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Nguyen L.D.,Ho Chi Minh City University of Technology | Kneppers J.,Inc. JKA | Garcia De Soto B.,Inc. JKA | Ibbs W.,University of California at Berkeley | Ibbs W.,Ibbs Consulting Group Inc.
Journal of Construction Engineering and Management | Year: 2010

Severe weather conditions can be disruptive to construction. Contractors typically obtain time extensions for weather days beyond normal conditions. However, contracting parties often dispute the extent of weather-related time extensions. Typical industry contracts may overlook many important points that can provide an acceptable resolution. This paper classifies seven factors causing discrepancies in analysis of adverse weather for time extensions; namely, the definition of normal weather, weather thresholds, type of work, lingering days, criteria for lost days, lost days equivalent due to lost productivity, and work days lost versus calendar days lost. An analysis of an actual weather-caused delay claim illustrates the impacts of those factors on the outcomes of the analysis. A contract should define anticipated weather delay days and their lingering days and provide threshold values for weather parameters to differentiate between predictable and unpredictable severe weather. The contract should clearly define how a time extension is granted in calendar days as a result of work days lost, and also address how a time extension is granted due to inefficiency caused by unusually severe weather. Future research may provide an appropriate mechanism for analyzing equivalent lost days to account for lost productivity. © 2010 ASCE.

Ibbs W.,University of California at Berkeley | Ibbs W.,Ibbs Consulting Group Inc. | Liu M.,North Carolina State University
International Journal of Project Management | Year: 2011

Quantifying economic losses on construction projects caused by labor inefficiencies is often a difficult and tedious task. A widely accepted way to quantify such losses is by using the "measured mile" approach. This technique compares the productivity achieved during an unimpacted or minimally impacted time period with productivity realized during an impacted period. The dependability of the periods that are chosen is vital and plays a key role in the determination of merit, liability and quantum. The work performed during the measured mile period should be substantially similar to the work that was affected. As currently practiced though, choosing the periods for measured mile analysis is usually made in a largely subjective manner. The objective of this article is to introduce and illustrate the statistical clustering method as a tool for selecting the similar working periods. This new approach is advocated because it determines similarity of work condition using objective criteria. The method is agile and can be easily applied in practice by project managers or construction consultants. In this paper the factors that affect the similarity of work are identified, and the clustering procedure is developed. An example is also included to show how the method works in practice. © 2010 Elsevier Ltd and IPMA.

Nguyen L.D.,Ho Chi Minh City University of Technology | Ibbs W.,University of California at Berkeley | Ibbs W.,Ibbs Consulting Group Inc.
Journal of Construction Engineering and Management | Year: 2010

Proving and quantifying lost productivity due to cumulative impacts of multiple changes are difficult tasks. This paper presents the most acceptable methods from case law and demonstrates their applications for analyzing the loss of productivity. These methods include earned value analysis, measured mile analysis, and combinations of these two. They are either well established or drawn from recent court and board decisions. A case study is used to illustrate and compare the use of these methods. These methods result in considerably different loss of productivity values though the actual amount (i.e., inefficiency in labor hours) is unique for a particular case and though these methods are often thought to be similar or even the same. How a measured mile analysis and its variants are employed affects the amount of lost productivity estimated. The variants can avoid some drawbacks of measured mile and earned value studies. Nevertheless, which method is more accurate and reliable is difficult to provide for a particular claim. Practitioners should choose between them based on the availability of project records and the nature of changes and cumulative impacts. Practitioners may also employ two or more methods to perform a "sensitivity analysis" of the chosen methods and persuade the other party and/or the jury that their estimate of lost productivity is sufficiently certain. © 2010 ASCE.

Liu M.,North Carolina State University | Ballard G.,University of California at Berkeley | Ibbs W.,Ibbs Consulting Group Inc.
Journal of Management in Engineering | Year: 2011

Different types of flow variation and how they affect construction project performance have been studied by previous researchers. One aspect that has not been well researched is how work flow variation and labor productivity are related in construction practice. To study that issue, 134weeks of project production data were collected and analyzed to explore this relationship. Labor productivity was found to be positively correlated with Percent Plan Complete (PPC), a measure of work flow variation. The relationship between productivity and the ratio of total task completion to planned tasks, weekly workload, weekly work output, and weekly work hours was also studied, and no significant correlation was found. The results suggest that productivity is not improved by completing as many tasks as possible regardless of the plan, nor from increasing workload, work output, or the number of work hours expended. In contrast, productivity does improve when work flow is made more predictable. These findings can help project managers focus on actual drivers of productivity. It can also help consulting companies pinpoint responsibility for productivity losses in claims. © 2011 American Society of Civil Engineers.

Ibbs W.,University of California at Berkeley | Ibbs W.,Ibbs Consulting Group Inc. | Nguyen L.D.,Ho Chi Minh City University of Technology | Simonian L.,University of California at Berkeley
Journal of Construction Engineering and Management | Year: 2011

This paper focuses on the subject of concurrent delay from a general contractor (GC)-subcontractor perspective. When there is a concurrent delay by multiple subcontractors, or between the GC and other subcontractor(s), there has not been a uniform approach as to how the liquidated damages are apportioned. Previous research seems to ignore this issue. This paper first reviews some relevant court cases. Using a warehouse project as a case study, it then examines different practices that the GC could take in apportioning damages of concurrent delays to both himself/herself as well as to the responsible subcontractors. Results are very inconsistent between and within the apportionment practices. This supports an alternative hypothesis that apportionment is an important issue. Practitioners should specify which apportionment practice will be used and under what circumstances it will be applied in their subcontracts. Researchers may develop a more consistent and reliable approach for this type of apportionment. © 2011 ASCE.

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