System Identification of Alfred Zampa Memorial Bridge Using Dynamic Field Test Data

Abstract

The Alfred Zampa Memorial Bridge (AZMB), a newly built long-span suspension bridge, is located 32km northeast of San Francisco on interstate Highway I-80. A set of dynamic field tests were conducted on the AZMB in November 2003, just before the bridge opening to traffic. These tests provided a unique opportunity to identify the modal properties of the bridge in its as-built condition with no previous traffic loads or seismic excitation. A benchmark study on modal identification of the AZMB is performed using three different state-of-the-art system identification algorithms based on ambient as well as forced vibration measurements. These system identification methods consist of: (1) the multiple-reference natural excitation technique combined with the eigensystem realization algorithm, (2) the data-driven stochastic subspace identification method, and (3) the enhanced frequency domain decomposition method. Overall, the modal parameters identified using these system identification methods are found to be in very good agreement for each type of tests (ambient and forced vibration tests). For most vibration modes, the natural frequencies and mode shapes identified using the two different types of test data also match very well. However, the modal damping ratios identified from forced vibration test data are in general higher than those estimated from ambient vibration data. The identified natural frequencies and Submitted to Journal of Structural Engineering, ASCE-2-mode shapes are finally compared with their analytical counterparts from a three-dimensional finite element model of the AZMB. The modal properties of the AZMB presented in this paper can be used as baseline in future health monitoring studies of this bridge.

Bridge Damage Detection Based on Vibration Data: Past and New Developments

“…Various modal parameters such as natural frequency shifts and other modal properties such as mode shapes, damping ratios, and modal curvatures have been traditionally used to detect damage (Casas and Aparicio, 1994). These properties should be dynamically obtained from a bridge before its initial opening, if possible with ambient and forced vibration, as Conte et al (2008) and He et al (2009) conducted with the Alfred Zampa Memorial Bridge.…”

Finite-Element Model Updating for Assessment of Progressive Damage in a 3-Story Infilled RC Frame

“…Outputonly system identification methods, which have been successfully applied for system identification of linear systems (He et al 2009;Moaveni et al 2011), are based on the assumption of a broadband (ideal white-noise) input excitation. However, in this set of experiments, the white-noise base excitation inputs were significantly modified by the shake table system dynamics, and consequently, the table motions did not satisfy the broadband assumption as illustrated in Fig.…”

Multimodel Structural Performance Monitoring

“…Several system identification approaches have been applied to full-scale civil engineering structures (Brownjohn et al 2003;He et al 2009;Morassi and Tonon 2008;Teughels and De Roeck 2004). Most of these methods are based on dynamic testing which have their strength and weaknesses.…”

“…Moreover, all significant modes may not be identifiable from ambient vibration measurements. He et al (2009) notes the advantage of several system identification methods for cross validation purposes in order to reduce the number of missing modes. Brownjohn and Xia (2000) report that when performing ambient vibration monitoring, fundamental hypothesis requiring input nonstationarity is inevitably violated.…”