Program Evaluation and Review Technique (PERT)

Program Evaluation and Review Technique (PERT)

PERT Bar charts and CPM networks assume all activity durations are constant or deterministic. The assumption of constant durations may not be realistic because of working conditions. To address the variability of project activities, the Program Evaluation and Review Technique (PERT) was developed. PERT incorporates uncertainty into the project by assuming that the activity durations of some or all of the project activities are variable.

PERT Three time estimates are required to compute the parameters of an activity s duration distribution: pessimistic time (t b ) - the time the activity would take if things did not go well most likely time (t m ) - the consensus best estimate of the activity s duration optimistic time (t a ) - the time the activity would take if things did go well Mean (expected time): t e = Variance: V t =δ 2 = t a + 4 t m + t b 6 t b - t a 6 2 Where, t b is the expected duration T b is the most optimistic duration estimate t m is the most likely duration estimate T a is the most pessimistic duration estimate

PERT Chart may look like

Draw the network PERT ANALYSIS Use PERT formula to calculate the expected duration for each activity of the project Analyze the paths through the network and find the critical path The length of the critical path is the mean of the project duration probability distribution, It follows a normal distribution The standard deviation of the project duration probability distribution is computed by adding the variances of the critical activities (all of the activities that make up the critical path) and taking the square root of that sum Probability computations can now be made using the normal distribution

Probability computation Determine probability that project is completed within specified time Z = - N where = t p = project mean time = project standard mean time N = (proposed ) specified time

Normal Distribution of Project Time Probability Z = t p x Time

PERT Example Activity t m t o t b Mean Variance 1 3 1 5 3 0.4 2 6 3 9 6 1.0 3 13 10 19 13.5 2.3 Path 1 = Activity 1,4,8 Mean = 17.5 Variance=3.7 Path 2 = Activity 1,5,6 Mean = 16.5 Variance=3.6 Path 3 = Activity 1,5,7,9 Mean = 17.5 Variance=5.4 Path 4 = Activity 2,6 Mean = 16.0 Variance=2.8 Path 5 = Activity 3,9 Mean = 17.0 Variance=3.6 4 9 3 12 8.5 2.3 5 3 1 8 3.5 1.4 6 9 8 16 10 1.8 7 7 4 13 7.5 2.3 8 6 3 9 6.0 1.0 9 3 1 8 3.5 1.4

What is the probability that the project can be completed in N days? Z = - N

Benefits of CPM/PERT Useful at many stages of project management Mathematically simple Give critical path and slack time Provide project documentation Useful in monitoring costs CPM/PERT can answer the following important questions: How long will the entire project take to be completed? What are the risks involved? Which are the critical activities or tasks in the project which could delay the entire project if they were not completed on time? Is the project on schedule, behind schedule or ahead of schedule? If the project has to be finished earlier than planned, what is the best way to do this at the least cost?

Limitations to PERT PERT assumes statistically independence between activities. This may not be appropriate PERT consistently underestimates the expected project completion time due to alternate paths becoming critical. The principal cause of this underestimation is a condition known as merge event bias PERT results are too optimistic To overcome the limitation, Monte Carlo simulations can be performed on the network to eliminate the optimistic bias

GANTT CHART vs PERT CHART

GANTT CHART vs PERT CHART GANTT chart visually shows the duration of Tasks whereas a PERT chart visually shows the sequence dependencies between tasks. GANTT visually shows the Time overlap of Tasks whereas a Network does not show time overlap but does show which tasks could be done in parallel. Some form of GANTT chart can visually show Slack Time available within an Earliest Start and Latest finish time. Most Project Managers find PERT very helpful for scheduling, monitoring and controlling Projects. PERT is recommended for Large Projects with high inter-task dependencies and the GANTT chart for simpler Projects. Most Project Management Case Tools nowadays (eg. MS-Project, Primavera ) allow the best feature of PERT to be incorporated into GANTT Charts.

Line of Balance Method

Line of Balance Method (LOB) A graphical method for production control integrating bar chart and production curve concepts. This is most suited and efficient for linear constructions and repetitive activities LOB focuses on the planned versus actual progress for individual activities and provides a visual display depicting their difference. LOB enables management to provide accurate control by prioritizing reallocation of resources. This assumes resources are interchangeable

Linear Construction Operations Often construction sites have linear properties that influence the production sequence. A road job may be subdivided into many sections. A set of work processes need to be completed in a particular sequence before a section is completed: (1) rough grading, (2) finish grading, (3) aggregate base installation, (4) 5-in.concrete pavement, (5) 9-in. concrete pavement, and (6) curb installation.

Linear Construction Operations Each of the 14 sections can be thought of as being processed by crews and equipment representing each of the six work processes. Work is proceeded from section 1, section 2,, to section 14. The six work processes are carried out in sequence. There are work activity overlaps such that several operations are in progress simultaneously during the middle of the job.

