Post-fire seismic behaviors of concrete stub columns in different fire exposure cases

Experimental investigations were carried out on reinforced concrete stub columns (RCSCs) subjected to quasi-static loading after being exposed to standard fire. The fire exposure cases chosen for study were: four faces exposure(1 specimen), three faces exposure (2 specimens), two adjacent faces exposure (1 specimen), and no face exposure to fire (1 specimen). The effects of the fire exposure case and horizontal loading direction on the failure pattern, shear strength, stiffness, ductility and hysteretic energy dissipation of the specimens were investigated. A finite element model was also developed to simulate the temperature distribution during fire exposure period and the behavior under post-fire push-over loading. The developed FE model was validated by experimental test results. The results show that the decrease of the number of fire exposure faces leads to the decrease of the maximum sectional center temperature and the decrease of the declination in shear strength and hysteretic energy dissipation after a fire of 120 min. The maximum sectional center temperatures in the columns, after a fire of 120 min, were measured and are found to be 341℃, 267℃ and 251℃, 191℃ for the 4-face, two kinds of 3-face, and 2-adjacent-face fire exposure, respectively. Compared with the RCSC with no face fire exposure, the shear strength of the RCSCs after exposure of 4-face, two kinds of 3-face, and 2-adjacent-face decreases by 41.2%, 18.6% and 18.8%, 6.6%, while the accumulated hysteretic energy dissipation of the stub columns at the end of a 1/50 displacement angle cycle test decreases by 46.2%, 27.6% and 28.9%, 12.4%, respectively. For the RCSCs exposed to 3-face fire, the seismic performances of the columns subjected to horizontal load along the symmetrical axis and perpendicular to the symmetrical axis are found to be nearly the same. The proposed numerical model can predict the temperature development process in the section and the shear strength of the post-fire specimens in different exposure cases. © 2020, Editorial Office of Journal of Vibration and Shock. All right reserved.