Researches On The Characteristics Of Near-Fault Vertical Ground Motion And It’s Effect On Continuous Beam Bridge

The peak acceleration ratio of vertical and horizontal of near-fault earthquakes is usually taken as 1/2-2/3. In recent years, researchs on ground motion show that this ratio is closely related to the magnitude, epicenter distance, and other factors. And some vertical peak acceleration is even greater than the horizontal peak acceleration, therefore, the taken ratio is maybe smaller than actural one. In general the seismic design and analysis, In seismic design of railway bridge, the influence of less than 9 degree earthquake is not considered. But with the investigation and research of earthquake damage phenomenon, and more and more seismic records show that, especially near-fault region and the epicenter of the region, the influence of the vertical ground motion is significant, resulting in the destruction of many of the structural. So, Characteristics of vertical ground motion and the effect on continuous girder bridge is particularly important and should be studied further.Four different span railway continuous beam bridge is analysised as the research objects. The structures are modled using finite element method to study the reaction of the bridge structure under vertical earthquake. The main contents of the research are as follows:(1). Through the processing of the massive seismic data, the relationship between the peak ratio of the vertical earthquake acceleration and the PGV/PGA and the relationship of the magnitude, the fault distance, the fault type and the shear wave velocity of the near fault is studied.(2).Based on the four groups of continuous beam model established by finite element software MIDAS, different vertical acceleration peak values are inputted to study on vertical seismic response of the continuous beam bridge superstructure; And the rule of the vertical seismic effect on different span continuous beam bridge is also revealed through analysis the reaction of structures under the same peak vertical acceleration.(3).The reactions of piers with different height under vertical ground motion are calculated, and relation between failure types and height of piers under vertical earthquake are revealed.