Research On Flexural Performance Of Steel-UHPC Lightweight Composite Beam Joints In Negative Moment Area

Relying on a flyover bridge of Changbao Expressway in Yunnan Province,this paper proposes a prefabricated steel-UHPC light composite continuous girder bridge.The bridge steel-UHPC composite continuous beam pier top adopts the method of setting concrete beam joints to solve the problem of easy cracking of the bridge deck in the negative bending moment area,and improves the negative bending moment area by strengthening reinforcement and cast-in-place UHPC material on the top.The stepped "T" wet seam resists bending and cracking.In order to verify the safety of the "T"-shaped wet joint used in prefabricated steel-UHPC light composite beams,a series of studies including model tests and finite element simulations are carried out.The main contents and conclusions are as follows:(1)Based on a flyover bridge of Changbao Expressway in Yunnan Province,a1:2 scale model flexural loading test was carried out on the segment in the negative bending moment area,and the load-deflection curve,load-strain curve and cross-section of the whole loading process were studied.Strain distribution,failure form,force transmission mode,etc.;theoretical calculation and analysis of the elastic flexural bearing capacity,cracking condition and plastic flexural bearing capacity of the experimental model are carried out,which are in good agreement with the experimental results;The similarity relationship verifies the safety of the real bridge in the negative bending moment area.(2)The failure pattern of the test model shows that due to the discontinuity of the steel fibers between the old and new UHPC materials,the section at the joint of the cast-in-place UHPC and the precast beam in the negative bending moment area becomes the weak position of the structure,and the flexural bearing capacity of the composite beam is also controlled by this section.The calculation method of the plastic flexural capacity of the joint section corresponding to the failure mode of the beam joint structure is proposed.The analysis shows that the theoretical calculation value of the flexural capacity is basically consistent with the experimental value,and the method in this paper can safely calculate this kind of beam Flexural bearing capacity of joint steel-UHPC composite beams in the negative moment zone.(3)The ABAQUS finite element simulation software is used to simulate the loading model.The results show that the analysis results of the simulation software and the model loading test results are in good agreement both in the whole and in parts,which can be used to predict the test results.The co mparison and analysis of the longitudinal stress distribution cloud map of the inner web of the pure bending section of the simulation model and the normal stress distribution cloud map of the end bearing plate at different loading times can verify the correctness of the aforementioned joint force transfer analysis and plastic ultimate bearing capacity calculation model.(4)According to the model test analysis,it is obtained that the weak section in the negative bending moment area is the connection between the end of the beam and the steel beam.The nominal cracking stress of the section is calculated by Midas software.Considering the structural complexity of the negative bending moment region,we continue to use ABAQUS to carry out segmental simulation of the negative bending moment region under the normal service limit state.The test and simulation results show that design meets the requirements of bridge structural cracking.(5)The construction method and construction process of the steel-UHPC light composite beam overall and the joints in the negati ve bending moment area are introduced,and two optimization schemes are proposed for the structural deficiencies found by the test and calculation analysis.By co mparing the mechanical behavior of the original structure and the optimized plan and the plast ic flexural bearing capacity of the joint section by means of finite element simulation and section calculation,the feasibility and effectiveness of the optimized plan are proved,which can be used for steel-UHPC in the future.Provide reference for the d esign of beam joints in the negative bending moment area of light composite beams.