8
C onstruction operations are often sensitive to weather con- ditions such as temperature, humidity, wind, rainfall and/or snow. The degree of sensitivity to these parameters varies significantly from one construction operation to another because of the specific nature of these operations and the methods used in their execution. In order to consider the unique sensitivity of individual construction operations to various weather parameters, studies have been conducted to estimate weather-relat- ed productivity losses in: masonry construc- tion [4, 12], electrical work [11], outdoor manual and equipment tasks [14], and gen- eral construction [5]. The findings of these studies have been incorporated in a deci- sion support system for estimating the impact of weather on the productivity and duration of construction activities [10]. The above studies have indicated that adverse weather has a significant impact on the productivity of many construction tasks, and accordingly is considered one of the main factors causing delays and cost overruns on construction projects [6, 7, 8, 9]. When exceptional adverse weather causes construction delays and/or cost over- runs, contractors often submit claims, requesting extension to the project comple- tion time and/or compensation for extra cost, citing adverse weather as the basis for their claims. In fact, many construction contracts include specific clauses that regu- late the basis and conditions for submitting weather-related claims such as the AIA doc- ument A201 [1, 3]. This document out- lines the general conditions of the contract and includes a specific clause (number 4.3.8) that covers “claims for additional time.” The second component of this clause (4.3.8.2) states, “If adverse weather conditions are the basis for a claim for addi- tional time, such claim shall be document- ed by data substantiating that weather con- ditions were abnormal for the period of time and could not have been reasonably anticipated, and that weather conditions had an adverse effect on the scheduled construction.” In other words, such clauses specifically stipulate that weather-related claims should be supported by appropriate documentation, substantiating that the weather conditions during construction were abnormal and unexpected and that the encountered abnormal weather condi- tions had an adverse effect on the construc- tion schedule. The first type of documentation can readily be provided by comparing actual weather conditions experienced on site to normal weather conditions as per historical weather data recorded at the closest weath- er station to that site. The production of the second type of documentation, however, is a more challenging task. It requires a satis- factory answer to the quantitative question of, “how many days did the abnormal weather conditions contribute to the expe- rienced construction delays?” The objec- tive of this article is to present a quantita- tive and effective procedure that assists in providing an answer to this essential ques- tion. The proposed procedure uses an expanded version of a recently developed decision support system named WEATH- ER [10]. Specifically, this article presents the following. List of symbols used in this article AD—as-possible activity duration in days. BD—as-built activity duration in days. ID—ideal activity duration in days. PD—as-planned activity duration in days. F P —planned productivity factor cal- culated by WEATHER system using the normal weather data recorded in previous years at the closest weather station to the con- struction site; F A —as-possible productivity factor calculated by WEATHER system using the actual weather data encountered during construc- tion, also obtained from the same weather station. 12 Cost Engineering Vol. 44/No. 8 AUGUST 2002 Analyzing Weather-Related Construction Claims Dr. Osama Moselhi, P.Eng. and Dr. Khaled El-Rayes TECHNICAL ARTICLE A BSTRACT : Adverse weather is considered one of the main factors causing delays and cost overruns on construction projects. These adverse effects often prompt contractors to submit claims for additional time and/or cost on the basis of unexpected weather conditions. The analysis of such claims is a challenging task because of the difficulties associated with quantifying the extent of construction delays caused by adverse weath- er conditions. This article presents an effective procedure for quantifying the impact of weather conditions on construction productivity, project schedule, and associated delays. The procedure uses a decision support system, named WEATHER, designed to facilitate the analysis of weather-related construction claims. The system has been recently expanded and is currently capable of considering various weather-sensitive construction tasks including: masonry construction, electrical work, outdoor manual and equipment tasks, earthmoving operations, construction of highway base courses and drainage layers, paving operations and general construction. An application exam- ple is analyzed to illustrate the use of the WEATHER system and demonstrate its capa- bilities in providing an objective and impartial analysis of weather-related construction claims. K EY W ORDS : Construction Claims, Claims Analysis, Construction Disputes, Weather Impact, Construction Productivity, Construction Planning and Scheduling, Highway Construction.

