**1. Introduction**

The main objective of this study is to identify practical issues in applying impacted as-planned (IAP) delay analysis method and to suggest improved approaches to them. Currently there are some disputes on how to apply the IAP delay analysis method in practice. So, this study reviews what kind of different IAP approaches are being used, and investigates what their advantages and limitations are through a sample project network, and suggests how to improve those problems. Most construction projects are delayed [1–5]. Many of them are the subject of allegations or engage in legal battles. As a result, almost every construction project includes construction claims [5,6]. Delay analysis is a critical component of every construction project since it determines who is accountable for delays. There are various techniques for analyzing delays such as as-planned vs. as-built, impacted as-planned (IAP), as-planned but for, collapsed as-built, window analysis, time impact analysis, etc. Each technique has pros and cons in analyzing the delay.

Several researchers have investigated those techniques. By assessing the research related to delay analyses from 1982 to 11 February 2021, two primary research areas were detected in this field, namely, improving the delay analysis methods and resolving the disputes before they occur [7]. Bubshait and Cunningham [2] evaluated three delay measurement techniques (as-planned schedule method, as-built schedule method, and

**Citation:** Kim, K.J.; Han, B.; Park, M.S.; Kim, K.; Kim, E.W. Application Issues of Impacted As-Planned Schedule for Delay Analysis. *Buildings* **2022**, *12*, 1442. https:// doi.org/10.3390/buildings12091442

Academic Editors: Srinath Perera, Albert P. C. Chan, Dilanthi Amaratunga, Makarand Hastak, Patrizia Lombardi, Sepani Senaratne, Xiaohua Jin and Anil Sawhney

Received: 21 July 2022 Accepted: 1 September 2022 Published: 13 September 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

modified as-built method (time impact analysis)) and found that each delay analysis technique may have different results of delay. Stumpf [8] looked at schedule delay analysis and showed how results differed. Kao and Yang [9] compared four windows-based delay analysis methods to identify their advantages and limitations, in terms of the perspectives of use prerequisite, functional capability, analytical procedure, and accuracy of analysis results. Kim et al. [10] suggested that the result of delay analysis was differently produced depending on the type of baseline schedule, update program using as-built data or not, and approach to dealing with concurrent delay and acceleration measures. Based on a case study, Braimah [11] analyzed delay investigation techniques and identified problematic issues and their improvement needs. Arditi and Pattanakitchamroon [12] evaluated the benefits and drawbacks of commonly used delay analysis methods, as well as the impact of several factors on the selection of a delay analysis method. Although much research has been directed toward improving the use of these delay analysis approaches, the continuing difficulties associated with such claims suggest the need for additional empirical analysis into the extent of use of the approaches, their success rates in dealing with delay claims resolutions, and the obstacles affecting their appropriate implementation in practice [13].

Certain considerations must be addressed while selecting a proper delay analysis method because each delay claim is unique, and its characteristics will define which delay analysis method to implement [14]. When selecting analysis methods, it is important to consider the timing of delay analysis and the quality of available data and documents because the delay effect must be quantified using reliable data [15]. The availability of contemporaneous documentation, the quality of available schedules, and the existence of updated schedules are important factors in selecting a delay analysis technique.

There are so many cases where impacted as-planned (IAP) schedule method is the only possible option to analyze delays and who are responsible for the delays. The IAP is not recommended for dispute resolution in courts. However, many construction projects still have only baseline schedule without as-built schedules, which are routinely evaluated, monitored, and updated as a project progresses. In this instance, the sole alternative is to use the IAP. In applying IAP, however, different approaches in their details are being utilized in practice. Each approach has advantages and limitations. This research recognizes and examines some problems in applying IAP to dispute resolution and suggests how to solve them. This research outcome is projected to be helpful for delay analysts in recognizing what kinds of problems occur in IAP methods.

To achieve the research objectives, this study identifies and categorizes four different techniques which are being applied in delay analysis as the name of IAP, and introduces a sample network schedule which is simplified to analytically compare and assess four techniques. With the sample network, a scenario was given about how works have progressed. Based on the sample network and the scenario, delay analyses by four techniques were performed. In discussion, the results of the analyses, the pros and cons of each technique were compared, and the recommendations were given.
