1、Unit14Cost EstimationText1 Costs Associated with Constructed Facilities The costs of a constructed facility to the owner include both the initial capital cost and the subsequent operation and maintenance costs.Each of these major cost categories consists of a number of cost components.The capital co
2、st for a construction project includes the expenses related to the initial establishment of the facility:Land acquisition,including holding and improvement Planning and feasibility studiesArchitectural and engineering design Construction,including materials,equipment and labor Field supervision of c
3、onstructionConstruction financingInsurance and taxes during constructionOwners general office overheadEquipment and furnishings not included in construction Text Inspection and testingThe operation and maintenance cost in subsequent years over the project life cycle includes the following expenses:L
4、and rent,if applicable.Operating staff.Labor and material for maintenance and repairs.Periodic renovations.Insurance and taxes.Financing costs.Utilities.Owners other expenses.The magnitude of each of these cost components depends on the nature,size and location of the project as well as the manageme
5、nt organization,among many considerations.The owner is interested in achieving the lowest possible overall project cost that is consistent with its investment objectives.TextIt is important for design professionals and construction managers to realize that while the construction cost may be the sing
6、le largest component of the capital cost,other cost components are not insignificant.For example,land acquisition costs are a major expenditure for building construction in high-density urban areas,and construction financing costs can reach the same order of magnitude as the construction cost in lar
7、ge projects such as the construction of nuclear power plants.From the owners perspective,it is equally important to estimate the corresponding operation and maintenance cost of each alternative for a proposed facility in order to analyze the life cycle costs.The large expenditures needed for facilit
8、y maintenance,especially for publicly owned infrastructure,are reminders of the neglect in the past to consider fully the implications of operation and maintenance cost in the design stage1.In most construction budgets,there is an allowance for contingencies or unexpected costs occurring during cons
9、truction.This contingency amount may be included within each cost item or be included in a single category of construction contingency.The amount of contingency is based on historical experience and the expected difficulty of a particular construction project.TextFor example,one construction firm ma
10、kes estimates of the expected cost in five different areas:Design development changes.Schedule adjustments.General administration changes(such as wage rates).Differing site conditions for those expected.Third party requirements imposed during construction,such as new permits.Contingent amounts not s
11、pent for construction can be released near the end of construction to the owner or to add additional project elements.2 Approaches to Cost EstimationCost estimating is one of the most important steps in project management.A cost estimate establishes the base line of the project cost at different sta
12、ges of development of the project.A cost estimate at a given stage of project development represents a prediction provided by the cost engineer or estimator on the basis of available data.TextAccording to the American Association of Cost Engineers,cost engineering is defined as that area of engineer
13、ing practice where engineering judgment and experience are utilized in the application of scientific principles and techniques to the problem of cost estimation,cost control and profitability.Virtually all cost estimation is performed according to one or some combination of the following basic appro
14、aches.(1)Production function.In microeconomics,the relationship between the output of a process and the necessary resources is referred to as the production function.In construction,the production function may be expressed by the relationship between the volume of construction and a factor of produc
15、tion such as labor or capital.A production function relates the amount or volume of output to the various inputs of labor,material and equipment.For example,the amount of output Q may be derived as a function of various input factors x1,x2,xn by means of mathematical and/or statistical methods.Thus,
16、for a specified level of output,we may attempt to find a set of values for the input factors so as to minimize the production cost.The relationship between the sizes of a building project(expressed in square feet)to the input labor(expressed in labor hours per square foot)is an example of a producti
17、on function for construction.Text(2)Empirical cost inference.Empirical estimation of cost functions requires statistical techniques which relate the cost of constructing or operating a facility to a few important characteristics or attributes of the system2.The role of statistical inference is to es
