System dynamics modeling of design and build construction projects

Design and build (D/B) construction methods have gained more importance in recent years for their potential advantages in improving project performance. There are, however, a number of problems that are commonplace in D/B procurement, which, when they interact with each other, can lead to project time and cost overrun problems. The most important among them are design changes, together with communication and coordination lapses among concerned parties. Past research has focused only on the characteristics of the traditional construction, or separate subsystems such as different phases or human resource input to projects. An attempt is made in this paper to improve D/B project time and cost performance. A generic system dynamics model is developed that incorporates major subsystems and their relationships inherent in D/B constructions projects. It is validated and calibrated for a typical large D/B infrastructure project using time and cost overrun problems experienced in Thailand. Extensive simulations with many policies, individually or in various combinations, show that improvement in time or cost can be made with proper policy combinations that reflect strong interactions between the whole design and build system and can be derived only if these interactions are accounted for. To achieve overall improvement in both time and cost, the combination of full overtime schedule, average material ordering, and fast track construction with moderate crashing of design is most appropriate. If cost is the focus, extending the construction schedule, combined with material ordering based on actual need, and design and build with traditional construction method is the best solution.