Project and Construction Management
Delivery and control
Projects are delivered by design-bid-build, design-build, or construction-manager-at-risk; each shifts risk and changes when the contractor enters. The schedule is a network: compute early start and finish forward, late start and finish backward, then total float = LS − ES = LF − EF. The critical path has zero total float and sets project duration. Crashing shortens the project by buying time on critical activities, cheapest first, until another path becomes critical.
Cost and performance
Earned value compares planned value (PV), earned value (EV), and actual cost (AC). Cost variance CV = EV − AC; schedule variance SV = EV − PV; CPI = EV/AC and SPI = EV/PV. CPI below 1 means over budget; SPI below 1 means behind schedule. Estimate at completion is often EAC = BAC/CPI when the current cost trend continues. Change orders, requests for information, submittals, and punch lists are routine controls that must be documented.
Traps
Float is not always positive; negative float signals an impossible deadline or an out-of-sequence constraint. The critical path can change after crashing. Confusing CV with SV, or CPI with SPI, is common. Do not compute EAC by simply adding all change orders unless the question asks for a bottom-up revision. Free float is the delay possible without affecting the next activity; total float is delay possible without affecting project completion.
Worked example
Activities: A (5 days), B (3 days, after A), C (6 days, after A), D (4 days, after B and C). Early finishes: B = 8, C = 11, so D starts at 11 and finishes at 15. Critical path is A-C-D; B has 3 days of total float.