Delay Analysis Methods – Simplified

Introduction

In my last July 2021 article[1], I provided a summary of the common delay analysis methods in the industry and in my August 2021 article[2], I explained the factors to consider when selecting and implementing the delay analysis methods. In my October 2021 article[3], I started sharing my experience on the common delay analysis methods in the industry, taking guidance from AACE International (AACE International) Recommended Practice No. 29R-03 (“AACE RP29R-03”), AACE International Recommended Practice No. 52R-06 (“AACE RP52R-06”) and the Society of Construction Law (SCL) Delay and Disruption Protocol[4] (SCL 2nd Protocol). I covered the following the following methods:
  • The Impacted As Planned Method,
  • The Time Impact Analysis Method, and 
  • The Time Slice Window Analysis.
In this current Article I discuss:
  • The As Planned versus As Built Windows Analysis,
  • The Retrospective Longest Path Analysis, and
  • The Collapsed As Built Analysis.

As-Planned versus As-Built Windows Analysis (ASAB-WA)[5]

Brief Description This method is considered to be an “Effect & Cause” analysis in that it does not simulate the impact of the delay event(s) (i.e. it is an observational method). The method starts by determining the as built critical path “contemporaneously” in windows and then identifying the delay periods at that point in time (the “Effect”). The analysis then attempts to link the delay to the claimed  event(s) (the “Cause”). It is important to note that this method differs from the As Planned versus As Built method, in that it is performed in windows and determines the contemporaneous critical path, while the As Planned versus As Built analysis is performed statically and grossly (i.e. one window) and determines the retrospective as built critical path. There are other terms which refer to the same basic method, including:
  • Windows Analysis
  • Contemporaneous analysis method
  • Contemporaneous period analysis
  • Snapshot analysis
Using the AACE International’s categorisation, this method falls under the following Observational, static logic groups:
  • 3.2 Periodic (Fixed Periods)
  • 3.2 Periodic (Variable Windows)
Product The result is usually a group of contemporaneous critical paths, together forming the as built critical path, taking account of the actual progress of works at the relevant point in time. The critical delay is calculated retrospectively (for the actual periods) as the difference between the key dates of the critical activities. The method relies on the analyst’s professional judgment in determining the critical path and delay periods. Requirements To perform the As-Planned versus As- Built Windows Analysis, the following are required:
  • A baseline program. This program does not have to be logic linked or produced using a software tool.
  • As built data – doesn’t necessarily have to be in a program format. There is no requirement to have any contemporaneous program.
Implementation Process
  • Identify the contemporaneous as built critical path in windows.
  • Compare the as built critical path to the baseline and determine the actual critical delay periods.
Limitations The method does not rely on programs or software tools and  heavily relies on the professional judgment and opinion of the analyst. Because of this subjective element, the analysis requires additional reasoning and justifications of the conclusions reached.   Suitability The method is generally suitable in cases where the purpose of the analysis is to contemporaneously assess the impact of the delay, without including a hypothetical modelling of the delay, but with less reliance on programs and software tools. Case Study In practice, the As Planned versus As Built Windows Analysis is performed in a manner similar to the Time Slice Windows analysis. The key difference is that As Planned versus As Built Windows Analysis does not necessarily rely on logic-based programs or software tools and it can measure the delay against a set of critical path activities rather than the impact on the overall completion date. Following the same case study discussed in my previous Article[6], let’s say the client asked for an As Planned versus As Built Windows Analysis. The project has 7 activities (A, B, C, D, E, F and G) (the “Project”)[7]. The Project’s baseline (the “Baseline Example”) starts on day 1 and ends on day 8. it has three paths, one of which is critical (in red), as follows: Baseline The project was actually completed on day 12. The contractor claimed that the delay was caused by two events as follows:
  • Delay Event 1 (DE1): Lack of access to activity A, 3 days (days 1 to 3 inclusive), and
  • Delay Event 2 (DE2): Lack of client supplied material 2 days (days 6 and 7).
In the first window, the analyst would likely determine that the critical path starts with Activity A. The commencement of Activity A is delayed for three days. However, the net effect is 2 critical days of delay because the activity is on a path which has 1 day of float. After investigation, the analyst would link this delay to Delay Event DE1.

