Use and interpretation of strong-motion records from highway bridges

This report describes how strong-motion records obtained from the earthquake-induced motions of highway bridges may be analyzed for use in the evaluation of bridge designs and bridge design procedures.

This report is divided into five principal sections. The first section describes strong-motion instrumentation and strong-motion records. In the second section, a mathematical model for the dynamic response of bridges to strong ground shaking is formulated. The third section describes how analog records scaled by hand can be analyzed. Force levels throughout bridges and mathematical model parameters are found from hypothetical strong motions for two example bridges. The fourth section describes how digitized records can be analyzed. A linear least-squares fitting procedure in the time domain for identifying mathematical model parameters from recorded strong motions is described. Hypothetical motions for three example bridges are analyzed using this procedure to yield best-fit mathematical models. The last section consists of appendices. Included are a more extensive introduction to dynamics of structures and listings of the programs used to identify the best-fit mathematical models.