Experimental and analytical study of innovative shape memory alloy-based FRP composite reinforcement for seismic applications

Permanent plastic deformation of steel rebars is among the main reasons for the disruption of the post-earthquake functionality of RC structures. It can also pose life threatening risks in case of strong aftershock occurrence. In an attempt to address the problem of excessive permanent deformations and their impact on the post-earthquake functionality of concrete moment resisting frame (MRF) structures, this paper studies a new type of reinforcing bars made of fiber reinforced polymer (FRP) with embedded superelastic shape memory alloy (SMA) fibers. This new type of composite material is characterized with both ductility and pseudo-elasticity which are two important characteristics that are sought in this study to enhance the seismic behavior and damage mitigation of MRFs under multiple strong seismic events (e.g. Strong main shock-aftershock sequences). Small diameter SMA wires are embedded in thermoset resin matrix with or without additional glass fibers to develop specimens of the new composite reinforcement. These SMA composite specimens are first tested under quasi-static cyclic tensile loading to achieve constitutive material response and then to develop analytical material models. Second, reinforcing bars made of the SMA-FRP are manufactured and used as reinforcement in small-scale concrete beam, experimentally tested under cyclic 3-point bending. Next, the calibrated material models of the new composite are used in structural level models to assess the performance of RC MRFs under seismic loading. Three storey, single bay prototype RC MRFs, reinforced with SMA composite, steel and glass fiber reinforced polymer (GFRP) reinforcements, are subjected to sequential main shock-aftershock ground motions to study their nonlinear behavior and impact of aftershocks by comparing accumulation of damage and residual drifts. It is found that the sequential ground motion records have a significant effect while sequential nonlinear time history analyses is a good means to perform post main-shock damage assessment. Numerical results also show superior performance of SMA composite reinforced MRF in terms of dissipation of energy and accumulation of lower residual drifts.