Profiles of Design Dimensions and Fundamental Natural Frequencies for Steel Interstate Highway Bridges in Southeastern Missouri

Abstract

Results from a research study funded by the U.S. Geological Survey as part of the National Earthquake Hazards Reduction Program are presented. The first objective of this study was the development of a database for all 211 bridges along Interstate 55 in the New Madrid region of southeastern Missouri. Profiles for five key dimension parameters (which are stored in the database) were developed, and the results for steel highway bridges are presented here. The second objective was to perform field ambient vibration analyses on 25 typical bridge spans along the I-55 corridor. These 25 spans included 17 steel girder spans. Eight seismometers were used to record ambient vibrations at four locations on each bridge span. These records of bridge motion versus time were each subjected to a fast Fourier transformation, and plots of amplitude versus frequency were generated. These plots were used to determine the fundamental vertical and lateral frequencies of the bridge spans measured. The third objective was to use these fundamental frequencies in conjunction with the dimension parameters stored in the database to develop empirical formulas for estimating fundamental frequencies. These formulas were applied to all 211 Interstate highway bridges in southeastern Missouri. Profiles for both the fundamental vertical and the lateral frequencies were then developed, and the results for the steel highway bridges are presented here.