Effect of vehicular loading on suspension bridge dynamic properties

Abstract

Effect of vehicular loading on suspension bridge dynamic propertiesSince the 1970s many researchers have attempted to use changes in natural frequencies as means for condition assessment of large civil engineering structures such as bridges, but have faced the challenge of decoupling frequency variations apparently caused by changing operational conditions. In the case of the Tamar Bridge in southwest England, time series of natural frequencies exhibit diurnal variations resulting from a combination of thermal and vehicular loading, whose effects would need to be compensated for in dynamics-based assessment.By examination of several years of monitoring data, the effects of traffic mass have been characterised and compared with other operational effects. While temperature changes appear to have a greater influence for lateral modes, traffic mass is a strong factor in all modes and the dominant factor for the vertical and torsional modes evaluated.Physics-based explanations for the variable effects of vehicle mass have been sought using a finite element model calibrated against experimental data. As a caution for performance prediction in structural dynamics, while acceptable reconciliation of natural frequencies from FE model and measurements was achievable, reconciling simulated effects of changing mass with observed behaviour has not been straightforward due to the complexity of the retrofitted suspension bridge structure studied.Keywords: bridges, long-span; bridges, suspension; cables; damage assessment; finite element method; roads & highways; structural dynamics; structural engineering; suspended structures; traffic engineering. Introduction: variations in bridge loading and dynamic response characteristicsStructural Health Monitoring (SHM) implementations on civil infrastructure (Brownjohn, 2007) have many purposes that include the tracking of time varying loads and responses in order to identify, characterise and diagnose anomalous performance. In particular, changes in dynamic response parameters, e.g. modal properties such as natural frequencies, have been regarded by many researchers as a possible indicator of structural 'damage' (Brownjohn et al., 2011). SHM systems may also be used to validate design assumptions, for example regarding thermal and vehicular loads. Hence there are strong motives for studying time series of structural loads (wind, vehicles and temperature) and dynamic response parameters and their relationships.For long span bridges in particular wind-structure interaction can result in modification of modal parameters and lead to catastrophic instability due to the phenomenon of aero-elasticity (Wyatt, 1992). Such effects can be observed not only in wind tunnel testing but also at full scale, using SHM systems (Diana at al., 1992) and there is a large body of research on the topic.Rather fewer studies have examined the link between thermal loads (diurnal and seasonal temperature variations) and dynamic properties, which are reviewed by Xia, Chen, Weng, Ni and Xu (2012). Of these only a...

Empirical Validation of Bayesian Dynamic Linear Models in the Context of Structural Health Monitoring

“…This model was used to further study the effect of temperature (Westgate et al 2014a) and the effect of extreme loads (Westgate et al 2014b) on the bridge behavior. The dependence between the structure frequencies and the traffic loading was confirmed by a study by Westgate et al (2015) where empirical data were compared with predictions obtained from the structure finite element model.…”

Variable mass loading effect on the long-term ambient response of a freeway bridge

“…In Westgate, Koo, and Brownjohn (2015), both temperature and mass loading effects are treated for a suspension bridge. Some foundations of this study are the hourly statistics of different vehicle classes and the diurnal variation of different resonance frequencies determined from vibration measurements.…”

A Kernel-Based Method for Modeling Non-harmonic Periodic Phenomena in Bayesian Dynamic Linear Models

“…For instance, in the field of dam engineering, the ambient air and water reservoir contribute to the establishment of a thermal gradient through the structure, which leads to a periodic nonharmonic pattern on the observed displacements time series (Léger and Leclerc, 2007;Tatin et al, 2015;Salazar and Toledo, 2018). In bridge monitoring, the effects related to traffic load variations generally display a non-harmonic weekly periodic pattern due to the day/night as well as the weekdays/weekend alternance (Westgate et al, 2015;Goulet and Koo, 2018).…”