Three-dimensional dynamic deflections and natural frequencies of a stiff footbridge based on measurements of collocated sensors

摘要

A redundant system of collocated geodetic sensors and an accelerometer were used to measure the displacements of a stiff, 40-m-long footbridge excited by essentially vertical synchronized jumps. A main output of the measurements was that excitations produced vertical deflections (of the order of several mm), lateral deflections with an amplitude about half that of the vertical, an effect known for various bridges, and also smaller-scale longitudinal deflections, probably induced by the vertical ones. This combination of deflections in three axes is not an artifact of measuring errors, or of limitations of specific instruments, and do not reflect random effects, for they have been observed in different experiments by different sensors (Global Navigation Satellite System-GNSS, i.e., Global Positioning System-GPS plus the Russian Global Navigation Satellite System-GLONASS), robotic total stations-RTS (or robotic theodolite), and an accelerometer, and were tested through control of the measurement errors from time series reflecting no bridge oscillations. In all cases, sensors provided similar estimates of deflections and of deflection-derived dominant frequencies, which were found equal to those derived from the accelerometer. The proposed instrumentation and methodology seem suitable to control deflections of bridges in cases that visibility of satellites is poor or is disrupted by vehicle circulation. Measurement-based modeling of bridges described might be useful for understanding the structural behavior of bridges under several types of dynamic loads and can contribute to the displacement-based design of structures. Copyright © 2013 John Wiley & Sons, Ltd.