Project Planning and Scheduling Methods

Planning Schedule Programming

• Planning is the coordination of activities, people, machines, and materials in a logical order to complete a project.
• Scheduling involves placing the plan on a calendar timetable and allocating equipment and manpower.

Methods of Planning

• Bar Chart Method
• Critical Path Method

Bar Chart Method

• Traditional bar charts show both functions simultaneously, which often results in incomplete answers and show a schedule for a plan that has been accepted without establishing that the plan is the most economical.

Critical Path Method (CPM)

• CPM is a technique that separates planning and scheduling, clarifying the relationship between time and cost.
• CPM began with a study initiated by E.I duPont Nemours in 1956, in conjunction with the Ubivac applications Research Center of Remington Rand.

CPM Inputs

• Network (Arrow Diagram)
• Duration (Estimates of Activities)
• Cost (Estimates of activities)
• Resource Estimates
• Trade (responsibility)
• The network or arrow diagram is usually created by all individuals involved in the project.

Network Diagram Terminology

• Event - A point in time signaling the beginning or end of one or more activities
• Dummy Activity - Represents no real work, having no duration and no cost.

Critical Path

• Critical Path is the longest route in the network of activities representing a project.
• The sum of the activities duration along this route is the duration of the project.
• The time required to complete a project is numerically equal to the length of the critical path.
• Activities along the critical path are called Critical Activities of the project; any delay may delay the project.
• There may be more than one critical path, and it can shift as the project progresses.

Time Factors

• Earliest Event - The earliest an event can occur without delaying the earliest start of any activity.
• Earliest Event Time - Numerically equal to the longest path of activities from the project start to finish. Unless specified, it's assumed to be zero for the starting event.
• Earliest Start - Cannot be earlier than the earliest event time, always equal to the earliest event at the beginning
• i-node - Of an arrow
• j-node - Point of an arrow
• Early Start - Not necessarily when the activity will be over, the earliest time it can occur, and the first day after the physical assumption of the activity.
• Earliest Finish - Of an activity is equal to its Earliest Star plus its duration or time.
• Latest Event Time - The latest time an event may occur without delaying project completion.
• Numerically equal to the length of the critical path minus the longest path from the project and event to the event in question.
• Latest Finish - Of an activity cannot be later than the latest event time of its j-node. All activities with the same j-node have the same late finish.
• Latest Event Time - J-node is the same as the latest event time at their common node.
• Latest Start - Plus duration equals the latest finish.
• Float - Activity Total Float or Activity Total Slack - Is the span of time an activity can be delayed after its earliest start time without delaying project completion.
• It is numerically equal to the total time for the activity minus the activity duration.
• Free Float - The span of time an activity can be delayed after its Early Start without delaying the Earliest Start of any succeeding actual activity.
• Free Float - The early Event time at the inode of the next succeeding real activity minus the EF of the activity.
• Independent Float - A portion of the activities Free Float that would remain if all its preceding activities used up all their float.
• It is numerically equal to the ES of the succeeding real activities minus the LF of the preceding activities minus the duration of activity in question.

Rules for Computing the Early Start (ES) and Early Finish (EF)

• The Earliest Finish (EF) for any activity is equal to its earliest starting time plus its expected duration time t.
• For nodes with one entering arrow, ES for activities at such node is equal to EF of the entering arrow.
• For nodes with multiple entering arrows, the ES for activities leaving such node is equals the largest EF of the entering arrow. Activity oriented CPM network diagram rules:
• When an activity is the only predecessor, the activity's Early Finish (EF) is equal to the Early Start (ES) of any successors.
• When two or more activities have a common successor, the successor's Early Start (ES) is equal to the Latest Early Finish of its predecessors.
• When an activity has only one Successor Activity, its Latest Finish (LF) is equal to the Latest Start (LS) of the Successor.
• When two or more activities have only one successor activity, the Latest Start (LS) of the successor activity is equal to the Latest Finish (LF) of any predecessors.

Computing techniques for finding project duration

• The activities with Zero Slack Time indicate the critical path.
• The critical paths are activities 1-2-4-5 having 11 days duration.
• For Nodes with several entering activities, the Early Start (ES) time for leaving activities of that Node is the Largest EF of the entering activities.
• Latest Start (LS) of an activity plus the duration equals the Latest Finish (LF).

Gantt Chart

• Popular for planning and scheduling simple projects and monitoring progress over time.
• Once completed, the chart shows activities, duration, and timing.

Chart Information

• Ongoing activities on any date can be seen on the diagram using a straight edge.
• The time extension request can be determined.
• The delay is due to conditions beyond control of man such as rain, flood and typhoon and such delay is along the critical path, the request should be considered.
• Time extension is not granted if the delay incurred is less than the total float of the delayed activity.

Manpower Leveling

• Employment fluctuation and equipment utilization adds to the cost of the project.
• It is a problem to keep employment at an acceptable level.
• The figure is a time scaled CPM network with manpower loading chart.
• A time scaled networks or is simply diagram where the arrows are indicated on time scale from left to right.
• Activities are shown above with their manpower loading, the corresponding time estimate for each activity.
• The network has all the activities scheduled at their earliest possible start dates.

Probable Time Estimate

• PERT Tool is suited for research and development projects, which are generally non-repetitive in nature.
• It is sometimes called "once through" projects.
• PERT handles the uncertainty problem using three time estimates.

Pert Time Types

• Optimistic time - The estimated minimum time an activity will take. Its probability is about 1 in 100 or 1% represented by letter a.
• Most Likely or Probabilistic Time - The estimated normal length of time an activity takes, represented by letter m.
• Pessimistic time - The estimated maximum time that will be required under the worst conditions. Its probability is about -1 in 100 or 1% represented by letter b.
• 1.Frequency distribution - the presentation of the numbers in a tabulated form which is called a frequency distribution presented in a graph form.
• 2. Normal curve or normal probability curve

Time Formulas

• Expected time: Et = a + 4m + b / 6
• Variance: v2 / 36 = ( b-a)2 / 36
• v path = √E( variance of activities on path)

The formula used to find the value of zis (table Appendix A)

Z = ( Expected path duration) / path standard deviation.

Rules of Thumb

• Treat the probability of timely completion of a path as 100% if its expected time pulse 2.5 of its standard deviations is less than the specified time-Activity times are independent of each other and activity is only in one path.