Research Of Several Key Problems On Seismic Design Of RC Girder Bridges Near Active Fault

In recent years, the near-fault groud motion is the hot problem in the engineering seismological field. It has been proven that because of the complicated and special feature of near-fault ground motion the infrastructure systems in near-fault zone are faced with higher seismic risk than that far from these zones.However, till now, no systematical method and theory are proposed for structure design and performance evaluation to consider the influence of near-fault ground motion. And based on the fact that the mechanism of structure resisting earthquake's impact is essentially a process of seismic energy consumption, energy-based design and performance evaluation method for strueture was proposed, and it can reflect more reasonably the integrated influence of the amplitude, the characteristic of spectrum and the earthquake duration to the structural damage. However, the domestic researches still focus on building structure, and the research on the seismic design of bridge is rarely.Consequently, according to the shortages in bridge seismie design, the peak attenuation relationship and the design spectra were studied in this paper; to take a continuous girder bridge for example,studied the earthquake resistance of bridge in the near-fault zones;and considered various parameters, the distribution rules of the hysteretic energy is investigated.The main contents are as follow:1.Based on the collection of 506 near-fault records from 23 worldwide earthquake events including the "5.12" WenChuan Earthquake, an attenuation model which considered the influence of magnitude and distance to fault rupture was proposed, and the parameter regression analysis for PGA,PGV and PGD was calculated by least square method. The peak attenuation relationship of near-fault earthquake ground motion was obtained. And the comparison with other attenuation relationships shows that the advised peak attenuation relationship can correctly reveal the peak attenuation in near-fault regions.2. Based on the near-fault earthquake records database, the near-fault coefficient k,attenuation coefficient c were introduced in the design spectra of "Guidelines for Seismic Design of highway Bridges" (JTG/TB02-01-2008) to adjust the height of acceleration-sensitive region and the attenuation rate of the velocity-sensitive region. And adjusted the characteristic period Tg. From the above study, the design spectra used in the near-fault zone is presented, it also can be refered for the revision of related codes.3.In order to studied the earthquake resistance of bridge in the near-fault zones, to take a continuous girder bridge for example.With reasonable near-fault earthquake records and simulated earthquake waves were input, an elastic-plastic bridge structure finite element model was analyzed by nonlinear dynamic time-history analysis. And then, base on the propose design spectra and other code design spectras, the response spectrum method was used to examine the seismic performance of the bridges.Research indicates that the structural response under earthquake near active fault were increase, and the brings are weak.4. A For the aim of considering the influence of seismic input motion parameters, a MODF equivalent single column model of bridge structure was established to investigate the rules of the layers distribution of the hysteretic energy. It can been found that the hysteretic energy always occurred in the bearings and the bottom of piers. The distribution of the hysteretic energy is of ladder-shaped pattern, and the hysteretic energy in the bottom is larger than that in the upper layers.The result also shows that the earquake parameters play important roles in the rules on the distribution of hysteretic energy. Research indicates that with the amplitude and the earthquake duration incresed the hysteretic energy in the in the bearings and the bottom of piers increased. The influence of the spectrum characteristics mainly reflects in predominant period.