Application Issues

Section 3.2.1 presented a detailed review of a standard impact analysis, which can be used for most situations. However, there are numerous analysis issues that arise during the application of this method that warrant further discussion. The following topics are aimed to resolve special case issues that may be experienced during the analysis.

Errors in As-Planned Durations

Whereas the impact analysis is generally based on the as-built duration of an impacted activity versus the as-planned duration of that activity, the accuracy of the as-planned duration becomes important. For clear-cut impacts that can be clearly identified in terms of total duration, errors in the as-planned are less important because the extension is made solely on the duration of the impact. However, in cases of modified or disrupted work where the discrete impact is difficult to separate from the rest of the planned work and the post-impact analysis is used due to uncertain scope or duration, an as-planned duration that is too short to begin with can inadvertently be included in the excusable delay calculation.

This potential over-extension of time leads to two observations. First, a reasonable, logical and well-reviewed as-planned schedule is critical. Since most Department CPM schedules are not resource loaded, the function of the Narrative and Scheduling Meeting is even more crucial to determine the full scope of the Contractor’s plan. Second, this threat stresses the importance of full and complete

documentation, especially surrounding all impacts. Detailed documentation will provide the best resource for determining the actual impacts to the project schedule. If there is a question about the as-built

duration, a measured mile analysis (see Section 2.3.2 and Appendix D) can help determine the contractor’s actual production rates and durations are, which can then be compared against what production is achieved during the impact.

For instance, suppose in the sample problem of Section 3.2.1 that it is decided that the duration of the extra work needed for the column retrofit and dimension change (Activity 8180WO) cannot be accurately separated from the planned work itself, and therefore a post-impact analysis is selected. After the completion of placing the columns, the analyst notes that the Contractor required 25 working days to complete the activity, including impact. The planned duration was 15 working days. Records and other documentation do not indicate that the impacted work really required 10 extra working days. The analyst can use the documentation to support what is felt to be the actual time extension, as it is less than the as- built duration of the activity. Furthermore, the analyst can use the actual durations compared to the planned durations on other identical spans of the bridge to support the case that the as-planned duration was too short.

Concurrent Impacts and Window Selection

Concurrent impacts are discussed in Section 1.4.5 of this manual. In cases of post-impact analysis, an issue can arise concerning the selection of the ‘window’ to use in cases of critical concurrent impacts. With single impacts occurring on a sole critical path, the window is selected to surround the dates of the actual impact as closely as possible. In cases of disruptions, the window may be selected to include the entire activity, and not simply the first and last disruption.

However, a challenge in window selection occurs when concurrent critical impacts occur, particularly since the start and completion of those impacts will rarely coincide – such as the following situation:

A 10-Day concurrent impact has occurred on a project with this dual critical path. Some methods, such as the Army Corps of Engineers technique, would suggest performing window analyses between Days 5 and 10, Days 10 and 15, and Days 15 and 20. This process, however would give 10 days of impact responsibility to the genesis of Impact Event 2, and none to the party responsible for Impact Event 1. In this case, the window should ideally be set from Day 5 through Day 20. Assuming both parties are responsible for one of the delays, the analysis would determine 10 days of concurrent delay. Entitlement would then be determined based on the table in Figure 1.4. If the event durations were not equal, as shown above, while both paths were critical, then the project has been delayed by the amount of the shorter duration. This shorter duration is also the length of the concurrent critical impact.

Usually, however, multiple impacts occurring on parallel paths are not the same duration, or are not critical for their entire duration, such as is shown below:

In this scenario, Impact Event 2 is not critical between Days 5 and 10. The Path 2 impact is non- critical until its float is consumed. Event 2 is concurrently critical with Event 1 between Days 10 and 15, and Event 1 is solely critical between Days 15 and 20. A changing critical path must be tracked and the windows selected accordingly. In these two scenarios, logic used in the But-For technique is useful in determining how to select the windows. In the first scenario, but-for either of the impacts, the other would

Path 1 Activity – 10 Days

Path 2 – 5 Days

Impact Event 1 – 10 Day Delay

Impact Event 2 – 10 Day Delay Path 2 – 5 Days

Path 1 Activity – 10 Days

Path 2 – 5 Days

Impact Event 1 – 10 Day Delay

still cause a 10-day delay. Therefore, they are fully concurrent and the window should incorporate both impacts. In the second scenario, but-for the second impact event, the first event would have caused a 10-day delay. But-for Event #1, Event #2 would have cause a 5-day delay. Therefore, the critical concurrency only runs for 5 days, and the window can either fully cover both impacts or be split at the point where Event #2 is no longer critical.

Recovery

As has been stated previously, the Contractor has the responsibility to attempt to mitigate and recover when a schedule impact has occurred. Impact recovery can happen via various means, namely: improved production rates, fewer weather impacts than expected, or accelerating or re-sequencing the work [Lehmann 2001]. Typically, there is little that the Owner can do to influence recovery. As such, recovery normally occurs when Contractor actions mitigate an ORI or CRI. If the time extension (and compensation) is agreed upon prior to the work, then the Contractor recovers time at its own cost (financially) and benefit (in time savings).

If the recovery occurs during an impact for which the post-impact technique will be used, then the Owner will share in the time savings, but will likely be responsible for any additional costs. The

completion date should not be extended past what is shown on the updated schedule if recovery does occur. If the Contractor is recovering its own impact, then the hastened completion date will act to reduce responsibility for liquidated damages. If the Owner is in some way able to bring about recovery to the schedule, such as by reduced work or modifications to a requirement or specification, then the completion date should be adjusted back as appropriate.

Float Ownership and Management

Float is the amount of time that an activity can be impacted before it becomes critical and begins delaying project completion. Float is a very important issue in impact analysis, as impacts on non-critical paths use up float up until the point they become critical. In general, float is considered a project resource that may be used by whichever party needs it. However, float is an important aspect to the Contractor’s flexibility in responding to changes and other risks, and ability to achieve the most efficient use of resources on the project [Householder and Rutland 1990]. Contractors will occasionally claim entitlement for Owner usage of float, raising the importance of Owner exposure to the implications of using float. A recommended article on float management is entitled ‘Who Owns Float?” by Jerry Householder and Hulan Rutland, printed in the Journal of Construction Engineering and Management. Schedule ‘Games’

The CPM Schedule can be manipulated to produce different desired results. The concept of the Schedule Impact Analysis is to eliminate all games in order to produce a fair and equitable resolution to impact events that may occur on the project. Nonetheless, it is important for the analyst to understand

some of the potential traps that a CPM submission, usually during the As-Planned submission, may contain which can later damage the resolution process or leave the Owner at greater risk and liability. James Zack in his article entitled “Schedule ‘Games’ People Play, and Some Suggested ‘Remedies’”, printed in the Journal of Management in Engineering, discusses some typical ‘games’ that can be played with the schedule and some suggested remedies to these games [Zack 1992]. This article is suggested ready for further understanding on the subject.