Study On Flexual Capacity Of RC Beams Strengthened With CFRP Bar At High Temperature

Fiber reinforced polymer(FRP)has many advantages,such as light weight,high strength,corrosion resistance,easy forming and convenient construction,making it more and more widely used in the field of building structure reinforcement.However,the poor fire resistance of FRP materials leads to poor fire resistance of structures strengthened with FRP materials.There is a potential safety hazard in structures strengthened with FRP materials.If the fire load is not considered in the reinforcement design process,once the building fires,the reinforcement structure will be destroyed rapidly due to the sharp decline of FRP material strength,resulting in immeasurable loss.Therefore,it is very necessary to study the fire resistance of the FRP reinforced structure.The reinforcement of reinforced concrete beams with embedded CFRP tendons has become a commonly used reinforcement method,and the research on its performance at high temperature is relatively inadequate.A simplified formula is applied to calculate the flexural capacity of reinforced beams with different aspect ratios,and the results are compared with those of finite element analysis.The least squares method is used to get the reduction coefficient of reinforced concrete beams embedded with CFRP barsThrough consulting related references,the thermal and thermodynamic properties of reinforced concrete beams reinforced with CFRP bars at high temperature are summarized.At the same time,the heat conduction equation,heating curve equation and finite element modeling type are briefly introduced.The use of finite element software ABAQUS to establish the model of operation and calculation,and test components and related references were analyzed respectively for reinforced beams under normal temperature.The load deflection curves,high temperature deflection time curves and temperature time curves were compared to establish the correctness of model validation.By comparing the relationship curves between the temperature field of two kinds of fire protection methods and the temperature of each measuring point with time,we choose the fireproof protection method that accords with the standard requirements,and conduct thermo mechanical coupling analysis.42 beam members are designed,and the influence of different concrete strength grade,CFRP diameter and structural adhesive type on the bearing capacity and fire resistance of reinforced beam under high temperature is analyzed and compared.Through theoretical deduction,a simplified calculation method for the bearing capacity of a reinforced beam under the effect of high temperature is established.The research shows that when the fire protection layer is completely installed on the bottom of the reinforcement beam,the full fire protection layer on the side is in conformity with the relevant specification requirements,and the fire protection method is adopted when analyzing the thermal force coupling.Reinforced concrete beams in the thermal mechanical coupling condition,with the increase of concrete strength,the flexural capacity is increased;with the increase of diameter of CFRP bar,the corresponding increase of flexural capacity of strengthening beam in fire protection;meet the relevant requirements,the use of polymers as structural adhesive reinforced beam Qikang flexural strength compared with epoxy resin as a structural adhesive reinforced beam is slightly larger.The fire resistance of reinforced beams increases with the increase of concrete strength and the increase of CFRP diameter.The fire resistance of beams strengthened with geopolymers as structural adhesives is significantly higher than that of epoxy beams used as structural adhesives.In the simplified calculation formula of flexural bearing capacity,calculation of bearing capacity of concrete beams strengthened the accuracy of less than two steps model using a step model precision.The calculated result of the optimized simplified formula is closer to the result of the finite element calculation.