A Study Of The Minimum Support Length Between The Pier And Girder Of The Girder Bridge Under The Seismic Action

The investigation of the damage of bridges shows that in many bridge disasters caused by earthquakes,the unseating of bridge superstructure is one of the most frequent and most serious disasters.In recent years,a large number of researches on the unseating prevention of bridge beams have been carried out at home and abroad,and a lot of unseating prevention devices have been proposed and unseating prevention systems have been established.The minimum support length of pier and grider is the first and the most basic protection measure in the unseating prevention system.It has been written into the 2008 edition of the “Guidelines for Seismic Design of Highway Bridges” and the revised “Specifications for Seismic Design of Highway Bridges”(review draft).However,the Specifications more reference from the related research results of foreign countries.The domestic research work is not sufficient.In this paper,according to the revised requirements of the “Specifications for Seismic Design of Highway Bridges”,the calculation of The minimum support length between pier and grider of the grider bridges is studied.The main research contents are as follows:According to the actual circumstances of fall-beam damage of the Bridges in our country,the rules and regulations of combination,different factors such as pier height,span and the length of a superstructure(for oblique and curved girder bridge,skew Angle and central Angle)should also be considered for the influence of pier-grider relative displacement of grider bridges.The influence of the relative displacement of the bridge girder is calculated and designed according to the uniform test design method.The value of the calculation formula of the minimum support length of pier and girders in the Specifications for Seismic Design of Bridges between China and foreign countries is compared and analyzed.SAP2000 software was adopted to establish the finite element model,and the influence of the values change on the relative displacement of the pier and grider was analyzed by using single factor control.According to the results of the finite element calculation,by using the least square principle and multivariate linear regression analysis,the formula of the minimum support length of the grider bridge is fitted,and the applicability of the fitting formula to simple bridge is verified.The results of the study indicate that,whether it is a simple grider bridge or a continuous girder bridge,the support length between pier and grider obtained by AASHTO in the United States is the minimum,and the Japan and China is high.Because of the high component coefficient of the pier height,the formula of the California standard in 1999 was significantly larger than that of the bridge with a height of over 20 m.For curved girder Bridges,only Japanese and Chinese regulations have rules,and the support length is mainly affected by the central Angle,which has little influence on the pier height and span length.the relative displacement of pier and grider increases with the increase of span,height and length,and the height of pier is the main influencing factor,followed by the joint length and finally the span.At the same level of the same pier,the difference of the relative displacement value of the pier grider is not obvious when the span arrangement and the un-equal span arrangement on the same magnitude.For 8 degrees?class area,high and low piers,for average pier height is not more than 40 m,specification gives the minimum support length value meet the requirements basically,but for the higher intensity area,worse situation and site conditions,seismic fortification should be considered separately.When the pier is equal,the average pier reaches 50 m,but the relative displacement value of the pier and grider is significantly smaller than that of unequal.Therefore,the pier height of the bridge structure should be designed as equal as possible,or not too large difference value.The value of the fitting formula takes into account the influence of different seismic intensity.Different seismic intensity factors should be multiplied by different scale factors to better reflect the law that the calculation results gradually increase with the intensity of the earthquake and consider it more meticulously.However,for high-intensity areas,there is an unreasonable situation in fitting the formula values.Therefore,for highintensity areas,the fortification cannot meet the requirements only from the design of anti-seismic measures,and it is recommended to adopt isolation-reducing measures or other limit devices.The analysis also shows that it is appropriate to use the formula of the minimum support length of pier and girder in the“Specifications for Seismic Design of Highway Bridges”(review draft)as the design of anti-seismic measures for girder bridges.The research results of this paper have some reference value for the design of earthquake resistant measures and engineering application.