ASAB-WA-Window 1[8]

In the second window, the analyst would determine that the critical path moved to Activity D and that the commencement of the activity was delayed by 4 days. However, 3 days out of these 4 days were identified in the previous window (2 days of critical delay and 1 day of float). Therefore, there is only 1 day of critical delay in this window. After investigation, the analyst would link this delay to Delay Event DE2.

ASAB-WA-Window 2

In the third window, the analyst would determine that the critical path remains in Activity D and observes that there is 1 day of further delay to the commencement of Activity D (because of Delay Event DE2). However, the analyst would also observe that Activity G is now on another critical path in this window, with 4 days of delay to the completion of the activity. However, 1 of these days occurred in the first window without causing critical delay and only 1 day out of the remaining three days would cause critical delay when compared to the delays of the previous window. This 1 day delay is not linked to any of the delay events and may be concurrent with delay event DE2[9].

ASAB-WA-Window 3

In the fourth and final window, the analyst would observe that there are three critical paths driven by Activity C, D and G. The forecast of activities D and G remained as per the previous window and therefore there is no more critical delay observed in the window.  Activity C suffered from 5 days of overall delay to its completion. However, none of these delays caused critical delays to the overall completion date (because of the float created by the other critical paths).
ASAB-WA-Window 4
 
 
 
In Summary, The As Planned versus As Built Windows Analysis demonstrated that:
  • Window 1: Delay event DE1 caused two days of critical delay on days 2 and 3,
  • Window 2: Delay event DE2 caused 1 day of critical delay on day 6,
  • Window 3: Delay event DE2 caused 1 day of critical delay on day 7. However, the contractor’s progress delays caused 1 day of concurrent critical delay on the same day 7.
  • Window 4: No further critical delay was observed.
In this case study, the As Planned versus As Built Windows Analysis produced similar results to the Impacted As Planned and the same results as the Time Impact Analysis and Time Slice Windows Analysis.

Retrospective Longest Path Analysis (RLPA)[10]

Brief Description This method is considered to be an “Effect & Cause” analysis in that it does not simulate the impact of the delay event(s) (i.e. it is an observational method). The method starts by creating an as built program and determining the as built critical path “retrospectively”. The analysis then identifies the critical delay periods comparing key dates along the as-built critical path against corresponding planned dates in the baseline program (the “Effect”). The analyst then investigates the project records to determine what events might have caused the identified critical delay (the “Cause”). The analysis is usually performed using programs and software tools. There are other terms which refer to the same basic method, including:
  • As Planned versus As Built method
  • Bar chart analysis
  • As Built bar chart method
Using the AACE International’s categorisation, this method falls under the following Observational, Static logic group:
  • 3.1 Gross
Product The result is usually an as built program along with a traced retrospective actual critical path. The critical delay is calculated retrospectively as the difference between the key activities on the critical paths. Requirements To perform the Retrospective Longest Path method, the following are required:
  • A baseline program. The program does not have to be a logic-based program.
  • As built program. The program does not have to be a logic-based program.
Implementation Process
  • Identify the retrospective as built critical path,
  • Compare the as built critical path to the baseline and determine the actual critical delay periods.
Limitations Because the software tools we generally use are planning tools, projects do not normally have logic linked as built programs. Tracing the retrospective critical path therefore might be difficult. However, the main limitation of this method is its limited capacity to recognise and allow for switches in the critical path during the course of the works. To overcome this limitation, the analysis can be performed in windows using the contemporaneous progress records. However, the analysis then becomes an “As Planned versus As Built Windows Analysis”.  Suitability The method is generally suitable in cases where the purpose of the analysis is to retrospectively assess the impact of the delay, without including a hypothetical modelling of the delay, with less reliance on programs and software tools but without identifying the potential switches of the contemporaneous critical path. Case Study Using the same case study analysed in previous methods, the Retrospective Longest Path Analysis starts by creating the as built program and then tracing the longest path. In this case study there are three critical paths as follows:

