This paper presents experimental and analytical work conducted to explore the feasibility of using an innovative technique for seismic retrofitting of RC bridge columns using shape memory alloys (SMAs) spirals. The high recovery stress associated with the shape recovery of SMAs is being sought in this study as an easy and reliable method to apply external active confining pressure on RC bridge columns to improve their ductility. Uniaxial compression tests of concrete cylinders confined with SMA spirals show a significant improvement in the concrete strength and ductility even under small confining pressure. The experimental results are used to calibrate the concrete constitutive model used in the analytical study. Analytical models of bridge columns retrofitted with SMA spirals and carbon fiber-reinforced polymer (CFRP) sheets are studied under displacement-controlled cyclic loading and a suite of strong earthquake records. The analytical results proves the superiority of the proposed technique using SMA ...

Strong earthquakes can result in large longitudinal displacements in multiple-frame bridges. This could lead to excessive displacements/openings at the intermediate joints. Bridges with small seat widths are vulnerable to the unseating of their superstructure. Seismic steel restrainers are currently used to limit the joint openings in bridges. However, past earthquakes have shown that restrainer cables have limitations in regards to preventing unseating in bridges. Other devices have been proposed to limit joint displacements, including metallic dampers, viscoelastic dampers, and shape memory alloys (SMAs), which are known for their ability to recover their original shape after being deformed. A sensitivity study and a case study are conducted using computer simulations to compare the effectiveness of SMA retrofit devices with other devices. The results show that the effectiveness of the devices is a function of the characteristics of the bridge frames and the ground motion characteristics. In all cases, ...

This experimental work focuses on enhancing the lateral cyclic behavior of RC columns by using an innovative active-confinement technique. The thermally triggered recovery stress of prestrained shape memory alloy (SMA) spirals is used to apply the active-confinement pressure. Four 1/3-scale RC columns, three of which are retrofitted with different schemes, are tested under quasi-static lateral cyclic loading. The plastic hinge region of the first retrofitted column is actively confined using the new SMA spirals, whereas for the second column, traditional passive confinement is applied by using a glass fiber-reinforced polymer (GFRP)/epoxy jacket. The third column is retrofitted by using a hybrid confinement approach, which is applied by using SMA spirals and GFRP jacket simultaneously at the plastic hinge zone. The confinement pressure of the three retrofitted columns is designed to be the same. The results show a significant increase in the flexural ductility capacity and energy dissipation capability of...

Despite growing interest in the use of shape memory alloys (SMAs) in civil structures, much is still to be understood about their behavior in real loading environments. This experimental work focuses on characterizing the thermomechanical behavior of a thermally prestressed NiTiNb SMA under thermal and loading conditions pertinent to civil structural applications. The work aims at exploring the feasibility of using this type of alloy in developing seismic retrofitting spirals that could be used to actively confine vulnerable reinforced concrete columns to improve their flexural ductility and shear strength under earthquake loading. Differential scanning calorimetry tests are conducted to determine the transformation temperatures of the used alloy. A testing program is carried out on 2-mm-diameter NiTiNb wires to examine the recovery stress of prestrained wires and the monotonic and cyclic behaviors of thermally prestressed wires under various testing durations and ambient temperatures. A thermal c...

Recent studies showed that concrete confinement using shape memory alloy (SMA) spirals is a promising technique for seismic retrofitting of reinforced concrete columns that lack flexural ductility. This technique is applied by wrapping prestrained SMA wires around concrete columns and activating the confining pressure by heating the wires. This study is the first step toward understanding the behavior of NiTiNb-SMA–confined concrete both experimentally and analytically. The paper aims at investigating the cyclic behavior of NiTiNb-SMA–confined concrete, and using the test results to develop an empirical stress–strain model for NiTiNb-SMA–confined concrete. A series of uniaxial cyclic tests are performed on NiTiNb-SMA–confined concrete cylinders having different concrete strengths, confining pressures, and loading protocols. The test results show that the effectiveness of NiTiNb-SMA confinement on strength and ductility enhancement increases as active confining pressure increases; and in the studied range of normal strength concrete, the residual stress is independent of concrete strength. The study also proposes empirical equations to predict stress–strain behavior of NiTiNb-SMA–confined concrete, including the peak stress, residual stress, and ultimate stress and strain of SMA-confined concrete.