Experimental and analytical investigation of continuous RC beams strengthened by SMA strands under cyclic loading

Abstract

Shape Memory Alloys (SMAs) are a new type of alloy that are capable of strengthening reinforced concrete structures. This study aims to investigate the behavior of continuous reinforced concrete (RC) beams strengthened by SMA strands. The superelastic behavior of Nitinol to recover the deformation of concrete beams under cyclic loading is discussed. We present the experimental results of research to determine the effects of reinforcement ratio and two types of normal and high strength concrete (NSC, HSC) in eight strengthened or non-strengthened continuous beams. The results indicate that SMA strands demonstrate acceptable superelasticity. High strength concrete beams strengthened by Nitinol strands show more ability to recover flexural cracks. However, the recovering capacity of midspan deflection and flexural crack width in SMA-NSC beams is more than their corresponding HSC beams. A better distribution of cracks is observed on both normal and high strength concrete beams strengthened by Nitinol strands. In addition, comparison between experimental deflection and predicted values based on the moment-area method exhibits a good agreement up to yielding of the steel reinforcements. Because of the superelasticity of SMAs, energy absorption capacity and residual stiffness of SMA RC beams increased significantly. Besides, the moment–curvature response leads to more ductile behavior of RC beams strengthened by SMA strands.