This study focuses on investigating the effects of the wrapping mode of shape memory alloy (SMA) spirals with a large pre-strain on the lateral cyclic behavior of the bridge columns. The seismic performance of RC columns confined with different NiTiNb SMA spirals spacing and wrapping heights is compared through a series of quasi-static tests. The confined columns are tested under compression and cyclic lateral loadings. The lateral cyclic behavior of confined columns is compared with that of the as-built column. The test results demonstrate that NiTiNb SMA with a large pre-strain significantly improves the ductility and energy dissipation capacity, and has a slight effect on the peak lateral strength of the bridge piers. The SMA spirals reduce the crashing concrete zone and delay the buckling of steel bars in spite of the crack range in the SMA specimens increasing compared with the control column. The reinforcement effect increases as the SMA spirals spacing decreasing, particularly in terms of ductility and energy dissipation. The damage pattern has a slight distinction in the specimens strengthened by different wrapping mode.

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Shape memory alloys (SMAs) are increasingly used as local reinforcements to control deformation and crack development of reinforced concrete members. This paper presented a new near-surface-mounted strengthening approach, in which the bond performance between SMAs and cement mortar is concerned. To ensure a reliable anchorage of smooth SMA wires embedded in cement mortar, three types of anchors, i.e. the U-shaped stirrups (AU), the block anchors with the flat head bolts (AF), and the block anchor with the hex socket bolts (AH), were suggested. The tensile and recovery tests were firstly undertaken to verify the anchorage performance between smooth SMA wires and the anchors. Then the bond performance of anchored SMA wires embedded in cement mortar was studied by pull-out tests. The results showed that the proposed AH anchor could ensure a reliable anchorage between smooth SMA wires and cement mortar within a short embedded length.

Ni47Ti44Nb9 shape memory alloys (SMA) were applied to bridge pier column to resist earthquake loads by the force of recovery stress over the past decades. However, the application of hot-drawn SMA on pier column reinforcement is hardly researched despite the advantages of cost savings and simplifying service process compared to annealed SMA. Aiming at exploring the usability of hot-drawn SMA on the reinforcement, this paper focused on certain behaviors about pre-strain, thermal activation and partial recovery of recoverable strain that influence the capacity of constraint SMA to gain recovery stress, and then researched recovery stress stability and tensile properties of constraint SMA under cyclic loads both at room temperature and low temperature. Test pieces adopted in this study were 2 mm diameter hot-drawn NiTiNb SMA wires. All setups involved in the tests were self-developed. The states of recovery stress and its stability were mainly evaluated by three tests: uniaxial tensile test, thermal activation test and cyclic loading test. The results marked that hot-drawn SMA could obtain sufficient recovery stress when deformed at room temperature. Moreover, the stability of recovery stress under cyclic loading and low temperature could satisfy the demands of pier column reinforcement for practical use.