Computers have been used extensively for the analysis, detailed design and drawing production of structures. However, they have not been utilized effectively in the preliminary design stage. During this stage, the structural framing schemes that are likely to offer an optimum solution for the given design constraints are identified. Once an appropriate framing scheme is selected, an analytical model which requires initial member sizes is developed to investigate the behavior and performance of the structure under the design loads. An engineer may have to perform an approximate analysis to select the preliminary member sizes; however, experienced engineers may be able to make a reasonable estimate of the required sizes using their past experience with similar structures. A prototype computer-based design tool that utilizes past engineering experience for selecting initial member sizes of structures has been developed and is described in this paper. This tool is applicable to the design of various types of structures through the use of knowledge base techniques. © 1990 ASME.