UC Berkeley

In the current practice of collecting construction cost data, the cost of an installed component is compiled by adding up the cost of materials plus the cost of all resources used to install that component. This total includes inefficiencies and wastes which are inherent in construction processes, especially in projects that do not rigorously use methods to eliminate process waste or that do not use continuous improvement. Traditional cost models such as Parametric, Assembly and System, and Unit Price and Schedule models rely on historical data to model the cost of new designs. These cost estimates are inflated by the wastes embedded in the historical databases, and result in increased estimated task durations and excessive estimated resource needs.

In Target Value Design (TVD), product- and process design are integrated and the design team needs rapid cost feedback to trade off design alternatives. However, traditional cost models do not reflect cost changes due to changes in process design. Therefore, a cost model that takes into account the cost implications of logistics and construction processes can better support TVD in integrating product- and process design. This raises a need for an alternative cost modeling method, which must be able to specify: (1) cost changes due to changes in product design (i.e., changes in materials, shapes, or dimensions), and (2) cost changes due to changes in process design (i.e., changes in sequencing, logistics plans, or construction processes). This dissertation provides a framework for a Process-Based Cost Modeling (PBCM) method including three phases: (1) collecting process- and cost data, (2) mapping process- and cost data to objects of a Building Information Model (BIM), and (3) providing cost feedback to inform TVD.

This dissertation develops a theoretical understanding of cost modeling in TVD and argues for the use of a PBCM to support TVD during the Design Development phase. It presents processes and tools that could aid in its implementation. It also examines the role of BIM in implementing the PBCM framework and explains the role of process modeling in a virtual construction environment in supporting PBCM.

This dissertation delivers a proof of concept of a PBCM framework and validates it through case studies and professionals' evaluations. The first case study analyzes conventional practices of designing, procuring, estimating, and installing a window system in a residential project inSan Francisco, CA. The second case study investigates the application of the model-based process simulation, the PBCM, and the Choosing By Advantages (CBA) Decisionmaking System to evaluate alternatives of Viscous Damping Wall (VDW) installation in the Cathedral Hill Hospital (CHH) project in San Francisco, CA. The third case study examines the application of a software tool to integrate product- and process cost of the VDW system with a BIM model.

Research findings illustrate the effectiveness of PBCM in providing rapid cost feedback to designers that facilitates the process of design to targets. In addition, PBCM helps to make both process-related cost and product cost explicit to designers when they are analyzing design alternatives. Further research can refine steps of PBCM applied in Design Development and explore the application of PBCM in design phases other than Design Development such as Conceptual Design or Construction Document phases. Further research is also needed to advance tools to facilitate the implementation of PBCM in the Lean Project Delivery System^TM.