MODEL FOR SCHEDULING AND ANALYZING CONSTRUICTION 1/2 .
1A MODELFOR SCHEDULING AND ANALYZING CONSTRUICTIONHEATHER DELAYS(U) PENNSYLVANIA STATE UNIV UNIVERSITYPAIK DEPT OF CIVIL ENGINEERING F A CANTHELL DEC 9?ASSIFIE N2G-95G-32?SF/O12/3AD-A165 624ALiCL1/2NI.
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OMl FILE COPY/0.The Pennsylvania State UniversityThe Graduate SchoolinDepartment of Civil Engineering'--aAModel for Scheduling and AnalyzingConstruction Weather DelaysA Report inCivil EngineeringbyFrank Anthony CantwellSubmitted in Partial Fulfillmentof the Requirementsoffor the DegreeMaster of Engineering'SEP251987"ADecember 1987I grant the Pennsylvania State University thenonexclusive right to use this work for the University's ownpurposes and to make single copies of the work available tothe public on a not-for-profit basis if copies are nototherwise available.IIrJprr,'Anthony 1"antwell.',Frank." 'n,. . l ' ed-:it38791811A.,0"
We approve the report of Frank Anthony Cantwell.Date of Signaturee93/-87.Gar.Smith, AssistantPr essor of Civil EngineeringReport AdvisorMichael S. Bronzini, Professorof Civil Engineering, Head ofthe Department of CivilEngineeringQUALI"*125','"'L1
iiiTABLE OF CONTENTSLIST OF TABLES . vLIST OF FIGURES . viACKNOWLEDGMENTS . viiI.INTRODUCTION . 1Background . 3Problem Statement . 6Objectives . 8Research Tasks . 8Research Methodology . 9II.LEGAL ASPECTS OF SCHEDULING WEATHER . 10Typical Contract Provisions for Schedulesand Time Extensions . 11Scheduling Clauses . 11Time Extension Clauses . 14Other Clauses . 15Delay Identification and Classification . 17Identification of Delays . 18Classification of Delays . 19Analysis of Legal Cases .22Legal Recognition of CPM . 23Legal Responsibility to ConsiderWeather . 23Climatological Data Period . 25Summary . 26III. THE WEATHER SCHEDULING MODEL . 28Introduction . 28Legal Principles behind Model . 28Detailed Discussion of Existing Models.30Computer Software Application During ModelDevelopment . 35The Critical Path Network for the Model . 39Weather Sensitivity Impact Factors . 44Local Contractor Survey . 46Non Local Survey . 49Personal Observations of LocalConstruction . 53Synthesis of Results from Surveys . 53Climatological Data . 56The Weather Scheduling Algorithm . 60Adjustment Process . 62Summary . 70
ivTABLE OF CONTENTS (Continued)IV.EVALUATION OF WEATHER-RELATED TIMEEXTENSION REQUESTS . 72Introduction . 72Weather Delay Analysis . 73Network Adjustment Technique Revisions.74Demonstration of Weather Delay Analysis . 76Project Review . 76Delay Categories . 78Network Adjustment . 80Analysis of Removed Weather Delays . 87Summary . 92V.CONCLUSIONS AND RECOMMENDATIONS . 95Conclusions . 95Recommendations for Future Research . 97BIBLIOGRAPHY . 98APPENDICES . 101Appendix A: Precipitation Observations over a TenYear Period in State College,Pennsylvania . 101Appendix B: Cumulative Frequency of RainfallObservations over Ten Years in StateCollege, Pennsylvania . 113Appendix C: Survey Form Used for LocalSurvey . 117Appendix D: Survey Form Used for Non-LocalSurvey . 121Appendix E: Organized Rain Data for WeatherScheduling Model . 125
