project scheduling tools. there are four possible sequencing modes in ms project. suppose b follows...
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Project Scheduling Tools
There are four possible sequencing modes in MS Project. Suppose B follows A. FS: Finish Start – Start B after A is completed SS: Start Start – Start A and B at same time FF: Finish Finish – Finish A and B at same time SF: Start Finish – Start A after B is completed
Lags are delays between work on activities
1. Sequencing
FS Sequence - Traditional
A
B E.g. Sand and Paint
A
BLag E.g. Sprinklers and Landscape
SS Sequence
A
B E.g. Plant Lawn
and Flowers
A
BLagE.g. Drywall: Hang
and Tape
FF Sequence
A
B E.g. Olympics
A
B
Lag E.g. Olympics
SF Sequence
A
B E.g. Not Practical
A
B
Lag E.g. Ocean Cruise
2. Activity Uncertainty
PERT assumptions (Richard Schonberger and Ken Mac Crimmon) Beta distribution assumption PERT approximation formula for mean and variance Estimates of a, m, and b
Errors of above up to 30%, but tend to cancel Worse problem is merge event bias
(probability near-critical path becomes critical) – estimates consistently optimistic
Example 2.1
A,1
C,3
D,1
B,2
Critical path is ACD but ABD is near critical. Criticality index: probability path critical.
Use Simulation or Monte Carlo Analysis
Generate random numbers (electronic, formulas, tables,
books) i.e. 28
• Convert to random probabilities i.e. .28 What is probability of probability?
• Convert random probability to random variate. Follows distribution of say actual activity time.
Finding Random Variates, Problem 2.1
B C PMF CDF
Mean – 1 1 2 .3 .3
Mean 2 3 .4 .7
Mean + 1 3 4 .2 .9
Mean + 2 4 5 .1 1.0
Random probability of .28 gives B random variate of 1; .46 gives C value of 3.
Simulation of Problem 2.1
RN B(2) RN C(3) Length Path
.28 1 .46 3 5 ACD
.97 4 .09 2 6 ABD
.63 2 .33 3 5 ACD
.53 2 .76 4 6 ACD
.73 3 .00 5 7 ACD
Expected length = 5.8 > 5 (merge event bias)
Criticality index of ACD = 0.8 or 80%
Project Simulation Simulation includes
GERT – Graphical Evaluation and Review Technique
Crystal Ball – Copy comes with text
Simulation includes Probabilistic branching from node – B may follow A Probabilistic times for activities – various distributions Flexibility in node realization – activity time can = 0 Looping permitted – rework
Critique of Simulation – R. Schonberger recommends intensive critical path scrutiny
3. Limited Resource Scheduling
Resources include labor, material, equipment, space, and money
Money versus time tradeoffs Methods
Crashing – How to shorten activities – cost penalties Resource loading – amount of resource needed per
period. Resource leveling or balancing – evening out resource
use, reacting to limited resources
Simulation programs can help level
