Abstract
The seismic performance of the SR99 Bridge with conventional and advanced details in Seattle, Washington, was studied via a nonlinear, time history analysis of a multidegree of freedom model. The bridge consists of three spans supported on two single-column piers and will be the first built bridge in the world in which superelastic shape memory alloy (SMA) and engineered cementitious composite (ECC) are implemented to reduce damage at plastic hinges and minimize residual displacements. Existing finite-element formulations in the finite-element software OpenSees are used to capture the response of the advanced materials used in the bridge. The earthquake induced by strike-slip fault was assumed to produce a surface rupture across the SR99 Bridge. The effect of the rupture was modeled by a static, differential ground displacement in the fault-parallel direction across the rupture. The synthetic suite of scaled bidirectional near-fault ground motions used in the analysis contains common near-fault features including a directivity pulse in the fault-normal direction and a fling step in the fault-parallel direction. Comparisons are made on behavior of two different bridge types. The first is a conventional reinforced concrete bridge and the second is a bridge with Nickel-Titanium (NiTi) SMA reinforcing bar at the plastic hinge zone and ECC in the whole column. Fault-parallel near-fault earthquakes typically exhibit a static permanent ground displacement caused by the relative movement of the two sides of the fault. When the fault is located between piers, the pier shows a higher demand. Fault-normal analysis results show effectiveness of the innovative interventions on the bridges in providing excellent recentering capabilities with minimal damage to the columns. But the maximum drift computed in the SMA bridge is slightly higher than reinforced concrete (RC) bridges, contributed by comparatively low stiffness of the superelastic SMA bars compared to the steel reinforcing bars.
Highlights
Experience with recent earthquakes, such as the Kocaeli and Duzce earthquakes and the 1999 Chi-chi Earthquake in Taiwan, shows that all bridges built close to known faults must have greater displacement capacities than those designed for far-field ground motions
Xtract had to be used because the fiber patch commands in OpenSees do not have the ability to create a circular mesh inside a square to represent the columns in the SR99 Bridge
Bond slip did not need to be considered in SR99-shape memory alloy (SMA)/engineered cementitious composite (ECC) due to the couplers acting as mechanical anchors at a shallow depth in the cap beam
Summary
Experience with recent earthquakes, such as the Kocaeli and Duzce earthquakes and the 1999 Chi-chi Earthquake in Taiwan, shows that all bridges built close to known faults must have greater displacement capacities than those designed for far-field ground motions. Cruz and Saiidi (2012) used advanced materials and details to minimize the earthquake damage and residual deformations in a quarter-scale, four-span bridge model subjected to strong shake table seismic excitations [12]. The combination of the high tensile strain capacity of ECC with the superelastic characteristics of the SMA material offers the potential of increasing ductility, while decreasing damage and residual displacement under cyclic loads. The main goals pursued in this study are to determine any beneficial effects of incorporating SMA and ECC details at critical zones of the columns of the innovative bridge in improving its seismic performance in terms of damage and residual displacements
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