The snapshot analysis technique consists of two major steps: the first is to determine the amount of delay that occurred on a project, and when the delay occurred; the second is to determine the cause or causes of the delay. The analysis uses the available schedules (mainly from the Contractor), called original or as-planned schedules, the actual or as-built schedule as it is compiled from different sources (as explained earlier) and any revised schedules that

may have been issued and/or used during the execution of the project In order to analyze the delays (or acceleration) on a project, the project duration is divided into a number of

time periods (windows). The amount of delay for each time period is calculated, and the reasons for the delay are then evaluated.

The breakdown of the project duration into time periods is achieved through the selection of a series of dates. Each date represents the end of one period and the beginning of the subsequent period. The dates are selected to coincide with major project milestones, including the implementation of significant changes in planning, in orde to isolate major known delays or group of delays.

Typically, delays (if any) in the interim are determined by comparing the planned completion date, as determined by the schedule in effect at the beginning of a period, with the projected completion date at the conclusion of that period. The project’s delay during that time is what caused the discrepancy between these dates. Once the duration of the delay that took place at that time is established, its reasons are evaluated.

Accordingly, the schedule is altered and used for the following period if the updated schedule is no longer thought to be valid due to changes in planning. The gap between the updated schedule’s expected completion dates and the corresponding revised schedule’s completion dates serves as a gauge for the degree of planning adjustments’ ability to accelerate (or relax) the timetable.

The process should be performed as many times as there are selected snapshot dates (or periods), and for each period, the delay, acceleration, or on-time progress is assessed in a second phase to determine the effectiveness of the analysis.

Steps to Follow

• Based on the schedule updates and the frequency of their availability, determine the time frame periods (usually 1 to 2 months).
• Start with the schedule update available at the beginning of the examined project time frame and consider it as the first as-planned schedule for the first period (provided that prerequisites for a valid as-planned schedule are satisfied as per the earlier section on evaluating and preparing the as-planned schedule).
• Copy the schedule update available at the beginning of the period.
• Status the copy created above at the end of the period from the information available in the next schedule update.
• Run the new schedule at the end of the period—the result is a snapshot schedule.
• Compare the resulting snapshot schedule at the end of the period with the planned schedule (update) at the beginning of the same period.
• Examine and assess the resulting delays (as described in the following section).

2. TIME IMPACT ANALYSIS

This approach is predicated on the analysis of delayed events as they happen. Therefore, this technique and the previously discussed snapshot technique differ significantly in two key ways.

The first difference is that in the case of TIA, the identification and quantification of the delay-causing events should be made before performing the analysis. The delay analysis will be restricted to determining the effect of these events.

The choice of the window durations is the other significant variation. In the snapshot method, the windows are determined by the availability of a schedule update at the end of each period, while in this approach it is the delaying event itself that dictates the beginning or the end of a period.

The TIA approach calls for inserting a delaying event or events (if within a reasonably short time frame) into a status schedule, that reflects the status of the project at the specific time of these events. A concern arises here, since the status schedule is usually not contemporaneously available (unless a delaying event coincides with a schedule update).

However, the status schedule is probably constructable from contemporaneous documents.

Steps to follow

• Assemble a list of delay-causing events in chronological order—identify the type of delay for each (excusable, compensable, etc.).
• Select the as-planned schedule that corresponds to the first delay-causing event.
• Update or status the above as-planned schedule at the time of the first delay-causing event starts—this is the status schedule.
• Insert the first delay-causing event into the status schedule and run the schedule—this is the impacted status schedule.
• The difference between the resulting completion dates of the impacted status schedule and the status schedule(if any) is the result of the inserted event.
• Repeat the process for the other events.
• Sum up the results

This approach must be used immediately and at the time the delay event happened for it to be effective. In other words, it is much easier to establish the status of the job from available documents on an ongoing project than on a completed project. However, this method is widely used as an after-the-fact approach and is being accepted as the preferred approach in many jurisdictions and on many cases.

