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Haygood Brothers Construction
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, the Haygood Brothers submit competitive bids for the construction
of proposed dwellings. Whenever their bids are accepted, various aspects
of the construction (electrical wiring, plumbing, bricklaying, painting,
and so forth) 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 the Haygood Brothers have 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, they deal with all bottlenecks promptly and avoid
all delays whenever possible. To minimize the time consumed in a construction
project, the Haygood Brothers use 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) of the Haygood Brothers:
1. Arrange financing (AB)
2. Let subcontracts (BC)
3. Set and pour foundations (CD)
4. Plumbing (CE)
5. Framing (DF)
6. Roofing (FG)
7. Electrical wiring (FH)
8. Installation of windows and doors (FI)
9. Ductwork and insulation (including heating and cooling units) (FJ)
10. Sheetrock, paneling, and paper hanging (JK)
11. Installation of cabinets (KL)
12. Bricking(KM)
13. Outside trim (MN)
14. Inside trim (including fixtures) (LO)
15. Painting (OP)
16. Flooring (PQ)
The PERT diagram is shown in Figure 1, and the optimistic (a), most likely
(m), and pessimistic (b) time estimates, are shown in Table 1. Any activities
in the network, but not in Table 1, are dummy activities that consume
no time.
TABLE 1
Haygood Brothers Construction Co.
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DAYS
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ACTIVITY
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a
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m
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b
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AB
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4
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5
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6
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BC
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2
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5
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8
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CD
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5
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7
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9
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CE
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4
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5
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6
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DF
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2
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4
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6
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FG
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3
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5
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9
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FH
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4
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5
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6
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FI
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3
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4
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7
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FJ
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5
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7
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9
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JK
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10
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11
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12
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KL
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4
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6
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8
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KM
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7
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8
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9
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MN
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4
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5
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10
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LO
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5
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7
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9
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OP
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5
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6
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7
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PQ
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2
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3
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4
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DISCUSSION QUESTIONS
1. What is the time length of the critical path? What is the significance
of the critical path?
2. Compute the amount of time that the completion of each event can be
delayed without affecting the overall project.
3. The project was begun on August 1. What is the probability that this
project can be completed by September 30? (Note: Scheduled completion
time = 60 days.)
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