ASTM E1946-2018 Standard Practice for Measuring Cost Risk of Buildings and Building Systems and Other Constructed Projects.pdf

1、Designation: E1946 18Standard Practice forMeasuring Cost Risk of Buildings and Building Systemsand Other Constructed Projects1This standard is issued under the fixed designation E1946; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision

2、, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This practice covers a procedure for measuring cost riskfor buildings and building systems and other con

3、structedprojects, using the Monte Carlo simulation technique asdescribed in Guide E1369.1.2 A computer program is required for the Monte Carlosimulation. This can be one of the commercially availablesoftware programs for cost risk analysis, or one constructed bythe user.1.3 This standard does not pu

4、rport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international stand

5、ard was developed in accor-dance with internationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Re

6、ferenced Documents2.1 ASTM Standards:2E631 Terminology of Building ConstructionsE833 Terminology of Building EconomicsE1369 Guide for Selecting Techniques for Treating Uncer-tainty and Risk in the Economic Evaluation of Buildingsand Building SystemsE1557 Classification for Building Elements and Rela

7、tedSiteworkUNIFORMAT IIE2083 Classification for Building Construction FieldRequirements, and Office Overhead and for general terms related to building economics,refer to Terminology E833.4. Summary of Practice4.1 The procedure for calculating building cost risk consistsof the following steps:4.1.1 I

8、dentify critical cost elements.4.1.2 Eliminate interdependencies between critical ele-ments.4.1.3 Select Probability Density Function.4.1.4 Quantify risk in critical elements.4.1.5 Create a cost model.4.1.6 Conduct a Monte Carlo simulation.4.1.7 Interpret the results.4.1.8 Conduct a sensitivity anal

9、ysis.5. Significance and Use5.1 Measuring cost risk enables owners of buildings andother constructed projects, architects, engineers, and contrac-tors to measure and evaluate the cost risk exposures of theirconstruction projects.3Specifically, cost risk analysis (CRA)helps answer the following quest

10、ions:5.1.1 What are the probabilities for the construction contractto be bid above or below the estimated value?5.1.2 How low or high can the total project cost be?5.1.3 What is the appropriate amount of contingency to use?5.1.4 What cost elements have the greatest impact on theprojects cost risk ex

11、posure?1This practice is under the jurisdiction of ASTM Committee E06 on Perfor-mance of Buildings and is the direct responsibility of Subcommittee E06.81 onBuilding Economics.Current edition approved Sept. 1, 2018. Published September 2018. Originallyapproved in 1998. Last previous edition approved

12、 in 2012 as E194612. DOI:10.1520/E194618.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3This practice is ba

13、sed, in part, on the article, “Measuring Cost Risk of BuildingProjects,” by D. N. Mitten and B. Kwong, Project Management Services, Inc.,Rockville, MD, 1996.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard wa

14、s developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.15.2 CRA can

15、be applied to a projects contract cost, con-struction cost (contract cost plus construction change orders),and project cost (construction cost plus owners cost), depend-ing on the users perspectives and needs. This practice shallrefer to these different terms generally as “project cost.”6. Procedure

16、6.1 Identify Critical Cost Elements:6.1.1 A project cost estimate consists of many variables.Even though each variable contributes to the total project costrisk, not every variable makes a significant enough contribu-tion to warrant inclusion in the cost model. Identify the criticalelements in order

17、 to simplify the cost risk model.6.1.2 A critical element is one which varies up or downenough to cause the total project cost to vary by an amountgreater than the total project costs critical variation, and onewhich is not composed of any other element which qualifies asa critical element. This cri

18、terion is expressed as:IF VY.VCRIT(1)AND Y contains no other element X where VX.VCRITTHEN Y is a critical elementwhere:VY5 (2)Max. percentage variation of the element Y!*Ys anticipated cost!Total Project CostVCRIT= Critical Variation of the Project Cost.6.1.3 A typical value for the total project co

19、sts criticalvariation is 0.5 %.4By experience this limits the number ofcritical elements to about 20. A larger VCRITwill lead to fewercritical elements and a smaller VCRITwill yield more. A riskanalysis with too few elements is over-simplistic. Too manyelements makes the analysis more detailed and d

20、ifficult tointerpret. A CRA with about 20 critical elements provides anappropriate level of detail. Review the critical variation usedand the number of critical elements for a CRA against theunique requirements for each project and the design stage. Ahigher critical variance resulting in fewer criti

