Seismic performance of RC moment resisting frame with steel, GFRP and SMA-FRP reinforcement

For the last century, steel has been used as a reinforcing material for most of the reinforced civil engineering structures. Despite requisite stiffness, strength, ductility and serviceability properties, steel reinforcing bars have shown deterioration over time due to corrosion. Fiber reinforced polymer (FRP) reinforcing bars have been used in concrete structures as alternate to conventional steel reinforcement, in order to overcome corrosion problems. However, due to their linear elastic behavior, they are not considered in structures which require ductility and damping characteristics. The use of shape memory alloys (SMAs) with their nonlinear super-elastic behavior in the composite could potentially provide solution for this problem. Small diameter superelastic SMA wires, coupled with polymer matrix and FRP is sought in this research as reinforcing bars in reinforced concrete (RC) moment resisting frames (MRFs) to improve the performance of the frames in terms of reduced residual inter-storey drifts and damage under quasi-static and seismic loading, while still maintaining the elastic characteristics associated with FRP. The new SMA-FRP composite reinforcement is placed at the plastic hinge region of the MRFs, where the nonlinearity is expected to accumulate. A three storey one bay RC MRF prototype structure is designed with steel reinforcement using equivalent static force procedure given in International Building Code (IBC) for particular seismic hazard. The RC MRF is then modified by replacing steel at the plastic hinge region in the beams with conventional Glass-FRP (GFRP) and SMA-FRP composite reinforcement using design acceleration response spectra achieved based on seismic demand. Incremental dynamic analysis is conducted to investigate the behaviors of the frame with the three different reinforcement types under a suite of ground motion records. From this study, it is found that the frame with SMA-FRP composite reinforcement exhibits higher performance levels including lower residual inter-storey drifts, high energy dissipation to residual drifts ratio and thus lower damage, which is of essence for the structures in high seismic zones.