IncorporatingreworkintoconstructionscheduleanalysisHegazyAutomationinConstructio.(1)

1、AUTOMATION IN CONSTRUCTIONAutomation in Construction 20 (2011) 1051-1059Con tents lists available at Scie nceDirectELSEVIERAutomation in Constructionjournal homepage: /locate/autconIncorporating rework into construction schedule analysisTarek Hegazya,*, Mohamed Said3,1, Moustafa Kass

2、abb,1a Civil and Environmental Engineering Department. University of Waterloo, Waterloo, Ontario, Canada N2L 3G1b Systems Design Engineering Department. University of Waterloo. Waterloo. Ontario, Canada, N2L 3G1ARTICLE INFOABSTRACTArticle history:Rework has bccn a primary cause of cost and schedule

3、overruns in large construction projects While severalAccepted 5 April 2011Available online 13 May 2011research efforts have analyzed the causes and effects of rework and provided guidclincs to reduce rework, almost no research exists to analyze the impact of rework timing and quantity on schedule de

4、lays and toKeywords:Construction management ReworkDelay analysisCostAccelerationSchedulingOptimizationComputer applicationsupport decisions on cost effective recoveiy. This research presents a quantitative mechanism for schedule analysis considering rework. The mechanism has three aspects: (1) a new

5、 schedule representation of rework magnitude as negative percentage complete for affected activities, documented on the specific date on which the rework is detected; (2) a modified daily-windows delay analysis to apportion project delays among the responsible parties; and (3) an optimization techni

6、que for determining the least costly corrective action strategy that recovers project delays. The proposed approach is applied to a case study to demonstrate its ability to consider rework impac 匚 in combi nation with other progress events by other project parties. This research offers an innovative

7、 quantitntive approach to consider rework timing and amoimt in delay analysis and corrective action optimization 2011 Elsevier B.V. All rights reseived.1. IntroductionRework is a serious problem facing large and complex construction projects, particularly industrial projects that involve multiple pa

8、rties such as contractors, suppliers, and trades In such a complex environment where many activities by many parties take place simultaneously, often errorst omissio ns, and misun dcrstandings cause undesirable outcomes that have to be reworked. Rework, thus, has been defined as the effort of re-doi

9、ng a process or activity that was incorrectly implemented the first time 22. In literature, the term rework has been related to other terms such as quality deviationsM 5t Mnon-conformanceM 1,3J Mdefectsw 17, and “quality failures |4. Since rework can occur at different stages in the project life cyc

10、le, the term “field rework* has been clarified not to incorporate change orders or ofl-site fabrication errors |8.Various researchers have studied rework from different perspectives such as rework cycle, root causes, and impact on project performance |19|. |7| introduced the concept of the rework cy

11、cle in projects, where the rework itself is not done properly, thus requiring further rework in a recursive cycle that can extend project duration far beyond what is originally conceived. This concept becomes important to the understanding of the interactions* Corresponding author. Tel: + 1 519 8884

12、567x32174; fax: +1 519 888 6197. E-mail addresses: tarekuwaterloo.ca (T. Hegazy), msaidengmail.uwaterloo.ca M. Said), wkassabengmail.uwaterloo.ca (M. Kassab).1 Tel.: +1 519 888 4567x338690926-5805/$ - see front matter 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.autcon.2011.04.006among vari

13、ous project factors including rework, which can be studied using system dynamics tools 24. With respect to root causes, several studies and surveys were conducted to identify and classify the root causes of rework such as |211; 25; 6; 28; 5; |23); |8|; 20|; |26| and 16. Almost all studies reported t

14、hat rework plays a major role in cost and schedule overruns. They identified the main root causes of rework as: errors, omissions, failures, damages, poor leadership, poor communication, and ineffective decisionmaking The survey of 21, for example, reported the direct and indirect costs of rework ob

15、served in various contract types and identified rework causes related to the design team, client, site management, and subcontractors Among the various project types, industrial projects have beeneported by 16 to exercise the most cost increase due to rework.With respect to the impact of rework on p

16、roject performance, various researchers reported observations from case studies, surveys, and interviews among professionals A summary of the rework cost reported in various studies is shown in Fig. 1. W让h most studies analyzing rework-related cost performancc, 16| recommended conducting further stu

17、dies on rework impact on schedule performance The direct costs of rework, however, have been reported to be in excess of 15% of the con tract value 4,19. Using a survey of 115 civil infrastructure projects, it was revealed that the following five significant predictors accounted for 25% of the varia

18、nce in total rework cost: (1) ineffective use of information technologies; (2) excessive client involvement in the project; (3) lack of clearly defined working procedures; (4) changes made at the request of the client; and (5) insufficient changes initiated by theT. Hegazy et al. / Automation in Con

