Self-Centering Hybrid GFRP-Steel Reinforced Concrete Beams for Blast Resilience

Abstract

Despite having a high strength-to-weight ratio and being chemically inert, fiber-reinforced polymer (FRP) reinforcing bars are not currently used in reinforced concrete protective design due to their brittle nature and lack of ductility. This paper presents research on the innovative use of blended mixtures of FRP and steel rebar to activate self-centering behavior to return blast-loaded elements to their original position after the inertial loads are removed. Self-centering blast-resilient members promise reductions in residual damage, repair cost, and facility downtime after a terrorist bomb attack or accidental explosion. Large-scale reinforced concrete beams with different combinations of steel and glass FRP (GFRP) rebar were designed, constructed, and tested under progressively increasing blast loads generated by the Virginia Tech Shock Tube Research Facility. The results demonstrated that beams with hybrid reinforcing experienced reduced overall residual damage in comparison with similar conventionally reinforced concrete members. Increasing the self-centering ratio (SC) of beams, defined as the ratio of the restoring moment provided by the FRP to the resisting moment provided by energy dissipating steel rebar, increased the blast self-centering tendencies of the hybrid beams. Additionally, if the GFRP rebar ruptured during the blast, the presence of steel prevented a brittle failure mechanism and provided additional energy dissipation and redundancy. To encourage the use of hybrid FRP-steel reinforcement in blast-resistant construction, a series of protective design recommendations are made. Furthermore, a new response limit based on a blast self-centering index (BSI) is proposed to explicitly account for the residual damage state in the protective design process.