Study On Residual Resistance Of Steel Tube Reactive Powder Concrete Columns After Fire

With the development of modern construction engineering,building structures must not only have high performance,but also have good working performance and durability.As an emerging composite structure,steel tube concrete structures have been widely used in many fields due to their characteristics of high strength,high toughness and high bearing capacity.This structure can not only greatly improve the strength and toughness of active powder concrete;It can also improve the stiffness of the steel pipe.In recent years,the occurrence of building fires has become more frequent,and the decrease in the bearing capacity of the structure caused by the fire will affect the safety and durability of the structure,and the serious may lead to the collapse of the building.For square steel pipe active powder concrete,its higher steel content leads to a more serious reduction in the mechanical properties of other structural components under the same fire conditions.Therefore,studying the mechanical properties of the active powder concrete column of the steel pipe behind the fire is of great significance for the design,reinforcement and repair of the structure.At present,there are few reports on the mechanical properties of the active powder concrete column of the steel pipe at high temperature and after high temperature,and its related research mainly focuses on room temperature,and the residual resistance after fire is not well studied.In this thesis,considering the effects of wall thickness(4 mm,6 mm,8 mm,10 mm),constant temperature duration(60 min,120 min,180 min)and stirrup spacing(40mm,60 mm,80 mm)of square steel pipes,the axial pressure performance test,finite element simulation and theoretical analysis of nine square steel pipe active powder concrete columns(CFRPC)after high temperature were carried out.The specific research content is as follows:(1)In order to study the performance of CFRPC axial compression columns at high temperature,the heating test of 9 CFRPC columns was carried out,and the time-temperature curves of the specimens were analyzed to explore the temperature field distribution law.(2)Through the high temperature postaxial compression test of nine CFRPC columns,the mechanical properties of the CFRPC columns were obtained,the failure of the CFRPC columns under different influencing factors was obtained,the load-displacement curve and height-span deflection curve of the specimen were analyzed,and the effects of the wall thickness,constant temperature duration and stirrup spacing on the ultimate bearing capacity of the specimen were studied according to the test data.(3)ABAQUS finite element software was used to simulate the temperature field at high temperature and the mechanical properties after high temperature for the nine CFRPC axial compression columns,compare the temperature field and load-displacement curve,analyze the error between the test value and the simulated value of the specimen,and explain the reasons for the error.The correctness of the FE software simulation is verified by experiments.(4)According to the temperature field distribution cloud of the specimen,the calculation method of equivalent compressive strength of CFRPC after high temperature is proposed.Based on the limit state design method and the equivalent compressive strength calculation method,the calculation formula of the positive section bearing capacity of the CFRPC bias column after high temperature is proposed.Main conclusions:(1)By comparing the heating curve of the specimen,it can be found that the closer the measuring point is to the surface of the specimen,the higher the temperature,the temperature of the measuring point subjected to fire on both sides is higher than that of the single-sided fire,and the temperature of the steel pipe is higher than the temperature of the active powder concrete.(2)By comparing the axial displacement-load curve of the specimen,it can be seen that the constant temperature time has the greatest influence on the ultimate bearing capacity of the specimen,the increase of the constant temperature time greatly reduces the ultimate bearing capacity of the specimen,and the ultimate axial displacement of the specimen increases with the increase of the constant temperature duration;With the decrease of stirrup spacing,its bearing capacity is significantly enhanced compared with the components without stirrups.The increase of the wall thickness of the steel pipe can increase the ultimate bearing capacity and ultimate axial displacement of the specimen,which is of great help to the increase of the bearing capacity of the active powder concrete column of the steel pipe after the fire.(3)With the increase of the wall thickness of the square steel pipe,the ultimate bearing capacity of the specimen is positively correlated with the wall thickness of the square steel pipe,and the thicker the wall thickness of the square steel pipe,the greater the ultimate bearing capacity.Compared with the RPC1 column of square steel pipe,the ultimate bearing capacity of square steel pipe RP2,RP3 and RP4 is increased by 7.33%,9.89% and 12.43%,respectively.(4)The ultimate bearing capacity of the specimen is negatively correlated with the constant temperature duration,and the longer the constant temperature duration,the lower the ultimate bearing capacity.Compared with the RPC6 column of square steel pipe,the ultimate bearing capacity of square steel pipe RP2 and RP5 is increased by 14.22% and 16.08%,respectively.(5)The ultimate bearing capacity of the specimen is negatively correlated with the spacing of the spiral stirrups,and the larger the spacing between the spiral stirrups,the lower the ultimate bearing capacity.Compared with the square steel pipe RPC7 column,the ultimate bearing capacity of square steel pipe RPC8 and square steel pipe RPC9 is reduced by 1.32%and 5.15%,respectively.(6)The temperature cloud map of the temperature field of the CFRPC column obtained by the ABAQUS finite element software has good consistency with the results obtained by the test,which shows that the CFRPC column model established by the finite element simulation software has high reliability,which provides a reference for the fire resistance and ultimate bearing capacity analysis of the active powder concrete column of square steel pipe.(7)The formula for calculating the residual bearing capacity of CFRPC columns after a fire,obtained through theoretical derivation,can better reflect the ultimate bearing capacity of the specimen,and is of great significance for the repair and reinforcement of structures after a fire.