18、timate the best parameter values or constants in an assumed cost function.Usually,this is accomplished by means of regression analysis techniques.(3)Unit costs for bill of quantities.A unit cost is assigned to each of the facility components or tasks as represented by the bill of quantities3.The tot
19、al cost is the summation of the products of the quantities multiplied by the corresponding unit costs.The unit cost method is straightforward in principle but quite laborious in application.The initial step is to break down or disaggregate a process into a number of tasks.Collectively,these tasks mu
20、st be completed for the construction of a facility.Once these tasks are defined and quantities representing these tasks are assessed,a unit cost is assigned to each and then the total cost is determined by summing the costs incurred in each task.The level of detail in decomposing into tasks will var
21、y considerably from one estimate to another.Text(4)Allocation of joint costs.Allocations of cost from existing accounts may be used to develop a cost function of an operation.The basic idea in this method is that each expenditure item can be assigned to particular characteristics of the operation.Id
22、eally,the allocation of joint costs should be causally related to the category of basic costs in an allocation process.In many instances,however,a causal relationship between the allocation factor and the cost item cannot be identified or may not exist.For example,in construction projects,the accoun
23、ts for basic costs may be classified according to:labor.material.construction equipment.construction supervision.general office overhead.These basic costs may then be allocated proportionally to various tasks which are subdivisions of a project.Text3 Types of Construction Cost Estimates Construction
24、 cost constitutes only a fraction,though a substantial fraction,of the total project cost.However,it is the part of the cost under the control of the construction project manager.The required levels of accuracy of construction cost estimates vary at different stages of project development,ranging fr
25、om ball park figures in the early stage to fairly reliable figures for budget control prior to construction.Since design decisions made at the beginning stage of a project life cycle are more tentative than those made at a later stage,the cost estimates made at the earlier stage are expected to be l
26、ess accurate.Generally,the accuracy of a cost estimate will reflect the information available at the time of estimation.Construction cost estimates may be viewed from different perspectives because of different institutional requirements.In spite of the many types of cost estimates used at different
27、 stages of a project,cost estimates can best be classified into three major categories according to their functions.A construction cost estimate serves one of the three basic functions:design,bid and control.For establishing the financing of a project,either a design estimate or a bid estimate is us
28、ed.TextDesign Estimates For the owner or its designated design professionals,the types of cost estimates encountered run parallel with the planning and design as follows:(1)Screening estimates(or order of magnitude estimates).(2)Preliminary estimates(or conceptual estimates).(3)Detailed estimates(or
29、 definitive estimates).(4)Engineers estimates based on plans and specifications.For each of these different estimates,the amount of design information available typically increases.In the planning and design stages of a project,various design estimates reflect the progress of the design.At the very
30、early stage,the screening estimate or order of magnitude estimate is usually made before the facility is designed,and must therefore rely on the cost data of similar facilities built in the past.A preliminary estimate or conceptual estimate is based on the conceptual design of the facility at the st
31、ate when the basic technologies for the design are known.TextThe detailed estimate or definitive estimate is made when the scope of work is clearly defined and the detailed design is in progress so that the essential features of the facility are identifiable.The engineers estimate is based on the co
32、mpleted plans and specifications when they are ready for the owner to solicit bids from construction contractors.In preparing these estimates,the design professional will include expected amounts for contractors overhead and profits.The costs associated with a facility may be decomposed into a hiera
33、rchy of levels that are appropriate for the purpose of cost estimation4.The level of detail in decomposing the facility into tasks depends on the type of cost estimate to be prepared.For conceptual estimates,for example,the level of detail in defining tasks is quite coarse;for detailed estimates,the
