• Resource type(s) and importance• Total work content (resource units per time

multiplied with the duration for all resources used on the activity)

• Available float

Formula if no initial scheduling exists:(Total work content) / (Float remaining)

In descending order (greatest first).

Placing• The best position is the one that gives the

lowest usage increase in the time span of the activity.

• Two ways of finding this position:– Visual – Sum of squares:

• Calculate the sum of squared resource needs of each period within the questionable time frame (between the ES and LF time of the given activity) for every possible positioning

• Choose the position with the lowest value

seminar

Defining resources for projects 2• SOW• WBS• Task list• Logical connections (PNT)• Gantt chart and histogram• Levelling

Using the bar chart

• Set up and analyse the network– Assign the resource data to the activities

• Draw the Gantt chart– Aggregate each resource time period by time

period throughout the total project

• Cumulating (Summation or S Curve):• Use levelling the load for optimization

Network with single resource data

START (0)

0 00

0 00

0

e (1)

10 130

10 133

0

d (2)

2 73

5 105

3

c (3)

2 100

2 108

0

b (4)

0 55

5 105

5

a (1)

0 20

0 22

0

FINISH (0)

13 130

13 130

0

Aggregation with a bar chart(single resource, earliest start)

activity 1 2 3 4 5 6 7 8 9 10 11 12 13

a 1 1

b 4 4 4 4 4

c 3 3 3 3 3 3 3 3

d 2 2 2 2 2

e 1 1 1Res. aggr. 5 5 9 9 9 5 5 3 3 3 1 1 1Cum. res. 5 10 19 28 37 42 47 50 53 56 57 58 59

Resource units11 10

987654321

1 2 3 4 5 6 7 8 9 10 11 12 13

Time

Aggregation with a bar chart(single resource, latest start)

activity 1 2 3 4 5 6 7 8 9 10 11 12 13

a 1 1

b 4 4 4 4 4

c 3 3 3 3 3 3 3 3

d 2 2 2 2 2

e 1 1 1Res. aggr. 1 1 3 3 3 9 9 9 9 9 1 1 1Cum. res. 1 2 5 8 11 20 29 38 47 56 57 58 59

Resource units11 10

987654321

1 2 3 4 5 6 7 8 9 10 11 12 13

Time

The S Curve analysis

• The minimum slope level is the less ‘critical’ from the viewpoint of availability

S Curve of the example

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13

ES

LS

smoothest

Scheduling with constraints

Three approaches:• Allocation: Activities are scheduled so that an

initially defined limit of resources or time is not exceeded.

• Levelling: A previously generated schedule must be given. Then it levels out the peaks and troughs without changing the TPT.

• Smoothing: A start time, a TPT and resource priorities.

Other possibilities

• Alternative resources• Alternative methods• Alternative sequences

(if there is no technical dependency)

Levelling the load• We must have a starting allocation of activities over

time and a resource constraint (previous example).Resource units

11

10

9

8

7

6

5

4

3

21

1 2 3 4 5 6 7 8 9 10 11 12 13

Time

• Trying to keep the original TPT unchanged means that critical activities should not be moved. Thus try to move activities with free float.

Resource units

11

10

9

8

7

6

5

4

3

21

1 2 3 4 5 6 7 8 9 10 11 12 13

Time

Solution• There are only 2 activities with free float: b & d• Which one to move and to where?

• Moving activity d 3 days in advance is eliminating the peak.

Resource units

11

10

9

8

7

654

3

21

1 2 3 4 5 6 7 8 9 10 11 12 13

Time

activity 1 2 3 4 5 6 7 8 9 10 11 12 13

a 1 1

b 4 4 4 4 4

c 3 3 3 3 3 3 3 3

d - - - 2 2 2 2 2

e 1 1 1Res. aggr. 5 5 7 7 7 5 5 5 5 5 1 1 1Cum. res. 5 10 17 24 31 36 41 46 51 56 57 58 59

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12 13

ES

LS

smoothest

leveled

S Curve

Effect of levelling• New „activity”: waiting for the resource

(it is a lag, not a true activity)

START (0)

0 00

0 00

0

e (1)

10 130

10 133

0

d (2)

5 100

5 105

0

c (3)

2 100

2 108

0

b (4)

0 50

0 55

0

a (1)

0 20

0 22

0

FINISH (0)

13 130

13 130

0

• Changes: new precedence relationship, floats, late start and finish times

Network with single resource data

START (0)

0 00

0 00

0

e (1)

10 130

10 133

0

d (2)

2 73

5 105

3

c (3)

2 100

2 108

0

b (4)

0 55

5 105

5

a (2)

0 20

0 22

0

FINISH (0)

13 130

13 130

0

• Resource limit: 5

Network with multiple resource data

START (0)

0 00

0 00

0

e (3B)

10 130

10 133

0

d (2B)

2 73

5 105

3

c (3A)

2 100

2 108

0

b (4B)

0 55

5 105

5

a (2A)

0 20

0 22

0

FINISH (0)

13 130

13 130

0

• Resource limits: 5A, 5B

f (3A)

5 85

10 133

5

Reading

• Lockyer – Gordon (2005): Chapter 17 & 18

Thanks for your attention