Investigation on axial resistance of steel reinforced concrete cross-shaped columns exposed to high temperature

Steel reinforced concrete (SRC) special-shaped columns have the advantages of high spatial utilization, flexible layout and good economic benefits, which are used in high-rise buildings. However, this composite structure has the disadvantages of high steel content and large fire area, which makes it easier to suffer damage in fire, and even cause the collapse of buildings. This paper presents mechanical properties of SRC cross-shaped columns exposed to high temperature. Seven SRC cross-shaped column specimens were analyzed. Temperature field distribution, failure mode, deformation and fire resistance of specimens were obtained under different axial compression ratios (0.4, 0.6) and eccentricity (0, 40, 60, 80 mm). The results showed that: (1) All specimens were in a condition of compression failure and section steel had partial bending failure with the concrete falling off. (2) The larger eccentricity and axial compression ratio were, the earlier cracks appeared, and the more cracks appeared, the more serious concrete shedding of specimen were. Moreover, the cracks were concentrated especially on the side of loading point (i. e., two sides close to the point where the applied load is located), and the cracks are adjacent to the support of specimen, which appear in the whole length of specimen. (3) Axial compression ratio had a significant influence on fire resistance of SRC cross-shaped columns, and influence of eccentricity on fire resistance was generally little compared with axial compression ratio. The fire resistance declined by 43.48-69.14% as axial compression ratio increased from 0.4 to 0.6. Fire resistance declined by 5.45-45.31% as eccentricity increased from 0 to 80 mm, and it was significantly reduced by 28.12-45.31% when axial compression ratio was 0.6. Finally, fire resistance calculation method of SRC cross-shaped column was obtained, which provided reference for fire resistance design of SRC structure.