Assessment of Long-Span Bridge Performance Issues through an Iterative Approach to Ambient Vibration–Based Structural Identification
Publication: Journal of Performance of Constructed Facilities
Volume 30, Issue 5
Abstract
This paper presents a diagnostic case study of a long-span bridge, which uncovered the root cause of unsymmetric vibration performance that appeared to point to deterioration. In this case study, two iterations of the structural identification (St-Id) process were applied to (1) develop a comprehensive finite-element (FE) model (inclusive of approach spans) representative of the general dynamic properties (frequencies and mode shapes), and (2) check that the response magnitudes were consistent with those expected from vehicular traffic. More specifically, this research confirmed the perceived vibration discrepancy with direct measurements, conducted a comprehensive (including approach spans) ambient vibration monitoring of the bridge, updated an FE model to match measured modal parameters, and performed a series of simulations to both validate the updated model and understand the root cause of the unsymmetric vibrations. Through this process, it was determined that the unsymmetric vibrations resulted from the approach span designs, which provided significantly different levels of lateral stiffness to the primary bridge. Additionally, upon repeating the test following the replacement of all expansion bearings with neoprene bearings, similar levels of vibration asymmetry were observed, which further supported the diagnosis that this behavior is an inherent characteristic of the bridge. In addition to introducing an iterative St-Id process that makes use of both modal parameters and magnitude information (derived from an ambient vibration test), this paper illustrates the importance of explicitly including the approach spans within the St-Id of long-span bridges. In this case, ignoring the influence of the approach spans would likely have resulted in the erroneous conclusion that some damage or deterioration within the main spans was causing the unsymmetric vibrations observed.
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Acknowledgments
The research reported herein was supported by the National Science Foundation under Grant No. CMMI-0846591. The writers would like to express their appreciation to the following individuals in light of their support in the extensive work carried out to obtain the vibration measurements reported herein: John Prader, Jeff Weidner, Charles Young, Jack DiGiovanna, and Michael Ott.
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© 2016 American Society of Civil Engineers.
History
Received: Aug 21, 2015
Accepted: Dec 22, 2015
Published online: Mar 15, 2016
Discussion open until: Aug 15, 2016
Published in print: Oct 1, 2016
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