Construction Planning, Estimating and Project Management
Construction Planning, Estimating and Project Management covers network scheduling, floats, cost estimation, rate analysis and contract management.
Core rules
- CPM is deterministic; PERT is probabilistic. PERT expected time te = (to + 4tm + tp)/6 and σ = (tp − to)/6.
- Total float = LS − ES = LF − EF; free float = ES of successor − EF of activity.
- The critical path has zero total float and fixes project duration; any delay there delays the project.
- Estimating types: plinth-area and cube-rate methods are approximate; detailed estimates use BOQ and rate analysis.
- Rate analysis includes material, labour, plant, overheads and contractor profit; contingency is separate.
- Contracts: item-rate, lump-sum and EPC; escalation clauses handle price changes.
Worked example
An activity has optimistic 6 days, most likely 9 days and pessimistic 12 days. Find te and σ. te = (6 + 4×9 + 12)/6 = 54/6 = 9 days. σ = (12 − 6)/6 = 1.0 day. The expected duration is 9 days, but the PERT distribution still allows a 12-day outcome; the critical path should be checked with te values, not most-likely values.
Traps
Using most likely time as the PERT mean; confusing total and free float; treating negative float as impossible; adding contingency as profit; using CPM for a clearly probabilistic first-of-a-kind project without risk allowance.