21、cal elements, ismore appropriate at the earlier stages of design.6.1.4 Arrange the cost estimate in a hierarchical structuresuch as UNIFORMATII (Classification E1557 for Buildings orClassification E2103/E2103M for Bridges; Practice E2514provides a presentation format for elemental costs). Table 1sho

22、ws a sample project cost model based on a UNIFORMATII Levels 2 and 3 cost breakdown for a building. TheUNIFORMAT II structure of the cost estimate facilitates thesearch of critical elements for the risk analysis. One does notneed to examine every element in the cost estimate in order toidentify thos

23、e which are critical.6.1.5 Starting at the top of the cost estimate hierarchy (thatis, the Group Element level), identify critical elements in adownward search through the branches of the hierarchy.Conduct this search by repeatedly asking the question: Is itpossible that this element could vary enou

24、gh to cause the totalbuilding cost to vary, up or down, by more than its criticalvariation? Terminate the search at the branch when a negativeanswer is encountered. Examine the next branch until allbranches are exhausted and the list of critical elements estab-lished (denoted by asterisks in the las

25、t column of Table 1).Table 1 and Fig. 1 show the identification of critical elementsin the sample project using the hierarchical search technique.6.1.6 In the sample project, Group Element B10 Superstruc-ture has an estimated cost of $915 000 with an estimatedmaximum variation of $275 000, which is

26、more than $50 000,or 0.5 % of the estimated total building cost. It is therefore acandidate for a critical element. However, when we examinethe Individual Elements that make up Superstructure, wediscover that Floor Construction has a estimated maximumvariation of $244 500, qualifying as a critical e

27、lement; whereasRoof Construction could only vary as much as $40 000, anddoes not qualify. Since Floor Construction is now a criticalelement, we would eliminate Superstructure, its parent, as acritical element.6.1.7 Include overhead cost elements in the cost model,such as general conditions, profits,

28、 and escalation (see Classi-fication E2083), and check for criticality as with the other costelements. Consider time risk factors, such as long lead time ordock strikes for imported material, when evaluating escalationcost.6.1.8 Allowance and contingency, as commonly used in theconstruction cost est

29、imates, include both the change elementand the risk element. The change element in allowance coversthe additional cost due to incomplete design (design allow-ance). The change element in contingency covers the addi-tional cost due to construction change orders (constructioncontingency). The risk ele

30、ment in contingency covers theadditional cost required to reduce the risk that the actual costwould be higher than the estimated cost. However, the riskelement in allowance and contingency is rarely identifiedseparately and usually included in either design allowance orconstruction contingency. When

31、 conducting CRA, do notinclude the risk element in allowance or contingency cost sincethat will be an output of the risk analysis. Include designallowance only to the extent that the design documents areincomplete. Include construction contingency, which repre-sents the anticipated increase in the p

32、roject cost for changeorders beyond the signed contract value, if total constructioncost, instead of contract cost, is used. See Classification E2168for information on which costs are properly included underallowance and contingency.6.1.9 The sample project represents a CRA conducted fromthe owners

33、perspective to estimate the construction contractvalue at final design. General conditions, profits, and escalationare identified as critical elements. Since the design documentsare 100 % complete, there is no design allowance. The contin-gency in the cost element represents the risk element and ist

34、herefore eliminated from the cost model. There is no construc-tion contingency in the model since this model estimatesconstruction contract cost only. If total project cost is desired,4Curran, M. W., “Range EstimatingMeasuring Uncertainty and ReasoningWith Risk,” Cost Engineering, Vol 31, No. 3, Mar

35、ch 1989.E1946 182TABLE 1 Sample UNIFORMAT II Cost ModelGROUP INDIVIDUAL EST MAX/ITEM GROUP ELEMENT INDIVIDUAL ELEMENT ELEMENT ELEMENT VARIATIONCOST COSTA10 FOUNDATIONS $150 000 $45 000A1010 Standard Foundations $100 000A1030 Slab on Grade $50 000A20 BASEMENT CONSTRUCTION $70 000 $30 000A2010 Basemen

36、t Excavation $20 000A2020 Basement Walls $50 000B10 SUPERSTRUCTURE $915 000 $275 000B1010 Floor Construction $815 000 $244 500 *B1020 Roof Construction $100 000 40 000B20 EXTERIOR ENCLOSURE $800 000 $250 000B2010 Exterior Walls $576 000 $172 800 *B2020 Exterior Windows $204 000 $102 000 *B2030 Exter

