Displacement-Based Seismic Design of Steel, FRP, and SMA Cable Restrainers for Isolated Simply Supported Bridges

Restrain devices, being of low cost and easy to install, are often used to limit the relative displacements between the decks and columns in a simply supported bridge. Although the current guidelines have provided different restrainer design methods, they do not adequately consider the dynamic interactions between the decks and columns in isolated bridge systems considering the flexibility of isolation systems. Additionally, due to a fiber-reinforced polymer (FRP) with a high tensile strength and shape memory alloy (SMA) with energy dissipation capacity and self-centering property, they are good candidates to be used as seismic restrainers. However, currently there is no appropriate design method for such restrainers in isolated bridges. The objective of this study is to propose a restrainer design procedure for simply supported bridges equipped with elastomeric isolation systems. Three types of restrainers, i.e., steel, SMA, and carbon fiber-reinforced polymer (CFRP) cables, are considered. The design procedure for restrainers is developed based on a linearized 2-degree-of-freedom (DOF) analytical model. A three-span simply supported highway bridge located in Vancouver, British Columbia, Canada, is chosen as a case study. The effectiveness of the proposed method is evaluated. The results show that the restrainers could remain functional and limit the relative displacement within a design value during earthquakes. The effectiveness factor, defined as the ratio of the yielding displacement to the peak restrainer displacement, ranges from 2.0 to 6.4. The relative displacements of the bridge retrofitted with steel, CFRP, and SMA cables at midspan supports could be decreased by 41.6, 49.2, and 58.1%, respectively, compared with the allowable design displacement. The total length of SMA cable restrainers is the smallest, and they are more efficient in limiting the relative displacement compared with elastic restrain devices. (C) 2018 American Society of Civil Engineers.