Estimating the plastic hinge length of rectangular concrete columns reinforced with NiTi superelastic shape memory alloys

Abstract Earthquake-induced damage in a reinforced concrete (RC) column is often concentrated in a region where the largest moment and deformation are expected. The length of this region is widely known as plastic hinge length. To help minimize the operational and repair costs of damaged plastic hinge region in concrete columns under earthquake loading, this study focuses on deriving an analytical expression for the plastic hinge length of rectangular concrete columns reinforced with nickel-titanium shape memory alloy (SMA) bars based on the results from well-calibrated nonlinear finite element models. A parametric study was conducted to investigate the effect of various parameters on the plastic hinge length, such as the axial load ratio, section information, and material properties of concrete and SMA. A multiple stepwise regression analysis was performed to derive an expression to estimate the plastic hinge length of SMA-RC columns, which can help designers determine the optimal length for SMA reinforcement. Two SMA-RC building frames with their plastic lengths determined using the proposed and existing plastic hinge length expressions were analyzed to compare their nonlinear response under earthquake loading. When the proposed plastic hinge expression is used, the SMA usage can be nearly halved, while the maximum and residual story drift remained similar to the result obtained using the existing expression.