Seismic performance upgrading of substandard RC frames using shape memory alloy bars

Abstract

Shape memory alloys (SMAs) have been utilized as an alternative to conventional materials for seismic retrofit applications in the last two decades. The effectiveness of SMAs to provide further improvement in seismic behavior of structures was demonstrated satisfactorily. Three 2/ 3-scaled, one-bay and one-storey substandard RC frames were constructed to represent the seismically vulnerable buildings with several deficiencies. The first RC frame was tested as a reference specimen under quasi-static reversed cyclic loading, which caused flexural plastic hinges at the column ends. Then, the rest of the two RC frames were upgraded with superelastic copper-aluminum-manganese (CuAlMn) alloy bars and conventional steel bars with the aim of enhancing seismic performance of substandard RC frames. The upgrading materials were attached to the RC frames through a retrofitting mechanism to provide tension-only retrofitting bars. Hence, the RC frame retrofitted by conventional steel bars was exposed to residual displacements after they yielded. The SMA-upgraded frame showed flag shaped hysteresis curve due to its superelastic behavior and caused considerable reduction in the residual displacement of RC frames.

Superelastic Cyclic Properties of Cu-Al-Mn and Ni-Ti Shape Memory Alloys for Seismic Mitigation

“…The equivalent viscous damping parameter (EVD) is generally a key factor to measure the efficacy of a device in damping vibrations [8]. The potential of SMAs in energy dissipation and damping parameter is also valid in consecutive cyclic loading conditions [3]. Similar damping parameters were also calculated for SMA materials in [8,9].…”

“…The reason for the growing popularity of SMAs is their capability of sustaining a large amount of inelastic deformations with negligible residual strains (superelasticity, SE) compared to conventional materials. From a civil engineering point of view, the advancements in superelastic alloys introduce new opportunities and innovative solutions to structural engineering problems with an extensive range of applications [1].…”

“…There are several studies showing the potential usage of SMAs in the field of structural engineering area; retrofitting, repairing, base isolation and in a form of several structural components such as bridge restrainer, seismic reinforcement, prestressing members, etc. [2,3]. Although the Ni-based SMAs are the most popular ones in the research area, much attention has been drawn to Cu-based SMAs due to their advantages in the cost of raw materials, machining and threading process [4].…”