Structural Behavior And Calculation Theory Of Fully Prefabricated Steel-UHPC Composite Beams

In this doctoral dissertation,a novel type of fully prefabricated steel-UHPC(Ultra-high Performance Concrete)composite beam system has been proposed for accelerated bridge construction,including Concrete Steel Link(CSL)between neighboring bridge decks,SteelConcrete Composite Link(SCCL)between the bridge deck and the steel beam.Totally 23panel-type and beam-type specimens have been completed and tested to investigate the cracking resistance of the interface between CSL and UHPC deck and static and fatigue bending performance of the prefabricated assembled steel-UHPC composite beam in depth.The crack constraint mechanics of CSL interface in potential weak position were revealed.And the theoretical calculation method of crack width of CSL interface have been obtained to analyze the influencing factors on the cracking resistance for optimizing the practical design.Moreover,the theoretical mechanical model of double-shear-interface composite beam have been established to calculate the prefabricated composite beam with different shear connection degree under negative bending moment.The ultimate bearing capacity of precast UHPC deck and assembled steel-UHPC composite beam have also been evaluated.Therefore,the following research work has been completed:(1)The rapid connection constructions between adjacent precast UHPC decks including active pattern and passive pattern have been proposed.And effects of different shearing connectors parameters on the cracking resistance of CSL interface and bending stiffness of precast bridge deck were discussed.According to the test results,the load-deformation relationship,the cracking developing pattern and failure modes have been obtained.Mechanism and effect of various factors were analyzed and summarized.(2)For the passive-pattern CSL,the mechanical model of equivalent cantilever rod of vertical steel plate was established according to the constraint mechanism of CSL interface and test results.Moreover,the theoretical calculation methods of crack width of CSL interface have been proposed.The sensitive analysis of shear connectors parameters,including the shear connectors dimension and position,was carried out.(3)For the active-pattern CSL,the calculation method of the prestress distribution on the UHPC end face have been obtained based on the elastic foundation beam theory,which were verified with the analytical results of the finite element model.The numerical solutions and analytical solutions of the initial cracking stress were proposed to investigate the effect of different prestress degrees and stiffener heights.Compared with the test results,the formular presented high calculation accuracy.(4)Comprehensively considering the bending performance of precast UHPC deck with different constructions,a general mechanical model of precast UHPC deck was established.The analytical solutions of deflection distribution of precast UHPC deck in linear elastic stage were derived by using the continuous subsection independently systematic integral method.Moreover,considering the cracking influence on the bending stiffness during different stages,the whole stage solution method of the mid-span deformation has been proposed.Meanwhile,the judgment criteria of the yielding and failure states and the bending bearing capacity calculation solution have been also obtained,which showed high calculating accuracy.(5)According to the concept of accelerated bridge construction of composite beam,three full-scale prefabricated assembled composite beam specimens were completed and tested by static and fatigue four-point bending load.The static bending test results showed that the high-strength bolts connectors with the screwing torque of the upper limit value required by the specification could ensure the complete shearing connection between the steel girder and the UHPC panel.And the failure mode was similar to the conventional composite beam.The fatigue bending test results showed that the under the total 6 million times of variable amplitude fatigue load,the bending stiffness was reduced within 20% and the maximum crack width didn’t exceed 0.05 mm.The fully prefabricated composite presented excellent fatigue performance.Based on the test results,FE model was established to carry out the numerical analysis for the numbers of precast UHPC decks and the distribution forms of high-strength bolt connectors.The results showed that reducing the number of the precast UHPC decks had little effect on the bending stiffness and bearing capacity of the composite beam but would improve the cracking resistance of the CSL interface.Meanwhile,the spacing of bolt connectors can be increased by 1.3 times to optimize the design method of the steel beam.(6)As the embedded bottom steel plate will introduce double shearing connection surfaces between UHPC decks and steel beam,the mechanical model of the composite beam with double shearing surfaces was proposed,from which the slippage-load relationship,the whole-process deformation-load relationship and bending bearing capacity under negative bending moment were obtained,respectively.Compared with the test results,the calculation methods showed high accuracy.