19、struction 20 (2011) 1051-10591061峠 Cost of rework (% of total project cost)s dA 二-(L)-ewsnpu-eoJ EEOO s-gc p_s ocs-ewsnpu- 一6U山(g)(寸)Abm -_ecc(9)(1) Cll (1989)(4) Abdul-Rahman (1995)(2 Josephson and Hammarlund (1999)(5) Burati et al. (1992) Love and Li (2000)(6) Nyldn (1996)Fig 1. Cost impacts of re

20、work reported in various studies, contractor to improve quality |19|. Since many rework causes emanate from the design phase, effective dcsign managcment has been reported as a key to reducing rework 211. Research undertaken by |29 who examined 161 projects revealed that design changes1 accounted fo

21、r 50% of rework costs incurred in projects.Based on the above discussion, rework clearly has a huge impact on the ability of construction projects to meet their time and cost constraints While the various studies in the literature help in recognizing the impact of rework and its root causes, no appr

22、oach has been proposed to incorporate rework within current scheduling and project control tools. The primary objective of this research is to propose a quantitative mechanism for incorporating rework into existing scheduling tools to clearly represent the evolution of progress events directly on th

23、e schedule, calculate a revised project duration, consider rework in project delay analysis, and help in devising cost- effective corrective actio ns. The research first discusses various ways that rework can affect activities and several strategies to accelerate the project to recover schedule dela

24、ys. Afterwards, the paper introduces a proposed approach for rework representation, schedule analysis, and corrective action optimization. A case study is then used to demonstrate the proposed approach and, its advantages, and future improvements 2. Rework Impact on the ScheduleDopending on the cons

25、truction schedule, there arc several situations by which a rework event can impact the project activities, completion, and resource use. Four specific cases, from a simple to a more involved case, are defined as follows:a) Rework on a single activity, without resource constraints: In this case, if t

26、he affected activity is non-criticalt the activity float can absorb the additional time needed to do the rework (if such additional time is within the activity total float). On the other hand, if the affected activity is critical, the amount of time it takes to do the rework constitutes a project de

27、lay (if no acceleration is done for the remaining part of the activity).b) Rework on a single activity, with resource constraints: a more practical case for rework impact on a schedule is when the project has limbed resources. In this case, even if the activity is non critical, the amount of time to

28、 do the rework will extend the activity duration, thus may cause a resource over allocation that, when resolved, may also lead to project delay.c) Gen era! rework case: in this general case, a rework situation affects multiple activities. For example, when a concrete column needs to be redone becaus

29、e of misalignment, rework becomes necessary in other related activities such as formwork, steel, and concrete .In this general case also, the schedule may have some activities experiencing various events such as contractor slow progress acceleration, or weather problems Therefore, rework becomes a d

30、ocumented progress event that combines with all others to impact the project time, cost, and resource useBased on this discussion, for a con tractor to qua ntitacivcly analyse the impact of rework on the project schedule, the following three steps are necessaiy:1. Record all progress events. includi

31、ng rework, and calculate the expected project delay;2. Accurately analyze the project delay to identify the number of days attributed to each party*s actions (contractor, owner, or neither)； then3. Analyze various acceleration options to determine the least costly action to recover the contractors o

32、wn delayIn terms of progress recording, this research extends the earlier research of 14| that represents the progress evolution of the project on a daily basis (calculated from the start and finish dates) for each activity (Fig. 2). The activities arc thus represented notas long bars (as in commerc

33、ial software) but as a group of adjacent cells, each is one day, making up the duration of the activity. This bar chart representation, thus, records not only the daily progress, but also the party responsible for any daily event such as work stops and their reasons / documents, etc As shown in Fig.

34、 2t if an activity is stopped for ownerelated reasons (e.g., late approval of drawings), an is shown on that day. In the same manner, if the delay is contractor- related (e.g., using slow resources), a “C is shown. In the case of events that are not attributable to the owner or contractor (e.g, weat

35、her), an uNn is shown. If an event occurs due to concurrent actions of several parties, then a combination of these three letters is shown (e.g.t “O + N or “O + C”)，with the reasons recorded as comments in the related cells. This representacion can therefore be extended to record rework events and f

36、acilitate its related calculations.It is important to note that this research assumes that all data related to resources, costs, delays, rework, and responsible parties can be collected and recorded While data collection is not part of the papers scope, the data can be obtained (to a good level of d

37、etail) from site reports, which can be daily, weekly, or month!y. With the absence of a detailed procedure for analyzing the impact of this data on the schedule and on corrective actions, the papers focus is on developing an analysis procedure that can produce as accurate results as the level of inf