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Page 1: Analyzing Weather-Related Construction Claims

Construction operations areoften sensitive to weather con-ditions such as temperature,humidity, wind, rainfall and/or

snow. The degree of sensitivity to theseparameters varies significantly from oneconstruction operation to another becauseof the specific nature of these operationsand the methods used in their execution.In order to consider the unique sensitivityof individual construction operations tovarious weather parameters, studies havebeen conducted to estimate weather-relat-ed productivity losses in: masonry construc-tion [4, 12], electrical work [11], outdoormanual and equipment tasks [14], and gen-eral construction [5]. The findings of thesestudies have been incorporated in a deci-sion support system for estimating theimpact of weather on the productivity andduration of construction activities [10].The above studies have indicated thatadverse weather has a significant impact onthe productivity of many construction

tasks, and accordingly is considered one ofthe main factors causing delays and costoverruns on construction projects [6, 7, 8,9].

When exceptional adverse weathercauses construction delays and/or cost over-runs, contractors often submit claims,requesting extension to the project comple-tion time and/or compensation for extracost, citing adverse weather as the basis fortheir claims. In fact, many constructioncontracts include specific clauses that regu-late the basis and conditions for submittingweather-related claims such as the AIA doc-ument A201 [1, 3]. This document out-lines the general conditions of the contractand includes a specific clause (number4.3.8) that covers “claims for additionaltime.” The second component of thisclause (4.3.8.2) states, “If adverse weatherconditions are the basis for a claim for addi-tional time, such claim shall be document-ed by data substantiating that weather con-

ditions were abnormal for the period oftime and could not have been reasonablyanticipated, and that weather conditionshad an adverse effect on the scheduledconstruction.” In other words, such clausesspecifically stipulate that weather-relatedclaims should be supported by appropriatedocumentation, substantiating that theweather conditions during constructionwere abnormal and unexpected and thatthe encountered abnormal weather condi-tions had an adverse effect on the construc-tion schedule.

The first type of documentation canreadily be provided by comparing actualweather conditions experienced on site tonormal weather conditions as per historicalweather data recorded at the closest weath-er station to that site. The production of thesecond type of documentation, however, isa more challenging task. It requires a satis-factory answer to the quantitative questionof, “how many days did the abnormalweather conditions contribute to the expe-rienced construction delays?” The objec-tive of this article is to present a quantita-tive and effective procedure that assists inproviding an answer to this essential ques-tion. The proposed procedure uses anexpanded version of a recently developeddecision support system named WEATH-ER [10]. Specifically, this article presentsthe following.

List of symbols used in this article

AD—as-possible activity duration indays.

BD—as-built activity duration in days.ID—ideal activity duration in days.PD—as-planned activity duration in

days.FP—planned productivity factor cal-

culated by WEATHER systemusing the normal weather datarecorded in previous years at theclosest weather station to the con-struction site;

FA—as-possible productivity factorcalculated by WEATHER systemusing the actual weather dataencountered during construc-tion, also obtained from the sameweather station.

12 Cost Engineering Vol. 44/No. 8 AUGUST 2002

Analyzing Weather-RelatedConstruction Claims

Dr. Osama Moselhi, P.Eng. and Dr. Khaled El-Rayes

TECHNICAL ARTICLE

ABSTRACT: Adverse weather is considered one of the main factors causing delays andcost overruns on construction projects. These adverse effects often prompt contractorsto submit claims for additional time and/or cost on the basis of unexpected weatherconditions. The analysis of such claims is a challenging task because of the difficultiesassociated with quantifying the extent of construction delays caused by adverse weath-er conditions. This article presents an effective procedure for quantifying the impact ofweather conditions on construction productivity, project schedule, and associateddelays. The procedure uses a decision support system, named WEATHER, designedto facilitate the analysis of weather-related construction claims. The system has beenrecently expanded and is currently capable of considering various weather-sensitiveconstruction tasks including: masonry construction, electrical work, outdoor manualand equipment tasks, earthmoving operations, construction of highway base coursesand drainage layers, paving operations and general construction. An application exam-ple is analyzed to illustrate the use of the WEATHER system and demonstrate its capa-bilities in providing an objective and impartial analysis of weather-related constructionclaims.

KEY WORDS: Construction Claims, Claims Analysis, Construction Disputes, WeatherImpact, Construction Productivity, Construction Planning and Scheduling, HighwayConstruction.

Page 2: Analyzing Weather-Related Construction Claims

Cost Engineering Vol. 44/No. 8 AUGUST 2002 13

• a quantitative procedure for analyzingweather-related construction claimsthat uses an expanded version ofWEATHER system;

• validation of the developed procedure;and

• an application example to illustrate theuse of the procedure and demonstrateits capabilities.

