the critical path methods for arch

CONSTRUCTION MANAGEMENT MWF 13:00-14:00 CS303LU YANG

THE CRITICAL PATH METHOD (CPM)

CPM basically is a technique that separates planning and scheduling. It also clarifies the inter-relationship time and cost.

CPM evaluates all the possible alternative plans for project and associates each plan with a schedule.

It is a technique for finding the ordered sequence of all the activities forming a project so that the project is completed on the shortest possible time coincident with the lowest cost.

In CPM, each arrow represents a job capacity. It has no dimension but shows the direction of the time work flow for the activity (time flows from the tail of the arrow to the head) for each plan, the cost related to the duration. As the pace of a project is forced, its cost will rise. Conversely, if it is allowed to drag, the cost will rise again because of continuing overhead expenses.

ARROW DIAGRAM FOR SMALL BUILDING

6 EVENT NUMBER, 25 ACTIVITY DURATION ----DUMMY ACTIVITY (finish and clean up cannot start until the walls have

been insulated)

CRITICAL PATH ACTIVITIES (dark arrow) ---------- (as shown it will take 51 days to complete the building)

PLANNING THE CPMIn preparing CPM, the contractor is required to perform the planning phase since he is the only

knowledgeable about his cost and methods of doing business in the best possible time for the best possible cost.

There are Five inputs which can be produced:1. A NETWORK (arrow diagram) defining the activities in the project.2. DURATION estimates of activities 3. COST estimates of Activity for Cost Monitoring and Cash requirement Calculation4. RESOURCE ESTIMATES for resource requirement calculations such as men money, materials

and equipment. The schedule produced for a project assumes that enough manpower and equipment is available to get the cities done

5. TRADE (Responsibility) INDICATORS for activity grouping such as subcontractors.


Subcontractor is primarily concerned with activities appear in their order of sequence as the structure is put together – and those responsible for various activities throughout the project must review the schedule to determine when they must act.

ELEMENTS OF NETWORK DIAGRAMMING

NETWORK INTERPRETATION Activity B cannot start until the job A is completed. The no. at the tail of any arrow must be less than

the no. at the head arrow Activity C cannot start until both job A and job B

are completed Activity B and activity C cannot start until both job

A and job B are completed

Both activity A and B must be completed before jobs C and D can start.

Both jobs A and B must be completed before activity C start.

Job D depends only on job B, and not on job A(E, here is called DUMMY)


1. EVENTS:An event is a point in time signaling the beginning or end of one or more activities. It is the point

which denotes the completion of all preceding activities and the beginning for all succeeding dependent activities.

NOTES: Keep in separate classification activities performed by different tradesman such as plumbers, carpenters,

masons etc.

Divide the project with respect to its structural elements. For example, the roof assembly would be separated

from wall construction, which in turn would be separated from the foundation.

Divide the contract for assignment of responsibility. As an example, the painting sub-contractor’s activity

functions shall not be lumped with that of the resident flooring sub-contractor.

Work for similar nature performed is different locations throughout the project should be considered separately

as should these operations performed at the same time but at considerably different locations within the

project.

It is required that all numbered activities be grouped in a line with one of the numbered phases. It does not,

however, follow that all activities which fall on the line with a particular phase start at exactly the same time.

2. DUMMY


“Not more than one activity may have the same Even Number”

It is sometimes necessary to use a “Convector” type of activity that doesn’t really represent work, but merely helps to observe the rule stated above. This type of activity is usually referred to as a “Dummy” this special activity is drawn dotted line and indicates that no work is involved in that activity. The dummy involves no duration and no cost. It serves only as a dependency connector or sequence indicator.

the critical path methods for arch

Documents