RLPA-As Built Program

The first path goes through activities A, B and C.  The start of activity A was delayed by 3 days (days 1, 2 and 3). Activity B was delayed by the same three days. Activity C was delayed by further 6 days, three of which were caused by the knock-on effect of the previous activities A and B 

RLPA-As Built Critical Path 1 Analysis

The second critical path goes through Activities A, D and E. There is an overall of 5 critical days delay on the path. These delays are caused by delay events DE1 (3 days) and DE2 (2 days) as follows:

RLPA-As Built Critical Path 2 Analysis

The third path goes through activities F and G. Activity F is delayed by 1 day and Activity G is delayed by four days, one of which is caused by Activity F delays. These delays are not linked to any of the claimed delay events.

RLPA-As Built Critical Path 3 Analysis

Effectively, there are three critical paths on the project. The Retrospective Longest Path analysis looks backwards at the paths, identifies the as built critical path and ignores the contemporaneous critical path, which may be different (e.g. the critical paths identified in the previously analysed methods, in windows). The decisions relating to the longest path and critical delay period requires professional judgment and has a subjective element. For example, it may be argued that the true longest path was going through Activities F and G which were not impacted by any of the delay events. In this case, the contractor may not get any extension of time.

RLPA- Summary of As Built Critical Paths (highlighting path not impacted by Delay Events)

The contractor may argue that the critical path was going through activities A, D and E, which were impacted by Delay Events 1 and 2. In the Retrospective Longest Path Analysis, the project is reviewed in one window and therefore the critical paths are likely to be treated equally. Therefore, the Retrospective Longest Path method in this instance would be vulnerable to arguments that the full 4 days of delay to the completion (i.e. day 8 to day 12) was concurrent

Collapsed As-Built Analysis (CAB)[11]

Brief Description This method is considered as a “Cause & Effect” analysis in that it does simulate the impact of the delay event(s) (i.e. it is a modelled method). The method starts by reviewing or creating an as built program “retrospectively”. The analysis then models the impact of the delay events on the as built program. The retrospective critical path is determined and the critical delay periods are identified by extracting the delay events from the as built program (the “Effect”). The method is sometimes performed in windows. There are other terms which refer to the same basic method, including:
  • But-for analysis
  • Modified as built
  • Time impact technique
  • Forensic scheduling
  • But-for-Backward Analysis
  • Collapsing technique
  • Impacted as built
  • As built less delay analysis
  • As built subtracting impacts
  • Modified but-for
  • Apportionment Delay Method
Using the AACE International’s categorisation, this method falls under the following Modelled, Subtractive groups:
  • 8 Single Simulation (Global and stepped extraction)
  • 9 Multi Simulation (Fixed periods and stepped extraction))
Product The result is usually an as built program along with simulated delay impacts. The critical delay is calculated retrospectively as the difference between the completion dates of the as built program and the as built program but for the extracted delay event(s). Requirements: To perform the Collapsed As- Built Analysis, the following are required:
  • As built program. The program needs to be logic-based so that it can simulate the critical path but for the delay events.
  • A selection of delay events to be modelled on the as built critical path.
Implementation Process
  • Review or create the as built program,
  • Model the delay events on the as built program,
  • Extract the delay events and assess the resulting critical path,
  • Determine the critical delay periods.
Limitations Because the software tools we generally use are planning tools, projects do not normally have logic linked as built programs. This method requires a logic based as built program that is capable of simulating the critical path but for the delay events. It is time consuming and difficult to reconstruct a logic linked as built program. The other main limitation to this method is its limited capacity to recognise and allow for switches in the critical path during the course of the works. The method measures only incremental delay to the critical path, because the completion date will not collapse further than the closest near critical path. Suitability The method is generally suitable in cases where the purpose of the analysis is to retrospectively assess the impact of the delay events, where there is no specific need to identify the critical path of the project. This method’s key advantage is that it does not require a baseline program. Case Study Similar to the Retrospective Longest Path analysis, the Collapsed As Built Analysis starts by creating and/or reviewing the As Built program, including the as built effect of the delay events. Using the same case study analysed in the previous method discussions, the project would have three critical paths as follows:

