Criteria for Preliminary Design of an Arched Steel Bridge on Shallow Foundation Under Soil Liquefaction Conditions

The research is based on a proposed new foundation design method of bridges on liquefiable soil, consisting of using a shallow foundation and exploiting the liquefiable soil layer as natural seismic isolation, replacing thus the commonly employed deep foundation method. The use of this concept may be hindered by detrimental effects, such as large displacements and rotations that are expected to take place at the foundation of the structure during a strong seismic event, associated with permanent displacements due to the liquefaction phenomenon.

The aim of the current study is to investigate the response of an arched steel bridge with two simply supported spans to displacements and rotations induced by soil liquefaction, delineate the acceptable limits of such ground movements that the bridge can sustain, avoiding the collapse of the superstructure, and define criteria for the preliminary design of the spread footing of the middle pier. To that effect, nonlinear analyses are performed, taking into account geometric and material nonlinearities. Displacements and rotations are imposed at the base of the pier and their amplitude is gradually increased until the first group of structural elements that reach failure is detected.

The values of displacements and rotations, for which failure occurs, specify the tolerable design limits. This is a first step towards investigating the feasibility of the above concept for bridges of this type.