Analysis Of The Causes And Countermeasures For Early Crack Of The Double-line Railway Bridge Pier

In the influence of the shrinkage and the heat of hydration of concrete, the double-linebridge pier is easy to appear early crack if early maintenance is not in place, thus it will affectthe durability and safety of the bridge structure.This paper combine a super major bridge of Lan Xin second double-line railway, and hascarried on the actual investigation and finite element analysis on early cracking of double-linebridge pier. It make a deep research mainly from the following several aspects in this paper:（1）Through the actual analysis of project and combining with the related data, there isa comprehensive system of exposition of the causes and classification of early crack fordouble-line bridge pier structure in the paper. It discuss the main cause that is the effect of theshrinkage and the heat of hydration of concrete of the early crack for double-line bridge pier.（2）The early mechanical properties of the double-line bridge pier construction siteconcrete structure were tested, so as to obtain the change law of the axial tensile strength,elastic modulus, ultimate elongation and shrinkage deformation of concrete with age. Thenget the calculation formula of tensile strength of concrete in any age. Discusses thecalculation method of constraint stress and the mechanical conditions for the formation ofcrack in concrete structures.（3）Finite element analysis of double-line bridge pier structure were carried out by thefinite element software MIDAS FEA, so obtained the development laws of concrete shrinkageand hydration heat effect and the change conditions of temperature stress. Through thefurther analysis, the tensile strength near the midline of double-line bridge pier is larger, andthe tensile strength is equal in symmetry position of midline. The position away from the pierbottom is higher and away from the midline is farther, the tensile strength will be smaller.Through the finite element comparison analysis of slotless and slotted bridge pier structure,we can obtain that the node tensile strength of slotted bridge pier structure in the sameposition is less than the slotless bridge pier structure, and the maximum tensile strength alsodecreases. The crack ratio of slotted bridge pier structure is larger than the slotless bridge pierstructure, it will be more conducive to avoid the formation of early cracks..（4）Through changing the parameters of the disposition of stirrup and the ship or size ofgroove for slotted bridge pier structure, the finite element analysis were carried out indifferent parameters form of bridge pier structure. In the five kinds of stirrup layout that theclean protection thickness of concrete is two, five, ten, fifteen, twenty centimeters, it concludethat the different stirrup layout have a little effect on the tensile strength through thecomparative analysis of finite element model. The groove shape of slotted bridge pier structure is assumed for the circular, rectangular, V shape, the tensile strength caused by thearc shaped is minimum and the V shaped is maximum. The groove size of slotted bridge pieris assumed for five, ten, twenty centimeters, the result of the analysis indicates that the groovesize is too big or too small will cause the tensile strength of bridge pier increase, so we mustchoose a reasonable size. In order to determine the more reasonable disposition of stirrup andthe optimal shape and size of the groove, so it advice that the optimal shape of the groove iscircular arc and the optimal size of the groove is ten centimeters.