Constructability reasoning based on a 4 d facility model

Improving the constructability of a facility design is a key concern for owners, designers, and builders of facilities. Prior research has shown that a product model based on a 3D CAD model of a facility can support constructability reasoning to assist a project team in identifying constructability issues. This paper shows how a 4D facility model (3D plus time) improves constructability reasoning. A 4D model helps expose constructability problems related to access, temporary support, availability of work space, and completion of prerequisite work. The paper explains the 4D model and its attributes in detail and gives specific examples of automated constructability reasoning. It discusses the advantages of 4D models over 3D models for recognizing constructability problems in the planning and design stages of a project. INTRODUCTION Improving the constructability of a facility design has become a key concern for owners, designers and builders of facilities as decreased construction costs and improved construction operations benefit everyone. Recognizing constructability issues early in the project delivery process can help to identify design constraints which limit a constructors ability to plan and perform construction operations effectively. These design constraints often cause improper construction sequencing which can result in construction delays, re-design, or decreased crew productivity, ultimately leading to higher costs and a sub-optimal project performance. Constructability reviews are routinely performed after conceptual design to ensure that construction knowledge is incorporated in the design phase and constructability problems are minimized. But how does one really know if a design is constructable? Constructability reviews are a part of the evaluation of a design but how much can one ascertain about how building components will go together when looking at a static 2D or 3D design. The best way to know if a design is truly constructable would be to test it. Four dimensional (4D) CAD models allow design and construction professionals to test different design and sequencing alternatives. A symbolic (object-oriented) 4D model has the potential to support automated constructability