A knowledge-based expert system for optimum design of bridge trusses

A prototype coupled knowledge-based expert system has been developed for performing detailed optimization of bridge trusses subjected to moving loads, called BTEXPERT. The scope of BTEXPERT is limited to the optimum design of four types of bridge trusses, i.e. Pratt, Parker, parallel-chord K truss, and curved-chord K truss for a span range of 100-500 ft. Design constraints and the moving loads acting on the bridge are based on the American Association of State Highway and Transportation Officials (AASHTO) specifications.;The structure and functions of various components of BTEXPERT are presented. Various focus control blocks are described along with the relevant heuristic rules and procedures. The approach to expert systems used in BTEXPERT is novel in at least two respects. First, mathematical optimization is introduced in the expert system. Second, the knowledge base of BTEXPERT contains not only heuristic rules and experiential knowledge but also knowledge obtained through machine experimentation.;A heuristic procedure is presented for finding the maximum tensile and compressive forces in statically determinate and indeterminate bridge trusses subjected to AASHTO moving loads. This approach is significantly more efficient than the brute-force method of generating the nodal load vectors due to the moving loads positioned at numerous locations along the span and performing numerous structural analyses.;For improving the convergence and efficiency of the bridge truss optimization process a hybrid optimization approach has been developed by combining the zero order explicit approximation formulation with the explicit stress constraints formulation.;A synergic man-machine approach has been presented for practical layout optimization of trusses. The synergic man-machine approach to layout/shape optimization is based on changing certain key-dimension(s) of the truss and performing optimization for each layout by taking advantage of the interactive environment of computers with graphic facilities. The synergic man-machine approach is used as a knowledge acquisition tool for finding the optimum layout for four types of bridge trusses used in BTEXPERT.;Finally a sample consultation session is presented to demonstrate the use of BTEXPERT as an "intelligent assistant" for obtaining a practical optimum design bridge trusses.