37、ior Doors $20 000 $8 000B30 ROOFING $54 000 $20 000B3010 Roof Coverings $54 000C10 INTERIOR CONSTRUCTION $240 000 $72 000 *C1010 Partitions $132 000 $45 000C1020 Interior Doors $108 000 $30 000C20 STAIRS $95 000 $40 000C2010 Stair Construction $75 000C2020 Stair Finishes $20 000C30 INTERIOR FINISHES

38、 $916 000 $300 000C3010 Wall Finshes $148 000 $45 000C3020 Floor Finishes $445 000 $178 000 *C3030 Ceiling Finishes $323 000 $129 200 *D10 CONVEYING $380 000D1010 Elevators and the low estimate about50 % of the most likely estimate. This serves as a check on therange estimates.6.5 Create a Cost Mode

39、l:6.5.1 The cost model is essentially the hierarchical costestimate. Treat all non-critical elements as constants. Simplifythe cost model by combining constants.6.5.2 In the sample project, the cost model becomes:(COSTCE1$1 249000!*11Profit!*11Escalation! (5)where:COSTCE= variable cost for the criti

40、cal elements1 through 18,$1 249 000 = total cost for all the non-criticalelements;Profit and Escalation = variable percentages.6.5.3 For triangular PDFs, the random cost of each criticalelement is calculated by the formula:COSTCE5 LE1RV*MLE 2 LE!*HE 2 LE!#0.5(6)if COSTCE# MLECOSTCE5 HE 2 1 2 RV!*HE

41、2 MLE!*HE 2 LE!#0.5(7)if COSTCE.MLEwhere:RV = a random variable between 0 and 1.Use the same random variable for each formula. Aftercalculating both formulas, use the one which satisfies thecorresponding condition on the right.6.5.4 For example, for the critical element FloorConstruction, if RV = 0.

42、3, the two equations become:COST Floor Const.! 5 $65200010.3 * $ 815 000 2 (8)$652000! * $1 059500 2 $652000!0.55$793162, which satisfies the condition COST#$815000COST Floor Const.! 5 $1 059500 2 0.7 * $ 1 059 500 2 (9)$815000! * $1 059500 2 $652000!0.55$795410, which does not satisfy the condition

43、 COST.$815000The result from Eq 8 will be used since it satisfies thecorresponding condition.6.6 Conduct a Monte Carlo Simulation:6.6.1 Run a Monte Carlo simulation once the risk in thecritical elements are quantified and the model set up. TheMonte Carlo method builds up a PDF for the bottom linepro

44、ject cost by repeatedly running the model with randomlygenerated numbers for the critical elements according to theindividual PDFs. Each Critical element will use a separaterandom number for the calculation. Each time the model is run,one point is generated for the total project cost risk PDF. Thepr

45、ocess is repeated until the total project cost risk PDF“converges” or settles into a final shape, which often requires1,000 or more iterations. See Guide E1369, Section 7.7, for amore detailed description of the simulation technique.6.6.2 To implement a CRA, use commercial software pro-grams or writ

46、e your own simulation software code.6.7 Interpret the Results:6.7.1 By inspecting the converged PDF for the bottom lineconstruction cost and its corresponding Cumulative Distribu-tion Function (CDF), obtain the following information:6.7.1.1 Expected (mean) total cost, which is the average ofall the

47、data points generated by the simulation.6.7.1.2 Standard deviation on the total cost, which is thestandard deviation of all the data points generated by thesimulation.6.7.1.3 The confidence level, which is the cumulative per-centage corresponding to those data points generated by thesimulation which

48、 are less than or equal to the estimated amounton the CDF. Fig. 2 illustrates the concept of a confidence level.Denote the low estimate as point “a” and the high estimate aspoint “b.” Because point a corresponds to the 1stpercentile of6Beeston, D. T., “One Statisticians View of Estimating,” Property

49、 ServicesAgency, Department of Environment, London, UK, July 1974.TABLE 2 Sample Critical Element Input ListCRITICAL ELEMENT LOW MOST LIKELY HIGHB1010 Floor Construction $652 000 $815 000 $1 059 500B2010 Exterior Walls $460 800 $576 000 $748 800B2020 Exterior Windows $142 800 $204 000 $306 000C10 Interior Construction $192 000 $240 000 $312 000C3020 Floor Finishes $333 750 $445 000 $623 000C3030 Ceiling Finishes $226 100 $323 000 $452 200D1010 Elevators cost risk analysis; Monte Carlo simulation;sensitivity analysis; UNIFORMAT IIASTM International take