The outcome of any delay-inducing event entered will be compared to the status schedule for the final assessment within a predetermined time frame. Similar to what was discussed in the snapshot section, an assessment of the delay(s) will be made. When used on modest projects with a controlled amount of delay events, TIA is a very reliable and effective strategy. Applying it to big networks with numerous delaying events (excuseable or not) could, however, make it very difficult, if not impossible.

3. WINDOW IMPACTED THEN PLANNED SCHEDULE

This approach is an improvement or correction to the well-known and established impacted as-planned schedule method, also known as the schedule entitlement method on occasion.

The typical technique considers the construction project as one giant window encompassing the entire era, however this approach just examines a window affecting intended duration. With this improved version, the entire time is divided into smaller chunks, enabling the use of interim schedule updates that take into account the actual plan, the current situation, and the dynamic character of the schedule. As a result, it takes into account the available delay-causing events for the same period and updates the schedule as anticipated for that period.

It resembles the time impact analysis method in several ways, with the exception that we are not required to create a status schedule at the moment the delay-causing event occurred. The limitation imposed by the frequency of schedule changes, which may or may not coincide with a delay occurrence, is the disadvantage, on the other side. When a new schedule update becomes available, the window under examination closes at the start of the subsequent window.

This method works best when adding a number of delay-causing events into a single schedule and evaluating their impact as a collection of, say, excusable or compensable delays on the schedule’s completion (if connected and occurring within a suitable time frame that coincides with the analyzed window). Comparison of the Window Direct Critical and Near Critical PathsThe straightforward comparison of two schedule updates inside a certain time period. One depicts the initial period’s intended timetable for a few specific tasks, and the other

provides the schedule as-built for the same chosen activities, over the same time period. The important and near-critical activities that were taken out of the scheduled timetable as the selected activities are typically those. TheFrom the contemporaneous records that are often available, such as the timetable, a similar as-built is produced.

Despite the fact that it seems to be a very simple and straightforward strategy, the dynamic nature is taken into consideration when employing the CPM critical route with the updated schedules. It has several unstated presumptions and flaws that could force the analyst to reevaluate and, in some cases, change course.

For instance, one can assume that the critical path is fixed for the duration of the window period if they heavily rely on the intended critical path and adopt it.

If the critical routes are the same at the start and the end of the analyzed period, which is a rare circumstance, then this might be the case.

This approach views delay analysis as more of a science than an artistic endeavor. The critical path must be acknowledged as the genuine, real, or following critical path in order for this strategy to be accepted and considered credible. Its optimum use may be as weekly or monthly look-ahead schedules in situations where there was little to no change in the critical path or where schedule updates are readily available.

4. WINDOW AS-BUILT BUT FOR ANALYSIS

The but-for methodology is one of the approaches to delay analysis that is simple to describe and comprehend. Despite the numerous arguments in favor of and against its use, this approach is still widely employed and very much alive.

In conclusion, the goal of this technique is to determine how one party’s share of the overall delay will affect the timetable while leaving the other side responsible for the remaining delay. In other words, had it not been for the owner’s delay, the contractor would have finished the job on schedule (or by a certain date).

Why not use this technique periodically if it is implemented over the course of the entire project, taking into account all delays caused by either one or the other party. The as-built would be created for a window time that has been isolated, and any delays (let’s say owner-caused delays) that occurred throughout that window period would be collapsed. The difference between the completion date resulting from this collapsed schedule and the completion date of the schedule in effect for that period is the contractor’s responsibility. Not as easy as it seems. In fact there are many technical difficulties and assumptions made in this approach. This is true whether it is used for the total project or for a specific window period.

First of all, it is not simple to build the as-built timetable by matching specifics to the intended schedule for the same timeframe. The problem of reducing the schedule based on the period’s actual critical path is the next. The historical era (as-built) that the analyst is working with in this case must be collapsed into a projected period by turning it around so that the historical data is fully projected into it, just as if it were planned data. This is necessary in order to determine a more accurate critical route that takes into account the real facts. This necessitates a significant amount of subjective input regarding the logical linkages, revisions, and scope shifts that occurred during the window.