Price association published in May 2009 in the whole process of the construction projects cost consultation regulation CWCA/GC4-2009, through to the domestic more than 20 years to implement the whole process cost consultation business experience summary, the obligations and responsibilities of cost consultation enterprises, unified specification cost consultation work content, scope, format, depth and quality standards, etc., this is the domestic cost consultation enterprises to carry out the whole process cost consultation industry guidelines.

In China, the whole process of construction project cost management is divided into five stages according to the different stages of construction: preliminary decision-making stage, design stage, transaction stage, construction stage and completion stage. In each stage, all needs to adopt the scientific calculation method and realistic valuation basis, according to a certain mode of valuation, reasonable estimation, budget control, budget, bidding price, bidding quotation, contract price, settlement and final accounts, etc. Various forms of engineering cost. And investment control of construction projects throughout the entire project construction process, including decision-making stage, design stage, stage of trading, the investment control of construction stage and completion stage, and the project decision-making and design stage is the most important stage affect the project, the highest degree of cost, cost savings may be the biggest.

Decision phase and design phase, at the early stages of the project cost consultation unit will help the government and the owner to determine investment intention and financial ability, to determine the size of the planned project feasibility research and standards, such as what type of project development level, size, standard, etc. The design stage of the project is the key to project cost control and management, and also the weak link to break through investment plan. The basis of the design is the government approved feasibility study report and design assignment letter, according to the domestic three-stage design (scheme design, expansion design, construction drawing design) and approval.

The decision phase and design phase of the early stage of the project, based on the function of the project positioning, construction standard, fast accurate objectives of construction project cost estimation, establish reasonable target cost is the key to the investment control. Based on the cost analysis and cost database of the previous period, this paper introduces the construction cost model and the application model of establishing cost estimation rapidly and scientifically.

I. overview of the construction cost model

Any construction project in the industrial and civil construction industry can be solved by building models if it is necessary to estimate its cost before construction is completed. So what is a model? What is the building cost model?

"Model" refers to a program that produces satisfactory output data through input of a set of established data and through a series of derivations. An ideal model should satisfy the following conditions: simple enough for the user to operate and understand; All the implications of the model object are fully representative and complex so that the system can be accurately described. The model is essentially a black box that is processed based on a set of input data. Only a better model can be unaffected by the original model data in the process of processing. The modeling process is shown below.

"Building cost model" refers to a set of basic parameters and characteristic attributes of buildings that are input into the system, and the system USES the data model to carry out analysis and calculation and output reasonable engineering estimation results. Cost model of the construction industry is usually variable, this is mainly due to the cost and price volatility, therefore, in the construction industry, the advantages of model mainly reflects in able to respond in a timely manner to the change of environment and making adaptive dynamic adjustment, to ensure accuracy. The accuracy of the model is a necessary index to test the applicability of the model. The following is a schematic diagram:

Ii. Development of building cost model

Raftery (1987) described the development of the building cost model and experienced the following stages:

The first stage: starting in the 1950s, cost analysis results based on BCIS can be appropriately adjusted to form corresponding cost plans. But because there are many factors which affected the project cost, such as engineering applications, the size, structure, characteristics, construction period, and presents a highly nonlinear relationship between these factors and the impact on the cost of the degree also differ, this one phase of the cost model is difficult to accurately reveal the relationship between different variables of the project and its impact on cost, leading to a lower cost model precision.

The second stage: beginning in the mid 1970s, this period is characterized by the gradual popularization of computer technology and the extensive application of regression analysis methods. Through multiple regression analysis method, to collect a large number of samples project, analyzed the construction cost and the independent variables and dependent variables and their relationships, and then through the statistical analysis method, in order to determine the importance of the dependent variable, and calculate the weight of each variable factor to draw multiple regression analysis construction cost model, but this kind of model extrapolation is poorer.

The third stage: from the 1980s to the present, combined with the computer application technology, there appeared the estimation method based on the theory of modern mathematics. The development of this period is mainly reflected in the following two characteristics:

(1) recognize the uncertainty and non-accuracy of the model, and try to analyze it through probability statistics, usually using monte carlo simulation method. (monte carlo simulation is a stochastic simulation method. A calculation method based on probability and statistical theory. The problem solved is connected with a certain probability model, and the statistical simulation or sampling is realized by the electronic computer to obtain the approximate solution of the problem.

(2) estimation methods for artificial intelligence and knowledge-based computer systems, such as artificial neural network (ANN). ANN method is automatic "learning" and "memory" function, can carry on the knowledge acquisition is very easy to work, it is "lenovo" function, so the only part of the information to be able to recall the outline of the system, since it has the nonlinear mapping ability, can automatically close to those depicting the best the best pattern of the sample data function, reveal the sample data of the nonlinear relationship.

