In China, the whole process cost management of construction projects is divided into five stages according to the different construction stages: pre-decision stage, design stage, transaction stage, construction stage and completion stage. At each stage, scientific calculation methods and practical valuation basis should be adopted, and various forms of project cost such as estimation, budgetary estimate, budget, tender control price, tender offer, contract price, settlement and final accounts should be reasonably determined according to a certain valuation model. The investment control of the construction project runs through the whole project construction process, including the investment control in the decision-making stage, design stage, transaction stage, construction stage and completion stage, in which the decision-making and design stage of the project is the most important stage affecting the project, which has the highest impact on the cost and may save the most cost.
In the early decision-making stage and design stage of the project, the cost consulting unit will assist the government and the owner to determine the investment intention and financial capacity, and determine the scale and standard of the proposed project through feasibility study, such as what type of project to develop, how big the scale is and how high the standard is. The design stage of the project is the key to project cost control and management, and it is also a weak link to break through the investment plan. The design is based on the feasibility study report and design task book approved by the government, and is carried out in China according to the three-stage design (scheme design, capacity expansion design and construction drawing design) and approval. In the pre-decision stage and design stage of the project, it is the key to quickly and accurately estimate the target cost of the construction project and establish a reasonable target cost according to the functional orientation and construction standards of the project. Based on the cost analysis and cost database in the previous period, this paper introduces the application mode of establishing cost model and establishing cost estimation quickly and scientifically.
First, the construction cost model outlines any construction project in the industrial and civil construction industries. If it is necessary to estimate its cost before the construction is completed, it can be solved by building models. So what is a model? What is the project cost model? "Model" refers to a program that inputs a set of given data and obtains satisfactory output data through a series of derivation processes. An ideal model should meet the following conditions: simple enough for users to operate and understand; It fully represents all the connotations involved in the model object, and at the same time it is sufficiently complex, so as to accurately describe the system. The essence of the model is based on a set of black boxes of input data, and only a better model can be unaffected by the original model data in the process of processing. The process of establishing the model is shown in the following figure. "Building cost model" means that by inputting a set of basic building parameters and characteristic attributes, the system analyzes and calculates by constructing a data model, and outputs reasonable engineering estimation results. The cost model of construction industry is usually variable, which is mainly due to the variability of industry cost and price. Therefore, in the construction industry, the advantages of the model are mainly reflected in the ability to respond to environmental changes in time and make adaptive dynamic adjustments 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:
Second, the development of the construction cost model Rafteri (1987) once described the development of the construction cost model, which went through the following stages: the first stage: from the 1950s, based on the cost analysis results of BCIS, through appropriate adjustments, the corresponding cost plan can be formed. However, there are many factors that affect the project cost, such as project use, scale, structural characteristics, construction period and so on. And these factors are highly nonlinear and have different impacts on the cost. The cost model at this stage is difficult to accurately reveal the relationship between the variables of the project and its impact on the cost, which leads to the low accuracy of the cost model. The second stage: it began in the mid-1970s. The typical feature of this period is that with the gradual popularization of computer technology and the wide application of regression analysis methods. Through multiple regression analysis, a large number of sample projects are collected, and the independent variables and dependent variables affecting the project cost and their relationships are analyzed. Then, through statistical analysis, the importance of dependent variables is determined in turn, and the weight factors of each variable are calculated, and the construction cost model of multiple regression analysis is obtained, but the model has poor extrapolation. The third stage: Since 1980s, combining with computer application technology, estimation methods based on modern mathematics have appeared. The development of this period is reflected in the following two characteristics: (1) admitting the uncertainty and inaccuracy of the model, and trying to analyze it through probability statistics, usually using Monte Carlo simulation method. (Monte Carlo simulation is a random simulation method. A calculation method based on the theory of probability and statistics. The solved problem is connected with a certain probability model, and the approximate solution of the problem is obtained by statistical simulation or sampling with an electronic computer. (2) Estimation methods for artificial intelligence and knowledge-based computer systems, such as artificial neural network (ANN). ANN method has the functions of automatic "learning" and "memory", and can easily acquire knowledge. It has the function of "association", so it only needs some information to recall the whole picture of the system. Because of its "nonlinear mapping" ability, it can automatically approximate the functions that describe the best internal laws of sample data and reveal the nonlinear relationship of sample data.
