Significance of non-uniform scour on the seismic performance of bridges

Multiple hazards such as flood-induced scour followed by earthquakes can adversely impact the performance of bridges spanning over waterways. Scour is the erosion of soil around the foundation of bridges, which can result in loss of the structure's lateral support and possible failure. The impact is specifically amplified when a flood event resulting in the development of a scour hole is followed by an earthquake event. Recent inspections have shown a non-uniformity in the scour depths at bridge foundations with multiple piers. More specifically, the upstream and downstream pier foundations are exposed to notably different scour depths. However, the practice falls short in capturing this effect as commonly, a uniform scour depth is assumed at all bridge foundations in the water stream when evaluating the lateral stability of the structure. A comparative case is used to identify the unintended consequences of uniform local scour depth assumption for bridges with multiple columns in the direction of flow. This analysis considers bridges with both uniform and non-uniform scour depth at the support foundations. The effects of variable scour depths on the behaviour of bridge components are evaluated by tracking the demand redistribution as the scour depth changes. The results help to understand the performance of bridges crossing waterways when they are subjected to multi-hazard effects from flood-induced scour and earthquakes.