Analysis of Weather-RelatedConstruction Claims

An objective analysis of weather-relat-ed construction claims requires the quan-tification of the impact of weather condi-tions on the construction schedule andconsequent delays. This impact can beidentified by analyzing the “as-planned,”“as-built,” “ideal,” and “as-possible” sched-ules (see Figure 1). In this article, the term“as-planned schedule” is used to refer tothe schedule prepared and submitted bythe contractor as part of the contract docu-ments, accounting for the prevailing nor-mal weather conditions expected on thejob site. The term “as-built schedule” isused to describe the actual schedule ofactivities as constructed on site. Also, theterm “ideal schedule” is used to describe aschedule that does not consider any delays

Start

Retrieve the as-planned schedule

Step 1: Generate the ideal schedule using:a) weather data from previous years; and

b) WEATHER system to calculate productivity factor Fp, andapply Eq. [3]

Step 2: Generate the as-possible schedule using:a) weather data recorded during the construction period; andb) WEATHER system to calculate productivity factor FA, and

apply Eq. [4]

Calculate weather-related delays by comparingthe as-possible schedule to the as-planned schedule

Calculate non-weather-related delays by comparingthe as-possible schedule to the as-built schedule

End

Figure 1—Analysis of Weather-Related Claims

Figure 2—As-Possible vs. As-Planned Schedule

Page 3: Analyzing Weather-Related Construction Claims

14 Cost Engineering Vol. 44/No. 8 AUGUST 2002

due to weather, and the term “as-possibleschedule” is used to describe the schedulethat would have been possible given theactual weather conditions experienced onsite. It should be noted that the “idealschedule” has no practical value and isused in this article as a reference base inperforming intermediate calculations lead-ing to the development of the “as-possibleschedule” (see Figure 1). Accordingly, theduration of a construction activity in an as-planned schedule (PD), as-built schedule(BD), ideal schedule (ID), and as-possibleschedule (AD) can be estimated as follows:

[1] PD = as - planned duration accountingfor expected normal weather condi-tions.

[2] BD = actual duration experienced onsite.

[3] ID = PD x FP

[4] AD = IDFA

Where,

FP planned productivity factor calculatedby WEATHER system using the nor-mal weather data recorded in previousyears at the closest weather station tothe construction site;

FA as-possible productivity factor calculat-ed by WEATHER system using theactual weather data encountered dur-ing construction, also obtained fromthe same weather station.

The factors FP and FA are calculatedusing a decision support system namedWEATHER. The system runs on MicrosoftWindows NT and 2000 and provides user-friendly interface to facilitate its use.WEATHER [10] was developed to estimatethe impact of weather conditions on con-struction productivity and schedule, usingfunctions, tables and/or rules of thumb.The application of WEATHER was limitedto the construction tasks of masonry con-struction, electrical work, outdoor manualand equipment tasks and general construc-tion. In order to provide a wider range ofpotential applications, WEATHER hasrecently been expanded to consider com-mon highway construction activities.

A set of if-then type rules has beendeveloped and incorporated in the expand-ed version of WEATHER to quantify theimpact of weather on the productivity andduration of highway construction opera-tions. The rule set covers four main activi-ties: earthmoving; construction of basecourses; construction of drainage layers;and paving operations. The rules wereacquired from experts in highway construc-tion, who indicated that weather-relatedproductivity losses for these tasks dependmainly on: the type of activity; intensity ofrainfall; period of rainfall; and drying con-ditions on site.

Construction MonthDistrict May June July August September October November

(1) (2) (3) (4) (5) (6) (7) (8)1 15 20 20 20 18 15 142 15 20 20 20 18 14 123 15 19 20 20 18 14 124 17 19 20 20 17 16 135 15 19 20 20 18 13 116 17 18 20 20 18 15 13

Table 1—Ministry of Transportation of Ontario Contract Working Days

Figure 3—As-Possible vs. As-Built Schedule

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Cost Engineering Vol. 44/No. 8 AUGUST 2002 15

Accordingly, a set of approximately200 rules of thumb has been developedand incorporated in the system to estimatethe impact of these factors on the produc-tivity of highway construction operations. Asample rule is shown below and others areincluded in Appendix I.

“If the construction task is earthmov-ing, and the amount of accumulated rain-fall exceeds 13 mm and is less than 25 mm,and the rain occurs in the morning workinghours from 8 a.m. to noon, and the dryingconditions on site after rain is average, thenthe earthmoving operations will be sus-pended during the rainy day and the fol-lowing day.”

