Research On Residual Resistance Of Shaped Steel Reactive Powder Concrete Biased Column After Fire

In order to meet the demand of building structure developing towards super high-rise and long-span,steel reinforced reactive powder concrete（SRRPC）structure has become a research hotspot in recent years.The structure not only inherits the characteristics of high strength and good seismic performance of steel reinforced concrete（SRC）structure,but also has the characteristics of high durability,high tensile strength,high compressive strength and high toughness of RPC.In recently,building fires occur frequently,and the residual bearing capacity of the structure after high temperature will affect its safety,which may lead to serious losses and building collapse.Investigating the mechanical properties of SRRPC structure after high temperature is of great significance for the design,repair and reinforcement of the structure.At present,the mechanical properties of SRRPC eccentrically loaded columns are mainly concentrated at room temperature,and there are fewer researches on the residual resistance after high temperature,which greatly limits the promotion and application of this structure.In this thesis,the biasing mechanical properties test,finite element simulation and theoretical analysis of 9 SRRPC columns after high temperature were carried out.The effects of eccentricity（0 mm,40 mm,60 mm,80 mm）,loading angle（0 °,45 °,90 °）and constant temperature time（0 min,60 min,120 min,180 min）at 600 ℃ were considered.The specific research contents and main conclusions are as follows:1.To explore the behavior of SRRPC eccentrically loaded column at high temperature,the heating under constant load tests of 9 SRRPC columns were completed.The timetemperature curve of the specimen,the observations of the specimen after high temperature,and the relationship between the axial displacement of the specimen in the constant temperature stage and the constant temperature time were analyzed.2.To investigate the mechanical property of SRRPC column after high temperature,the biasing performance tests of 9 SRRPC columns after high temperature were completed.The failure mode of the specimens under different influencing factors are obtained.The loaddisplacement curve and mid span deflection curve of the specimens were analyzed.According to the test data,the effects of eccentricity,loading angle and constant temperature time on the ultimate bearing capacity of the specimens were investigated,and the calculation formulas of the ultimate bearing capacity of SRRPC biased columns after high temperature under different parameters were established.3.Based on test,the mechanical properties of 9 SRRPC eccentrically loaded columns at high temperature and after high temperature were simulated by ABAQUS finite element software.The temperature field,failure mode,load-displacement curve of the specimens was compared.The error between the test value and the simulation value was analyzed,and the causes of the error were given.The feasibility of the finite element model was verified by comparative analysis.Based on the established model,the expansion parameter analysis was carried out to further study the effects of fire condition and maximum heating temperature on the residual bearing capacity of SRRPC eccentrically loaded columns.4.According to the temperature field of the specimen,the calculation method of equivalent compressive strength of RPC after high temperature was proposed.Based on the limit state design method and the equivalent compressive strength calculation method,the calculation formula of the normal section bearing capacity of SRRPC eccentrically loaded columns after high temperature was proposed.Main conclusions:（1）The test results show that a platform appears in time-temperature curve for the moisture inside the specimen evaporates and absorbs heat with the increase of furnace temperature.The deeper the measuring point depth is,the slower the temperature platform of the curve appears.After high temperature,the surface color of the specimen changes from gray to gray-white.（2）The results show that the failure mode of SRRPC column after high temperature is the strength failure of material rather than the instability failure of structure.The eccentricity and constant temperature time are the main factors affecting the failure mode of SRRPC biased column after high temperature.With the increase of eccentricity,the ultimate bearing capacity of the specimen decreases gradually.Compared with the specimen with eccentricity of 0 mm,the ultimate bearing capacity of 40 mm,60 mm and 80 mm decreases by 25.4%,32.5% and41.8% respectively;With the increase of constant temperature time,the ultimate bearing capacity of the specimen decreases gradually.Compared with the specimen with constant temperature time of 0 min,the ultimate bearing capacity of the specimen with constant temperature time of 60 min,120 min and 180 min decreases by 3.7%,16.3% and 26.2%,respectively;When the loading angle is 0 °-45 °,the ultimate load of the specimen decreases gradually with the increase of the loading angle;When the loading angle of the specimen is45 °-90 °,changing the loading angle has little effect on the residual bearing capacity of the specimen.Compared with the specimen with loading angle of 0 °,the ultimate load of the specimen with loading angle of 45 ° is reduced by 3.6%,and the ultimate load of the specimen with loading angle of 90° is reduced by 2.8%.With the increase of fire surfaces and the maximum heating temperature,the ultimate bearing capacity of the specimen decreases gradually.（3）Based on the limit state design method and the equivalent compressive strength calculation method,the calculation formula of the normal section bearing capacity of SRRPC eccentrically loaded columns after high temperature was proposed.The proposed formula is suitable for the calculation of the bearing capacity of SRRPC eccentrically loaded columns after high temperature.