Construction Planning & Scheduling

Construction projects

A project is a temporary endeavour with a defined beginning and end, undertaken to create a unique product, service or result within constraints of time, cost and quality.

Characteristics of construction projects

• Unique — each site, design and set of conditions differ.
• Temporary organisation assembled for the project.
• Work carried out at the site, exposed to weather and ground uncertainty.
• Involvement of many stakeholders — owner, consultants, contractors, subcontractors, suppliers, regulators, public.
• Large capital, long durations, high risk.
• Mix of skilled and unskilled labour, heavy equipment.

Project life cycle

The ability to influence cost is highest in early phases and decreases as the project advances, while the cost of changes increases with time.

Objectives of construction management

The traditional triple constraint — time, cost and quality (scope) — plus safety, environment and stakeholder satisfaction:

• Complete the project within the scheduled time.
• Within the budgeted cost.
• To the specified quality and scope.
• Safely, with minimum environmental and social impact.

Functions of management

Following classical management theory (Fayol and others):

Scheduling

Scheduling is fixing the start and finish times of each activity on a calendar, respecting logic, durations and resource limits.

Purposes

• Know when each activity will be done; determine the completion date.
• Plan procurement of materials, labour and equipment.
• Coordinate subcontractors and agencies.
• Provide a baseline for monitoring progress and cash flow.

Bar chart (Gantt chart)

Developed by Henry L. Gantt (early 20th century). Activities are listed vertically and each is shown as a horizontal bar along a time scale; bar length represents duration.

Construction of a bar chart

1. List the activities (from the WBS).
2. Estimate durations.
3. Decide the sequence and start dates.
4. Draw bars against the time scale; show actual progress by a second bar or shading.

Advantages

• Simple to prepare and understand — even by non-technical people.
• Clear visual picture of time-scale and overlapping activities.
• Useful for small projects and for presenting summaries.
• Can show planned vs actual progress and resource loading.

Limitations

1. Interdependencies between activities are not shown — the effect of delay in one activity on others cannot be seen.
2. Does not identify critical activities or floats.
3. Uncertainty in durations cannot be represented.
4. Difficult to update and to use for large, complex projects with many activities.
5. Progress in terms of physical percentage is judged subjectively.
6. No time–cost trade-off analysis.

These limitations led to milestone charts and later network techniques (CPM, PERT).

Linked bar chart

A bar chart with arrows linking dependent activities — shows logic partially; modern software displays Gantt charts linked to network logic.

Milestone chart

A milestone is a significant event (point in time, zero duration) — e.g. "foundation completed", "roof slab cast".

• A milestone chart is an improvement over a bar chart in which milestones are marked on bars, dividing long activities into sub-activities with key events.
• Helps monitoring long activities and showing some sequence within an activity.
• Still does not show interdependencies between milestones of different activities — which led to network diagrams (milestones connected by arrows became the forerunner of PERT networks).

Monitoring progress on bar charts

• Planned bar vs actual bar drawn beneath or shaded.
• A status (time-now) line drawn at the reporting date; activities behind the line are behind schedule, ahead are ahead of schedule.
• Percentage completion marked on bars.

Line of balance (LOB)

A technique for repetitive projects — multi-storey buildings (floor by floor), housing units, pipelines, highways.

• Plots cumulative units completed (vertical axis) against time (horizontal axis) for each activity/crew — each crew's progress is a line whose slope = production rate.
• Parallel lines indicate balanced crews moving continuously from unit to unit; converging lines indicate conflicts (crews catching up).
• Helps maintain continuity of work and identify bottlenecks.