Keywords: three-dimensional computer-aided design, parametric modeling, product data model, STEP, ISO.

Civil engineering infrastructure is developed retaining design knowledge and intent. Generating structure drawing data using computer-aided design (CAD) software during the design phase is one effective means toward that objective. Using CAD software functions, model generating procedures and operations helps to retain the design intent of construction engineers. An environment should be provided in which three-dimensional structure information can be efficiently and smoothly used throughout the project lifecycle. Presently, two-dimensional drawing data are primarily used in the design and construction stages, and the use of three-dimensional information has only recently started. A three-dimensional CAD engine should be therefore developed and operated to create and modify three-dimensional shape information.

This paper proposes a three-dimensional CAD engine for creating and modifying three-dimensional data that retains the design intent of civil infrastructure projects. There are three design concepts required for retaining design intent and applying that information to international construction projects: the parametric modeling approach, data models based on international standards, and consideration of temporal attributes. The proposed three-dimensional CAD engine is composed of a data model that manages data about each function and application program interface. The three-dimensional CAD engines data model is composed of three-dimensional geometric shape data, and manages three-dimensional model data, sketches, modelling operational histories, attributes with temporal elements, and assembly data that manages data represented by assembly models.

Parametric modelling considers both the final geometric shapes and constraint conditions on those shapes, and can recreate three-dimensional geometric shapes by processing constraint conditions and modelling operation histories. The function that determines the final geometric shapes by calculating the geometric constraint on shapes could be subject to geometric constraint problems. The proposed method adopts a graph-solving algorithm for triangular shapes that transforms line segments and circular arcs created by the user into lines and circles according to the constraint conditions. Three-dimensional information should be standardized to ISO 10303, based on accepted international standards. Spatial and temporal information must be used to perform effective structure management. Information is generated over the civil infrastructure lifecycle, including spatial information such as geographical and positional attributes, and temporal information such as the time that a service opens and closes to the public.

The three-dimensional CAD engine prototype system was evaluated using the construction of three-dimensional models of a retaining wall, a prestressed concrete girder, and a gravity retaining wall. The prototype system included the functional requirements for sketching, model extrusion, sweeping, corner chamfering, filleting, and offsets. Experimental results indicate that modelling functions can create three-dimensional model data. Construction engineers create sketches and input geometric constraint conditions using the three-dimensional CAD software based on the proposed engine.

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