Study On The Mechanism And Effect Of The Floor Crack Of Long Span Continuous Rigid Frame Bridge

Long-span continuous rigid frame bridge is one of the most widely used bridge at present.Due to the imperfect design theory,construction quality defects,this type of bridge often occurs disease during construction and operation,the bursting crack in bottom slab is one of them.The main reason lies in underestimated the equivalent radial force and effect,and the unreasonable design parameters to against collapse.The bursting crack will have a very negative impact on the structural safety,durability and the normal use of the structure.So far,much Investigation and analysis on these accidents has been carried out in fields of engineering and academic,based on referring to a lot of literatures and the previous results,by using two methods,including mathematical calculation and finite element program,this paper analyzes the mec hanism of bursting cracks in bottom slab,the space influencing factors of box girder,the design parameters of anti-collapse in bottom slab.Firstly,a systematic study of equivalent radical force of prestressing tendon in tapered box girder is carried out,the way and degree of influence of the shape of the curve of bottom plate,positioning error of bellows and cantilever-construction are analyzed,and ways of controlling equivalent radical forces by adjusting the three factors are studied,and on the basis of these analysis,calculation formula of equivalent radical force are modified.This paper researchs the effect of temperature gradient and poisson's effect on concrete box girder floor stress,and corresponding suggestions are put forward.Secondly,based on the typical continuous rigid frame box girder,by spatial finite element modelin,the design parameters of anti-collapse in bottom slab are carfully analyzed,this paper summarize the formula for anti-collapse steel reinforcements and bellows protective layer thickness.Through changing the hole rib thickness,bellows protective layer thickness and the thickness of the bottom plate of the background bridge,the effects of these changes are compared on the stress of the bottom plate.Finally,aiming at the issue of bursting cracks in a bridge in Yunnan,the paper analyzes the reason of bursting cracks in this bridge and verifies that the formulas for calculating equivalent radical force and anti-collapse design parameters proposed in the paper are appropriate.Through the comparison of the reinforcement scheme of the bridge,and according to the design and construction experience of the box girder bridge at home and abroad,this paper summarizes some mature experiences for reference.