Study Of Vertical Earthquake On Anti-seismic Performance Of Girder Bridges With Laminated Rubber Bearings

Small and medium span girder bridges are the most common among highway girder bridges in my country,and girder bridges with plate rubber bearings are the most widely used.The support of a plate-type rubber-bearing girder bridge is usually placed directly between the piers and the main girder,without bolts and other fixed connection measures.The sliding friction between the support and the main girder under the action of an earthquake is often difficult to avoid.The Wenchuan earthquake showed that one of the typical earthquake damages of small and medium-span girder bridges is the slippage of the plate rubber bearings.This slip phenomenon is not only related to the constant and live loads transmitted by the superstructure,but also closely related to the vertical ground motion.my country’s current "Code for Seismic Design of Highway Bridges" stipulates that vertical earthquakes can be obtained through horizontal seismic reduction.Horizontal and vertical earthquakes only adopt different regulations for site coefficients and characteristic periods.In fact,the response spectrum ratio of vertical and horizontal ground motions is related to many factors such as structural period,focal distance and magnitude.In some earthquakes,the measured vertical acceleration peaks even exceed the horizontal acceleration peaks.Based on the above background,this article firstly analyzes the characteristics of vertical ground motion and its influence characteristics,and then takes a typical small and medium-span simply supported beam bridge as an example to establish a dynamic analysis model to discuss the impact of vertical earthquake on slab rubber-bearing beam bridge earthquake The influence law of the response is finally combined with the current norms to compare and analyze the consideration methods of vertical ground motions.The main research work and conclusions of this paper include:(1)Select 100 sets of actual ground motions,discuss and analyze the characteristics of vertical ground motions from the aspects of magnitude,site type,fault type,etc.,establish a simplified analysis model to explore the response law of beam bridges under vertical ground motions.Studies have shown that the complex seismic spectral characteristics make the V/H dispersion greater.After the V/H ratio exceeds0.6,the sliding displacement of the support will increase with the increase of the vertical component,but it will often reduce the deformation and curvature response of the lower pier column.;The change of pier height and span has a significant impact on the seismic response of the support.(2)Taking a typical small and medium-span simply supported girder bridge as an example,the OpenSEES software is used to establish a finite element analysis model.The main study discusses the impact of vertical earthquakes on the seismic response of a slab rubber-bearing girder bridge.The influence of the resistance coefficient on the structure response,and the IDA method is used to analyze the response law of the structure under typical vertical earthquakes.Studies have shown that whether the ratio of the displacement of the main girder to the vertical earthquake is up to 1.66,whether the ratio of the sliding displacement of the support to the vertical earthquake is considered to be up to 1.84,and whether the vertical earthquake will cause the main girder and support The result is not safe;and as the coefficient of friction increases,the impact of vertical earthquakes is greater;contrary to supports,vertical earthquakes often cause the curvature response of the pier column to decrease,and the response of key components does not increase with the increase of PGA And linear increase.(3)On the basis of the above-mentioned typical simply supported girder bridges,through the establishment of different vertical considerations and analysis conditions,the structural response is compared and analyzed,and the influence of the vertical earthquake on the seismic performance of the structure is discussed and analyzed.Finally,the vertical seismic requirements in the code are The method is discussed.Research shows that the overall difference in structural response under different working conditions is small,and it is feasible for the code to consider vertical earthquakes by reducing horizontal earthquakes;vertical ground motions will aggravate the damage to the support and reduce the damage to the pier.The lateral damage of the pier column is more serious than the vertical damage;the result obtained with the 0.8times horizontal seismic reduction factor recommended by the code can more accurately reflect the maximum value of the actual vertical earthquake structure response,but it is different from the actual vertical earthquake structure response There is a slight difference.The code is conservative in solving the sliding displacement response of the support,but it is unsafe for solving the curvature response of the pier column.