Study On Fire-resistant Protective Layer Of Concrete Beam Strengthened With Steel Or Carbon Fiber Reinforced Polymer

There are many reinforcement methods for concrete structures,among which the sticking reinforcement method is most commonly used because it is convenient and economical,and does not change the size and force of components.However,due to the poor high temperature resistance of structural adhesives,if the effective fire-resistant protection is not applied to the strengthened members,the strengthened members will lose their reinforced bearing capacity at high temperature,resulting in greater potential safety hazards.On the other hand,due to the lack of research on the fire resistance of bonded reinforced structures in the industry,the existing codes in our country have not yet put forward clear requirements for fire protection measures to be taken for bonded reinforced structures under different fire-resistant grades.In view of this,this paper studied the fire resistance of bonded reinforced beams under the protection of cement mortar and fire retardant coatings for steel structures,in order to provide reference for the selection of fire-resistant protective coatings for bonded reinforced beams.This paper adopted the research method of numerical simulation,taking ABAQUS finite element software as the research tool and the fire-resistance test of the concrete beams strengthened with bonded steel and carbon fiber composite materials completed by our team as the data basis.Through sequential coupled thermal-stress analysis,the following research contents were mainly completed:1.The temperature field models of five test beams were established.The comparative fitting between simulated temperature field and test temperature field was carried out,and the fire-proof and heat-insulating effects of thick-thin combined fire retardant coatings and cement mortar were compared.2.The high-temperature mechanical models of five test beams were established.The results of temperature field calculation were imported into the model as known conditions for stress-strain field analysis,and the comparative fitting between simulated mid-span displacement and test mid-span displacement was completed to verify the correctness of finite element model and finite element method.3.On the basis of the established finite element models,L1 was selected to analyze the thickness parameters of cement mortar,and L3 was selected to analyze the thickness parameters of thick fire retardant coatings and thick-thin combined fire retardant coatings,in order to study the influence of different thickness of fire protection layer on the fire resistance of bonded reinforced beams,and to put forward engineering suggestions for the choice of fire-resistant protective coatings for bonded reinforced beams.The research results show that the cement mortar layer cannot provide effective protection for more than 1 hour at high temperature,and it is suggested that it can be used only when the fire resistance grade of bonded reinforced beams is four.Besides,Thick-thin combined fire retardant coatings has better fire resistance effect,and can reduce the spraying thickness of about 10 mm compared with thick fire retardant coatings,which effectively reduces the difficulty of construction and the risk of delamination and shedding at high temperature,and has high engineering practical value.Therefore,it is suggested that thick-thin combined fire retardant coatings should be used as fire protection layer for bonded strengthened beams at three and above fire-resistant grades.