Seismic assessment and design of R/C bridges with irregular congiguration, including SSI effects

This work investigates the effect of a modelling approach, also including the interaction phenomenon between supporting ground and the pier plus deck system, on the seismic response of reinforced concrete (R/C) bridges with irregular configuration, as well as its ramifications on the design of the piers. The focus is on a four span highway bridge with piers of unequal height crossing a mountain valley. The bridge and its foundation system, including the surrounding soil, are modelled by finite elements plus the spring/dashpot/added mass discrete parameter system. A hierarchy of finite element meshes is developed, starting with shell elements, and ending with linear elements whose performance as far as dynamic loads are concerned is gauged to be completely satisfactory. Moreover, two basic types of foundations are examined, namely spread footings versus pile groups. Following a preliminary design of the bridge, a series of time history analyses of the combined deck–pier–foundation system are performed, the results of which are used in assessing the influence of foundation compliance on the superstructure. Furthermore, the influence of key construction details such as pier–to–deck connection on the dynamic displacement and force fields that develop, is also examined. Finally, a series of recommendations are given on when and how to account for the influence of the ground in the design of the piers.