38、ormation availableAs mentioned earlier, delay analysis is an important step in determining the amount of time that needs to be shortcned fromFig. 2. Progress recording.Fig. 3. Project acceleration ject duration to remain within the project deadline Delay analysis is an analytical proce

39、ss to apportion the project delays among the responsible parties 15|. One of the most credible methods described in the literature is the windows delay analysis method 29,12,13,18,27. In order to capture and consider all variations in critical path(s)f multiple baselines, and the impact of delays on

40、 resource over allocation. the Daily Windows Analysis method proposed by 12 is utilized and improved in this study to consider rework Once the amount of delay time attributable to a specific party is determined, that party can overcome its own delays through various acceleration strategies. As shown

41、 in Fig. 3, the three common types of acceleration strategies include: (1) changing the logical relations among the activities (i.e“ having more parallel, rather than sequential, relations to save time); (2) expcditing the delivciy of materials with long lead time; and (3) selecting more productive

42、construction methods (using overtime or more resources) in the projecfs critical activities to reduce project duration (sometimes referred to as schedule compression or schedule crashing). Logically, critical activities are the ones to target for crashing. However, the selection of which critical ac

43、tivity(ies) to accelerate and which of their construction method to use (slow and cheap versus fast and expensive) is basically a cost minimization problem.3. Schedule Analysis Considering ReworkThe proposed schedule analysis mechanism incorporates three main aspects: (1) new schedule representation

44、 of rework; (2) a delay analysis procedure considering rework; and (3) an optimization mechanism to accelerate the project by the number of identified delay days, in a cost effective manner. These are discussed in detail in the following subsections3.1. Representing Rework on a Single ActivityAvaila

45、ble project management tools have standardized schedule representation for the activities and their progress percentage complete, as shown in Fig. 4 This representation, as such, shows only the activitys latest status, without any details about the evolution of events that led to this status. Since

46、each activity is a continuous bar of with a given durati on, it can not show on the schedule a rework event on a specific date and with a specific amount. While it is possible to manipulate the software by splitting the activity, aciding a new activity for the rework event, and adjusting the logical

47、 relationships, this process, however, is cumbersome and con fusing for projects with a large number of activities.For better progress documentation and project control, this research proposes a new representacion of rework events on the schedule It considers rework amount as a negative percentage c

48、omplete that is assigned on a specific date to the affected activity As an example, Fig. 5 shows a concreting activity for 10 columns, with the rate of 2 columns per day (planned duration is 5 days). During construction, by the end of the third day where 6 columns were completed (1 column in day 1,

49、an accelerated progress of 4 columns in day 2, and a 1 column in day 3), the site supervisor discovered a misalignment in 2 of the previously constructed columns, which need to be redone With the amount of rework being 20% (2 columns), a UC- 20%” is added to the progress of day 3 (bottom bar in Fig.

50、 5) to signify both the progress that is done (10%) plus the obscived rework (C- 20%). As such, the activity total percent complete at the end of day 3, considering the rework amount becomes 40% (10%+ 40%+10% 20% = 40%). With this simple and logical representation, the schedule can show all the info

51、rmation about rework timing, amount, and responsibility This approach, therefore, can be a simple extension to the daily progress representation shown earlier in Fig 2. It is important to note that in practice, minor rework can happen and can possibly be accommodated within the regular work of that

52、day, thus requires no specific rework documentation on the schedule The representation in Fig. 5, therefore, is for the rework items that meaningfully impact the remaining activity progressIn terms of rework amount, the rework percentage is calculated as a percentage of the total activity quantity.

53、Having the rework represented as a negative progress, it is then possible to calculate a modified activity percentage complete (MPC%), as follows:MPC% = Actual Progress To Date (%)-Rework Amount (%)(1)Accordingly. Modified Activity Duration can be calculated as follows:Modified Activity Duration = A

54、ctual Duration To Date+ Remaining DurationWhere. Remaining Duration = Planned Duration * (1 MPC) (3)For example, in Fig. 5, the rcmaining duration of the activity after the end of day 3. according to Eq. (3), becomes 5x(1 0.4) = 3 days, as shown in the figure 3.2. Representing Rework on Multiple Act

55、ivitiesSince rework can affect more than one activity, it is important to adjust the representation to clearly show the activity that initiates the rework As such, a generic rework representation is shown in the example in Fig. 6. Fig. 6a shows a 10-day plan with all resources within the specified l

56、imit (2/day). In the first 8 days, several progress events arc shown, including work stops by the owner and the contractor. On the current progress date (day 9), a rework was identified and documented as shown in Fig. 6b In this case, where the rework affects multiple activities, a (C-25%) is recorded for activity E,Task NameBaseine OiMion% CompteteActual OrationRemainng CXiationA2 days100%2 daysOdays84 days25%1 day3 daysC2 days50%1 day1 da