Comparison of seismic performance of three restrainers for multiple-span bridges using fragility analysis

Abstract

Steel restrainer cables for multiple-frame bridges in California in the United States showed the effectiveness to prevent the unseating at the internal hinges during the past several earthquakes. After that, the steel restrainer cables are being tried to apply for multiple-span-simply-supported (MSSS) bridges in the central and the southeastern regions in the United States. In addition, shape memory alloy (SMA) bars in tension are being studied for the same application. In multiple-frame bridges, the developed seismic forces are transferred to piers through the restrainers; however, in MSSS bridges, the seismic forces are transferred to abutments by the restrainers. Therefore, the abutment's behavior should be investigated as well. This study assesses the seismic performance of the three types of restrainers-steel restrainer cables, SMA bars in tension, and SMA bars in bending for MSSS bridges-due to moderate to strong ground motions using a deterministic seismic analysis. Also, a fragility analysis is conduced to assess the seismic resistance for the overall bridge system. For these analyses, the bending test of an SMA bar is conducted and its analytical model is determined. Then, nonlinear time history analyses are conducted to assess the seismic responses of the as-built and the retrofitted bridges. The deterministic analysis illustrates how the restrainers influence the components of the bridge. However, it could not explain the effects on the whole bridge system. The fragility analysis shows the effects of the three restrainers on the overall bridge system. The fragility analysis indicates that the SMA bars in bending are the most effective ones.

Seismic Effectiveness of Multiple Seismic Measures on a Continuous Girder Bridge

“…The researchers used experiments [7,8] and numerical simulation techniques to study different seismic measures, such as concrete shear keys [9][10][11], steel bar restrainers [12,13], cable restrainers [7,14], viscoelastic dampers, and innovative devices [15,16]. Numerical simulation techniques (including quasi-static [17][18][19], the seismic design method [20][21][22], and dynamic simulation [23][24][25][26]) are widely used for anti-seismic research on the prevention of pounding and unseating because of their advantages that they consume few resources and acquire a large amount of physical information.…”

New SMA Short Fibers for Cement Composites Manufactured by Cold Drawing

“…Martensitic SMAs that exhibit the shape memory effect are used for energy dissipation or for the prestressing of concrete. Superelasticity contributes to provide a self-centering capacity (Choi et al, 2010a) or self-healing of concrete (Song et al, 2006). For these purposes, several types of SMAs such as bars, cables, or wires have been used.…”

Analytical and Experimental Study on the Response of a Seismic Restrainer System for Bridges

“…In addition, improved seismic response of bridges especially against increased seismic longitudinal movements can be achieved with the use of steel or cable restrainers [12]. It is common in practice the cable restrainers to be used in retrofit solutions of existing bridges for limiting the relative longitudinal movements between the abutments and the deck of the bridge and between intermediate joint spans and joints in simply supported bridges while they can be used in bridge design, as well.. A lot of researchers have focused on studying the design of this seismic restraining system [12]- [14] and the seismic response of bridges with steel restrainers [15], [16] or restrainers with enhanced materials like shape memory alloys [16]- [18].Although, the restrainers are considered effective in limiting longitudinal displacements, there are issues related to their response since a) they present the limitation of developing unilateral response, because they are activated only under tension loading, b) they are designed with a slack which can result in their late activation under seismic excitation and c) as it is stated in Caltrans [19] an effective design method hasn't been proposed yet. As a result there are cases were steel restrainers failed under strong earthquakes such as in Loma Prieta 1989 and Northridge 1994.…”