Graphics based preliminary structural design

The development of graphic based preliminary design programs is appealing because preliminary design involves the consideration of alternatives as concepts or sketches. The use of such a program would allow engineering students and new graduates to gain design experience directly, through their own trial and error. This paper describes a graphic based preliminary design program that was developed to facilitate teaching architect and engineering students about structural design. Graphics Based Preliminary Structural Design Mary Lou Maher, A.M.ASCE and Weiguang Zhang 1. Structural Design Of Buildings The structural design process can be divided into three phases: preliminary design, analysis, and detailed design. During preliminary design, alternative structural configurations are explored and one or more alternatives are selected for further consideration. During analysis, a structural configuration is analyzed and modified until its response to expected loads is satisfactory. During detailed design, the structural configuration is completely specified such that all relevant design constraints are satisfied. The use of graphical interfaces is becoming popular during the analysis and detailed design phases, where graphics provides a friendly interface to conventional analysis and component sizing programs. The development of graphic based preliminary design programs is appealing because preliminary design involves the consideration of alternatives as concepts cr sketches. The formal education of a structural engineer typically emphasizes behavior and analysis cf structural members and systems, that is. the mechanics of evaluating the response of a specified system to its intended environment. The student has very little exposure to th,3 synthesis of structural systems. The practicing structural engineer slowly acquires enough experience, through analysis and detailing, to be prepared to undertake a design problem. Most of the experience of the new graduate is acquired indirectly. The use of a graphics based preliminary structural design program would allow engineering students and new graduates to gain design experience directly, through their own trial and error. This paper describes a graphics based preliminary design program that was developed to facilitate teaching architect and engineering students about structural design. Current work >.n this area involves the development of an 'intelligent' graphical environment in which tf ? program contains knowledge about both the graphical representation of the design and ir j structural implications of the design. 2. SDU: A Structural Design User Interface SDU[11][6] is an environment in which the engineer can graphically 'build a structure using a mouse to move icons representing structural components. The structure can be bu t from components such as beams and columns or from user-defined subsystems such as rig J frames and braced frames. After the structural system is graphically defined, SDU provides 3 set of design aids to help the engineer evaluate the design. These aids include an on-I/* ? calculator, a database of steel sections, a stability checking routine, and a finite elemert Assistant Professor of Civil Engineering, Carnegie Mellon University, Pittsburgh, PA 15213 2 Rese2ch Assistant, Department of Civil Engineering, Carnegie-Ve'ion University, Pittsburgh, PA 15213 University Libraries Carnegie Mellon University Pittsburgh, Pennsylvania 15213 program. The interaction among these aids is handled by SDU and is transparent to the user. 2.1. Design Considerations of SDU Computer software in structural engineering is usually a forwarding only process: the sequence of processes is input-calculate-output. Generally, the user cannot modify the input data after execution has begun. The user-machine interface, data input/output, is a bottle neck of most engineering application software. This issue is especially critical to the development of software to aid preliminary structural planning and design. Structural planning is the study of structural system alternatives within the context of an unique set of program criteria. The goal of structural planning is to select the most appropriate, efficient and economical structural system which satisfies the design criteria while integrating the mechanical requirements and enhancing the intended aesthetic. The structural planning process is most effective if initiated during preliminary design, when major decisions regarding form, function, and aesthetics are being firmly established [10]. SDU was developed to aid the preliminary structural design phase of building design. The design of a building involves coordinating two major disciplines: architecture and structural engineering [4]. In most cases, the structural engineer is expected to meet the requirements of the architectural design. The preliminary structural design is critical to the performance cf the building since many structural systems are feasible. To choose an effective structural configuration, the structural engineer needs to compare and modify alternative feasible configurations. SDU supports this process by facilitating the development and analysis of structural configurations. 2.2. Structural Design Using SDU SDU supports three major activities: synthesis, analysis and feedback. These activities are represented by the following three modules. I.The synthesis module provides a 3D structural system editor for defining the structural system. This module also performs a completeness check and a stability check to insure that a valid input file can be prepared for the analysis program. The displays of 2D structural planes and the 3D structural system give the user visual feedback on the structural system he synthesized. 2. The analysis module provides an automatic interface to a finite element program. The interface translates the structural system description data into the format that can be accepted by the analysis program and then translates the analysis results into SDU's data representation after the analysis finished. 3. The feedback module provides some simple warning signals by checking the maximum stress and maximum deflection of the structural system under the specified load conditions. The magnitude of the internal force of specific components can be displayed by pointing to the component on the screen. SDU focuses on the synthesis and feedback activities and these are discussed in more detail below.