In the developed rules, the intensity ofrainfall is expressed by the total amount ofrain accumulated during a given period ofthe day. The intensity of rainfall has beengrouped into four main classes bounded bythreshold values of 1/8, 1/4, 1/2 and 1-inchof rain (i.e. 3, 6, 13 and 25 mm). The peri-od of rainfall has been classified into fourmain periods (i.e., overnight, morning,afternoon, and combined morning andafternoon) based on the construction peri-od of a working day. The drying conditions

on site have been grouped into three maincategories (i.e. good, average, and poor)depending on the soil conditions, availabil-ity of drainage system, and prevailingweather conditions after rainfall that affectthe evaporation of the accumulated rainsuch as sunshine hours and wind.

The application of the incorporatedrules of thumb, tables and functionsrequires the utilization of a weather data-base that contains hourly records of rain,snow, temperature, wind and humidity.The database represents historical andactual weather conditions experienced onsite and therefore should be obtained fromthe closest weather station to the site.WEATHER currently incorporates histori-cal weather database for a period of over 30years obtained from five weather stations intwo major Canadian cities (Montreal andToronto). The system, however, is alsodesigned as a portable system that caninterface with weather databases for othercities, where data is available.

The application of WEATHER systemfacilitates the analysis of weather-relatedclaims and enables the quantification ofthe impact of weather conditions on theproductivity and duration of constructionactivities. For example, consider an earth-

moving activity that was scheduled to havean as-planned duration of 36 days (PD =36) which accounts for the prevailing nor-mal weather conditions expected on thejob site. During construction operations,however, assume that the activity was con-structed in an as-built duration of 50 days(BD = 50) because of the impact of adverseweather conditions among other factors. Inorder to consider only the impact of theencountered adverse weather conditions,an as-possible duration needs to be estimat-ed. Using the developed set of rules ofthumb, WEATHER is first used to calcu-late the two productivity factors FP and FAdescribed earlier. These factors are thenused to calculate the as possible duration ofthe activity being considered. In this casethe planned productivity factor (FP) andthe as-possible productivity factor (FP)were calculated to be 0.83 and 0.67,respectively. Using equations [3] and [4],the two factors were then used to calculatethe ideal and as-possible durations for theactivity being considered to be 30 and 45working days, respectively. Analyzing andcomparing the as-planned, as-built, and as-possible durations reveal vital and quantita-tive information about the impact of theencountered abnormal weather anddemonstrate to what extent it contributedto the delay of the activity. In this simplifiedexample, it can be shown that the contrac-tor has suffered an excusable delay of onlynine days (i.e., AD - PD = 45 - 36 = 9)because of weather related factors, and anon-excusable delay of five days (i.e., BD -PD = 50 - 45 = 5) because of other non-weather related factors.

This method of analysis can be appliedto a single activity, a group of activities, or

Table 2—Validation Analysis for Earthmoving Operations

Ideal Finish Date DifferenceWeather Start Working Calendar % of calendar daysStation Date Days MTO WEATHER Days in construction period

(1) (2) (3) (4) (5) (6) (7)1 1-May 108 31-Oct 4-Nov -4 -2.2%2 1-May 108 31-Oct 2-Nov -2 -1.1%3 1-May 108 31-Oct 2-Nov -2 -1.1%

Average = -1.4%

Figure 4—Validation Analysis for Earthmoving Operations

Page 5: Analyzing Weather-Related Construction Claims

16 Cost Engineering Vol. 44/No. 8 AUGUST 2002

an entire project depending on the typeand size of the claim being considered. Inmost weather-related claims, the as-planned and as-built schedules are readilyavailable and can easily be analyzed. Acomparison of these two schedules revealsthe total delay experienced, if any. Thistotal delay, however, is often caused by acombination of weather and non-weatherrelated factors. An objective analysis ofweather-related construction claimsrequires the isolation and quantification ofdelays attributed only to weather. This canbe achieved by developing an “as-possible”schedule that considers the impact of onlyabnormal weather conditions encountered

during construction and comparing it tothe as-planned and as-built schedules. Thecomparison between the as-possible and as-planned schedules substantiates the effectsof adverse weather conditions on the con-struction schedule and quantifies theextent of weather-related delays (see Figure2). The comparison between the as-possi-ble and as-built schedules reveals vitalinformation on the extent of delay, if any,caused by non-weather related factors (seeFigure 3).

