| At present,small and medium-span bridges account for more than 90% of the totalnumber of highway bridges.Prestressed concrete hollow slab bridges have become one of the preferred bridge types due to their simple structure and good economic benefits.However,with the improvement of service life,due to design,construction and other reasons,hollow slab bridges have defects such as joint cracking and bottom slab cracking.Longitudinal cracks in the bottom slab are one of the most serious diseases of hollow slab bridges.The appearance of longitudinal cracks seriously affects the durability,bearing capacity and aesthetics of the hollow slab structure.However,"Code for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts"(JTG3362-2018)does not provide for the calculation of longitudinal section crack resistance.Therefore,clarifying the mechanism of longitudinal cracks in hollow slabs and proposing prevention measures are of great significance to the construction and maintenance of hollow slab bridges in the future,and according to the characteristics of longitudinal cracks in the bottom slab,targeted reinforcement methods are proposed.Therefore,the research contents and conclusions of this article are as below:In this paper,based on the research background of a 20 m span post tensioned prestressed concrete hollow slab bridge,on the basis of summing up the mechanism of concrete cracks,a refined finite element model of single beam and the whole bridge of hollow slab bridge is established by using ANSYS software to analyze the transverse stress and strain of the bottom slab in the prestressed tension stage and operation stage of hollow slab bridge,and the mechanism of longitudinal cracks in the bottom slab is obtained,the results show that:the longitudinal cracks near the bending point of the prestressed reinforcement are mainly caused by the Poisson effect of concrete;the longitudinal cracks under the prestressed duct are mainly caused by the additional radial force caused by the upward deviation of the prestressed duct;the longitudinal cracks extending from the middle part of the inner side of the bottom slab to the middle part of the outer side of the bottom slab are mainly caused by vehicle load and vertical positive temperature difference,which are mostly seen in the carriageway area;the longitudinal cracks extending from the outside middle of the bottomslab to the inside middle of the lane area are mainly caused by the vertical negative temperature difference,which are mostly seen in the non traffic area.Then this paper summarizes the strengthening principles and construction process of the two currently commonly used hollow slab bridge reinforcement methods,transverse tensile prestress and laterally bonded steel plates,and uses the finite element software to analyze the strengthening effects of the two strengthening methods on the hollow slab bridge.The results show that the two kinds of strengthening methods can effectively restrain the longitudinal crack of hinge joint,reduce the mid span deflection of each mid beam,and improve the overall performance of hollow slab bridge.However,these two methods can not effectively solve the problem of longitudinal cracks in the bottom slab.Finally,in view of the characteristics of longitudinal cracks in the bottom slab,this paper proposes a method of using a smart material shape memory alloy near the surface to reinforce the longitudinal cracked hollow slab bridge.This method can effectively adjust the transverse stress state of the longitudinal cracks in the bottom slab by using the recovery stress of the shape memory alloy as the prestressing force,and at the same time,it can effectively solve the limitations and difficulties of the existing active reinforcement methods such as low prestress,stress concentration in the anchorage area,and difficulty in mechanical tensioning. |
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