Dynamic behaviour of steel–concrete composite under-deck cable-stayed bridges under the action of moving loads

•Dynamic behaviour of steel–concrete composite under-deck cable-stayed bridges is characterised.•High accelerations are registered, mainly when eccentric loads are applied.•Amplification and cancellation speeds are identified.•Parametric analysis identifies key features to control maximum accelerations cost-effectively.•A comprehensive set of design criteria from the dynamics viewpoint for this bridge type is proposed.

The dynamic response of under-deck cable-stayed bridges with steel–concrete composite decks under moving loads is presented, and different parameters are considered. The vibrational modes with a strong contribution in the response, the key parameters that control the modal frequencies, and those that reduce the maximum accelerations registered on the deck in a cost-effective manner, are identified. It is found that relatively high accelerations occur and that these can be increased by large load eccentricities. It is also found that maximum accelerations are conditioned by the amplification and cancellation speeds of the loads. Increasing the depth of the deck is determined to be the most effective way to reduce the maximum accelerations. Decks formed by I-beams seem to be quite appropriate from the perspective of dynamic behaviour, while box sections tend to increase the overall cost of the bridge. The findings provide effective strategies to define the most efficient configurations that satisfy the limit state of vibrations, which is critical for this type of bridge.