Earthquake Resistance Optimization and Evaluation of Bridge Piers Structural Form and Dimensions Based on Demand to Capacity Ratio and Yielding Points of Force-Displacement

The evaluation of structural safety must be taken after each earthquake. The importance losses of life and materials carries the significance of the works in the field of earthquake engineering. The purpose of this study was to optimize and evaluate the earthquake resistance of bridge piers by adopting different cross-section forms and dimensions for bridge supports under earthquake action. Two methods of seismic design were used in the optimization and evaluation process. These methods were demand to capacity ratio (DCR) and yielding point. The results of demand to capacity ratio shown that the values of DCR for all piers forms models were increased when the dimension of pier cross section were increased and the values of DCR became less than 1.0, indicating that the increasing in dimensions leading to rise the capacity of bridge supports to carry the earthquake loads in transverse and longitudinal direction. Comparing with models, solid wall pier form had the lower value of DCR, indicating that solid wall piers were suitable in the design of bridge supports to resist the lateral loads of earthquake and it has enough stiffness and capacity under earthquake action. The results of performance points shown that the yielding points were increased when the dimensions of piers were increased for all piers form in transverse and longitudinal direction. The maximum values were appeared within support No. 1 and support No. 4. Solid wall form of pier had the higher values of yielding points, meaning that this type of piers form had higher seismic capacity and it will resist the earthquake action more than others piers form. This study recommended that to use third model for each pier form in the design of bridges structures to resist the earthquake load. Also this study was recommended to use solid wall piers as supports in construction of bridge structure within areas had earthquake action.

Stochastic Transverse Earthquake-Induced Damage Track Irregularity Spectrum Considering the Uncertainty of Track-Bridge System

The track irregularity spectrum of longitudinally connected ballastless track (LCBT)-bridge systems of high-speed railway was proposed in this paper. First, a simulation model of an LCBT-continuous girder bridge was established by considering the influences of approach bridges and subgrade with track structure. Further, a large number of sample analyses were carried out by taking into account the uncertainty of LCBT-bridge systems and stochastic behaviors of ground motions based on the simulation model. The damage laws of residual deformation of track-bridge system after earthquake actions were studied. Then, an interlayer deformation coordination relationship (IDCR) considering the track irregularity caused by earthquake-induced damage of bearings was developed, and the superposed track irregularity samples were obtained. Finally, by using the improved Blackman–Turkey method and Levenberg–Marquardt algorithm, the LCBT irregularity spectrum, track irregularity spectrogram, track irregularity limit spectrum, and a fitting formula for the track irregularity spectrum on a bridge after the action of earthquakes were obtained. Results obtained from the fitting formula and IDCR were compared, and they indicated that tracks undergone significant high-frequency irregularity diseases after the earthquake action. It was found that the track irregularity spectrum could be roughly divided into three ranges: high-, medium- and low-frequency wavebands. Consequently, this led to an application of a three-segment power function for the fitting of the track irregularity spectrum after the earthquake action. The track irregularity spectrum after the action of earthquakes provides an important theoretical basis for the establishment of seismic design methods for high-speed railway bridges based on the traffic safety performance.

Seismic Design Assessment of Bridge Piers Location Effect on the Structural Capacity of Supports under Earthquake Action

The objective of this study was to assess the seismic performance of two types of bridges structures under effect of earthquake by using different locations and numbers of piers. The results of D/C ratio showed that simply supported I girder bridge appeared higher structural capacity than continuous box girder bridge which was resisted the seismic demand. Continuous box girder bridge had higher seismic demand and lower structural capacity comparing with simply supported I girder bridge. Commonly, the seismic design for two types of bridges models with increasing of piers numbers was suitable to resist the earthquake action for region type B. The results of non-linear static analysis (pushover method) showed that the increasing of piers numbers had significant effects on the seismic design of bridges structures to increase the displacement capacity, force capacity, and decreasing of seismic demand to reduce the effects of earthquake action on the bridges structural members. The bridge type simply supported I girder had higher capacity in longitudinal direction than continuous box girder bridge. Whereas, for continuous box girder bridge appeared higher capacity in transverse direction than simply supported I girder. The performance points which were based on displacement were decreased with increasing the piers numbers for bridges structures supports.