Study On Flexural Behavior Of Reinforced Concrete Beams Strengthened With Steel Plates After High Temperature

Concrete structure will lose part of the bearing capacity due to the degradation of material properties after high temperature,which will affect the safety of buildings,except for buildings that collapsed after fire,some buildings can still be used after targeted reinforcement on the premise of safe use,the reinforced concrete beam is one of the important bearing components of buildings,which has a great influence on the overall deformation coordination ability of buildings.Because of the advantages of simple construction and reasonable economy,steel bonded reinforcement method is widely used in the field of engineering reinforcement.Therefore,it is of great practical significance to study the flexural behavior of reinforced concrete beams strengthened with steel plates after high temperature.In this paper,experimental study,numerical analysis and theoretical calculation are used to analyze and discuss the flexural behavior of the specimens strengthened with bonded steel after high temperature.The research contents and achievements are as follows:(1)According to the international standard temperature rise curve,four reinforced concrete beams were heated at high temperature,and the variation of temperature values with heating time was obtained;The simulation results are compared with the experimental results.The results show that:The temperature of the measuring point is the lowest when it is far away from the direct heating surface and has less direct heating surface around it;The temperature time curves of most measuring points are approximately straight in the range of 100 ℃ to 130 ℃.(2)Six reinforced concrete members were tested under four-point flexural test bending loading,the advanced DIC measurement technology is used in data acquisition.Research shows:The ultimate bearing capacity and stiffness of the members decrease after high temperature;The ultimate bearing capacity and stiffness increase greatly after the bottom bonded steel plate reinforcement.(3)Based on the cohesive element,the finite element fitting analysis model of steel bonded strengthened beam after high temperature is established,according to the comparison between the existing test data and the finite element numerical simulation results,it is found that the load deflection development curve obtained from the simulation is basically consistent with the curve obtained from the test,the reliability of the analysis results of the finite element model is illustrated.The influence of the length of steel plate and the thickness of adhesive layer on the strengthening effect of concrete beams strengthened by steel plate after high temperature is considered.Research shows that:The increase of steel plate thickness and steel plate length can effectively improve the stiffness and ultimate bearing capacity;The influence of the change of adhesive layer thickness on the flexural performance of the component is too small to be ignored.(4)The weakening formulas of concrete and steel bars after high temperature are collected,combined with the temperature field of beam section,the calculation method of bending capacity of beams strengthened with bonded steel after high temperature is put forward,and compared with the experimental results.The results show that:The results show that the error between the two methods is small and the calculation results are slightly safe,which shows that the proposed calculation formula has high accuracy,it can provide a reference for the reinforcement and repair work in practical engineering.