Analysis On Shear Lag Effect Of Three-span Continuous Steel Box Girder Subjected To Seismic Action

Along with the great leap forward of infrastructure construction,curved girder bridge has been extensively used in bridge engineering at the busy place such as intersections and highway for its superior performance.Curved bridges are mainly constructed with curved thin-walled box girders,which are subjected to complex stress such as shear lag effect.This,however,has great negative influence on the safety and durability of box girder structure.Present studies on shear lag effect in box girders are mainly focused on reinforced concrete box girder,loads mainly centered on static loads action,geometry parameters mainly concentrated on crosswise parameters such as cross section,the box girder is mainly singlespanned.This analysis is about shear lag effect of three-span continuous box girder which is subjected to seismic action.To start with,finite element program ANSYS.is used to establish a special model of the three-spanned continuous curved box girder to obtain the most unfavorable seismic input direction under seismic action.Seismic waves are input in this direction to analyze the law of time-history normal stress.Ultimately,under this unfavorable seismic input direction,the influence of geometry parameters in longitudinal direction such as span direction on the three-spanned continuous curved box girder is investigated.Research contents are as follows:1,Horizontal seismic waves are input into the continuous finite element model with the angle range from 0 to 350,and step is 10.In all this 36 input direction,maximum value and minimum value of specified node across the different input direction remain almost unchanged.That is,horizontal input direction has no impact on the maximum and minimum value of inner joint nodes and outer joint nodes.Dynamic response of featured nodes under seismic action on analytical sections are also worked out.Followed by procedures to determining the most unfavorable input direction of seismic waves and finally 150° is figured out to be the input direction.2,Computational analysis on the finite element model of three span box girder is conduct under the seismic most unfavorable of 150°in horizontal direction and Z direction.Results show that extreme value of the inner joint node and its outer counterpart in the midspan of the same span(side span or middle span)has a certain phase difference in stress response.Yet,however,extreme value of inner joint node of side span or middle span phase difference in stress response.This law is true of outer joint node of side span or middle span.3,In virtue of ANSYS program,identical radius of curvature and identical central angle,identical radius of curvature and different central angle,different radius of curvature and identical central angle,the overall dip angle of box girder and different ratios of top deck width to radius are five lengthways parameters that were taken to conduct transient dynamic analysis on the finite element model of the three-span continuous box girder.Then,shear lag coefficient of analytical cross sections and featured nodes are obtained to study shear lag law of nodes in analytical cross sections and featured node in time history terms.Laws shows that:(1)When the three spans are of the same length,no matter in the side span or the middle span,the shear lag coefficient of inner joined node is greater than its outer counterpart.(2)When the three spans are of identical radius of curvature but of different central angle,the ratio of shear lag coefficient of inner joined node and its outer counterpart increase as the decrease of central angle.(3)When the three spans are of identical central angle but of different radius of curvature,the ratio of shear lag coefficient of outer joined node and its inner counterpart increase as the decrease of central angle.(4)Shear lag coefficient stays almost the same with the increase of dip angle.(5)As the increase of top deck width to radius ratios from 1 to 5,the shear lag coefficient of inner and outer joint nodes of midspan in side span and middle span would converge to around 1.Choosing a reasonable ratio of deck width to radius can release the impact on curved box girder。...