Reinforced Concrete (RC) moment resisting frame structures are commonly used for lateral load resisting systems. However, such structures have often suffered devastation caused by earthquake events, including permanent damage and/or failure where beamcolumn joints (BCJs) have been identified as the weakest link in such systems. If BCJs could regain their original shape after an earthquake, then problems associated with permanent damage could be mitigated. Therefore, the objective of this study is to develop a smart BCJ which can undergo large deformations but potentially recover its original shape after earthquake loading. Superelastic (SE) Shape Memory Alloys (SMA) have the potential to be used in the development of such smart RC BCJs.

This study examines the fundamental characteristics of SMAs, their constitutive material models and the factors influencing its engineering properties. Some of the potential applications of SMAs are also discussed including the reinforcement and repair of structural elements, prestress applications, and the development of kernel components for seismic devices such as dampers and isolators. This study also critically examines the basics of available sensing devices emphasizing the factors that control their properties. SMA along with various sensing devices has been used herein to construct a conceptual smart RC bridge that can detect and repair damage, and adapt to changes in the loading conditions. Future trends and methods to active smart bridges are also proposed.

An experimental investigation has been performed in the present study where two BCJs designed according to current seismic standards, one reinforced with SE SMA rebars and the other with regular steel, have been tested under reversed cyclic loading. The seismic behaviour of the two specimens has been compared in terms of their load-storey drift, moment-rotation and energy dissipation ability. The steel RC frame experienced large amount of permanent deformation and was unserviceable. Although there are different approaches in the literature for improving ductility and damage tolerance of BCJs (e.g. using headed bars at the joint region to relocate the plastic hinge away from the column face, the use of additional diagonal bars at the joint to enhance strength and improved bond condition, the use of high performance fibre-reinforced cement composites at the joint area to improve the damage tolerance), all such methods experience large residual-drift at the end of seismic loading. Conversely, the main advantage of using SE SMA in BCJ is its low residual storey-drift at the end of cyclic loading and the formation of plastic hinges away from the column face. Since the SMA-RC BCJ was able to recover nearly all of its post-yield deformation, it required minimum repair work. Testing of the repaired specimen proved restoration of the full capacity of the intact specimen.

SMA has a relatively lower modulus of elasticity and smaller hysteretic loop compared to that of steel. Therefore, using SMA as reinforcement in RC sections may result in significant changes in the behaviour of RC structure, thus having practical implications in design. This study explores critical and essential design features of SMA RC structures from the analytical point of view. It identifies disparities in the moment-curvature relationship between SMA- and steel-reinforced sections. Then it examines the applicability of existing methods developed for steel RC members to predict the length of the plastic hinge, crack width, crack spacing, and the bond-slip relationship for superelastic SMA RC elements. A finite element (FE) program is used to simulate the behaviour of SMA RC elements. The predicted load-displacement, moment-rotation relationships and energy dissipation capacities have been found in good agreement with corresponding experimental results. The FE program has also been validated with the shake table test results of a three-storey RC frame. Static nonlinear pushover analyses were performed both for steel and SMA RC frames to determine their capacity, investigate their failure mechanism, and compare their residual drift and recentering capability. Time history analyses were subsequently performed for both types of frames to determine the characteristic differences in terms of inter-storey drift, inter-storey residual drift, top-storey drifts, and top-storey residual drift. The results show that SMARC frames are able to recover most of its post-yield deformation, even after strong earthquake events.