Research On Local Stability And Design Method Of I-sections Steel Stub Columns At Elevated Temperatures

Compared with normal section steel,I-section steel has higher lateral stiffness,stronger bending resistance,reasonable and economical stress.However,steel is heat-resistant but not fire-resistant.Research on I-section steel columns at elevated temperatures in China mainly focuses on the overall stable bearing capacity of normal steel and high-strength steel under axial compression,while there is relatively little research on local stable bearing capacity.The research on normal steel and high-strength steel at elevated temperatures abroad is relatively mature,mainly focusing on the mechanical properties of steel at elevated temperatures and the overall stability performance of components such as steel pipes and rectangular steel.The research on the local stability of I-section steel compression and bending components at home and abroad needs to be supplemented,especially for thin and flexible sections and high-strength steel.Most of the current fire resistance design methods have been proven to be unreasonable,ignoring the differences in strength and stiffness degradation of high-strength steel at elevated temperatures.When designing compression bending components,the current fire resistance design specifications use interaction curves.Its shape is defined by the interaction coefficient,and the two ends are the stable bearing capacity of the component under axial compression and bending,respectively.Due to the shortcomings of current standards,the design of the two end points often experiences inaccuracies,resulting in significant deviations during design.These shortcomings prompted the research in this article.This thesis adopts numerical simulation method to establish a finite element model of I-shaped short columns considering initial geometric defects.A systematic study was conducted on the design method for the local stable bearing capacity of three types of I-shaped short column uniaxial compression bending members with different strengths(355MPa,460 MPa,690MPa).Taking into account different cross-sectional dimensions,temperature levels,and load conditions,a large number of numerical results have been generated.By comparing with the numerical results generated by finite element analysis,the European Code for Fire Resistance Design of Steel Structures(EN 1993-1-2)and its upcoming new version,prEN 1993-1-2,have been compared,The section design method proposed by foreign scholar Kucukler,which considers the aspect ratio of elevated temperature sections,has been evaluated for the accuracy of the ultimate bearing capacity design of ordinary steel and high-strength steel at high temperatures.Extend the continuous strength method to the design of thin flexible sections at high temperatures,and use the continuous strength method to calculate the axial compression and bending moment endpoints of compression and bending components.Based on the finite element numerical results and more accurate axial compression and bending moment endpoints,a suggested bending design formula was proposed and evaluated.The results indicate that for the design of local stable bearing capacity of I-section steel short columns under uniaxial compression and bending,the proposed formulas provide more accurate,safe,and consistent prediction of ultimate bearing capacity.