| In recent years,prestressed concrete beam bridges have developed rapidly.In addition,with large torsional stiffness and uniform internal force distribution,box-girder has become the main cross-sectional form of large-span prestressed concrete beam bridges in China.However,due to the properties of ordinary concrete: low tensile strength and obvious shrinkage and creep effects,the main beams of ordinary concrete prestressed box girder bridges are excessively deflected and the box girder body cracks.The deflection of the main beam will aggravate the crack development of the beam body,and the deflection of the beam body will aggravate the deflection of the main beam.These two diseases have long troubled the bridge engineering community and become the bottleneck of the development of this type of bridge.With the birth and development of UHPC(Ultra High Performance Concrete)materials,the bridge teaching and research team of Hunan University School of Civil Engineering proposed a thin-walled box girder system with dense diaphragms.It is a new structure between ordinary concrete box girder and steel box girder.This structure makes full use of UHPC’s superior mechanical properties and minimal shrinkage and creep.It is expected to fundamentally solve the cracking and main beam of ordinary concrete box girder bridges.Scratch these two diseases.The team has mastered many structural properties of the box girder system through relevant experiments,and the diaphragm-type steering block under this thin-walled system needs further study.The structure and weight of the traditional steering block are large,and the reinforcement is relatively complex,which is not suitable for the dense transverse diaphragm thin-walled box girder system.Therefore,based on the excellent mechanical properties of UHPC and the structural characteristics of UHPC box beams,this paper mainly conducts research work from the following aspects:(1)Taking the Beijiang Fourth Bridge in Yingde City,Guangdong Province as the engineering background,based on the structural characteristics of the thin-walled box girder structure with dense diaphragms and the overall external prestressed system,the design concept of the external beam UHPC steering block structure is briefly introduced.And clarify the arrangement of each external beam and its steering situation,two types of UHPC diaphragm type steering block construction forms are proposed.(2)The ANSYS software is used to establish elastic local models for the two types of UHPC steering blocks.The results of local check calculations show that the addition of vertical rib UHPC steering blocks can reduce the local principal tensile stress of the tunnel by 30% and have little effect on the local principal compressive stress.Through the Midas Civil software,the whole bridge overall calculation of the engineering background bridge is carried out.The overall calculation results show that the UHPC box girder solution meets the requirements of the standard under the standard combination,frequent combination and quasi-permanent combination;The stress is superimposed on the stress result of the steering block in the local check,and the result is 5.7MPa,which is less than the specification limit,which proves the feasibility of the new box girder structure bridge scheme.(3)Design the test model from the longitudinal and transverse bridge dimensions,and use the ABAQUS large-scale general-purpose software to perform finite element analysis on the two types of diaphragm-type steering blocks with the largest beam steering angle of the whole bridge.The vertical component force under the action of external prestressed beams is calculated and loaded into UHPC box beam segment models with different beam lengths,the longitudinal length of the test model is determined,and the steering cloud is determined after observing the stress cloud image.The local effects are the splitting effect of the channel,the shear effect of the web,the compression effect of the vertical ribs,and the pulling effect of the bottom plate.The maximum principal tensile stress of the four effects is between0.74～2.17 MPa.The transverse bridge direction simulates the double vertical rib structure without webs and the symmetrical structure of the box girder(considering the web).The results show that: when considering the force of the double vertical rib diaphragm,the role of the web cannot be ignored.(4)Design a 1:2 scale test model of UHPC diaphragm-type steering block,load the vertical force of the test model through the loading device,and investigate when UHPC diaphragm-type steering block is subjected to vertical force Web,floor,vertical ribs and their own response.The strain change,crack development and failure form of each plate are summarized.The safety reserve factor of UHPC diaphragm-type steering block can be 6.51.(5)The nonlinear large-scale general finite element software ABAQUS is used to track and analyze the entire loading process of the test beam section.Comparing the results of the finite element analysis and the test results,the results show that the finite element model can better simulate the stress of the test beam section.On this basis,parameter analysis was conducted to explore the influence of reinforcement,thickness of steering block,UHPC axial tensile strength and compressive strength on the local stress of the test model.By comparing the parameters of the UHPC diaphragm type steering block structure and the ordinary concrete steering block structure,it is found that the UHPC diaphragm type steering block can save materials and reduce the weight of the bridge. |
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