Construction Management
Construction Management tests planning, scheduling and control. Expect network problems on CPM floats and PERT expected time, crashing and cost slope, bar charts, contract types and the tender process.
Networks
An activity consumes time; a dummy shows logical dependence and has zero duration. The critical path has the longest duration and zero total float, and it fixes the project completion time.
- Forward pass gives earliest start and finish: EFT = EST + duration.
- Backward pass gives latest finish and start: LST = LFT - duration.
- Total float = LST - EST; free float = EST of successor - EFT of the activity.
PERT
Expected time te = (to + 4tm + tp)/6, standard deviation = (tp - to)/6 and variance is its square. PERT is probabilistic and used for research-type work; CPM is deterministic and used for repetitive construction.
Worked example
Activities: A (0-4), B (0-2), C after A (3), D after B and C (2). Forward pass: A EFT 4, B EFT 2, C EST 4 and EFT 7, D EST = max(2, 7) = 7 and EFT 9. Project duration is 9 days along A-C-D. Latest start of B = 7 - 2 = 5, so total float of B = 5 - 0 = 5 days.
Contracts and tendering
Item-rate contract for measured work, lump sum for small well-defined jobs, turnkey for design plus build, BOT for infrastructure concessions. Tender steps: notice, sale of documents, EMD, submission, opening, scrutiny, award, security deposit.
Traps
- Assigning a duration to a dummy activity.
- Confusing free float with total float.
- Computing crash cost without first finding the cost slope, which is (crash cost - normal cost)/(normal time - crash time).
- Treating every activity on the longest path as critical when two paths tie.