Buckling of concrete filled steel hollow columns in case of fire

Abstract

The use of concrete filled steel hollow sections (CSHS) in building construction has increased in the last decade. This type of columns has several advantages linked to their high load bearing capacity and good fire performance. However, when the columns are inserted in a building structure, the effect of the restraining to their thermal elongation, change significantly their fire behavior. The high restraining forces developed during the fire, associated to the degradation of the mechanical properties, will lead to their buckling sooner than they are isolated. In order to study these phenomena a series of fire resistance tests on CSHS columns was carried out in University of Coimbra. Several parameters expected to have influence in the fire resistance of these columns were studied: the slenderness of the column, the load level, the stiffness of the surrounding structure, the percentage of steel reinforcement and the thickness of the concrete layer inside the column. This paper presents some results of the fire resistance tests and analyzes the different buckling phenomena observed in the tested columns.