Seismic response and design

Bridges are the most vulnerable transportation network component to damage from natural disasters as compared to roads and railway lines. It is therefore of priority to adequately design new bridge structures and reassess the response of existing bridges in areas subjected to earthquake hazard. This chapter briefly addresses a number of topics related to seismic response and design of bridges, namely damage observations in previous earthquakes, conceptual design and modern seismic codes. Commonly observed bridge failure modes following damaging earthquakes are presented. This shows that despite the advancement in seismic design practice, there are repetitive damage patterns due to the increased number of bridges of complex configurations and the heightened consequences of bridge damage in developed societies. Features of layout and configuration that are favourable to controlled and predictable seismic response of bridges are also discussed. Various options available from foundations through to the superstructure, and connections between various components, are presented and their likely effects on the response are discussed. Finally, a brief review of seismic design codes in Europe, the USA and Japan is presented. The review highlights the differences and their origin, which is an important step towards improved understanding of seismic design procedures.