Crack Resistance Method In Negative Moment Region Of Steel-concrete Composite Continuous Beam Based On Interface Slip

The cracking of the concrete deck in the negative moment region of the steel-concrete composite continuous beam is a problem that has plagued the academic community for a long time.At the same time,the effect of steel-concrete interlayer slip is also a research hotspot.In previous studies,the interface slip effect is rarely linked to the crack resistance of the concrete deck.However,a small amount of research literature and Uplift-Restricted Slip-Permitted(URSP)connector cited in several practical projects have closely linked the two,that is,the interlayer slip may be beneficial to improve the crack resistance of concrete deck in negative moment region.In order to explore the relationship between interlayer slip and crack resistance of concrete deck in negative moment region,this paper analyzes the influence of slip effect on the crack resistance of concrete deck according to the technical characteristics of URSP connector,so as to verify a new design method to improve the crack resistance and reveal the working mechanism of this design method.Therefore,this paper designed two phases of model experiments.The first phase was a threespan steel-concrete composite continuous beam model experiment.After the completion of the experiment,it was found that the beam height of the bottom steel box girder was low and the stiffness was insufficient.As a result,the crack resistance of the combined structure using URSP connectors is not as expected.On the basis of careful analysis of the reasons,the second phase of local reverse loading experiment in negative moment region was designed,and the structure size was modified accordingly to achieve the expected experimental effect and deepen the understanding of the relationship between the interlayer slip effect and the crack resistance of composite structure.Based on the experimental research,based on the second phase of the negative bending moment region local reverse loading experimental members,the Diana finite element model is established.Considering the two analysis conditions of prestressed and non prestressed,the mechanical characteristics of interlayer slip effect to improve the crack resistance in the negative bending moment region are analyzed and studied,and two working mechanisms of improving the anti-crack performance of sliding effect are proposed.Finally,the parameterized sensitivity analysis of the finite element model based on the partial reverse loading experiment in the negative bending moment region is carried out,and the key influencing factors to improve the crack resistance of the negative bending moment region are proposed,which enriches the connotation of the structural design method.The main conclusions of the full text are as follows:(1)The improvement of the crack resistance of the slip effect is reflected in two aspects: on the one hand,the slip effect weakens the shear force of the connector and reduces the shear force transmitted from the steel box girder to the concrete deck under the action of the negative bending moment.On the other hand,the slip effect can improve the effect of prestressing,effectively retaining the prestress in the concrete deck,preventing the prestress from being transmitted to the steel box girder through the connectors,thereby improving the crack resistance of the composite structure.(2)The prerequisite for the slip effect to improve the crack resistance of concrete is that there is a sufficiently large stiffness gap between the steel box girder and the concrete deck The greater the stiffness gap between the steel box girder and the concrete roof,the more obvious the crack resistance improved by the slip effect.If the rigidity gap between steel box girder and concrete is too small,and the ratio of bending rigidity between steel box girder and concrete roof is lower than the critical value of 11.7,the slip effect will not only improve the crack resistance but will reduce the crack resistance.(3)Since the slip effect reduces the shear force transmitted from the steel box girder to the concrete deck under the action of the negative bending moment,the slip effect can make the stress distribution of the concrete deck in the negative bending moment region more uniform and avoid excessive concentration of tensile stress in the section of the middle fulcrum.As the load increases,the tensile stress on the top surface of each section of the concrete in the negative moment area increases uniformly.Therefore,the slip effect makes the cracks have the characteristics of slow development,wide distribution and small width.(4)The use of URSP connectors in steel-concrete composite beam bridges will weaken the overall stiffness of the structure,thereby reducing the bearing capacity of the structure.According to the existing experimental data,it can be seen that most of the failure forms of the structure are the yield failure of the steel box girder bottom plate,and the slip effect reduces the failure load by 4% to 5%.