*3.3. Stepwise Insertion without Using Constraints*

All delay events are incorporated step-by-step and chronologically into an as-planned schedule using the approach. A delayed event or a fragnet should only be placed into the as-planned schedule by connecting them to logically linked predecessor and successor activities according to Kim and Kwon [21], and constraints should not be used. As shown in Figure 6, they are pointing out that if the delay event (the activity X) is added into the network by using constraints based on its actual start and finish date, the delay of the project completion could be overestimated.

**Figure 6.** Overestimation of a delayed impact.

This approach requires adding the delay event with its duration into the network and connecting it to its logical predecessor and successor without changing anything of the as-planned schedule and without considering the actual start and finish date of the delay event. As the constraints reflect the actual date of each delay, but the as-planned schedule does not reflect updated actual progress, this approach needs only the duration of the delay event and logical relation should be employed and that constraint on the delay event should not be given.

The process to analyze delay impact in stepwise insertion without constraints is as follows: The IAP schedule by "delay event 1" is the same as Figure 3. The project is delayed as much as 5 days. The owner is liable for the delay, which is classified as an "EC" type. Figure 7 shows the IAP schedule by "delay event 1" and "delay event 2" on the planned schedule. As delay event 1 modified the critical path, there is no extra delay. Therefore, delay event 2 does not have an extra impact on the duration of the project. Here, delay events 1 and 2 are identified as concurrent delays, which is the type of "excusable and non-compensable (EN)" delay.

**Figure 7.** Impact of delay events 1 and 2.

"Delay event 3" happened for 5 days, and it had an impact on the start of activity G (Figure 8). To calculate the impact on the duration of the project, the delay event should be added to the as-planned schedule. The delay event 3 happened after "activity F" and had an impact on the start of "activity G". Activity F was completed 3 days earlier than planned. However, the IAP does not consider the actual performance of the as-planned schedule, as well as the actual start and finish date of the delayed event [17]. Therefore, the delay event 3 connected just to activity F as its logical predecessor and activity G as its logical successor.

**Figure 8.** Impact of delay events 1, 2, and 3.

Figure 8 shows the IAP schedule by delay event 3. In addition, the project is 5 days behind schedule. The owner is responsible for the delay, which is classified as an "EC" type. It is analyzed as the total delay of this project is 10 days: 5 days are concurrent delays and 5 days are owner-caused delays.