CAB – As Built Program

There are two delay events to analyse. The as built program can be collapsed once (two events at the same time) or in windows (1 event each time). For the purpose of this case study, I will analyse the delay in two windows. The As Built program finished on day 12. But for Delay Event DE2, the project would have completed on the same day 12 i.e. delay event DE2 did not cause critical delay.

CAB-  As Built Program – DE2 Extracted

Similarly, but for Delay Event DE1, the project would have completed on the same day 12 i.e. delay event DE1 did not cause critical delay.

CAB-  As Built Program – DE1 and DE2 Extracted

As has been determined in the iterative methods such as Time Impact Analysis and Time Slice Windows Analysis, the order of the delays is crucial in determining the delay events that impacted the actual critical path. The Collapsed As Built method identifies that after you remove DE1 and DE2, the maximum entitlement to an EOT is only 3 days (i.e. day 9 to day 12).  This is because the Collapsed As Built method demonstrates that Activity C would not have been completed until at least day 9 – even after DE1 and DE2 had been removed. If we take out that the critical path of activities F and G, the critical delay caused by Delay Events DE1 and DE2 would be 3 days only (day 12 minus 9).  This is because the Collapsed As Built CAD method demonstrates that Activity C wouldn’t have been completed until at least day 9 – even after DE1 and DE2 had been removed. Therefore, the Collapsed As Built method in this instance would be vulnerable to arguments that the full 4 days of delay to the completion (i.e. day 8 today 12) was concurrent.”

Summary and Recommendation

In this article and the previous one[12], I summarised the key delay analysis methods in the industry and linked the Society of Construction Law Delay and Disruption protocol’s 6 key methods with the AACE International’s 9 retrospective forensic scheduling groups. In practice, the selection of the delay analysis method requires professional judgment of the analyst considering the factors which I discussed in my previous articles. In my next Articles, I’ll discuss the approach I follow personally including the identification of the critical path, analysing the delays and structuring the delay report.

Disclaimer: This article is intended to provide an update on the current industry practice in terms of delay analysis.  However, it does not in any way constitute any type of legal or professional advice. 

[1] Delay Article 1: https://www.astonconsult.net/delay-analysis-what-is-the-most-appropriate-method/ [2] Delay Article 2: https://www.astonconsult.net/delay-analysis-methods-factors-to-consider/ [3] Delay Article 3: https://www.astonconsult.net/delay-analysis-methods-simplified-1-2/ [4] 2nd Edition, February 2017 [5] SCL 2nd Protocol, 11.5 (d) [6] Delay Article 3: https://www.astonconsult.net/delay-analysis-methods-simplified-1-2/ [7] This example scenario will be used for the 6 methods discussed in this article [8] While the figures identify the remaining activities as though it had been calculated by software (in the same manner as Time Slice Analysis), the order, logic and criticality of these remaining activities are the analyst’s view and interpretation of the remaining activities using their knowledge of the project, judgement and experience [9] Changing the window period will likely change the result (e.g. daily windows may demonstrate that the progress delay was not critical).  [10] SCL 2nd Protocol, 11.5 (e)  [11] SCL 2nd Protocol, 11.5 (f)  [12] Delay Article 3: https://www.astonconsult.net/delay-analysis-methods-simplified-1-2/
2021-11-23T02:40:46+00:00 November 23rd, 2021|Insights, News|0 Comments