بررسی عوامل موثر بر هزینه در بخش پروژه های ساخت و ساز

Construction cost overrun is a common problem in construction industries. The objective of this research is to extract the key cost-influencing factors with new concept and methods to help control the expenditure. Hence, this research adopts the Modified Delphi Method (MDM) with 2 groups and 2 rounds and Kawakita Jiro method (KJ) to consolidate the experts' opinions and identify and rank the key factors that affect project costs. Ninety cost-influencing factors are collected from literary review and interviews with experts with practical cost control experiences in the construction companies (Group 1). The KJ method is used to consolidate these factors into 4 categories and down to a total of 42 factors. 2 rounds of questionnaires are then conducted to filter the key factors. In order to verify views of those in the first group, Group 2 consists of experienced experts from the public sectors, consulting firms and construction companies as a comparison. Results of the analysis indicate that there are 16 key cost-influencing factors. Severity Index computation was then adopted to rank these key cost-influencing factors. The study renders that clearly defined scope of project in the contract and cost control are the major determinants for cost overrun.

It's customary in construction industries to win projects with the lowest bids. Therefore, without controlling key cost-influencing factors, construction companies will not be able to control the expenditure effectively, which will in turn increase project costs and affect overall profit. In fact, construction cost overrun is a common problem in construction industries. Flyvbjerg et al. (2002) pointed out that historically, large construction projects have been plagued by cost and schedule overruns. Shane et al. (2009) stated that final project costs have been higher than the cost estimates prepared in too many cases. Doloi (2011) brought up that cost overrun is a chronic problem for most projects. Love et al. (2013) calculated cost overruns from 276 construction and engineering projects and revealed a mean cost overrun of 12.22%. No significant differences for cost overruns were found among contract size, project type, and procurement method. Kaming et al. (1997) also discussed construction time and cost overruns in developing countries such as Nigeria, Saudi Arabia and Indonesia. However, construction overrun is not unique to developing countries. It is a worldwide issue worsened by the global financial crisis due to increasing price competition. As construction companies usually rely on various financing approaches to meet their capital needs during construction, the inherent financial constraint poses further influence on the overall costs and the ultimate profit if the key cost-influencing factors cannot be controlled. Therefore, this paper takes the standpoint of the construction companies to explore and discuss key factors that affect project costs during construction. The methodology integrates literary review, interviews, the KJ method (Kawakita Jiro method, affinity diagram), and the Delphi Expert Assessment (with 2 groups and 2 rounds) to locate the key cost-influencing factors from various layers, and to assist the construction companies with effective cost control both during the preparation stage and after the construction proceeds in order to reduce risks derived from costs or escalating expenditure.

Many literatures and actual projects indicate that construction cost overrun is a common problem in the construction field. Identifying the cost-influencing factors is the first step toward addressing such problem. If construction companies can effectively control these key factors and formulate prevention strategies, it is possible not only to avoid cost overrun, but also to increase the overall profits for the project. In order to factually provide the key cost-influencing factors to the construction companies, the cost-influencing factors are analyzed and discussed from the perspectives of the construction companies. The KJ method and MDM with 2 groups and 2 rounds are utilized to improve the traditional Delphi method, and Severity Index (SI) computation was adopted to rank the factors. According to the result of the SI, the highest to the lowest categories are Scope of Contract, Project Risks, Management and Technique, and Environmental and Circumstantial Influence. There are 16 key cost-influencing factors in these 4 categories. Factors with the strongest influence include Clearly Define the Scope of Project in the Contract, Cost Control and Contract Dispute. In practice, construction companies must clearly understand the client's needs through communication during the initial stage of the project. They must have clear understanding of the scope of the contract and ask the clients for necessary clarifications regarding the drawings and specifications prior to signing the contract to avoid pricing disputes. Additionally, during project implementation, the contractors should fully implement cost-control measures. Construction companies can also use the remaining factors to conduct a thorough investigation that is tailored to the characteristics of the project and the client prior to the project commences in order to minimize uncertainties and reduce the chance of cost overruns.