Study Of Shear Lag Effect On П Shape Girder Of Wide Thick Rope Cable-stayed Bridge

Shear lag problems have been intensely studied for decades. However, the issue of shearlag of the aviation structures didn’t gain great attentions until1970s-1980s, because of somebridge damage accidents caused by shear lag. Although some significant progress has beenachieved in the last forty years, kinds of issues about the shear lag effect are occurring withrapid development of traffic transport. Among of the various issues, we made detailinvestigations about the wide Π shape girder in the cable stayed bridge. This dissertationincludes three parts as following.Firstly, an equation demonstrating the effects of shear-lag on the wide Π shape girder wasderived by monitoring and analyzing the energy changing.Secondly, the Dongsha bridge of Nantong was selected as the model to analyze the effectsof shear-lag on the main beam. The measured stress of the main beam was confirmed andanalyzed by the finite element analysis. As a result, we found out the distribution rule of theshear-lag effect and stress uniformity coefficient in different construction stages. Havederived the shear lag coefficient envelope of longitudinal direction, we analyzed thedistribution of the shear lag coefficient in longitudinal direction and the stress nonuniformitycoefficient caused by the shear lag. From the above results, we can conclude that the shear lageffect is significant at the folded section of side span as well as the root of bridge tower underthe finished bridge state, while the shear lag effect is moderate in the main beam between twolocations, where the positive and negative shear lag occurs alternatively.Finally, some factors of the shear-lag effect are investigated on the completed bridge byadding small longitudinal beam and increasing the girder roof thickness. Some strategies arepurposed to weaken the shear lag effect, aiming at giving a better guidance to optimizeddesign. According to our calculation results, it can make the stress of girder more uniform byadding one or two small longitudinal stringers. Based on the cost consideration, it should be abetter choice to utilize only one small longitudinal stringer. It can make the stress moreuniform for the roof of most of the girder by increasing the thickness in the roof of the girder,whereas the main girder section will suffer from the increased shear lag.