VLIST OF TABLES1Contract Scheduling Clauses . 132Contract Time Extension Clauses . 163PennDOT Schedule of Productive Workdays . 184Principle Types of Delay . 205Activities and Durations for Shaffer Model . 336Operation Efficiency Factors . 337Activity Data . 338Weather Sensitivity Corrections .9Activity Data for Example Network . 4010Holidays for Example Network . 4011Weather Sensitivity Factors . 4512Local Survey Lost Rain Days . 4813Local Survey Sensitivity Factors . 4914Non Local Survey Sensitivity Factors . 5315Visual Survey of Local Construction . 5416Visual Survey Sensitivity Factors . 5417Comparison of Results of Surveys . 5518Comparison of U.S. Weather Bureau DailyRain Recordings (inches) with PrivateWeather Organization Recordings . 5819Explanation of Model Rain Data Organizationrainfall readings excerptedfrom Appendix E . 6020Summary of Delays Reduced . 9121Summary of Removed Weather Delays . 9122Completed Summary of Delays Reduced . 9323Summary of Delays Reduced, By Category . 9334
viLIST OF FIGURES1Cumulative Frequency of Rainfall Observations forJanuary in State College, Pennsylvania(1976-1987) . 382CPM Network Diagram Used for Example . 413Initial Schedule Calendar Dates for Example . 424Original Schedule . 645Schedule After First Iteration . 656Schedule After Second Iteration . 677Schedule After Third Iteration . 688Schedule After Fourth Iteration . 699Schedule After Fifth and Final Iteration . 7110As Built Construction Schedule . 7711Adjusted Network After First Iteration . 8112Adjusted Network After Second Iteration . 8313Adjusted Network After Third Iteration . 8414Adjusted Network After Fourth Iteration.8515Adjusted Network After Fifth Iteration . 8616Adjusted Network After Sixth Iteration . 8817Adjusted Network After Seventh Iteration. 8918Adjusted Network After Eighthand Final Iteration . 90
viiACKNOWLEDGMENTSI would like to thank Dr. Gary R. Smith for his wisdomand guidance in the preparation of this report.Specialthanks are also expressed to the contractors, constructionmanagers, and scheduling consultants who participated in theresearch and shared their knowledge of scheduling weathercontingency on construction projects.
1Chapter IINTRODUCTIONWeather is one of the most difficult factors for contractors to evaluate in the preparation of constructionplans.Because of this problem, some contractors eitherinadequately consider weather impacts or disregard themaltogether.Consequently, they may fail to complete workwithin the time period allotted by their contracts.Adverseweather is considered by contractors, architects, and engineers to be the most prominent cause of lost time anddelays on construction projects [l].When weather condi-tions create safety hazards (eg. structural steelwork in icyconditions) or poor productivity (eg. earthwork in rainyconditions), contractors delay work until conditions improve.Construction contracts usually require contractors toconsider normal weather delays in the preparation of theirschedules.Furthermore, these contracts allow time exten-sions when unusually severe weather impacts the scheduledconstruction.This implies that time extensions will not begranted for the impacts on construction caused by typicalweather.What are 'normal' weather and 'unusually severe'weather?The inability of many contractors to answer thesequestions is often the root cause of their failure to consider potential weather impacts in their schedules.For anowner, the inability to answer these questions makes evaluation of weather-related time extension requests difficult.
