Fire resistance of partially encased steel columns with restrained thermal elongation

The behaviour of composite columns made of partially encased steel sections subjected to fire has been studied numerically by several researchers. Experimental studies are scarce and there are still many phenomena to study. The influence of the axial and rotational restraint on the behaviour of these types of columns subjected to fire is still under research. This paper presents the results of a series of fire resistance tests on these types of columns with restrained thermal elongation. A new experimental set-up, specially conceived for fire resistance tests on building columns, was used for the tests. The experimental set-up was conceived so that the axial and rotational restraint of the columns would be similar to the conditions in a real building. The parameters studied were the load level, the axial and rotational restraint ratios and the slenderness of the column. The main conclusion of this work is that for low load levels the stiffness of the surrounding structure has a major influence on the behaviour of the column subjected to fire. Increasing the stiffness of the surrounding structure led to reductions in the critical times. The same behaviour was not observed for the high load levels.

Research highlights
► Fire resistance tests on partially encased steel columns.
► Columns axially and rotationally restrained.
► Increasing stiffness of the experimental set-up reduces columns’ critical time.
► Small reduction in the columns’ critical times with increasing slenderness.
► Concrete encasement prevented local buckling of the columns’ flanges.