Research On Influence Of Cross Effect On Fatigue Behavior Of Steel Box Girder With Large Cantilever

The steel box girder with large cantilever has a novel structure and large cross cantilever.Under fatigue load,the cross beams in the open-web cross diaphragm system will produce cross effect.In order to research the influence of cross effect on the fatigue behavior of orthotropic steel bridge decks in steel box girder with large cantilever,this thesis established the main beam segment model of steel box girder with large cantilever using the finite element software ANSYS.Firstly,the cross beam was divided into four regions according to the support position of cross beam,such as the root of cross beam,the middle of cross beam,the end of cantilever,and the extension of cross beam.The longitudinal history of the first principal stress under a single wheel load was compared with the stress inspected points of the deck-to-U rib detail and the cross beam web-to-U rib detail in the four regions.It was investigated whether the wheel load has the cross-regional effect characteristic due to the cross effect.Then,according to the lane distribution of the highway load part,the stress amplitude of the most unfavorable position of various fatigue details in each lane was calculated and compared.With the lane 1 as the object,the overall bending and shearing effect of cross beam dominated the cross effect was determined.And it was discussed whether the calculation of stress amplitude needs to consider the multi-lane effect.Finally,for the cut-outs detail of cross beam web affected greatly by the overall bending and shearing effect of cross beam,the stress distribution at each cross position of these details under typical load was analyzed,and the cross influence range of the cut-outs detail of cross beam web in the key cross regions was determined.And considering the effect of composite bridge deck,the improvement effect on overall bending and shearing effect of cross beam and multi-lane effect of the cut-outs detail of cross beam web was researched.The research found that the cross effect is dominated by the overall bending and shearing effect of cross beam,and the effect on fatigue behavior of steel box girder with large cantilever is reflected in two aspects: first,the stress state of the same fatigue detail in different cross regions is different;second,the cross influence range of fatigue details increases.The main conclusions are as follows:(1)Under the same wheel load,the stress state of the deck-to-U rib detail is basically the same in the four regions,such as the root of cross beam,the middle of cross beam,the end of cantilever,and the extension of cross beam.While there is a certain difference between the stress state of the cross beam web-to-U rib detail in the four regions.(2)For the cross beam web-to-U rib detail,the wheel load has the cross-regional influence characteristic.(3)The overall bending and shearing effect of cross beam increases the cross influence range of the cross beam web-to-U rib detail,so that the stress amplitude at the most unfavorable position of the side cut-outs detail of cross beam web in Lane 1 is significantly different from the other lanes.The calculation of the stress amplitude of the cross beam web-to-U rib detail needs to consider the multi-lane effect.(4)In the cross regions close to the supporting position of cross beam,the overall bending and shearing effect of cross beam is obvious.In these regions,the cross influence range of the side cut-outs detail of cross beam web can reach the entire vehicle’s cross driving range.And the composite bridge deck can reduce the overall bending and shearing effect of cross beam,but the multi-lane effect still needs to consider when calculating the stress amplitude of the side cut-outs detail of cross beam web.