34、 level of detail can be quite fine.As an example,consider the cost estimates for a proposed bridge across a river.A screening estimate is made for each of the potential alternatives,such as a tied arch bridge or a cantilever truss bridge.As the bridge type is selected,e.g.the technology is chosen to
35、 be a tied arch bridge instead of some new bridge form;a preliminary estimate is made on the basis of the layout of the selected bridge form on the basis of the preliminary or conceptual design.TextWhen the detailed design has progressed to a point when the essential details are known,a detailed est
36、imate is made on the basis of the well defined scope of the project.When the detailed plans and specifications are completed,an engineers estimate can be made on the basis of items and quantities of work.Bid Estimates For the contractor,a bid estimate submitted to the owner either for competitive bi
37、dding or negotiation consists of direct construction cost including field supervision,plus a markup to cover general overhead and profits.The direct cost of construction for bid estimates is usually derived from a combination of the following approaches.(1)Subcontractor quotations.(2)Quantity takeof
38、fs.(3)Construction procedures.The contractors bid estimates often reflect the desire of the contractor to secure the job as well as the estimating tools at its disposal.TextSome contractors have well established cost estimating procedures while others do not.Since only the lowest bidder will be the
39、winner of the contract in most bidding contests,any effort devoted to cost estimating is a loss to the contractor who is not a successful bidder5.Consequently,the contractor may put in the least amount of possible effort for making a cost estimate if it believes that its chance of success is not hig
40、h.If a general contractor intends to use subcontractors in the construction of a facility,it may solicit price quotations for various tasks to be subcontracted to specialty subcontractors.Thus,the general subcontractor will shift the burden of cost estimating to subcontractors.If all or part of the
41、construction is to be undertaken by the general contractor,a bid estimate may be prepared on the basis of the quantity takeoffs from the plans provided by the owner or on the basis of the construction procedures devised by the contractor for implementing the project.For example,the cost of a footing
42、 of a certain type and size may be found in commercial publications on cost data which can be used to facilitate cost estimates from quantity takeoffs.However,the contractor may want to assess the actual cost of construction by considering the actual construction procedures to be used and the associ
43、ated costs if the project is deemed to be different from typical designs.Hence,items such as labor,material and equipment needed to perform various tasks may be used as parameters for the cost estimates.Text Control Estimates For monitoring the project during construction,a control estimate is deriv
44、ed from available information to establish:(1)Budget estimate for financing.(2)Budgeted cost after contracting but prior to construction.(3)Estimated cost to completion during the progress of construction.Both the owner and the contractor must adopt some base line for cost control during the constru
45、ction.For the owner,a budget estimate must be adopted early enough for planning long term financing of the facility.Consequently,the detailed estimate is often used as the budget estimate since it is sufficient definitive to reflect the project scope and is available long before the engineers estima
46、te.As the work progresses,the budgeted cost must be revised periodically to reflect the estimated cost to completion.A revised estimated cost is necessary either because of change orders initiated by the owner or due to unexpected cost overruns or savings.TextFor the contractor,the bid estimate is u
47、sually regarded as the budget estimate,which will be used for control purposes as well as for planning construction financing.The budgeted cost should also be updated periodically to reflect the estimated cost to completion as well as to insure adequate cash flows for the completion of the project.N
48、ew Words and PhrasesProfits,n.利润overhead,n.企业一般管理费用control estimate,.控制估价budget estimate,.财务预算cost estimation,.成本估算 land acquisition,土地获得 project life cycle,项目生命周期 land rent,.土地租金 periodic renovations,.周期性更新 financial costs,.财务成本 construction cost,.施工建设费unexpected costs,.不可预见费用 cost engineers,造价工程师
49、cost engineering,工程估价cost control,成本控制production function,产出函数 bid estimate,投标估价 the amount or volume of output,产出总量 production cost,生产成本 empirical cost inference,经验成本推论 bill of quantities,工程量清单 unit cost,单位成本 New Words and Phrasesjoint costs,联合成本 accuracy of cost estimates,估价精度 design estimate,设计估价
50、 direct construction cost,直接施工成本 initial capital,创办成本；初始投资 field supervision of construction,现场施工监督 operation and maintenance costs,运行与养护费用 detailed estimates(or definitive estimates),详细估计(或确定估计)preliminary estimates(or conceptual estimates),初步估算(或概念性估算)screening estimates(or order of magnitude esti
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