Performance of Eccentrically Loaded Reinforced Concrete Columns Confined with Shape Memory Alloy Wires

摘要

Smart materials such as Shape Memory Alloys (SMA) are recently utilized for strengthening and repairing of concrete structures. The most common form of SMA wires used for concrete confinement applications is Nickle Titanium (NiTi) because it possesses unique thermo-mechanical properties such as the Shape Memory Effect (SME) along with high recovery stress (up to 600 MPa) and strain (up to 8 %). Initial investigations reported in the literature show that actively confining concrete columns with SMA wires can enhance the strength and significantly increase the ductility of concrete. To date, the vast majority of experiments on SMA-confined concrete have considered short, unreinforced, small-scale concrete cylinders subjected to concentric axial loading.;The objective of this study is to present a systematic study of medium-size reinforced concrete circular columns, internally reinforced with longitudinal steel bars and transverse steel stirrups and externally confined with SMA wires, subjected to eccentric loading. Test data are compared against identical unconfined reinforced concrete (RC) columns, and confined RC columns strengthened passively using Carbon Fibre Reinforced Polymer (CFRP) wrap sheets, in order to quantify and verify the effectiveness of the active SMA-confinement method. In addition, an analytical model is presented to describe the behaviour of SMA-confined RC columns subjected to combined axial loads and bending moments. A parametric study was conducted to evaluate the effects of certain parameters on the overall response and the axial-flexural diagrams of the SMA-confined RC columns.;The results of this study show that the RC columns confined with active SMA spirals exhibited significant enhancement in the strength and ductility compared to the unconfined RC columns subjected to varying load eccentricity. Additionally, the SMA-confined RC columns demonstrated superior overall performance when compared to the conventional passive CFRP-confined RC columns. The results of this study also show that the proposed analytical model conservatively predicted the axial load-bending moment response of the SMA-confined RC columns. The RC column confinement parameters investigated, namely the concrete compressive strength, the volumetric ratio of the SMA spirals, and the internal longitudinal steel reinforcement ratio, significantly influenced the load-moment interaction response of the SMA-confined RC columns.