Structural Health Monitoring for Performance Assessment of Bridges under Flooding and Seismic Actions

Bridges can be subjected to damaging environmental actions due to flooding and seismic hazards. Flood actions that result in scour are a leading cause of bridge failure, while seismic actions that induce lateral forces may lead to high ductility demand that exceeds pier capacity. When combined, seismic actions and scour can lead to effects that depend on the governing scour condition affecting a bridge. Loss of stiffness under scour can reduce the ductility capacity of a bridge but can also lead to an increase in flexibility that may reduce seismic inertial forces. Conversely, increased flexibility can lead to deck collapse due to support loss, so there exists some uncertainty about the combined effect of both phenomena. A necessary step towards the performance assessment of bridges under flooding and seismic actions is to calibrate numerical models that can reproduce structural responses under different actions. A further step is verifying the achievement of performance goals defined by codes. Structural health monitoring (SHM) techniques allow the computation of performance parameters that are useful for calibrating numerical models and performing direct checks of performance goal compliance. In this paper, various strategies employed to monitor bridge health against scour and seismic actions are discussed, with a particular focus on vibration-based damage identification methods

Field Deployment of an Ambient Vibration-Based Scour Monitoring System at Baildon Bridge, UK

Scour, the loss of material around bridge foundations due to hydraulic action, is the main cause of bridge failures in the United Kingdom and in many other parts of the world. Various techniques have been used to monitor bridge scour, ranging from scuba divers using crude depth measuring instrumentation to high-tech sonar and radar-based systems. In contrast to most other techniques, vibration-based scour monitoring uses accelerometers to provide real-time monitoring whilst also being robust and relatively simple to install. This is an indirect technique that aims to measure changes in the dynamic response of the structure due to the effects of scour, rather than attempting to measure scour directly. To date, research on vibration-based scour monitoring has been limited to laboratory-based experiments and numerical simulations, both of which have indicated that the natural frequencies of bridges should indeed be sensitive to scour. Due to pre-existing scouring, and planned repair work, Baildon Bridge in Shipley, Yorkshire provided a rare opportunity to validate vibration-based scour monitoring in both a scoured and a repaired state. A sensor system was deployed with 10 Epson low-noise, high-sensitivity accelerometers to measure the ambient vibration of the bridge before, during, and after the repair. This paper describes the installation of the accelerometer-based system, the numerical modelling of the bridge and the model updating carried out with the initial findings. Initial operational modal analysis has found two consistent vibration modes of the bridge that were scour sensitive according to the updated numerical model. But the variability of the measured frequencies, compared to the expected scour induced change in frequency, indicates a potential challenge for monitoring scour of small span bridges with vibration-based methods

Effect of Pier Inclination Angle on Local Scour Depth Around Bridge Pier Groups

The primary objective of this study is to investigate experimentally local scours around bridge pier groups at various inclination angles of piers and also to develop empirical local scour depth equations. In the study, two bridge pier groups are used. In each pier group, the most upstream and downstream piers are placed in an inclined manner at 10 degrees and 15 degrees. The vertical case was also employed for comparison purposes. Seventy-two experiments each lasting 6 h are conducted under uniform-flow and clear-water conditions for a range of water depths and velocities on the uniform bed material. This study confirms that inclination of cylindrical piers located at the most upstream and downstream locations of pier groups directly affects the local scour in a favourable manner, with a substantial reduction in the local scour, especially around the most upstream pier. Moreover, the flow intensity and relative flow depth are important factors that characterize the local scour. An empirical scour depth equation is developed for each pier inclination angle for design engineers. Comparisons with previous studies are made and results discussed