The Challenge of Representing Rework

On day 8, activity 4 (concrete coating) was progressed another 20 % but then defects were observed in the pipe coating that had been completed earlier and that was estimated to be about 20 % of the activity. Accordingly, a decision was made to redo the defective pipes. To represent this situation, on day 8, 20 % progress is first entered for the activity on that day, as shown in Fig 5.7.

Fig. 5.7: Recording the Progress for Day 6, Before Rework Completed Remaining

Then, since the magnitude of the rework is calculated as 20 %, a rework event is then entered as a negative percentage complete. Thus, the total amount of progress for the activity on that day is zero, as shown in Fig 5.8.

Fig. 5.8: Updating Activity 4 on Day 6 Based on the Observed Rework

As a result of the rework, the duration of the activity is extended by the amount of time needed to perform the rework, in this case, from 5 days in Fig. 5.7 to 6 days in Fig. 5.8. It should be noted that the remaining part of the activity duration is calculated using Eq. 4.1. Therefore, activity 4 is scheduled to finish on day 10 rather than day 9. Moreover, the extended duration of activity 4 was assessed and found to affect other activities as follows:

• Successor activity 5 (curing) must be performed for the reworked pipes, and a curing rework of 13 % must therefore be added, which will extend the total duration for curing to 9 days (ending on day 14)

• Transportation activity 7 must be rearranged, and transportation will thus take 5

20% (progress) + C-20(20% rework)

Once these changes are made to the schedule, the project duration is extended to 26 days rather than 25, as shown in Fig. 5.9.

Fig. 5.9: Revised Schedule Showing the Rework in Activity 4 and Its Consequences

Concurrently with the Contractor events on day 8 described above, the Owner was contemplating another rework on the same day, due to a design change for activity 3 (FBE coating), which represented 25 % of the total work for the activity. This rework caused by the Owner is expected to impact other activities, mainly sandblasting (activity 2) in order to remove the old FBE coating (also 30 % of the work executed in activity 2). The updated schedule resulting from these events is shown in Fig 5.10.

Fig. 5.10: Effect of Rework on Multiple Activities

As a result of these schedule events, the Contractor is not in a rush to complete the transportation activity with the as-planned speed. To ensure the continued flow of transportation activity and to save money, the Contractor decided to slow down the remaining transportation activity, perceiving that it will not have a negative effect on the schedule. However, the schedule in this case as shown in Fig. 5.11, also included a resource over-allocation for day 12 due to the extension of activity 5 (FBE pipes transportation). It is noted that the Contractor’s action of slowing down some activities is common in practice and has been referred to in the literature as a pacing delay, which changes the pace of some activities to match the pace of others (Zack, 1999).

O-25 for 25% rework forced by the Owner in activity 3 Additional O-25 for related Owner rework of 25% for activity 2

Fig. 5.11: Updated Schedule Showing the Resource Over-Allocation

To resolve the resource over-allocation, the Contractor was forced to introduce a start delay of one day to activity 7 (concrete coated pipes transportation). This start delay affects the project duration by one day, so, the final updated schedule for the project has 27-day duration, with a total delay of 2 days compared to the baseline. After all the rework events and their effects on the project schedule are taken into consideration, and after all the resource over-allocations are resolved, the schedule is updated as shown in Fig. 5.12.

Over Allocation due to slow down

Based on the delay penalty amount mentioned in the project information (delay penalty = $5,000 per day), the project team decided to investigate the mitigation strategies available to enable them to meet the original project deadline.

Accelerating the project schedule involves changing some of the execution methods by selecting faster (although more costly) ones. First, the responsibility for the delays should be apportioned among the project parties. Both the traditional and the extended daily window analysis were used to compare the results.

The traditional window analysis was used first when the project was analyzed as one window of 27 days without considering the effect of resource over-allocation as shown in Fig. 5.13, the 2 days of project delay were apportioned to the Contractor.

Fig. 5.13: Traditional Window Analysis Using One Window of 27 Days Contractor Delayed Activities indicated Critical-Path has all Contractor events.

Result:

2 days project delay is Contractor Responsibility

When the extended window analysis is used, on the other hand, the analysis focused on days 8 and 9, as follows:

Window for Day 8 (Fig. 5.14): The Contractor experiences a rework event that delays

activity 4 by one day and extends the preceding activities (5 and 7) by one day so that the project duration is extended to 26 days. Adding the Owner’s rework does not change the project duration. One day delay is therefore attributed to the Contractor.

Fig. 5.14: Extended Windows Analysis - Window for Day 8 Before Owner Rework

Window for Day 9 (Fig. 5.15): The Owner forced a rework of activity 3 on day 8, which

results in an additional Owner delay for activity 3, which is caused by the rework for activity 2 that is necessary for the proper execution of the work. This delay causes an extension to activity 6 of one day, leading to a resource over-allocation on day 12, as shown in Fig 5.15.

To resolve this over-allocation, a start delay was introduced to activity 7, which leads to the extension of the project from 26 days to 27. The cause of this delay was therefore attributed to the Owner.

a) With Resource Over-Allocation

b) After Resolving Resource Over-Allocation

Fig. 5.15: Window for Day 9 After Owner Rework

Over Allocation due to slowdown

Start Delay = One day

The results of the analysis the project delays are as follows; • One day of Contractor rework delay on day 8

• One day of Owner resource over-allocation delay on day 12

Based on this analysis, the project team then investigates the options for mitigating the rework delay, as explained in the following subsection.