| During the 13th Five Year Plan period,China has taken the prefabricated building as the direction of transformation and upgrading of the construction industr y and strategic industry development.In the bridge engineering,the prefabricated technology has been widely used in the superstructure.However,due to the heavy self weight of the traditional concrete cover beam and the difficulty of overall hoisting,the assembly of the large cantilever cover beam has become a major obstacle to the development of the prefabricated bridge.At the same time,ultra-high performance concrete(UHPC)is a new type of civil engineering material with super mechanical properties,which has been widely used in bridge engineering.In order to promote the application of UHPC in the bridge engineering and solve the disadvantages caused by the transportation and pouring of the traditional capping beam,this paper applies UHPC to the large cantilever capping beam of the urban viaduct,and carries out a series of research work,as follows:(1)It is the first time to put forward the design scheme of fully prefabricated light UHPC thin-wall cap beam with partial prestressing force;it has completed 2model tests of 1 large-scale UHPC thin-wall cap beam with similarity ratio of 1:2;it has obtained the test results of key load,deformation law and crack distribution form of the model from loading to failure.The test and analysis results sh ow that the UHPC capping beam proposed in this paper has the characteristics of 40% reduction in self weight,fast construction,etc.,can make full use of UHPC’s ultra-high tensile properties and strain hardening characteristics,and has excellent diagona l section crack resistance and shear resistance.(2)Based on the formula of material mechanics and considering the strain hardening characteristics of UHPC,a new theoretical calculation method of the cracking shear force of the inclined section of UHPC s tructure is proposed,and the calculation formula of the width of the inclined crack is modified based on the common concrete code and considering the crack distribution form and the structural shape coefficient of UHPC structure.The calculation shows tha t the calculation results of this formula are in good agreement with the experimental cracking shear force and the crack width,which can provide a reference for the crack resistance design of UHPC in practical engineering.(3)The results show that the shear capacity of UHPC structure is underestimated by the national codes.In order to further analyze the ultimate value of shear capacity of UHPC cap beams,this paper is based on the modified compression field theory,MCFT),the nonlinear calculation progr am of the bearing capacity of the prestressed UHPC cover beam under the bending shear coupling action is compiled.The MCFT method can predict the failure load of the cover beam well,which can provide a reference for the calculation of the bearing capacit y of other UHPC structures.In addition,the finite element method is also used to calculate the shear bearing capacity of the UHPC cover beam,and the finite element results are in good agreement with the test phenomenon.(4)Based on the model test and parameter analysis,this paper puts forward optimization suggestions for the structural size,reinforcement method and construction technology of UHPC capping beam.It is suggested that the bending reinforcement should be cancelled,the prestressed reinforc ement should be increased properly,and the anti floating measures should be added when pouring UHPC.This research content can provide reference for the application of UHPC capping beam and other UHPC structures. |
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