Evaluation of construction processes: Traditional practices versus lean principles

Lean manufacturing theory has been the focus of research in several fields in the last decade, including the construction industry. The main philosophy behind lean theory is to differentiate value from waste. To implement lean theory there are five key lean principles that need to be taken into account. They are: (1) specify value, (2) map the value stream, (3) make value flow, (4) pull value and (5) pursue perfection (Womack and Jones 1996).;Transferring these principles from the manufacturing to the construction domain is not easy and requires careful examination. Modifying real construction processes is expensive, time consuming and difficult. This study evaluates the applicability of lean principles when applied to construction processes using computer simulation. Evaluating the applicability of lean principles implies considering the peculiarity of the construction industries. This raises several questions, including: Which principles are most effective? What are the consequences of such an implementation to construction processes? Are construction buffers effective? And to what extent do project characteristics influence lean application to construction?;To answer these questions, field observations on several steel projects were conducted to study, analyze and evaluate their erection processes. Data for structural steel erection processes were modeled in ExtendRTM to form the experimental tool for evaluating lean principles. In all case studies, ranging from simple to complex, the simulated principles improved project performance and performance improved dramatically when all principles were simultaneously applied. Moreover, results of simulation analysis indicate that the more complex projects exhibit increased "lean" process improvement when compared to the simpler projects. However, the erection process became volatile and fragile when it was subjected to changes and uncertainties from outside of the process.;In implementing lean theory to construction, certain lessons were learned. First, site layout and site planning are very crucial in reducing the magnitude of contributory activities. Second, redesigning construction processes requires not only reducing non-value adding activities but also reconsidering the efficiency and the sequence of value adding activities. Last but not least, managing the supply chain, where sequences and times of deliveries are specified, significantly improved construction processes.