Fire resistance of steel columns with restrained thermal elongation

The behavior of steel columns subjected to fire depends on their interaction with the surrounding building structure. To improve knowledge of the phenomenon a great many fire resistance tests have been carried out on steel columns with restrained thermal elongation. A new experimental system was designed and constructed to carry out the tests.The columns tested had slenderness of 50.6 and 63.3, an initial applied load of 30% and 70% of the column's design value of the buckling load at room temperature and an axial stiffness of the surrounding structure of 13, 45 and 63.3 kN/mm. Also tested were columns with initial applied loading eccentricity equal to the width of the cross-section in the direction of the weak inertia axis or both principal inertia axes.The results showed that increasing the stiffness of the surrounding structure may not lead to a reduction of the column's critical temperature. This is because, associated with an increase of the axial stiffness is an increase of the rotational stiffness, which has an opposite effect to the first one. It was also noted that the higher initial applied load levels resulted in shorter critical temperatures of the columns.