In countries such as the United States and the United States, building cost models have developed to a certain extent and are widely used. UK BCIS online approximate estimation software package; The architectural cost model of bucknell Austin; Davis langton and Everett cost models and so on. The cost model to assess the value of construction projects prophase project provides a good solution, making early decision phase and design phase of the cost and fast to establish possible, of course need cost database support.

3. Construction cost model establishment

3.1 purpose of modeling

The purpose of establishing the cost model determines the form and parameters of the cost model. Currently, the most important architectural models include the following two types:

(1) design optimization model

This model is mainly used in the design stage, it is to ensure the value of the design of the building material, also can be used as an important part of the cost of construction planning process, the main methods of this model is to plan will be selected.

(2) bidding price prediction model

This model is mainly used in the transaction stage to predict the bidding price that the tendering contractor may provide, and it can also be used to confirm the estimated variation rate of the contractor and the influencing factors of the market price. The parameters involved in the prediction model are less reliable than those in the design optimization model, so the prediction results are likely to be inaccurate.

3.2 methods of modeling

Avos and worthashandskritmort discovered a number of methods in 1982 to improve the accuracy of estimates as the engineering design phase approached the final completion during the bidding process. Wilson later pointed out in a 1984 article that these findings led to the emergence of the following two methods of cost modeling. The former is more used in the early stage of engineering design. Later, more applications are applied after the design is formed.

Deductive model: this model is mainly based on the statistical analysis of the past engineering data, and the common statistical analysis method is regression analysis.

Induction model: this model tries to introduce the more detailed methods commonly used by contractors in the engineering design stage. The common method is engineering simulation.

3.3 model types

In 1991, in order to classify the existing construction cost model research, Newton (Newton) reviewed the history of cost modeling research, which involves the application of industrialists in the building industry can all kinds of models. Generally speaking, it includes dynamic programming, expert system, functional dependency, linear programming, manual operation, monte carlo simulation, network method, statistical model and regression analysis.

4. Application of building cost model

The purpose of building cost model is to determine the cost of a proposed project quickly and accurately. Accurately determine the overall distribution of the internal cost variables of a certain construction project design to ensure the reliability of cost prediction and design optimization.

Construction cost model application is very broad, in the past a lot of the cost of the project data and the processing of design parameters, cost modeling for new projects, engineering design and cost planning has brought a lot of convenience. Specific applications include:

(1) budget each stage of the project life cycle

(2) identify cost sensitive design parameters, especially those related to spatial functions, service facilities and cost planning.

Below, we take MeansCostWorks.com, an American online cost estimation tool, as an example to introduce how to use the cost model to quickly determine the estimated project cost. The process is very simple, including the following steps:

1. Establish estimation: determine the name of estimation, select project location, release time of data (four times of quarterly release in the whole year), and service form.

2, step1: select the item type and basic properties of project types including more than 70 types of buildings (British construction project categories: such as apartment 1-3 layer, apartment 4 to 7, 8-24 apartments, and halls, Banks, hospitals,... ); For the selected project type, the wall type and structure type need to be determined, such as precast concrete slab/steel frame structure, and more properties are provided in the drop-down list.

3, step2: based on the choice of project types, the model will provide the sample as shown in the figure below, then need to input the basic parameters of the buildings including the building area, building outside perimeter, layer, layer; Make it clear that it does not include basements and then assign rates to some of the cost items.

Step3: click the calculation button, and the model will automatically establish the cost model according to the input attributes and parameters, and browse the cost summary of the cost model in time.

5. Check the detailed cost report: according to the cost model, the estimation results including detailed detailed composition and construction standards specification, as shown in the figure below, the elements that allow for any of them, of course, the flexible adjustment cost, in order to obtain a higher degree of relevant engineering value.

Five, the conclusion

To be sure, the establishment of the construction cost model to our scientific, accurate and fast determine the cost of the proposed construction project to provide great convenience, for owner's construction project decision-making and design scheme comparison made a significant contribution. And based on the research of the various cost model, which can be found that the the common characteristic of the model is based on a sample project and the common characteristics of the proposed construction project, through a variety of ways to find out the mapping relationship between the results of the common features and cost, to establish the appropriate cost estimation model.

Construction project engineering cost industry in our country, with the continuous development of information technology, and the cost of industry business model, we build up the project cost information data standards and industry/enterprise project cost information resource platform, and on this basis, through the development and application of construction cost model, the valuation of engineering for industry practitioners to bring new solutions.

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