圆钢管约束型钢混凝土柱防火设计方法

To improve the fire protection design methods of steel tube confined steel-reinforced concrete（STCSRC）columns，a sequential thermal-mechanical coupling finite element （FE） model was developed using ABAQUS software. The effects of key parameters，including fireproof layer thickness，load ratio，and slenderness ratio，on the cross-sectional temperature field and fire resistance of the columns were systematically investigated. The results indicate that increasing the fireproof layer thickness reduces both the temperature and the temperature gradient within the cross-section. After 180 min of fire exposure，increasing the diameter from 400 mm to 1 500 mm results in a cross-sectional temperature reduction of approximately 15% to 84%. Furthermore，the thickness of the fire protection layer exhibits an approximately linear relationship with the fire resistance of the column，whereas the increasing load ratio and slenderness ratio lead to a significant decrease in the fire resistance rating by 37% to 96%. Notably，for columns with a slenderness ratio between 12 and 50，a diameter of 400 mm，and a load ratio of 0. 5，a fire protection layer of less than 10 mm is generally sufficient to achieve a 4-hour fire resistance. Based on the parametric analysis，a simplified formula for estimating the cross-sectional temperature was proposed. Furthermore，a high-temperature load-bearing capacity calculation method was established，which is consistent with the current normal-temperature design formula. These developments form a systematic design approach focused on determining the required fireproof layer thickness.