An integrated two and three dimensional data structure for a structural engineering CAD system

The uptake of CAD in structural engineering has been low when compared with other engineering disciplines. A legacy of the low level of CAD usage is that many of the currently available systems originated outside the industry and, generally, do not adequately meet the needs of the structural engineer. These needs are re-evaluated within the context of a virtual RAM environment, and a set of corresponding user-requirements identified. It is argued that the key to addressing these lies in the underlying data structure of the CAD system. A prototype data structure is proposed based on new concepts. The prototype data structure seeks to provide an effective integration of 2D drafting and 3D modelling enabling both techniques to be applied to the greatest advantage. It is designed as a hybrid system composed of a hierarchical (graphical) data structure which is bound to an extensible quasi-relational (non-graphical) data structure. Other features of the data structure include its user-orientated nature, which makes it visible and manipulable by the designer, and its departure from the layering concept. It also employs a `dual view concept', which provides for mutual coordination of the physical and logical aspects of a design, and adopts a flexible and problem-oriented approach to the organisation of design information. Ease of use and the ability to work at a high level of abstraction are also key attributes. The concept of integration embodied in the design of the data structure permits four levels of integration to be addressed to varying extents: 2D drafting and 3D modelling; graphical and non-graphical data; the user interface and the data structure; and linkage of the system to other applications. The consistent philosophy of the data structure also provides for the incorporation of an efficient memory management system. Evaluation of the prototype data structure was based on two examples which are presented in the thesis. The examples served to demonstrate the above concepts which proved beneficial to the structural engineeer in many respects. The integration of these concepts into the design of CAD systems for structural engineering is recommended.