2It is difficult to include anticipated weather delaysinto a construction schedule for several reasons:1.weather forecast accuracy affects short termplans.2.the forecasting period affects the accuracy of thepredicted weather.3.weather conditions can vary significantly within ageographic region.4.literature on scheduling techniques inadequatelydetail methods for including weather contingency.Weather forecasts are not always accurate.Contractors haveoccasionally deferred scheduled concrete pours on the basisof predicted precipitation, only to find that the forecastwas incorrect and the pour could have been made as originally planned.The forecast period affects consideration ofweather effects on the schedule in that, as the period isextended, the accuracy of the forecast decreases.A five-day weather forecast is less accurate than a twenty-fourhour forecast.Variability of weather conditions withingeographic regions is also a major concern in schedulingweather contingency.The weather recorded by the NationalWeather Service or a private meteorological organizationclosest to a construction site may be vastly different thanthe weather conditions experienced at the site.Only inregions where adverse weather extremes for precipitation,temperature, relative humidity, and wind seldom occur canweather be ignored.Finally, contractors are ill-equipped
3to estimate weather delays that will occur during the timeallowed for contract completion.Scheduling handbooks pro-vide caveats to contractors that weather delays must beconsidered in their schedules without providing guidance onhow to interpret and incorporate climatological information.This report presents a model enabling contractors toinclude normal weather delays into Critical Path Method(CPM) schedules through proper application of historicalclimatological data.Furthermore, the model enables anowner to assess weather-related time extension requests.The timely acquisition of new facilities or facilityrehabilitation is essential to the needs of both public andprivate owners.For private owners, reliance might beplaced on construction completion dates to project incomefrom rentals, manufacturing, or other sources.For publicowners, construction completion dates represent the culmination of planning and legislative processes to acquire facilities needed for services such as defense, law enforcement,and public transportation.Because delayed construction canseverely impact on the needs of public and private owners,the time allowed for contract completion is a crucial aspectof construction contracts.Contractors on construction contracts are required tocomplete construction no later than the completion datespecified in their contract; however, circumstances that
4include change orders, acts of God, unusual weather, andother causes beyond the control of the contractor, oftenprevent this.Delays may also occur when a contractor failsto plan or control adequately the construction process for aproject, resulting in out-of-sequence activity performanceand work space congestion.When delays beyond the controlof the contractor occur, the contractor is permitted torequest an extension of the contract completion date.Per-tinent excerpts from the Federal Acquisition Regulations(FAR) cited in Federal construction contracts regarding timeextensions are listed below:".(b) The Contractor's right to proceed shall not beterminated nor the Contractor charged with damagesunder this clause, if(1) The delays in completing the work arises fromunforeseeable causes beyond the control and without thefault or negligence of the Contractor. Examples ofsuch causes include (i) acts of God or o.f the publicenemy, (ii) acts of the Government in either its sovereign or contractual capacity, (iii) acts of anotherContractor in the performance of a contract with theGovernment, (iv) fires, (v) floods, (vi) epidemics,(vii) quarantine restrictions, (viii) strikes, (ix)freight embargoes, (x) unusually severe weather, or(xi) delays of subcontractors or suppliers at any tierarising from unforeseeable causes beyond the controland without the fault or negligence of both the Contractor and the subcontractors or suppliers. "t2].Contractors are also required to submit detailed schedules showing their breakdown of construction operations andthe time frames within which the operations will be performed.Schedules are vital to both the constructiontractor and to the owner.con-For the contractor, the scheduleprovides a plan for attack of meeting his contractual obligations.For the owner, the schedule provides a benchmark
5for monitoring the contractor's progress and it also provides assurance that the contract will be completed on time.Pertinent FAR clause excerpts regarding scheduling arelisted below:(a) The Contractor shall within five days or anotherperiod of time determined by the Contracting Officer,prepare and submit to the Contracting Officer for approval three copies of a practicable schedule showingthe order in which the Contractor proposes to performthe work, the dates on which the Contractor contemplates starting and completing the several salientfeatures (including acquiring of materials, plant andequipment). The schedule shall be in the form of aprogress chart of suitable scale to indicate appropriately the percentage of work scheduled for completionby any given date during the period. If the Contractorfails to submit a schedule within the time prescribed,the Contracting Officer may withhold approval of progress payments until the Contractor submits the required schedule [3].When the contract requirements for scheduling and timeextensions are read as a whole, it is clear that contractorswill not be entitled to time extensions for normal weatherdelays, and therefore, normal delays must be incorporatedinto the construction schedules.There are important legal considerations regardingschedules and time extensions.When contractors are enti-tled to a time extension for a verified weather-causeddelay, the owner is obligated to provide an equitable adjustment to the contract completion time.Should the owner failto fulfill this obligation, he or she will become legallyliable for the constructive acceleration of the contractors'efforts, should the contractor strive to meet the currentcontract completion date.This report describes a method for contractors to in-