Unlike the as-planned and as-builtschedules which are either readily availableor can directly be generated from the proj-ect records, the development of an objec-

tive “as-possible” schedule can be morechallenging. The “as-possible” scheduleshould isolate the effects of actual weatherconditions experienced on site and quanti-fy their impact on construction productivi-ty and project schedule. In this article, the“as-possible” schedule is generated usingWEATHER, based on the readily availableas-planned schedule, in two main steps asshown in Figure 1. In the first step, theideal schedule is generated using WEATH-ER system using the following.

• the as-planned schedule;• historical weather data obtained from

the closest weather station to the site;and

• equation [3].

In the second step, the as-possibleschedule is developed using the idealschedule generated in the first step; theactual weather conditions experienced dur-ing construction, also obtained from theclosest weather station to the site; and theequation [4].

The as-planned and as-possible sched-ules, in this analysis, are developed usingthe same ideal schedule and WEATHERsystem that uses the same criteria to quanti-fy the impact of weather conditions on con-struction schedule. As such, any differencebetween the as-planned and as-possibleschedules can only be attributed to the dif-ference between the normal and abnormalweather conditions. Contrasting the as-planned, as-built and the developed as-pos-sible schedules reveals vital informationthat facilitates the analysis and resolution ofweather related construction claims (seeFigures 2 and 3). This procedure has beensuccessfully applied in the analysis of arecent multimillion-dollar weather relatedclaim. In this claim, adverse and abnormalweather conditions were encountered dur-ing construction, leading to significantdelays. In order to compensate for thesedelays and meet the specified project dead-line, the contractor had to speed up con-struction operations, and as a result hasexperienced significant productivity lossesand additional costs. The above procedurehas been applied to substantiate and quan-tify the extent of delays attributed to adverseweather conditions, and ultimately led tosuccessful negotiations and settlement ofthis claim.

Table 3—Validation of WEATHER System

Average Difference BetweenActivity MTO & WEATHER Software

(1) (2)Earthmoving Operations -1.4%Base Construction 6.7%Drainage Layer Construction 8.3%Paving 3.1%

Average = 4.9%

Figure 5—As-Planned Schedule for Paving Activity

Page 6: Analyzing Weather-Related Construction Claims

Cost Engineering Vol. 44/No. 8 AUGUST 2002 17

VALIDATION ANALYSIS

Productivity and duration estimatesproduced by WEATHER system using thedeveloped procedure for highway construc-tion operations are validated by comparingthem to those used by the Ministry ofTransportation of Ontario in Canada. Forother provinces and states in NorthAmerica, a similar validation analysis canbe performed. The Ministry ofTransportation of Ontario (MTO) identi-fies the contract working days (i.e., totalproductive working days) for the 6-monthsconstruction period (i.e., May toNovember) for different districts inOntario. These working days are estimatedbased on productivity losses caused by rain-fall patterns experienced in different geo-graphical districts within the province.Table 1 shows the contract working days fora sample of 6 of the 20 districts in Ontario.It should be noted that the working daysshown in Table 1 are applied equally to thehighway construction operations of earth-moving, base courses, drainage layer, andpaving. This assumes that the productivityof these different operations is affectedequally by the same weather conditions. Inreality, however, each construction opera-tion is affected differently. WEATHER sys-tem is designed to account for this reality inits incorporated set of rules which considerthe unique sensitivity of each constructiontask to rainfall as described earlier. As such,it is expected that the difference betweenthe estimates of WEATHER and those ofMTO will vary from one constructionoperation to another.

A separate validation analysis is per-formed for the construction activities of:earthmoving; base construction; drainage

layer construction; and paving. The firstvalidation analysis is performed for earth-moving operations by comparing the dura-tion estimates produced by WEATHER tothose produced based on MTO productivedays during the 6-months construction sea-son. For this type of construction, MTOestimates that the total productive workingdays within the construction period, May 1through October 31, to be 108 days for thecity of Toronto (see district 6 in Table 1).Accordingly, a hypothetical earthmovingactivity that starts on May 1 and requires108 productive working days (i.e., idealduration = 108) should finish on October31. This MTO-estimated finish date iscompared to that obtained using WEATH-ER system for the same activity, under nor-mal weather conditions. Normal weatherconditions here are represented by the aver-age of available hourly weather recordsfrom 1965 to 1994 in three weather stationsin the Toronto area. The results of theanalysis indicate that the finish dateobtained using WEATHER system isalmost identical to that established basedon MTO contract working days, where theaverage difference between the two is 1.4percent (see Table 2 and Figure 4). A simi-lar validation analysis was conducted forthe remaining three activities. As expected,the difference between WEATHER systemand MTO estimates varies from one con-struction operation to another as shown inTable 3. The results indicate that the finishdate obtained using WEATHER system foreach of the four activities is close to thatobtained based on the MTO contract work-ing days. The overall average difference isless than 5 percent (see Table 3).

