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.