The issue of protecting infrastructure against multiple extreme events is gaining popularity in the field of civil engineering. This research focuses on the protection of highway bridges against two hazards, namely earthquakes and blasts. A similarity between seismic and blast events in relation to bridges is that they can both induce large inelastic deformations in key structural components. Since many bridges are (or will be) located in areas of moderate to high seismic activity, and because any bridge can be a potential target for terrorists, there is a need to develop structural systems capable of performing equally well under both events.

The objective of this research is to present the development and experimental validation of a multi-hazard bridge pier concept that is capable of providing an adequate level of protection against collapse under both seismic and blast loading. A multi-column pier-bent with concrete-filled steel tube (CFST) columns is the proposed concept and is tested against the blast hazard. For comparison, two conventional systems known to provide ductile performance during seismic events (RC columns and steel jacketed RC columns) were also tested under blast loads.

This dissertation describes development of the multi-hazard pier concept, design of the prototype bridge pier bent with multi-hazard resistant columns and the one with seismically resistant conventional columns under blast and seismic loading, specimen design, experimental set-up, and experimental results. The results from the blast experiments are compared with the results from simplified method of analysis considering an equivalent SDOF system having an elastic-perfectly-plastic behavior. Additionally, SDOF and 2D nonlinear dynamic response-history analyses were used to simulate the behavior of these columns subjected to blast loading and to better understand their ultimate behavior.

It is found that prototype bridge CFST columns can be designed to provide both satisfactory seismic performance and adequate blast resistance. It is also shown that, in two series of tests at 1/4 scale, the CFST columns exhibited ductile behavior while the RC and steel jacketed columns failed at their base in shear. Based on the experimental and analytical observations, simplified analytical methods for the design of bridge columns under explosive loads were proposed.