APPLICATION EXAMPLE

An application example of a section ofa highway construction project is analyzedto illustrate the use of WEATHER anddemonstrate its capabilities in analyzingweather-related construction claims. Thesection considered includes four construc-tion activities, performed in two segmentsas shown in Figure 2 and Table 4. Each ofthese activities is constructed using a singlecrew that moves from the first to the secondsegment, sequentially. The precedencerelationships in this example satisfy joblogic and crew availability constraints. Thejob logic constraint requires, within eachsegment, precedence relationships of startto start with a lag of one calendar weekamong the four activities. This constraint isspecified to avoid space congestion andwork interference among succeeding con-struction crews within each segment of theproject. For example, the constructioncrew for the base courses activity can startin the first segment after at least one weekfrom the start of the earthmoving crew toavoid space congestion. The crew availabil-ity constraint, on the other hand, requires aprecedence relationship of finish to startwith no lag between the same activity intwo succeeding segments. For example theearthmoving crew can start in the secondsegment only after finishing the same activ-ity in the first segment.

In this example, the contract specifiesa start date of May 1, 1996, and a comple-tion date of October 4, 1996. It further stip-ulates that the owner is entitled to withholdfrom the contractor, as liquidated damages,the sum of $5,000 per day for each calen-dar day beyond the specified completiondate. The as-planned schedule submitted

Table 4—Analysis of Application Example

Pre-Analysis Data Post-Analysis DataActivity As-Planned Schedule (1996) As-Built Schedule (1996) Ideal Schedule As-Possible Schedule (1996)

Start Duration Finish Start Duration Finish Duration Start Duration Finish First Segment of Project

Earthmoving May 01 64 July 29 May 01 79 Aug. 19 52 May 01 77 Aug. 15Base Courses May 08 61 July 31 May 08 76 Aug. 21 54 May 08 74 Aug. 19Drainage Layer May 15 62 Aug. 08 May 15 73 Aug. 23 55 May 15 70 Aug. 20Paving May 22 65 Aug. 20 May 22 71 Aug. 28 57 May 22 69 Aug. 26

Second Segment of ProjectEarthmoving July 30 32 Sep. 11 Aug. 20 37 Oct. 09 25 Aug. 16 34 Oct. 02Base Courses Aug. 06 35 Sep. 23 Aug. 27 42 Oct. 23 31 Aug. 23 38 Oct. 15Drainage Layer Aug. 13 37 Oct. 02 Sep. 03 41 Oct. 29 32 Aug. 30 38 Oct. 22Paving Aug. 21 33 Oct. 04 Sep. 10 40 Nov. 04 28 Sep. 06 40 Oct. 31

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18 Cost Engineering Vol. 44/No. 8 AUGUST 2002

by the contractor as part of the contractdocuments is shown in Figure 2 and Table4. It is assumed that this schedule was pre-pared by the contractor prior to construc-tion, considering the impact of normalweather conditions on construction pro-ductivity and schedule. During construc-tion in 1996, abnormal weather conditionswere encountered in the form of heavyrainfall and cloudy conditions. This led tosignificant losses in construction productiv-ity and frequent suspensions of construc-tion operations. Accordingly, the actual as-built finish date was delayed by a total of 31calendar days beyond the specified as-planned completion date (see Table 4),holding the contractor liable to pay a totalsum of $155,000 in liquidated damages.This prompted the contractor to submit aclaim requesting time extension on thebasis of abnormal weather conditions. Inorder to analyze this claim and facilitate itsresolution, the procedure described earlieris applied in two steps (see Figure 1). Theideal schedule is generated in the first step,and the as-possible schedule in the second.

