Gul Polat

The JIT materials management system in developing countries

The just‐in‐time (JIT) approach to materials management appears to be superior to a just‐in‐case (JIC) approach in terms of reducing cost and improving productivity under most circumstances encountered in industrialized countries. However, is it truly more advantageous than the more commonly used approaches in developing countries? Contractors in developing countries may be compelled to keep excessive inventory under some circumstances to help manage uncertainty in the supply chain and production process, high inflation rates, available discounts on prices of large amounts of materials, and price cuts in case of early purchasing. This study presents a comparison of the JIT and JIC materials management systems in terms of total cost of inventory by means of a simulation model that makes use of actual data obtained from an ongoing trade centre project in Istanbul, Turkey. The study suggests that had the JIT system been used in the project in Istanbul the total cost of inventory would have been 4.4% higher than the total cost of inventory in the JIC system currently used.

Predicting the risk of contractor default in Saudi Arabia utilizing artificial neural network (ANN) and genetic algorithm (GA) techniques

The construction project is subject to several risks, one of the most important of which is contractor default because contractor default may increase the final project cost considerably. In the US construction industry, owners commonly shield themselves from the risk of contractor default by transferring this risk to the contractor, who in turn transfers this risk to a surety company. On the other hand, the General Directorate of Military Works (GDMW) of the Kingdom of Saudi Arabia retains the risk of contractor default rather than transferring it to a third party. An artificial neural network (ANN) and a genetic algorithm (GA) are used in this study to predict the risk of contractor default in construction projects undertaken for the Saudi armed forces. Based on this prediction, the Saudi GDMW can make a decision to engage or not to engage the services of a contractor. In case the models are not able to generate reliable predictions (or generate contradictory outcomes), the GDMW will have to augment its budget with contingency funds to be used in the event of contractor default. The outcome of this study is of particular relevance to construction owners because it proposes an approach that can allow them to replace an indiscriminate blanket policy by a policy that is rational, effective, prudent and economical.

Resource Leveling in Line-of-Balance Scheduling

Resource leveling involves minimizing resource fluctuations without changing the completion time of a project. A smooth distribution of resources minimizes logistical problems and results in cost savings. Line-of-balance (LOB) is a resource-based scheduling system that is used in projects that exhibit repetitive characteristics, performs resource allocation as a matter of course, but does not deal with resource leveling. In the past, researchers experienced declines in productivity whenever they leveled resources in different linear scheduling models by adjusting activities’ production rates. The objective of this research is to develop a genetic algorithm-based resource leveling model for LOB schedules that does not impact productivity negatively. This model is based on the “natural rhythm” principle, according to which a crew of optimum size will be able to complete an activity in the most productive way. The “natural rhythm” principle allows shifting the start time of an activity at different units by adjusting the number of crews without changing the duration of the activity in any one unit and without violating the precedence relationships between activities. An LOB schedule is established for a pipeline project and is used to illustrate the proposed resource leveling model. It was observed that the model provides a smoother resource utilization histogram. Performing resource leveling in LOB scheduling without sacrificing productivity is the major contribution of the proposed model.

Multiresource Leveling in Line-of-Balance Scheduling

AbstractLine-of-balance (LOB) methodology produces a work schedule in which resource allocation is automatically performed to provide a continuous and uninterrupted use of resources, but the distribution of resources could be further improved by resource leveling even if multiple resources are involved. The objective of this study is to develop a genetic algorithm (GA)-based multiresource leveling model for schedules that are established by LOB. The proposed model postulates that the production rate and duration of an activity are governed by the resource that requires the longest duration in completing a unit. Once the LOB schedule is established, resource leveling is performed according to the principle of optimum crew size that makes use of a utility data curve, which shows that productivity will suffer if the crew size is different than the optimum crew size, and the principle of natural rhythm that allows shifting the start times of an activity forward or backward at different units of production by ...

