Parametric 3D modeling in building construction with examples from precast concrete
Introduction
The theoretical benefits of computer-integrated construction—lower engineering costs due to automated analysis and drafting, lower production costs due to reduced error rates and data integration supporting management functions and automated fabrication—have been widely stated [6], [34]. Practice, however, lags far behind theory. Computer-aided design and drafting (CADD)1 has been widely adopted by precast concrete design and fabrication companies, as it generally has by the rest of the construction industry. A survey of North American precast concrete producers found that 96.3% use CADD in-house; the remainder outsource their design work to consultants, whom the survey found to be 100% CADD users [23]. However, electronic drafting has not resulted in any change in the process workflows. In CADD, computers are used to generate drawings, which are the medium of communication during the production and erection stages of the precast process. CADD drawings are only readable as graphics, so that information transfers for process activities such as structural analysis, bills of material, coordination between building systems, quality control, rebar fabrication and piece production, must be done by people. For many of these activities, the labor cost of translating data from CADD to some automation application negates the economic viability of the automation; manual data entry is also prone to human error. In practice, little of the design and production automation potential inherent in information technology is exploited with CADD; in terms of the business, design and production process, CADD has simply replaced physical drawing boards with electronic ones.
In many manufacturing industries, on the other hand, drafting has been replaced by computer-aided design based on 3D solid modeling. Solid modeling supports a wide range of automation and quality control applications that utilize the information generated. In the field of building design and construction, the parallel potential benefits include the use of knowledge-based design tools, automated detailing and drawing production, automated interfaces to structural, thermal, vibration and other analyses and quality improvements. The impacts are not limited to design and engineering—automatic fabrication and assembly is also possible (e.g., [20], [22]).
With few exceptions (most notably Frank Gehry's use of CATIA and Xsteel for the Walt Disney Concert Hall [16]), parametric solid modeling software has not been applied in the architecture, engineering and construction (AEC) industry. The primary reason is the additional human effort required to build a geometrically and topologically accurate solid model of a building and the corresponding absence of economic incentive for building designers to undertake that effort [9]. However, a new generation of 3D parametric modeling tools is now becoming available (e.g., Autodesk Revit, Graphisoft ArchiCAD, Bentley Triforma, Design Data SDS/2, Tekla Xsteel). These hold the potential to make modeling of buildings and their subsystems, such as precast concrete structures, cost effective, thus opening the door to many additional design, production and erection benefits.
This paper surveys technical issues associated with the use of parametric solid modeling to design buildings at construction levels of detail. It begins with a review of solid and parametric modeling concepts and software, describing their essential features as they apply to the building industry. Several examples are reviewed. We then detail a range of issues that must be considered in any implementation of parametric modeling software for building design and construction. The issues focus on the specific characteristics of building design. The first set is applicable to computer modeling of buildings in general; the second set relates specifically to parametric modeling. An example of a parametric model of a small precast concrete assembly is presented to illustrate some of the issues discussed. The work is based upon the authors' involvement with the North American Precast Concrete Software Consortium's (PCSC) specification of a software system for integration and automation of its engineering design procedures [8]. Although the examples are drawn from the realm of precast concrete, the discussion applies in principle to other sectors of the construction industry.
Section snippets
Early solid modeling
The manufacturing and aerospace industries began using three-dimensional computer-aided design (CAD) systems based on surface modeling in the early 1970s. These industries recognized that accurate representation of a part's geometry could lead to automatic analysis of the part's behavior (structural, thermal, acoustic, etc.) and support its automated fabrication. However, defining the 3D shape of a mechanical part was very complicated, tedious and error prone, requiring cutting and trimming of
General considerations for computer modeling of buildings
The following characteristics apply not only to parametric modeling; they are desirable for any practical building modeling system. In the case of parametric modelers, however, they are essential conditions for realization of the benefits that can be achieved by implementing the functionality outlined in the previous section.
Special considerations for parametric modeling of buildings
In building design, priority is given to integration across different systems and assemblies; in mechanical design, priority is often placed on optimization of individual components for mass production. This influences the functional and performance requirements of parametric CAD systems for building design, when compared with the design of mechanical parts. Firstly, buildings are composed of very large numbers of distinct parts, arranged in various functional and production-specific
Precast modeling example
The following simple test structure (Fig. 8) illustrates the complex parametric behavior required to support the typical operations a precast designer must perform in order to build and maintain a 3D model of a building. The structure consists of one bay of a building, defined by two sets of parallel grid lines (denoted A, B, 1 and 2). Two columns, positioned relative to the intersections of axes A-1 and A-2, support a spandrel beam at the level of the first-floor construction plane. The
Conclusions
In the first CAD revolution in the AEC industry, designers moved from manual drafting to computer-aided drafting. This revolution is largely complete, as most architectural and engineering practices have now adopted the technology. New releases of commercially available software deliver gradually decreasing levels of functional enhancements over their predecessors. The second CAD revolution in the AEC industry, introducing 3D parametric solid modeling, has begun; research and development
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