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Earthquake-induced poundings have been identified as a critical factor influencing bridge seismic behavior. However, most previous studies on this topic did not consider link-slabs in the continuous deck, which would influence the pounding occurrence and thus the subsequent seismic response. This paper uses a probabilistic method to evaluate the seismic vulnerability of a simply-supported bridge considering pounding and link-slabs. The damage states of girder ends due to poundings are proposed according to the cumulative damage. To analyze the seismic vulnerability of the whole bridge, both the joint probabilistic seismic demand model considering multiple engineering demand parameters and the joint damage state model considering the capability of each bridge component are established. Based on these models, the fragility curve of the whole bridge is obtained using the Monte Carlo method. The effects of gap sizes between pounding components and pier heights on the bridge seismic vulnerability are also investigated. The result reveals that the fragility of the whole bridge system is higher than that of any individual component. Ignoring the contribution of damage to each component to the whole system will lead to an overestimation of the seismic resistance of the overall bridge, which is detrimental to structural safety. [ABSTRACT FROM AUTHOR]

China railway track system II (CRTS-II) slab ballastless track is usually constructed on high-speed railway (HSR) bridges to ensure the rail smoothness and the running safety of high-speed trains, but the use of the longitudinal continuous track system would significantly alter the dynamic characteristics of the bridges and therefore influence the bridge seismic responses. The pounding at shear keys has also been identified as one of the critical factors affecting the seismic behavior of bridges. To investigate the effects of shear keys and CRTS-II track system on the seismic behavior of HSR simply-supported bridges subjected to transverse earthquake excitations, detailed 3D finite element models are developed by using ABAQUS. The seismic responses calculated from the bridges with and without considering shear keys are firstly compared. The result shows that the shear keys can effectively limit the development of pier-girder relative displacement and thus decrease the potential of girder dislocation. However, large pounding forces would be generated between the shear keys and bearing pads and transferred to bridge piers, which will amplify the seismic responses of the bridge piers. The result of seismic analyses of multiple-span simply-supported bridges with and without considering the track system shows that the track system will significantly influence the distribution of seismic forces among the bridge spans. For a bridge with equal pier heights, considering the track system will reduce the seismic responses of side spans (close to subgrade) but will increase those of the middle spans. Whereas an opposite trend is found for bridges with high middle piers and short side piers. [ABSTRACT FROM AUTHOR]

This article proposes a seismic optimization strategy to reduce the cost of piers of simply-supported bridges for high-speed railway (HSR) in China. The dimension and reinforcement ratio of piers are defined as variables. The running safety of high-speed trains during normal operation is considered by novelly setting the vibration amplitude of running trains to satisfy the corresponding constraint condition. Other constraint conditions include the structural fundamental frequency, buckling stability, and longitudinal stiffness, as well as the stress and crack width of piers during earthquakes. An improved genetic algorithm with a double-filter strategy is proposed to increase the efficiency of the optimization calculation. Six HSR simply-supported bridges with different pier heights are selected as examples to verify the effectiveness and applicability of the proposed optimization method. The result shows that for the example bridges, the cost of the optimised piers that are not higher than 30 m can be reduced by 33.38% to 50.65%. The optimised piers can ensure the integrity of the HSR bridges subjected to the considered earthquakes and can provide sufficient stiffness to ensure the running safety and stationarity of high-speed trains. [ABSTRACT FROM AUTHOR]