In the first step, the ideal duration orthe number of working days that can beproductive during the as-planned construc-tion period is calculated for each activity,using: 1) WEATHER system; and 2) hourlyrain data recorded in the closest weatherstation to the construction site from 1965 to

1994. It should be noted that this period ofweather data would have been available tothe contractor prior to construction inorder to prepare the as-planned schedule.The ideal durations estimated usingWEATHER system for the project activi-ties are summarized in Table 4. For exam-ple, Figure 5 shows the output of WEATH-ER system for the paving activity in the sec-ond segment. The system, in this case, esti-mates an ideal duration of 28 working days,given a) the activity's as-planned duration is33 working days and its finish date isOctober 4,1996, and b) rainfall historicaldata from 1965 to 1994. This is identical tothe original as-planned schedule for thisactivity shown in Figure 2. The ideal dura-tion for each of the four activities in thisexample was estimated in a similar mannerso as to reproduce an as-planned schedulethat is identical to that submitted by thecontractor prior to construction (see Figure2).

In the second step, the as-possibleschedule is estimated for each activitybased on: 1) the ideal duration calculatedin the previous step; and 2) the actualhourly rain data recorded at the sameweather station, but only for the calendaryear 1996. The as-possible schedule esti-mated by WEATHER system for each ofthe four activities is shown in Table 4. Forexample, Figure 6 illustrates the as-possible

schedule estimated for the paving activity.It estimates that the as-possible activityduration and its finish date based on 1996rain data to be 40 days and October 31,1996, respectively. The as-possible sched-ule at both the activity and project levels isgenerated in compliance with the job logicand crew availability constraints consid-ered in the original as-planned schedule(see Figure 2). This is achieved by usingthe WEATHER system in combinationwith any commercially available softwarefor planning and scheduling. The planningand scheduling software is used to developan as-possible schedule based on: 1) the as-possible activity durations generated byWEATHER; and 2) the original job logicand crew availability constraints of the as-planned schedule.

In order to analyze and quantify theimpact of abnormal weather conditions onthe project completion date, the generatedas-possible schedule is compared to the as-planned schedule (see Figure 2) and to theas-built schedule (see Figure 3). The firstcomparison indicates that the contractorhas suffered an excusable delay of 27 cal-endar days (see Figure 2), all attributed toweather related factors. The second com-parison shows that a non-excusable delay of4 days (see Figure 3) occurred because ofother, non-weather related, factors.Accordingly, the liquidated damages thatthe contractor could be liable for, in thiscase, should be revised from $155,000 (i.e.,$5,000 x 31 days) to $20,000 (i.e., $5,000 x4 days). The application of WEATHER inthe analysis of this example provides anobjective and unbiased estimate of theadverse effects of abnormal weather condi-tions on the schedule as it uses the samecriteria to quantify the impact of normaland abnormal weather conditions. This,accordingly, provides a realistic estimate ofliquidated damages resulting from adverseweather conditions.

Aquantitative procedure for theanalysis of weather-related con-struction claims has been pre-sented. The procedure uses a

decision support system named WEATH-ER in order to substantiate and quantifythe impact of abnormal weather conditionson the project schedule. WEATHER hasrecently been expanded to consider com-mon highway construction activitiesincluding: earthmoving, base construction,Figure 6—As-Possible Schedule for Paving Activity

Page 8: Analyzing Weather-Related Construction Claims

Cost Engineering Vol. 44/No. 8 AUGUST 2002 19

drainage layers, and paving. A set of if-thentype rules has been acquired from expertsin this construction domain for estimatingthe impact of weather conditions on con-struction productivity and project sched-ule. A total of approximately 200 rules hasbeen developed and coded in the system.The results obtained from WEATHERusing these rules were validated by com-paring them to those produced based onthe Ministry of Transportation of Ontariodata on productive days. The validationanalysis indicates close agreement betweenthe results obtained using the two methods,with an average difference of less than fivepercent. WEATHER can be used to gener-ate an objective and impartial as-possibleschedule that considers the impact ofencountered adverse weather conditionson construction productivity. Comparingthe generated as-possible schedule to thereadily available as-planned and as-builtschedules reveals vital quantitative infor-mation on the extent of construction delayscaused by weather and by non-weatherrelated factors. This facilitates the quantifi-cation of damages arising from adverseweather conditions and assists in negotiat-ing equitable and speedy resolution ofweather-related construction claims. �

APPENDIX I

Sample If-Then Rules

Rule 1—"If the construction task isearthmoving, and the amount of accumu-lated rainfall exceeds 6 mm and is less than13 mm, and the rain occurs in the morningworking hours from 8 a.m. to noon, and thedrying conditions on site after rain is aver-age, then the earthmoving operations willbe suspended during the morning andafternoon of the rainy day."

