Experimental study on the effects of whole heating cycle on post-fire behavior of restrained high strength structural steel columns

This paper presents the results of an experimental study of post-fire behavior and residual strength of restrained high strength structural steel (HSSS) columns, including loading tests of columns at ambient temperature to failure, restrained columns under sustained loading going through heating and cooling cycle in fire and then followed by post-fire loading tests to failure. All the columns were axially restrained in fire. The investigated parameters include with and without rotational restraint, load eccentricity, load ratio and maximum experienced temperature. It was found that if the column failure mode was predominantly overall buckling (columns without rotational restraint in this study), the heating and cooling process would result in a large residual lateral deflection in the column, and the post-fire load carrying capacity of the column would be much lower than without fire exposure. On the other hand, if the column slenderness was low and its failure mode was mainly cross-section yielding (columns with rotational restraint in this study), the post-fire residual lateral deflection was low and the post-fire column would be able to retain a very high proportion of its load carrying capacity without fire exposure, and sometimes even exceeded this value due to strain hardening, which indicated complete reusability of such columns.