Basic Theoretical Studies On Intelligent Concrete Beams Using Unbonded External SMA Wires

Shape Memory Alloy (SMA) is a new type functional material, which is characterized by shape memory effect, transformation super-elasticity, pseudo-elasticity (PE), a modulus of elasticity varying with temperature as well as high damping properties, etc.The unbonded SMA intelligent concrete beam is designed with externally arranged SMA wires, which is in the martensitic state under normal temperatures and can be pretensioned and used to replace external prestressed tendons. Experimental and theoretic studies are carried out to investigate the behaviors of this kind of beam. The main works are as follows:1. Material mechanics behaviors of SMA wiresAccording to DSC, the transformation temperatures of the SMA wires are tested and the curves of specific heating changes are achieved, while we can get that processing technologies have effects on the material properties of SMA wires. Researches of bonding tests indicate that it's not obvious for using epoxide resin as cohesive materials to improve the wires' bonding performance. During tensile test of SMA wires under normal temperature, the phenomenon of necking can not be observed, and it's modulus of elasticity is constant while some of strength properties of the wires represent to be different with different length.2. Researches of recovery force of SMA wiresIt is observed that the strain of the SMA wires exhibits a little recovery with its elongation shortening when the wires are pretensioned to the maxi designed strains at room temperature. At fully constrained conditions, the transformation temperatures of the SMA wires drift to high temperature, and recovery stress of SMA wires exhibit obvious hysteretic shape. Based on the experimental studies of the present paper, the Liang and Rogers models using to simulate the recovery stresses of SMA wires which are in constrained conditions are certificated.3. Experimental studies and nonlinear FEM analysis of unbonded SMA intelligent concrete beamsTests are conducted on unbonded SMA intelligent concrete beams. Studies show that the load capacity of the concrete beams could be effectively improved by SMA wires. The mid-span deflection of these beams reduces about 8% after heating of...