It is generally perceived that ground motion duration has an effect on structural seismic response and damage, despite the neglect of current seismic codes. Based on friction SDOF systems, this paper investigates the duration effect of ground motions on seismic responses and damage of sliding bearings. Ground motions are divided into long-duration (LD) and short-duration (SD) cases, taking the significant duration of 25[Formula: see text]s as the boundary. Each case consists of natural records and spectrally equivalent artificial ground motions to decouple duration from other earthquake characteristics. Results from response history analyses implicate that duration has hardly any effect on seismic responses of the system exhibiting an approximate linear elasticity. Nevertheless, for systems with distinct frictional nonlinearity, selecting LD ground motions as seismic inputs usually leads to a conservative result. By performing incremental dynamic analysis (IDA), nonlinear systems in SD cases bear 10% higher damage risk than those in LD cases without considering the influence of temperature rise. The same is true for systems with a small friction coefficient of 0.005 when earthquakes are in the low intensity range. It was also found that damage exceedance probabilities of these small friction coefficient systems are almost unaffected by the duration as the peak ground acceleration increases to more than 0.6[Formula: see text][Formula: see text]. When the effect of temperature rise caused by friction is considered, the damage exceedance probability in LD cases is higher than SD cases. The damage probability of friction SDOF system under LD earthquake will be underestimated without considering the influence of temperature rise.
The classification and quantitative description of damage of track structure for high-speed railway girder bridges (HRGBs) are still in the exploratory stage, which seriously interferes with the performance-based seismic damage assessment of HRGBs. In view of this, firstly, from the safety and stability of train operation, this paper defines the damage grade of track structure (intact, slight, moderate, severe and complete damage state) by refining the train operation index value. Secondly, based on the simple supported and continuous girder bridge structures of high-speed railway, the train-track-bridge system (TTBS) model is established, and the additional lateral irregularities of the rail caused by the lateral deform of the girder after the earthquake are induced. Finally, the influence of the lateral displacement amplitude of the rail and the train velocity on the train safety and stability is discussed. The results indicate that the rail lateral displacement by the reverse translation of the adjacent simply supported spans and the reverse rotation of the adjacent simply supported spans have the greatest impact on the train safety and stability, respectively. The lateral displacement of rail is proposed as an index to measure the damage of the track structure, and its critical value corresponding to each damage grade in the range of train velocity from 200km/h to 400km/h is determined, which can be used for the seismic vulnerability analysis of track structures for HRGBs.
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