Comparison of the Performance of RC and CFFT Bridge Piers under Multiple Hazards

Recent mega-disasters, such as the 2011 Great East Japan Earthquake, have prompted the technical community to understand the resilience of infrastructure when subjected to extreme events and the shortcomings of conventional structural systems under multiple hazards. Columns are the most critical load carrying elements of bridge structures, and the resilience of a bridge is significantly dependent upon the structural performance of its columns. The objective of this research is to compare the resilience of reinforced concrete (RC) and concrete-filled fiber reinforced polymer (FRP) tube (CFFT) bridge columns under multiple hazards through combined experimental and analytical studies.The experimental work includes blast and fire testing of one-fifth scale RC and CFFT bridge columns. The performance of each type of column is studied under two severities of exposure to each type of hazard. Subsequently, axial capacity tests are performed on eight damaged columns as well as two undamaged benchmark columns, one of each type. The residual axial load carrying characteristics are used to quantify and compare the resilience of RC and CFFT columns to blast and fire. The experimental results show that CFFT columns outperform RC columns during and after blast and fire events. The FRP tube provides sufficient confinement to resist shear crack initiation in the concrete core during blast loading resulting in retention of its axial load carrying capabilities. Conversely, the RC column suffered reductions in axial ductility due to a shear-type failure under axial load. The Tyfo-CFP system allowed the concrete temperatures of the CFFT columns to remain low during fire exposure, resulting in retention of axial capacity and stiffness. The concrete temperatures of the RC columns exceeded degradation thresholds for both strength and stiffness resulting in reduced axial capacity after fire exposure.Analytical work consists of using an OpenSees model allows further study of the effects of blast loading on RC and CFFT columns. The model is advanced to study the seismic resilience of RC and CFFT columns, expanding the multihazard aspect of this research. The residual axial capacities of RC and CFFT columns are analytically compared after two levels of biaxial seismic ground motions. Finally, a design methodology for CFFT bridge columns with minimal amounts of longitudinal steel reinforcement is developed to facilitate the adoption of CFFT bridge columns in multihazard resilient bridge designs.