Investigation On Fire Resistance Of Stainless Steel Columns With Axial Restraint Under Eccentric Compression Loads

With the promoting of building industrialization process in China, steel structures occupy a rising proportion in building structures recently with numerous advantages. As a branch of steel structures, stainless steel structures have remarkable corrosion resistance and perfect appearance, which have obtained the favor of architects and engineers. However, structure fire frequently occurs in buildings in current years, which makes the security of structures in fire a tremendous challenge. As a structure system of new material, stainless steel structures are usually free of fire protection in order to obtain more excellent appearance. So the behavior response and mechanical performance of stainless steel structures in fire are of great significance. Currently, investigation of mechanical properties of stainless steel material is severely inadequate and experimental research of restrained stainless steel member in fire is almost blank. Based on the above background, the author conducts an experimental study and numerical simulation of stainless steel columns with axial restraint under eccentric compression loads in fire, which indicate the behavior response and failure mechanism of each specimen. Furthermore, the relevant fire resistance design theory is given in the paper.Based on the domestic S30408 austenitic stainless steel material, experimental study on mechanical properties of tens test specimens is conducted, including mechanical property test of 8 specimens at room temperature, steady state mechanical property test of 18 specimens and transient state mechanical property test of 35 specimens at elevated temperature. The experimental results show that the modified two-phase Ramberg-Osgood constitutive model recommended by Rasmussen can precisely simulate the nonlinear stress-strain curve of stainless steel at room temperature, and the modified two-phase Ramberg-Osgood constitutive model recommended by Chen can precisely simulate the nonlinear stress-strain curves of stainless steel at elevated temperature. The stress-strain curves obtained from steady state and transient state test at elevated temperature are almost in the same shape when the temperature is lower than 700 ?, but differences between results from the two test methods increase when it is higher than 700?. Additionally, expression formulas of mechanical property parameter reduction factors are fitted based on the existing test data.The experimental study of 7 stainless steel column specimens with axial restraint under eccentric compression loads in fire is also conducted, which investigates the effect of load ratio n, load eccentricity e and axial restraint stiffness ratio ? on fire resistance performance. Heating curves of specimen, axial displacement-time curves, mid span lateral displacement-time curves and buckling temperature are obtained from the experiment. The experimental results show that load ratio n, load eccentricity e and axial restraint stiffness ratio ? perform important impacts on fire resistance performance of stainless steel columns with axial restraint under eccentric compression loads in fire. After the buckling temperature reached, the specimens can continue bearing loads before it fail.Nonlinear analysis software ABAQUS is used to establish the finite element model and numerically simulate the 7 test specimens in fire. Heating curves of specimen, axial displacement-time curves, mid span lateral displacement-time curves, axial force-time curves, buckling temperature, failure temperature and failure mode are obtained from numerical simulation analysis. The precision of finite element model has been verified by comparing the finite element results with test results.Based on the former finite element analysis method, parametric analysis has been performed on fire resistant performance of stainless steel columns with axial restraint under eccentric compression loads. The analysis results show that load ratio n and axial restraint stiffness ratio ? are external key factors, while slenderness ratio ? and load eccentricity e are internal key factors.Finally, based on the existing fire resistance design method of stainless steel columns under eccentric compression loads without axial restraint, implicit expression formula of buckling temperature has been proposed, whose accuracy has been verified by finite element analysis methods. Additionally, difference between buckling temperature and failure temperature are investigated by finite element parametric analysis.