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.

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In infrastructural networks, bridges can be considered key elements and their functionality must be preserved. Floods (leading to scour erosion) and earthquakes could be considered among the most critical natural events that may become more frequent with climate change, causing significant damage to bridges. Several regions in Europe have both seismic and scour hazards. The two types of hazards are actually independent as to the generation process but the loss of surrounding soil due to scour may significantly reduce the lateral strength of pile foundations thus increasing the earthquake damage potential. Bridge assessment has thus to take into account the possible increased risk induced by the joint action of the two phenomena. Monitoring systems can be an effective support in bridge assessment procedures providing updated information about the structural state and performance thus allowing both the prompt detection of a possible damage state after an event and also support for long term assessment of the structural conditions. Several performance parameters can be used to perform bridge assessment with respect to several hazards at different levels: element, structure, and network. The aim of this paper is to give an overview of monitoring-based performance parameters that can be used for separate seismic and flood related hazard in order to identify possible selection of parameters effective in describing the joint hazard due to both phenomena.@en