Rule 2—"If the construction task isconstruction of highway base courses, andthe amount of accumulated rainfallexceeds 6 mm and is less than 13 mm, andthe rain occurs in the morning workinghours from 8 a.m. to noon, and the dryingconditions on site after rain is average, thenthe activity will be suspended during themorning of the rainy day."

Rule 3—"IF the construction task isearthmoving, and the amount of accumu-lated rainfall exceeds 6 mm and is less than13 mm, and the rain occurs in the after-noon working hours from 13:00 to 18:00

p.m., and the drying conditions on site afterrain is average, then earthmoving opera-tions will be suspended during the after-noon of the rainy day."

Rule 4—"If the construction task isearthmoving, and the amount of accumu-lated rainfall exceeds 6 mm and is less than13 mm, and the rain occurs in the morningworking hours from 8 a.m. to noon, and thedrying conditions on site after rain is poor,then the earthmoving operations will besuspended during the morning and after-noon of the rainy day and a following day."

REFERENCES

1. American Institute of Architects AIA 1987.General Conditions of the Contract forConstruction. AIA Document A201,Washington D.C.

2. Baldwin, J.R., J.M. Manthei, H. Rothbart,and R.B. Harris. 1971. Causes of Delay inthe Construction Industry. ASCE Journalof the Construction Division, 97(CO2):177-187.

3. Clough, R.H., and G.A. Sears. 1994.Construction Contracting. Sixth edition,John Wiley and Sons Inc., New York.

4. Grimm, C.T., and N.K. Wagner. 1974.Weather Effects on Mason Productivity.ASCE Journal of the ConstructionDivision, 100(CO3): 319-335.

5. Koehn, E., and G. Brown. 1985. ClimaticEffects on Construction. ASCE Journal ofConstruction Engineering andManagement, 111(2): 129-137.

6. Isom, S. 1985. Weather Delay TimeExtensions. Highway & HeavyConstruction, July 1985: 41.

7. Koehn, E., and D. Meilhede. 1981. ColdWeather Construction Costs and Accidents.ASCE Journal of the ConstructionDivision, 107(CO4): 585-595.

8. Korman, R., S.W. Setzer, and M.B.Powers, 1992. Rains Wreck SummerSchedules. Engineering News Record,McGraw-Hill Construction Weekly,August 31: 6-7.

9. Laufer, A., and D. Cohenca, 1990. FactorsAffecting Construction Planning Outcomes.ASCE Journal of ConstructionEngineering and Management, 116(1):135-156.

10. Moselhi, O., Gong, D., and El-Rayes, K.1997. Estimating Weather Impact onDuration of Construction Activities.Canadian Journal of Civil Engineering,24(3): 359-366.

11. National Electrical ContractorsAssociation, 1974. The Effect ofTemperature on Productivity. Washington,D.C.

12. Sanders, S. R., and H.R. Thomas, 1991.Factors Affecting Masonry-Labor

Productivity. ASCE Journal ofConstruction Engineering andManagement, 117(4): 626-644.

13. Smith, G. R., and D.E. Hancher. 1989.Estimating Precipitation Impacts forScheduling. ASCE Journal ofConstruction Engineering andManagement, 115(4): 552-566.

14. U.S. Army Cold Regions Research andEngineering Laboratory, 1986. Firms FaceFrigid Facts. Engineering News Record,March 20: 168 pp.

About the Authors:

Dr. Osama Moselhi,P.Eng., is professor andchair of the Departmentof Building, Civil andE n v i r o n m e n t a lEngineering at Concordia

University. He held several industrial and aca-demic posts in Canada and internationally, in awide spectrum of the engineering profession,ranging from structural analysis and design toconstruction engineering and management, onbuilding projects, and heavy civil engineeringincluding bridges, offshore and harbor facilities,and nuclear power plants. Dr. Moselhi is a pro-fessional engineer and a member and director ofa number of professional associations. He is aFellow of ASCE and CSCE. He authored andco-authored over 150 scientific publications.

Dr. Khaled El-Rayes isan assistant professor inthe Department of Civiland EnvironmentalEngineering at theUniversity of Illinois at

Urbana-Champaign, specializing in the devel-opment of information technology and decisionsupport systems for construction engineeringand management applications. He has over 15years of professional experience in both acade-mia and the construction industry. Prior to join-ing the University of Illinois at Urbana-Champaign in 2000, he was an assistant profes-sor of civil engineering at Concordia Universityand the University of Newfoundland in Canada.He has also industrial and consulting experi-ence in planning and scheduling, constructionproductivity, highway construction, and infor-mation technology applications in construction.