**3. Four Approaches**

The IAP method is used to calculate the hypothetical impact of those inserted activities on a network by adding or inserting activities that represent delays or changes into a network. AACE (Association for the Advancement of Cost Engineering) International [14] recommends global or stepped insertion. This research focuses on chronological, stepped insertion since it is more generally used. In practice, delay analysis professionals use various approaches in adding or inserting the fragnet (an activity or activities representing the delay(s)) into an as-planned schedule. They can be divided into four categories. The first method involves inserting a single delay event into an as-planned schedule without additional delay events. The second approach is to insert delay events into a network in a chronological order based on the logical relationship with their predecessors and successors, without regard for the delayed events' actual dates. The third approach is to insert delay events into the network in a chronological order based on logical relation and using constraints based on the actual date of delay events. The fourth approach is to insert delay events caused by only the owner or only the contractor into the as-planned schedule. This research reviews the issues in applying these approaches and identifies improvement needs.
