Free and ambient vibration of Brent-Spence bridge

The main objective of this study is to assess the structural integrity of the double-deck through-truss Brent-Spence bridge when subjected to a seismic event from the New Madrid, Wabash Valley, or Anna seismic zones. To achieve this, the scope of work was divided into several tasks as follows: field testing of the main bridge, analytical modeling, determination of the site-specific ground motion, and seismic response analysis. This paper deals with the first two tasks. The ambient vibration properties of the main bridge were determined through field testing under traffic induced excitation. The purpose of measuring the ambient vibration properties was to determine the mode shapes and the associated natural frequencies. These vibration properties were subsequently used as the basis for calibrating the finite-element model for seismic response analysis. A three-dimensional finite-element model of the main bridge was developed for the free vibration analysis. The seismic response analysis using this calibrated finite-element model is presented in the second part of this two-part paper.