Economics of on‐site vs. off‐site fabrication of rebar

Many contractors prefer on‐site fabrication of rebar while others find that off‐site fabrication is more advantageous. The economics of on‐site and off‐site fabrication of rebar need to be compared on the basis of several factors that include the project environment, wages, labour considerations, the initial investment for equipment, waste of rebar, the cost of inventory, cycle time, and supply chain management. This study presents an economic comparison of the on‐site and off‐site fabrication practices of rebar by means of a simulation model that makes use of the factors mentioned earlier. The model is populated with actual data obtained from a trade centre project in Istanbul, Turkey. The article indicates that the off‐site fabrication practice would have been more costly than the on‐site practice in the project in Istanbul, a finding that was to be expected in circumstances that prevail in most developing countries.

Graduate Education in Construction Management

Construction management has become a vital aspect of the construction process over the years. This paper reviews the Master’s programs in construction engineering and management (CEM) offered by departments of civil engineering in the United States. The findings indicate that only 20% of the American educational institutions, which offer accredited civil engineering programs, offer Master’s programs in CEM. Most of the Master’s programs in CEM constitute an effort to convey information to students on mainly six categories, namely, contract administration, project management, scheduling, equipment management, construction technology, and CEM research. It seems that the Master’s programs in CEM do not differ much from program to program in terms of content. When the trends in course offerings are compared in 1982, 1996, and 2008, there seems to be minimal change except for the number of courses in project management that went up significantly while the number of courses in cost estimating went down. The tre...

Impacts of different objective functions on resource leveling in construction projects: a case study

AbstractA review of the recent literature on the models that focus on resource leveling in Critical Path Method networks shows that different objective functions have been used to optimize resource utilization. The main objective of this study is to investigate the impacts of using different objective functions on resource utilization histograms in Critical Path Method networks. For this purpose, nine different resource leveling objective functions were optimized via a genetic algorithm-based model. The model was developed using actual data obtained from a steel framed industrial building construction project. It was found that each of these objective functions generates different resource utilization histograms. In order to determine the improvement levels achieved by resource leveling using nine different objective functions, the improvement percentage in each parameter and the average improvement percentage for each objective function were calculated. Even though the objective function that involves th...

Subcontractor selection using the integration of the AHP and PROMETHEE methods

Abstract.On many construction projects, especially building projects, 80–90% of the tasks are performed by subcontractors. Since the success of the project highly depends on the performances of the subcontractors, selecting the right subcontractor for the right job is critical. Main contractors generally tend to select the subcontractors that offer the lowest bid price. However, working with unqualified and insufficiently financed subcontractors may result in inefficiencies and failures. Thus, a combination of several compromising and conflicting criteria underpinning financial capacity and competencies of the subcontractors should be considered during the subcontractor selection process. This paper proposes an integrated decision approach, which employs analytic hierarchy process (AHP) and preference ranking organization method for enrichment evaluations (PROMETHEE) together, for the subcontractor selection problem. In the proposed approach, AHP is used to analyze the structure of the subcontractor selec...

ANP‐based marketing activity selection model for construction companies

Purpose – The purpose of this paper is to provide construction companies with an analytic model, namely a four‐level analytic network process (ANP) model, to assist them in prioritising and thereby selecting marketing activities which offer maximum return on investment, for which they should primarily allocate their limited resources.Design/methodology/approach – The research methodology of this study mainly involves: reviewing the literature on marketing and construction marketing in order to identify the marketing activity selection criteria and their constituent sub‐criteria; determining the marketing activity alternatives in which construction companies may consider to invest; constructing an analytic model, namely a four‐level ANP model – to assist them in selecting the most viable marketing activities for which they should primarily allocate their limited resources; and conducting two case studies, one in a bidding contractor and the other in a developer, in order to illustrate how the model works.F...

Using ANP priorities with goal programming in optimally allocating marketing resources

Purpose – Construction companies typically allocate limited resources, i.e. human resources and funds, for marketing activities; so, they commonly face the problem of deciding in which marketing activities they should primarily invest and how much resource they should allocate for the selected marketing activities. Indeed, the problem of selecting the best set of marketing activities should be treated as a multi‐objective optimisation problem with multiple obligatory and flexible goals with different priorities, several interdependencies, and multiple constraints on resources. The main objective of this paper is to solve the problem of optimal allocation of scarce marketing resources using the combination of analytic network process (ANP) and zero‐one‐goal‐programming (ZOGP) models.Design/methodology/approach – The research methodology of this paper mainly involves: reviewing the relevant literature on marketing and construction marketing; identifying the marketing activity alternatives in which construct...