Shape memory alloys (SMAs) have been widely used in civil engineering applications including active and passive control of structures, sensors and actuators and strengthening of reinforced concrete (RC) structures owing to unique features such as the shape memory effect and pseudo-elasticity. Iron-based shape memory alloys (Fe-SMAs) have become popular in recent years. Use of iron-based SMAs for strengthening RC structures has received attention in the recent decade due to the advantages it presents, that is, no ducts or anchor heads are required, friction losses do not occur and no space is needed for a hydraulic device to exert force. Accordingly, Fe-SMAs embedded in a shotcrete layer have been used for pre-stressing RC beams at Empa. The aim of this study is to present an approach to model and analyze the behavior of RC members strengthened and pre-stressed with Fe-SMA rebars embedded in a shotcrete layer. The lack of research on developing finite element models for studying the behavior of concrete structures strengthened by iron-based shape memory alloys is addressed. Three-dimensional finite element models were developed in the commercial finite element code ABAQUS, using the concrete damaged plasticity model to predict the studied beams’ load–displacement response. The results of the finite element analyses show a considerably good agreement with the experimental data in terms of the beams’ cracking load and ultimate load capacity. The effects of different strengthening parameters, including SMA rebar diameter, steel rebar diameter and pre-stressing force level on the beam behavior, were investigated based on the verified finite element models. The results were compared. The load-displacement response of an 18-m concrete girder strengthened and pre-stressed with iron-based SMA bars was examined by the developed finite element model as a case study.

This study presents a new way to improve masonry wall behavior. Masonry structures comprise a significant part of the world’s structures. These structures are very vulnerable to earthquakes, and their performances need to be improved. One way to enhance the performances of such types of structures is the use of post-tensioning reinforcements. In the current study, the effects of shape memory alloy as post-tensioning reinforcements on originally unreinforced masonry walls were investigated using finite element simulations in Abaqus. The developed models were validated based on experimental results in the literature. Iron-based shape memory alloy strips were installed on masonry walls by three different configurations, namely in cross or vertical forms. Seven macroscopic masonry walls were modeled in Abaqus software and were subjected to cyclic loading protocol. Parameters such as stiffness, strength, durability, and energy dissipation of these models were then compared. According to the results, the Fe-based strips increased the strength, stiffness, and energy dissipation capacity. So that in the vertical-strip walls, the stiffness increases by 98.1%, and in the cross-strip model’s position, the stiffness increases by 127.9%. In the vertical-strip model, the maximum resistance is equal to 108 kN, while in the end cycle, this number is reduced by almost half and reaches 40 kN, in the cross-strip model, the maximum resistance is equal to 104 kN, and in the final cycle, this number decreases by only 13.5% and reaches 90 kN. The scattering of Fe-based strips plays an important role in energy dissipation. Based on the observed behaviors, the greater the scattering, the higher the energy dissipation. The increase was more visible in the walls with the configuration of the crossed Fe-based strips.

Superelastic shape memory alloys (SMAs) have the potential to create a spontaneous recentering mechanism on the connections of a structural system under seismic actions, which results in mitigation of the damage in the main structural members. In this article, innovative types of steel beam-to-column moment connections incorporating SMA bolts and plates are introduced and studied through a numerical approach. First, SMA bolted end-plate connection model is produced and analyzed by means of the finite element method to validate the numerical analysis against the prior experimental results. Then, the performance of eleven different end-plate moment connection models subjected to cyclic loading is investigated. By selecting the lower values for the moment capacity based on bolts strength in comparison to the flexural resistance of the beam, the plastic hinge is transferred from the beam section to the beam–column interface. Hence, employing superelastic materials at the connection interface could be potentially effective in providing the desired self-centering effect in the connection. To this end, the impact of utilizing superelastic SMA bolts and end-plates instead of using the conventional structural steel on the overall cyclic response of the connections is evaluated in this study. Results show that extended end-plate connections equipped with SMA bolts and end-plates, if properly proportioned and detailed, not only exhibit a clear reduction in the residual drifts after a seismic event, but also can meet the ductility requirements with good energy dissipation and sufficient stiffness.

Vertical component of seismic excitations tremendously affects the performance of bridges during the earthquakes. Several conducted studies identified the lack of engineering attention to the vertical seismic excitation as the main reason of various considerable bridge damages during the past earthquakes. Thus, in this article, an innovative system with superelastic properties is proposed for retrofitting and also new design of the bridges which can simultaneously mitigate the effects of vertical and horizontal seismic excitations. In order to investigate the efficiency of the new system, an evaluation is performed through many nonlinear time history analyses on a three-dimensional model of a detailed multi-span simply supported bridge using a suite of representative ground motions of the bridge region. The analyses are conducted separately on the pertinent issues that affect the performance of the new proposed system. As a part of the study, to identify the sensitivity of the new system and evaluate the overall seismic performance, several assessment parameters are utilized. The results show that the proposed system is efficient for reducing bridge responses as well as improving nonlinear performance of the columns during vertical and horizontal seismic excitations.

The use of shape memory alloys as a rebar in concrete structures has been receiving increasing attention among researchers. In this study, it is intended to evaluate the application of superelastic Nitinol in reducing the damage to the coupling beams and opening corners within a concrete shear wall. Abaqus finite element software was utilized to develop three verified coupled shear wall models. First, a model without diagonal and shape memory alloy rebars is developed to assess conventional shear walls with openings. Steel diagonal rebars are embedded in the coupling beams of the second model, and shape memory alloy diagonal rebars are embedded in the coupling beams of the third model. Shape memory alloy is also implemented in the opening corners of the third model. All models are subjected to cyclic loading to evaluate the concrete damage. Results indicated that the diagonal rebars reduced damage to the coupling beam and opening corners. The damages were the least when shape memory alloy diagonal rebars are utilized in the model. The superelastic behavior of the shape memory alloy also reduced permanent displacement of the shear wall subjected to substantial lateral loadings.