Design Iteration Control Framework for Offsite Building Projects

Abstract: During the course of the studies this thesis is based upon a designiteration control framework for offsite building projects wasconceptualized. The ultimate goal was to develop a robust tool to assistproject managers to find the optimal balance between maintainingsufficient project-by-project iteration to solve complex designproblems, and avoiding excessive iteration, which unnecessarilycomplicates design and scheduling. In total three frameworkcomponents were developed. The thesis describes the problemaddressed, presents background information, describes the developmentof the framework components, and discusses their potential utility inconstruction contexts.Offsite building has been advocated as an effective means toincrease product quality while reducing project duration and cost,provided the design process is efficient. A main challenge in managingthe design process is iteration. It must be possible to alter details inorder to react to changes in conditions and meet project-specificrequirements, but unplanned design iteration should be avoidedbecause it can lead to departures from planned activity sequences,thereby increasing both scheduling and design complexity. In projectmanagement literature, two groups of approaches (system dynamic andmodel-based) for managing design have been established. The firstgroup is used to identify factors that affect design iteration and thusactions that could improve the process, while model-based approachesare used to investigate and predict possible effects of specific designiterations on project outcome. A problem is that current methods donot support attempts to quantify effects of specific improvementactions on project outcome, which could greatly facilitate effectivemanagement of resource-constrained projects.Due to the notion that all building projects are unique (which isprevalent in construction management literature) and the complexstructure of design processes, it is generally difficult to identify and mapiteration phases, cycles or loops in terms of specific actions.However, in offsite building projects it is reasonable to assume thatthe same design activities have to be carried out in all projects(regardless of the variation in their conditions), albeit to varying extentsand, furthermore, that the precedence relations between activities isinvariant. Thus, in this thesis (and the underlying studies) offsitebuilding design projects are considered as realizations of a process thatis characterized by varying activity extent but invariant precedencerelations.The suggested framework is a model-based continuousimprovement approach (plan-do-check-act cycle). Essentially it consistsof cycles of observing effects of applied actions over the course ofseveral projects, drawing inferences about the effectiveness of theactions from the observations, identifying improvements, applyingimproved actions and observing their effects. The frameworkincorporates techniques such as design structure matrix (DSM)-basedsimulation and Monte-Carlo inverse analysis. It comprises a method tocalibrate DSM-based simulation models, a relative measure of designiteration, and a method to identify the most critical process phases (interms of design iteration). The framework is mainly based on datarelated to the design process of a two-storey offsite timber framebuilding, supported by probability density functions for 35 other offsitetimber frame multi-storey building projects. The practical applicabilityof the framework components has been tested in simulationexperiments where they were applied to assess design processes relatedto this type of project, with variations in key conditions. To a lesserdegree the framework was also applied to a planning and buildingapproval process. The results of the simulations indicate that thecomponents have high potential practical applicability, providedaccurate records of activity execution sequences and correspondingwork amounts are available.