Assignment

ADM2302 M, N and P Assignment # 6

Problem 2 (CASE STUDY): Haygood Brothers Construction Company

George and Harry Haygood are building contractors who specialize in the construction of private home dwellings, storage warehouses, and small businesses (less than 20,000 sq. ft. of floor space). Both George and Harry entered a carpenter union’s apprenticeship program in the early 1990s and, upon completion of the apprenticeship, became skilled craftsmen in 1996. Before going into business for themselves, they worked for several local building contractors in the Detroit area.

Typically, Haygood Brohers submits competitive bids for the construction of proposed dwellings. Whenever its bids are accepted, various aspects of the construction (e.g., electrical wiring, plumbing, brick laying, painting) are subcontracted. George and Harry, however, perform all carpentry work. In addition, they plan and schedule all construction operations, frequently arrange interim financing, and supervise all construction activities.

The philosophy under which Haygood Brothers has always operated can be simply stated: “Time is money.” Delays in construction increase the costs of interim financing and postpone the initiation of their building projects. Consequently, Haygood Brothers deals with all bottlenecks promptly and avoids all delays whenever possible. To minimize the time consumed in a construction project, Haygood Brothers uses PERT.

First, all construction activities and events are itemized and properly arranged (in parallel and sequential combinations) in a network. Then time estimates for each activity are made, the expected time for completing each activity is determined, and the critical (longest) path is calculated. Finally, earliest times, latest times, and slack values are computed. Having made these calculations, George and Harry can place their resources in the critical areas to minimize the time of completing the project.

The following are the activities that constitute an upcoming project (home dwelling) for Haygood Brothers:

1. Arrange financing (A)2. Let subcontracts (B)3. Set and pour foundations (C)4. Plumbing (D)5. Framing (E)6. Roofing (F)7. Electrical wiring (G)8. Installation of windows and doors (H)9. Ductwork and insulation (including heating and cooling units) (I)10. Sheetrock, paneling, and paper hanging (J)11. Installation of cabinets (K)12. Bricking (L)13. Outside trim (M)14. Inside trim (including fixtures) (N)

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15. Painting (O)16. Flooring (P)

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The immediate predecessors and optimistic (a), most likely (m), and pessimistic (b) time estimates are shown in the table below

ACTIVITYIMMEDIATE

PREDECESSORSTIME (DAYS)

a m bABCDEFGHIJKLMNOP

-- ABBCEEEE

D, IF, G, H, JF, G, H, J

LKN

M, O

42542343510474552

55754554711685763

689669679128910974

Discussion Questions

1. Create a network diagram2. Use a forward pass and a backward pass to determine the critical path (i.e. compute ES, EF,

LS, LF and Slack for each activity)3. What is the time length of the critical path? What is the significance of the critical path?4. Compute the amount of time that the completion of each activity can be delayed without

affecting the overall project.5. The project was begun August 1. What is the probability that the project can be completed

by September 30? (Note: Scheduled completion time = 60 days.)

Source: Professor Jerry Kinard, Western Carolina University; and Brian Kinard, Mississippi State University.

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