In order to realize the self-centering, high energy consumption, and high ductility of the existing building structure through strengthening and retrofit of structure, a method of reinforced concrete (RC) beam strengthened by using Shape Memory Alloy (SMA) and Engineered Cementitious Composites (ECC) was proposed. Four kinds of specimens were designed, including one beam strengthened with enlarging section area of steel reinforced concrete, one beam strengthened with enlarging section area of SMA reinforced concrete, beam strengthened with enlarging section area of SMA reinforced ECC, and beam strengthened with enlarging section area of steel reinforced ECC; these specimens were manufactured for the monotonic cycle loading tests study on its bending behavior. The influence on the bearing capacity, energy dissipation performance, and self-recovery capacity for each test specimens with different strengthening materials were investigated, especially the bending behavior of the beams strengthened by SMA reinforced ECC. The results show that, compared with the ordinary reinforced concrete beams, strengthening existing RC beam with enlarging section area of SMA reinforced ECC can improve the self-recovery capacity, ductility, and deformability of the specimens. Finally, a revised design formula for the bending capacity of RC beams, strengthened with enlarging sections of ECC, was proposed by considering the tensile capacity provided by ECC, and the calculated values are in good agreement with the experimental value, indicating that the revised formula can be well applied to the beam strengthening with enlarging section of SMA-ECC Materials.

In order to explore the crack development mechanism and damage self-repairing capacity of ECC beams reinforced with hybrid bars, the smart aggregate-based active sensing approach were herein adopted to conduct damage monitoring of ECC beams under cyclic loading. A total of six beams, including five engineered cementitious composite (ECC) beams reinforced with different bars and one reinforcement concrete counterpart, were fabricated and tested under cyclic loading. The ultimate failure modes and hysteresis curves were obtained and discussed herein, demonstrating the multiple crack behavior and excellent ductility of ECC material. The damage of the tested beams was monitored by smart aggregate-based (SA) active sensing method, in which two SAs pasted on both beam ends were used as actuator and sensor, respectively. The time domain analysis, wavelet packet-based energy analysis and wavelet packet-based damage index analysis were performed to quantitatively evaluate the crack development. To evaluate the self-repairing capacity of the beams, a self-repairing index defined by the difference of damage index at loading and unloading peak points was proposed. The results in time domain and wavelet packed analysis were in close agreement with the observed crack development, revealing the feasibility of smart aggregate-based active sensing approach in damage detection for ECC beams. Especially, the proposed damage self-repairing index can describe the same structural re-centering phenomena with the test results, showing the proposed index can be used to evaluate the damage self-repairing capacity.

Ultra-high performance concrete (UHPC) and fiber-reinforced polymer (FRP) have been more and more widely used in large-scale constructions. Using FRP at the shear and bending section of concrete can increase the strength and fatigue resistance of the concrete members. However, the performance of FRP-UHPC composite structure depends mainly on the interface connection between FRP and UHPC. Therefore, to prevent the bond-slip of FRP-UHPC composite structure from causing destructive structural damage, it is essential to detect the bond-slip of interfaces for providing early warning of composite structures. Glass fiber reinforced polymer (GFRP) and concrete can be combined through several interface bond methods to form innovative composite structures. This study experimentally investigated the bond-slip detection of the shear interface of GFRP-concrete composite members using piezoceramic smart aggregates (SAs). Two groups of eight GFRP-concrete composite members with different bond methods were fabricated and tested. Both UHPC and regular concrete materials were considered. Six kinds of bond types were employed, including bolted, epoxy bonded, bonded by GFRP stay-in-plane form and their combinations. The push-out experimental results were analyzed in detail, involving the load versus slip displacement curves and failure modes. Meanwhile, the bond-slip between GFRP and UHPC interfaces was detected by the SA-based active sensing approach. A pair of SAs attached at both sides of each composite member was employed as an actuator and a sensor, respectively. The wavelet packet-based analyses, including the energy indices and damage index, were applied. Using an SA-based active sensing approach, the initiation and development of bond-slip for GFRP and UHPC composite members with different bond methods were successfully captured and quantitatively evaluated.