HIBIC: Expert system for highway bridge dynamics

The current highway bridge design codes treat the dynamic effect of traffic loads by applying an empirical amplification factor, called the “impact factor,” which is a function of span length only and has little theoretical basis. This paper presents a new and more rational approach for determining the dynamic response of highway bridges to random traffic loads. This approach integrates design-independent knowledge about the dynamic effects of traffic loads into the algorithmic design process. The integration has been done by developing HIBIC (Highway Bridge Impact Consultant), an expert system for determining the most suitable impact stress amplification factor for use in the design of highway bridges. This approach uses heuristics concerning pavement and traffic conditions, as well as a detailed numerical methodology based on concepts of random vibrations and finite elements. The knowledge encoded in the expert system was extracted from the literature, bridge experts, and practicing engineers and was organized into rules. The prototype expert system was tested in several consultation sessions by the researchers and produced very satisfactory solutions in each case. Results of a consultation session for a 70-ft, single-span, composite steel girder/concrete deck structure are presented and discussed. The approach of integrating expert systems with numerical methods used in this paper will have applications in many other design areas.