6corporate normal weather delays into their constructionschedules.The report also describes a method for owners toevaluate time extension requests due to weather-relateddelays.Given the legal ramifications of a project sched-ule, this method could serve as an evidentiary tool inclaims concerning weather-related time extensions.Themethod could also benefit both parties by providing betterplanning and reducing claims.Problem StatementContractors for public and private construction contracts are required to complete their work within the timeallowed and according to their construction schedules.Insome instances, contractors plan to complete work earlierthan the contract completion date.Contractors must includenormal weather delays within their schedules.The contractwill not allow time extensions for average weather encountered by the contractors during the course of construction.Literature on CPM scheduling frequently states that contractors should consider lost time due to weather [4,5,6,7,8,9].Weather scheduling methods include:1.Add a final activity to the network or schedule toaccount for the cumulative effect of weather delays.2.Remove dates from the project calendar in a mannersimilar to the way holidays are excluded to allowfor lost time due to weather.This, in effect,
7shortens the available work calendar.3.Use shortened work weeks during adverse weatherperiods.4.Increase the durations of activities that areconsidered weather-sensitive.None of these methods have been confirmed as entirelysuccessful at factoring lost weather time into schedules.Each of these heuristic methods has its limitations.Thefinal-activity approach does not link estimated lost timedue to weather toweather-sensitive activities.It alsomakes weather-related time extension requests difficult toevaluate and Justify while the Job is in progress.Usingshorter work weeks or removing calendar dates impacts onnon-weather-sensitive activities.Increasing activity dura-tions to account for weather is the most preferable approach, but it causes'difficulty in evaluating planned versus actual productivity.Also, techniques for quantifyingthe duration increase are either complicated or arbitrary.Weather simulation models have not gained acceptance due totheir complex, probabilistic nature.Calendar-Day algo-rithms apply weather factors that inadequately considerhistorical climatological data.A straightforward methodology that enables contractorto identify when average weather delays will probably occurshould be developed.The methodology could be adjusted toenable an owner to adequately evaluate time extension requests due to weather.In other words, the adjusted method
8should allow the owner to identify the weather conditionsthat impacted the schedule.It should also quantify thedifference between the weather conditions that caused thedelay and historically average weather to determine theextent to which the contract should be extended.The primary objective of this study was to develop amethod that would enable a contractor to effectively consider and incorporate reasonably anticipatory weather delaysinto CPM construction schedules, and to enable an owner toappropriately evaluate weather-related time extension requests.The report explains a methodology for factoring raindelays into the construction schedule.The procedure usedan as-planned network for weather scheduling and an as-builtnetwork for time extension evaluation.The as-planned sched-ule was based on an initial assumption of ideal weatherconditions causing no lost time.Research TasksThree tasks were undertaken to achieve the primaryobjective of the study:Task One - Develop impact factors to rate constructionactivities according to their weather sensitivity.Task Two - Tabulate ten years of historical climatological data for State College, Pennsylvania for use increation of the model.
9Task Three - Create a model to integrate impact factors, historical weather data, and the constructionschedule to incorporate anticipated weather delays intothe construction plan.Research MethodoloavThree research techniques were used.First, pertinentliterature on CPM was reviewed with particular emphasis onhow to handle weather-related lost time.The literaturesearch provided background knowledge of the topics of properCPM scheduling, legal principles behind scheduling and timeextensions, and impact factors for sensitivity of construction operations to weather.Second, a sampling of construc-tion contractors, scheduling consultants, and constructionmanagement firms were surveyed on how they consider weatherin the development of their schedules. Questionnaires weremailed to these firms to gain knowledge of how they considerweather when scheduling, their methods for justifying weather-related time extension requests, and thresholds of rainfall at which decisions are made to stop work.Finally, amodel was developed and tested for its ability to includerain delays in the construction plan.Historical climato-logical dat
weather effects on the schedule in that, as the period is extended, the accuracy of the forecast decreases. A five-day weather forecast is less accurate than a twenty-four hour forecast. Variability of weather conditions within geographic regions is also a major concern in scheduling weather contingency. The weather recorded by the National
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