《专业英语》课件Unit_14.pptx
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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
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