Three Point Technique to Estimate Task Duration, Es-Ef, Ls-Lf Procedure to Indentify Critical Path.

The total duration of the construction project by adding the estimated task duration serially would give us 70 weeks. But some tasks within some activities can be done in parallel sequence or simultaneously, which would significantly reduce the construction project completion time using the critical path method (CPM). In this method the longest path is the critical path which runs through one of the route in the project network diagram from start to finish. This project network diagram is illustrated on the printed assignment page, we have 10 tasks listed from A to J. Below is an activity list of the tasks; ACTIVITY | ACTIVITY DESCRIPTION | IMMEDIATE PREDECESSORS | ESTIMATED DURATION (WEEKS) | A | Clearing the vacant lot | none | 7 | B | Securing permits | A | 11 | C | Digging a foundation | A | 12 | D | Putting in forms for the concrete | A | 9 | E | Pouring the concrete foundation | B | 2 | F | Putting up structural framing | B, C | 10 | G | Running electrical/water/sewage | C | 3 | H | Finishing the interior | D,E,F, G | 2 | I | Finishing the exterior | D | 6 | J | Landscaping the property | H, I | 8 | | Total estimated task duration | | 70 WEEKS |
Figure 1.1
The variables provided for the optimistic, most likely and pessimistic task time estimates in the printed assignment table were used to calculate the estimated duration in Figure 1.1 above. The formula below used to derive at the estimated task duration in Figure 1.1 above was the three-point technique;
E= (O +4(M) + P) 6 The critical paths for this construction project and the path lengths are highlighted below; we would use this to calculate the earliest finish time for the project. CRITICAL PATH TASKS | PATH LENTHS IN WEEKS | 1. start: A-B-E-H-J- finish | 7 + 11+ 2+ 2+ 8 = 30 | 2. start: A-B-F-H-J- finish | 7 + 11+ 10+2+8 = 38 | 3. start: A-C-G-H-J- finish | 7 + 12+ 3+ 2+ 8 = 32 | 4:start: A-C-F-H-J- finish | 7+