Comparison between Shape Memory Alloy Seismic Restrainers and Other Bridge Retrofit Devices

TLDR

Strong earthquakes can cause large longitudinal displacements in multi‑frame bridges, leading to excessive joint openings and potential superstructure unseating, especially in bridges with narrow seat widths; while steel restrainers are commonly used, their limitations have prompted consideration of alternative devices such as metallic dampers, viscoelastic dampers, and shape‑memory alloys. The authors performed a sensitivity study and a case study using computer simulations to compare the effectiveness of SMA retrofit devices with other seismic restrainers. The simulations revealed that device effectiveness depends on bridge frame and ground motion characteristics, with steel restrainers being the least effective and SMA devices markedly reducing residual joint displacement.

Abstract

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, the steel restrainer cables were the least effective in limiting joint displacements. The SMA devices have the additional benefit of significantly limiting the residual joint displacement in bridges.