Cable-stayed Slab Cracks In Cable-stayed Slab Bridges And Discussion On Reinforcement Technology

The cable-stayed slab bridge,a special structure system,is formed by wrapping the cable-stayed cable with concrete,which combines the advantages of cable-stayed bridge,rigid cable and low tower.Cable-stayed bridge and low-pylon cable-stayed bridge technology is becoming more and more perfect,the force of cable-stayed slab bridge is not clear,and it is difficult to ensure that large area of cable-stayed slab does not crack.So far,the construction of cable-stayed slab bridge is very few,but some cable-stayed slab bridges are still in use,so the research and analysis of cable-stayed slab bridge is still valuable.Based on the engineering background of a cable-stayed slab bridge,serious cracks occurred in the cable-stayed slab of the bridge.The causes of cracks,crack development,crack direction and reinforcement of the cable-stayed slab are studied in this paper.The specific research contents are as follows:(1)In view of the prestress loss,temperature,shrinkage and creep,moving load and wind load which may cause the cracking of cable-stayed slab,the finite element model of the whole bridge is established and analyzed by MIDAS/Civil and FEA.The maximum principal stress and minimum principal stress of the cable-stayed slab are used to judge the occurrence of the crack combined with the first strength theory and the second strength theory.The results show that different factors have different influence areas on the cable-stayed slab.The loss of prestress mainly affects the junction area between the cable-stayed slab and the main tower and the 1/3 area of the lower edge of the cablestayed slab;the temperature load mainly affects the lower edge area of the cable-stayed slab;the wind load mainly affects the restrained area of the cable-stayed slab(the junction area between the cable-stayed slab and the main girder of the main tower);and the lane load affects the whole area above the cable-The principal stress has an effect on the whole cable-stayed slab,while the shrinkage and creep have little effect on the whole cablestayed slab.(2)By analyzing the influence of temperature,shrinkage and creep,moving load and wind load on the cable-stayed slab,the order of influence on the cable-stayed slab is: moving load > temperature load > wind load > shrinkage and creep.Prestress loss,temperature drop,shrinkage and creep life increase,moving load increase and wind load increase by the same percentage.The order of influence on cable-stayed slabs is: loss of prestress > increase of moving load > decrease of temperature > increase of wind load > increase of shrinkage and creep life.Correspondingly,when the load acts alone or increases by the same percentage,the greater the influence on the cable-stayed plate is,the more easily the cable-stayed plate cracks.Prestress loss,moving load and temperature load are the main factors affecting the cracking of cable-stayed slabs,that is,the main reason for the cracking of cable-stayed slabs,while shrinkage,creep and wind load are the secondary reasons.(3)The FEA is used to establish the dispersive total strain crack model,and to analyze the generation,development,direction and width of the crack.The results show that the most easily cracked area of the cable-stayed slab is the junction between the cablestayed slab and the main tower and the junction between the cable-stayed slab and the main girder,then the crack extends to the lower part of the cable-stayed slab,and finally the crack extends to the whole upper part of the cable-stayed slab;the direction of the structural crack,the area where the crack occurs and the actual crack direction and crack area are approximately the same,and most of the cable-sta The direction of the crack is perpendicular to the plane of the cable-stayed slab,that is,the direction of the crack is perpendicular to the direction of the inclined upward tension of the cable-stayed slab,and the crack area is all over the inclined area of the cable-stayed slab.(4)Based on the mechanical properties of the cable-stayed slab and the causes of cracks,the reinforcement methods of the cable-stayed slab are discussed.The principal stresses of the cable-stayed slab are compared and analyzed by three reinforcement methods: thickening the cable-stayed slab,sticking steel plates on the cable-stayed slab and stretching external prestressing.The results show that the most effective reinforcement method is external prestressing,followed by bonded steel plate,and the reinforcement effect of thickened cable-stayed plate is not obvious.