Study On Bending Behavior Of Bolted Region In Steel Bridge Deck

In order to solve the problems of steel structure fatigue and bridge deck pavement which are frequently encountered in the traditional orthotropic steel bridge deck,the author’s research team proposed a new type of composite bridge structure-steel-STC lightweight composite bridge structure,which connects ultra-high toughness concrete and orthotropic steel plate as a whole by welding short studs on the steel panel.The ultra-high toughness concrete layer can effectively improve the overall stiffness of the steel deck,which not only can greatly improve the stress state of the flexible pavement on the bridge deck,but also can significantly reduce the fatigue stress in the steel structure under the local wheel load.Fundamentally solve the two categories of disease problems.However,the survey found that built in the last century a lot of long-span steel box girder bridge,using the steel bolting technology,in the design of bridge maintenance scheme,if considering the use of steel-STC lightweight composite bridge structure scheme,then the STC layer thickness of the bolted region is bound to be thinner due to the presence of the bridging steel plate,resulting in a decrease in local stiffness and an increase in deformation,leading to local premature cracking of the STC layer.Therefore,for the bolted steel bridge,the bolted region should be paid more attention to.Based on the above considerations,this paper designs the traditional orthotropic steel bridge strip model and the steel-STC light strip model with bolted region,and the negative bending moment test and finite element simulation have been carried out.The main contents of research are as follows:(1)The preliminary design and calculation of the Queshi Bridge in Guangdong Province was carried out on the bridge deck maintenance with the steel-STC lightweight composite bridge structure scheme.First,the full-bridge model was established by using Midas Civil software.Considering the overall load effect,the magnitude of the STC layer under the main beam system was calculated.Then the beam model was established by ANSYS software.The local load effect was considered and the stress of the bridge deck STC layer was calculated.Finally,the three system computational stresses are superimposed to obtain the maximum tensile stress of 11.45MPa.(2)In order to study the mechanical behavior of bolted connections in traditional orthotropic steel bridge decks,the static bending test at the elastic stage is carried out for the traditional orthotropic steel deck strip model with bolted region.The test results show that the flexural stiffness of sections in bolted region is much smaller than the other sections in the traditional orthotropic steel bridge deck,namely the bolted region greatly weakened the overall stiffness of the structure.In the design and calculation of bolt connected region the adverse effects can not be ignored.If the adverse effects of the bolted connection area are taken into account in the design calculation,it can be assumed that only the spliced steel plate is involved in the actual force in the bolt connection area,and the original stitch structure is regarded as a complete long variable cross section structure.Then the structure can be calculated according to the general structural mechanics formula.(3)In this paper,the finite element software is used to simulate the complex frictional shear connection of high strength bolts.The concept of force ratio is used to reveal the uneven force of bolts in bolted region which is larger on the outside and smaller in the middle area.This paper makes a statistical analysis of possible high strength bolt diseases and their causes in bolted steel bridges,and sums up corresponding prevention and control measures.(4)In order to verify the feasibility of applying the steel-STC lightweight composite bridge structure scheme to the bridge deck with the bolted region,the STC layer is laid on the above orthotropic steel bridge strip model to form the steel-STC lightweight composite strip model,and static damage test and finite element analysis have been carried out.The experimental results show that the construction of STC layer on orthotropic steel bridge deck to form steel-STC lightweight composite bridge structure can effectively enhance the overall stiffness of the deck structure,but at the same time due to the existence of the spliced steel plate,the thickness of the STC layer in the joint region is suddenly thinned,and early cracking phenomenon will be appearing.The experimental results also show that the micro-crack width of the top surface of the STC layer can be retarded in different degrees when the local optimization designs of the bolted region in the STC layer have been carried out.The specific local optimization design mainly adopts two strengthening construction measures:1)increasing the arrangement density of shear studs;2)making longitudinal reinforcement and spliced steel plate welded.A total of four different schemes were designed:1)no strengthening construction measures were taken;2)only the first measure was taken;3)only the second measure was taken;and 4)two measures were taken at the same time.It is proved that when scheme 3 or scheme 4 is taken,the general area will be cracked before the bolted region,that is,if the scheme 3 or scheme 4 is taken in the design,the risk of premature cracking of the STC layer in the bolted region can be effectively avoided,and the scheme 4 for the best results.The finite element calculation results show that the nominal cracking stress of the STC layer is 17.67MPa,which is much larger than the maximum tensile stress 11.45MPa of the STC layer in Queshi Bridge.In other words,when the scheme 3 or scheme 4 is used,the steel-STC lightweight composite bridge structure scheme applied to its bridge maintenance is completely feasible.At last,the scheme 4 was adopted,and construction has been successfully completed,the bridge deck is operating in good condition.