In Britain and the United States and other countries, the project cost model has developed to a certain extent and has been widely used, such as www.meancost.com, an online estimation tool provided by Rsmean Company in the United States; British BCIS online approximate estimation software package; Bucknall Austin's construction cost model; Davis Langton and Everett cost models and so on. These cost models provide a good solution for the project evaluation in the early stage of the construction project, which makes it possible to quickly and accurately establish the cost in the early decision-making stage and design stage, and of course, it also needs the support of the cost database.
3. Building cost model 3. 1. Purpose of modeling The purpose of establishing a cost model determines the form and selected parameters of the cost model. At present, the most obvious architectural models include the following two categories: (1) design optimization model. This model is mainly used in the design stage to ensure that the design of the building is value-added, and it can also be used as an important part of the building cost planning process. The main way of this model is to implement the plan. (2) Bid price prediction model This model is mainly used to predict the possible bid price provided by the bidding contractor in the transaction stage, and can also be used to confirm the estimated change rate of the contractor and the influencing factors of the market price. The parameters involved in the prediction model are not as reliable as those in the design optimization model, so the prediction results are likely to be inaccurate.
3.2. Modeling methods Abos and Skrit Mort found many methods in 1982 to improve the estimation accuracy of the engineering design stage when it is close to the final completion during the bidding period. Subsequently, Wilson pointed out in an article in 1984 that these findings led to the following two cost modeling methods. Among them, the former is mostly used in the early stage of engineering design; Later, it was more used after design and molding. Deductive model: This model is based on the statistical analysis of previous engineering data, and the commonly used statistical analysis method is regression analysis. Inductive model: This model attempts to introduce more detailed methods commonly used by contractors in the engineering design stage, and the common method is engineering simulation.
3.3. Model type 199 1 year. In order to classify the existing research results of construction cost model, Newton reviewed the historical research of cost modeling, which involved various models that can be applied by industrialists in the construction industry. Generally speaking, it includes: dynamic programming, expert system, functional dependence, linear programming, manual operation, Monte Carlo simulation, network method, statistical model and regression analysis. Fourthly, the purpose of establishing a cost model is usually to determine the cost of a proposed project quickly and accurately; Accurately determine the overall distribution of internal cost variables in building project design to ensure the credibility of cost prediction and the optimization of design. Building cost model is widely used. By processing the cost data and design parameters of a large number of projects in the past, it brings a lot of convenience to the cost modeling, engineering design and cost planning of new projects. Specific applications include: (1) making the budget of each stage of the project life cycle; (2) Determine the cost-sensitive design parameters, especially those related to space function, service facilities and cost planning.
Next, taking MeansCostWorks.com, an online cost estimation tool in the United States, as an example, we introduce how to quickly establish the estimated cost of a project by using the cost model. The process is simple. * * * includes the following steps: 1, estimation establishment: determination of estimation name, selection of project location, data release time (once every quarter * * four times a year) and labor service form.
2.step 1: Select the project type and basic attributes, in which the project type includes more than 70 building types (British building project classification: apartment 1-3, apartment 4-7, apartment 8-24, auditorium, bank, hospital); For the selected project type, it is necessary to determine the wall type and structure type, such as precast concrete slab/steel frame structure, and more attribute options are provided in the drop-down list.
3. Step 2: According to the selected project type, the model will provide an example, as shown in the following figure. Next, you need to input the basic parameters of the building, including building area, building perimeter, number of floors and building height; Make it clear whether the basement is included, and then give a rate to some expense items.
4. Step 3: Click Calculate, and the cost model will be automatically established according to the entered attributes and parameters, and the cost summary of the cost model can be browsed in time.
5. Check the detailed cost report: For the cost model, the estimation results include detailed composition and construction standard description, as shown in the following figure. Of course, any one of these elements allows flexible cost adjustment, so as to obtain a more suitable project evaluation.
Verb (abbreviation of verb) Conclusion The establishment of building cost model can provide great convenience for us to determine the cost of the proposed project scientifically, accurately and quickly, and make great contributions to the decision-making of the owner and the comparison of design schemes. Through the study of various cost models, it can be found that the similarity of these models lies in finding out the mapping relationship between these characteristics and cost results in various ways based on the characteristics of sample projects and proposed projects, so as to establish a suitable cost estimation model. In China's construction engineering cost industry, with the continuous development of information technology and the maturity of the business model of the cost industry, we have gradually established the engineering cost information data standard and the industry/enterprise engineering cost information resource platform, and on this basis, through the development and application of the construction engineering cost model, we have brought brand-new engineering pricing solutions to the industry practitioners.
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