Uncertainty management in repetitive building projects using WIP buffers

Abstract

Variability in production as a special kind of uncertainty is one of the largest factors that negatively impacts construction project performance. A common construction practice to protect production systems from variability is the use of buffers (Bf). Construction practitioners and researchers have proposed buffering approaches for different production situations, but these approaches have faced either theoretical limitations in its formulation or practical limitations in their application. For overcoming these limitations, a general methodology to design and manage Bf at strategic, tactical and operational scheduling levels based on lean production principles is proposed in this thesis. This methodology is focused on repetitive building projects in which Work-In-Process (WIP) is used as Bf. At strategic level, the methodology considers a multiobjective analytic model (MAM) to design WIP Bf which is based on simulation optimization (SO) modeling and Pareto Front concepts. At tactical level, the methodology uses the SO modeling approach to design WIP Bf which applies Evolutionary Strategies (ES) as optimization search approach. Both approaches MAM and SO modeling allow for the design of optimum WIP Bf sizes by optimizing different projects objectives (e.g. project cost, time and productivity). At operational level, the Rational Commitment Model (RCM) is used in the methodology to manage WIP Bf. RCM is an operational decision-making tool for production planning and commitment negotiation which is constructed as a statistical model. RCM helps to determine optimum WIP Bf sizes optimizing labor productivity. Nomographs for WIP Bf manipulation of practical use were developed for the MAM and the RCM. The application advantages of the WIP Bf design and management methodology were demonstrated through its hypothetical and real application in repetitive building projects at the different scheduling levels. The main results were reduction of the variability impacts, leading to general improvements over project performance. A closer examination of these results showed that the most important impacts were the reduction of project costs and the increment of labor productivity. In addition, this research motivated the explicit use of WIP Bf in the studied projects, changing in some cases the Bf management culture in on-site organization. Further research should be made in order to explore and test the application of the general methodology to WIP Bf design and management as a whole.