Research On Shear Lag Effect Of Steel Box Girder Of Self-anchored Suspension Bridge

In the past ten years,China's steel output has continuously increased,which has made steel structural bridges continue to increase.Therefore,steel box girder has been gradually promoted and applied on domestic steel bridges.Steel box girder uses steel instead of traditional concrete.Due to the low self weight of steel,the self weight of the upper structure of the bridge is reduced,especially for large-span bridges.With the increase of its span,the reduction is more obvious,so the dead load of the bridge structure can be greatly reduced.In the box girder structure,the shear lag effect can not be ignored.At present,the research on shear lag effect of concrete box girder structure in China is quite mature,but the research on shear lag effect of steel box girder is not comprehensive enough,especially for the self anchored suspension bridge,which is a complex bridge type.Therefore,the research on shear lag of steel box girder of self anchored suspension bridge is of special significance.In this paper,the single box four chamber steel box girder is taken as the research object,the shear lag effect of the single box four chamber steel box girder section is analyzed by the method of analogy bar,and the differential equation of the uniform load and the concentrated load acting on the simple supported beam and the cantilever beam is deduced,and the shear lag effect of the statically determined structure is solved.Finally,the analysis and comparison of the examples show that the error between the two is basically controlled at 7%.It can meet certain calculation accuracy requirements;Using Midas/civil software,the steel box girder of self anchored suspension bridge is discretized into spatial plate element model,and the shear lag effect under three kinds of loads is analyzed.The results show that the positive shear lag effect is obvious at the junction of web and roof and the junction of sling and roof;After adding two kinds of loads to the most unfavorable load position of each section,it is found that the shear lag effect is more serious,and the maximum value of the shear lag coefficient is increased to a certain extent compared with that of the whole bridge;Compared with the corresponding plane beam element stress value,the maximum stress value of the roof of the spatial plate element section is found to be greater than that of the corresponding plane beam element;The longitudinal shear lag effect of steel box girder of self anchored suspension bridge is analyzed.The results show that under three kinds of loads,the position where the shear lag coefficient changes abruptly is near the side support of steel box girder,near 1/4 of each span of bridge,near the middle support,near the side cable anchorage area,near the tower support and in the middle span.Among them,the most serious position of shear lag effect is near the side support and the side cable anchorage area.In the construction stage of self-anchored suspension bridge,the steel box girder sections of two different construction stages before and after "system conversion" were selected for shear lag coefficient analysis,the results show that the shear lag coefficients of the main box steel box girder before and after the "system conversion" are very different,which is caused by the different stress mechanism of the two.In the closing stage of the main beam,the maximum value of the shear lag coefficient is 1.41;in the initial tension stage of the sling,the maximum value of the shear lag coefficient is 1.74.