Study On The Axial Compressive Properties Of High-strength Concrete Columns Confined With Steel Tube-CFRP Stirrups After High Temperatur

With the construction industry rapidly developing,building structures are increasingly utilizing high-strength concrete and FRP materials.Among these materials,steel tube-CFRP hoop-confined high-strength concrete columns have emerged as a popular option due to their remarkable compressive strength and ductility.However,given the prevalence of building fires,adequate fire protection measures are essential.This paper examines the mechanical behaviour and failure modes of high-strength concrete columns with confinement from steel tube and CFRP hoop reinforcements after high temperature,and evaluates the compressive performance of such column specimens after fire.The specific content and results are presented as follows:(1)Twenty specimens with varying cross-sectional shapes were subjected to high-temperature testing and axial compression testing after being heated.The high-temperature test results were used to analyze the temperature-time curves of the steel tube surface,hoop surface,and concrete,respectively.The study investigated the influence of parameters such as fire exposure time,steel tube wall thickness,and cross-sectional shape on the temperature fields of the specimens.The mechanical behaviour of the specimens after high temperature were analyzed based on their axial compression test results including test phenomena,load-axial strain curves,and load-Poisson’s ratio curves.The study delved into a detailed discussion on the impact of different parameters on the specimens’ mechanical performance after exposure to high temperature.(2)The impact of various parameters on the initial stiffness,ultimate bearing capacity,and ductility of steel tube-CFRP hoop-confined high-strength concrete columns after exposure to high temperature was studied by analyzing loaddisplacement curves of different specimens.Parameters such as fire time,steel tube section shape,steel tube wall thickness,number and width of CFRP hoop layers,hoop type,and hoop ratio were analyzed in depth.Results suggest that parameters such as fire time,steel tube wall thickness,section shape,and hoop type significantly affect the initial stiffness,ultimate load capacity,and ductility of steel tube-CFRP hoop-constrained high-strength concrete columns after high temperature exposure.(3)Thermal parameter-time equations proposed by scholars at home and abroad were compared for different materials such as steel tube,concrete,and CFRP.The relatively reasonable thermal parameter equations were selected.A temperature field model was established for steel tube-CFRP hoop-confined highstrength concrete columns with different cross-sectional shapes after exposure to high temperature using ABAQUS finite element software.The high-temperature test results were compared and analyzed with the temperature field model calculation results to find that the finite element model accurately simulated the temperature distribution of the specimens.(4)Based on the test results mentioned above,the researchers integrated the constraint effects of hoop reinforcement into the calculation formula for the axial compressive bearing capacity of concrete filled steel tubular columns.As a result,they derived a new formula for predicting the axial compressive bearing capacity of steel tube-CFRP-hoop-constrained high-strength concrete columns at the room temperature.Additionally,taking into account the strength degradation of steel tube,concrete,and CFRP materials at high temperatures,the researchers proposed a new formula for predicting the residual bearing capacity of steel stube-CFRPhoop-confined high-strength concrete columns after being exposed to high temperatures.