CFFT Bridge Columns for Multihazard Resilience

Bridges play a significant role in postevent recovery and disaster resiliency of communities. Recent megadisasters, such as the 2011 Great East Japan Earthquake, have prompted the technical community to understand the robustness 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. Enhancing the robustness of bridge columns can improve the resiliency of the bridge itself and the surrounding community by reducing repair costs and downtime after an extreme event. In recent years, the concrete-filled fiber reinforced polymer (FRP) tube (CFFT) system has been widely investigated as a durable and cost-effective alternative design for more robust bridge columns. However, the current AASHTO guide specifications are limited to nonductile, unreinforced CFFT elements. This study summarizes the findings of blast, fire, and seismic experiments performed on CFFT specimens containing minimal longitudinal reinforcement. The residual axial load-carrying capacities of damaged reinforced concrete (RC) and CFFT columns are obtained as a measure of robustness, and estimated restoration times and repair costs are presented for each type of column and each hazard. Subsequently, a set of experimentally validated design equations are developed for the axial and flexural resistance of lightly reinforced CFFT columns in a compatible format with the AASHTO load resistance factor design (LRFD) Guide Specifications for the Design of CFFTs. A formulation for displacement-based seismic design of lightly reinforced CFFT columns is presented, and a provision for the fire protection of this column system is proposed. By presenting a set of experimentally validated design formulations, this study is expected to promote the application of lightly reinforced CFFT columns to enhance the multihazard resilience of bridge infrastructure.