Many types of projects exhibit a kind of rigid work sequence and have a train effect. High-rise building Each floor has to pass a set of operations: erect formwork, install reinforcing steel and pure concrete. Tunnel Drill, blast, remove muck, and advance drilling shield..

There are four Elements of LOB 1. The objective chart 2. The program chart 3. The progress chart 4. The comparison Elements of LOB Objective chart A segmental curve showing cumulative end products to be produced over a calendar time period. Objective chart

Program Chart It is a flow process chart of all major activities, illustrating their planned, sequenced interrelationships on a lead-time basis. Three Aspects to Consider in Developing Program Chart (1) Operations to be performed (2) Sequence of operations (3) Processing and assembly lead time

Progress Chart Progress chart indicates the cumulative progress or status of actual performance at each monitoring point.

Comparison of Actual Progress and Expected Progress

LOB Applied to Construction A road project has 40 same sections and each section has 8 activities. Suppose they are balance production. Each week has 40 working hours. The production curve and the lead time are shown as follows. Calculate the LOB values (completed sections) of each control points at the beginning of fifth week. Sections 40 9 8 7 6 5 4 3 2 1 30 28 A B C D E F G H 20 60 58 44 40 34 18 16 8 0 2hr 14hr 4hr 6hr 16hr 2hr 8hr 8hr 12 10 Lead time 0 0 0 1 2 40 80 3 120 4 160 5 200 6 240 7 280 Weeks Hours Production curve

40 Planned Progress Chart 30 20 10 0 A B C D E F G H Activity Answer: LOB(1)= 0.1 3 40+0.2 1 40 LOB(2)= 20+0.2 8 LOB(3)= 21.6+0.2 8 LOB(4)= 23.2+0.2 2 LOB(5)= 23.6+0.2 16 LOB(6)= 26.8+0.2 6 LOB(7)= 28+0.15 4 LOB(8)= 28.6+0.15 14 LOB(9)= 30.7+0.15 2 Section 40 30 = 20 sections = 21.6 sections 20 = 23.2 sections = 23.6 sections = 26.8 sections 10 = 28 sections = 28.6 sections 0 = 30.7 sections = 31 sections A B C D E F G H Activity Comparative Progress Chart

Scheduling with Computer Software

Introduction to Computer software Project planning and scheduling are key factors to completing a construction project within budget, on time and with few problems The most efficient way to develop a construction schedule is to use computer programs Computer programs also proved useful in resource allocation. The lesson learned from previous projects could also be stored in historical files. This improved future planning as well as estimating process A wide variety of affordable project management software packages are available for purchase. These packages allow the project manager and project team to plan and control projects in a completely interactive mode.

Common features of project management software Create lists of tasks with their estimated durations Establish interdependencies among tasks Work with a variety of time scales, including hours, days, weeks, months, and years Handle certain constrains Track team members, including their pay rates, hours worked thus far on project and upcoming vacation dates Incorporate company holidays, weekends, and team members vacation days into calendaring systems Handle shifts of workers (day, evening, night) Monitor and forecast budgets

Common features of project management software Look for conflicts; for example, resource over allocated and time conflicts Generate a wide variety of reports Interface with other software packages such as spread sheets and database Sort information in a variety of ways; for example, by project, by team member, or by work package Handle multiple projects Work on-line and respond quickly to changes in schedule, budget, or personnel Compare actual costs with budgeted costs Display data in a variety of ways, including both Gantt charts and network diagrams

Computer Software for Project Management Various computer programs have been established so far with regard to preparing schedules: Microsoft Project Mac Project Power Project Primavera Project Planner Project Scheduler Project Workbench (Microsoft Corp.) (Claris Corp.) (ASTA Development Inc.) (Primavera) (Scitor Corp.) (ABT Corp.) However, out of which Microsoft project and Primavera Project Planner are two popular software programs used in construction industry.

Benefits of using project management software Organizing the plan and thinking through the details of what must be done Scheduling deadlines that must be met Scheduling the tasks in the appropriate sequence Assigning resources and costs to tasks and scheduling tasks around resource availability Fine-turning the plan to satisfy time and budget constraint or to accommodate changes Preparing professional looking reports to explain the project to owners, top management, supervisors, workers, subcontractors and the public.

Limitations of using project management software Although scheduling software packages have supported resource-loading activities for sometime, they still require manual input of resource information and do not represent the reasons behind the selection of a particular crew and crew size In most cases, computer programs give adequate solutions; however, when resource requirements exceed the resources available, the computer programs do not provide the optimum scheduling solutions.

Activity Codes Calendars

Activity Bar Activity ID Activity Description Activity codes Screen Layout of Project SNP1 in Primavera Project Planner 3.1

Relationship between Activities

Bar Chart

Data for Each Activity in The Project

Table of Resources Needed in The Project

Layout for Project Reporting

PERT or PDM View

Graph of Resources which Needed in This Project

Screen Layout of MS Project

Relationship between Activities

Assigning Resources Needed in The Project

Layout of network diagram