Study On The High Temperature Flexural Behavior Of Reinforced Concrete Simply-supported Beams Strengthened By Steel Plates With Direct Shear Anchor Bolts

Anchor bolt steel plate reinforcement technology is to use the shearing bolt to anchor the steel plate to the concrete and ensure the two work together,so as to improve the bearing capacity of members and the ductility of the structure after reinforcement.However,due to the gap between bolt rod and the hole wall of the steel plate,the reinforcement effect is affected.The improved method uses direct shear anchors to achieve seamless contact between the anchor rod and the steel plate hole wall,which ensures the coordinated force of the reinforced steel plate and concrete to the greatest extent,and has been verified in the engineering reinforcement.However,under high temperature condition,the material performance loss is serious,resulting in a considerable degree of safety risk for the reinforced structure.Therefore,it is necessary to explore the high-temperature bending performance of the beams strengthened by direct shear anchor bolt steel plates,and put forward the improvement measures to ensure the performance of the strengthened structure at high temperature.In this paper,starting from the high temperature experiment of the reinforced beam,the development process of the temperature,deflection and stress state of the structures under high temperature are studied by means of numerical analysis,and through parametric analysis and summary,the guiding methods and suggestions for engineering reinforcement application at high temperature are proposed.The work and conclusions of this thesis is as follows:(1)By comparing the temperature field of the high-temperature experiment and numerical simulation of the reinforced beam,it is found that the heating curves of the two are in good agreement: the reinforced steel plate and the direct shear anchor bolts of the beam L1 are heated rapidly,and the overall increase trend is similar to the furnace temperature,and the tensile rebar and the concrete can reach a higher temperature in the later stage.However,the temperature of each part of beam L2 sections rises more slowly,and the temperature at each point is significantly less than L1,indicating that the fireproof coating has a good thermal insulation effect.(2)The stress field of the strengthened beam is solved by the method of sequential coupled analysis,it is found that the deflection simulation curve are in good agreement with the experiment curve,and the stress-strain process of concrete,steel plate,reinforcements and other components are consistent with experiments,which shows the accuracy of the numerical analysis in this thesis.In addition,the dilation angle of concrete has a significant effect on the deflection of the reinforced beam,and it should be reasonable selected based on the model.The coefficient of thermal expansion of the steel is close to experiment results according to the EC3.And the Coulomb friction model can better simulate the contact between steel plate and concrete,and correctly reflect the deflection and stress changes of components.(3)Parametric analysis includes 20 finite element models.The results show that the increase of concrete strength can significantly improve the bearing capacity and reduce the deformation of the component under high temperature;and the increase of the thickness of concrete cover can reduce the temperature of the strengthened beam and prolong the failure time.The change of steel strength also affects the bearing and deformation capacity of the member,and the degree of influence decreases with the increase of temperature;the thickness of steel plate will cause a difference in the temperature of the steel plate in the early stage,which will affect the deformability of the member,but the deflection curve increases in parallel as the temperature of the steel plate is gradually the same at the later stage.The change of the diameter of the direct shear anchor bolt has little effect on the reinforced beam L1 at high temperature;the increase of the thickness of the fire protection layer can significantly reduce the temperature of the internal reinforcement and concrete of the component,so that it can maintain a higher bearing capacity and extend the fire resistance time of the beam at high temperature;with the increase of the load ratio,the deflection of the reinforced beam increases faster,resulting in the continuous reduction of fire resistance.