Project Planning

Project planning schedules and controls construction. Learn work breakdown structures, bar charts, network diagrams, the critical path method (forward/backward pass, float), PERT probabilities, resource levelling, crashing and earned value management.

Big projects contain thousands of activities with dependencies — you can't pour a slab before the formwork and reinforcement. Planning figures out the sequence, the shortest possible duration and which activities are critical.

Once work starts, control compares progress and cost with the plan to take corrective action early.

An analogy

Planning a project is like cooking a big dinner: some dishes must wait for others, some can be done in parallel, and the longest chain of dependent steps decides when dinner is served.

WBS and bar charts

The work breakdown structure divides the project into manageable deliverables and activities. Gantt (bar) charts show when each activity happens — easy to read but weak at showing dependencies.

Critical path method

Draw activities with dependencies (activity-on-node). A forward pass gives earliest times, a backward pass latest times. Activities with zero float form the critical path — any delay to them delays the project. Non-critical activities have float to absorb delays or level resources.

PERT and uncertainty

When durations are uncertain, three estimates (optimistic a, most likely m, pessimistic b) give a mean and standard deviation. Summing along the critical path estimates the probability of finishing by a target date.

Resources, crashing and earned value

Resource levelling smooths labour and equipment demand using float. Crashing shortens the project by adding resources to critical activities with the lowest cost slope. Earned value management integrates scope, time and cost: CPI < 1 means over budget, SPI < 1 behind schedule; EAC forecasts final cost. Software: Primavera P6, MS Project.

Formulas

• Forward pass: ES = max(EF of predecessors), EF = ES + duration
• Total float: TF = LS − ES = LF − EF (critical if 0)
• PERT: t_e = (a + 4m + b)/6, σ = (b − a)/6
• Probability: z = (T − T_e)/σ_path
• Earned value: CPI = EV/AC, SPI = EV/PV, EAC = BAC/CPI

Worked example: Critical path

Given: A 3; B 4 (after A); C 2 (after A); D 5 (after B); E 3 (after C); F 2 (after D, E) — weeks

Find: Project duration and floats.

• Path A–B–D–F = 3 + 4 + 5 + 2 = 14
• Path A–C–E–F = 3 + 2 + 3 + 2 = 10
• Critical: A–B–D–F; float of C and E = 4 weeks

Answer: 14 weeks

Worked example: Earned value

Given: BAC = 1 000 000; At month 6: PV = 500 000, EV = 450 000, AC = 480 000

Find: CPI, SPI, EAC.

• CPI = 450/480 = 0.94 (over budget)
• SPI = 450/500 = 0.90 (behind)
• EAC = 1 000 000/0.9375 = 1 066 667

Answer: CPI 0.94, SPI 0.90, EAC ≈ 1.07 M

Common mistakes

• Wrong: Focusing on non-critical activities while critical ones slip. — Right: Monitor the critical path and near-critical paths closely.
• Wrong: Measuring progress by money spent. — Right: Use earned value — spending isn't progress.

Applications

• Construction scheduling: Baseline programmes, look-ahead plans and delay analysis.
• Project control: Monthly EVM reporting to owners and lenders.
• Claims: Time-impact analysis for extensions of time.

Key takeaways

• WBS → network → forward/backward pass → critical path.
• PERT: t_e = (a + 4m + b)/6.
• EVM: CPI = EV/AC, SPI = EV/PV.
• Control the critical path; forecast early.

Going further

• Line-of-balance: Repetitive projects (high-rise floors, pipelines) scheduled by production rates.
• Monte Carlo schedule risk: Simulates thousands of outcomes to get P50/P80 completion dates.
• 4D BIM: Links schedule to model for visual sequencing and clash-in-time checks.