Fire resistance of steel columns with elastically restrained axial elongation and bending

Structures impose elastic restraint to the axial elongation of steel columns submitted to fire and also to the rotation of their extremities. A computer program, based on the Finite Element Method, is used to analyse the influence of these two kinds of elastic restraint on the critical temperature of columns. The values of the load eccentricity, the column slenderness, and the axial and rotational restraint imposed by the structure were chosen as to cover the great majority of situations to be found in practice. It is shown that axial restraint diminishes, in general, the critical temperature of steel columns, while rotational restraint increases it. The fife design situation, proposed in ENV 1993-1-2, of column with fixed ends and no axial restraint, is acceptable only for less slender columns and in the cases where the frame provides sufficiently high rotational restraint to the ends of the column. When the axial restraint is high and the rotational restraint is low, the real critical temperature of steel columns can be much lower than the critical temperature calculated according to the simplifications proposed in ENV 1993-1-2. (C) 1999 Elsevier Science Ltd. All rights reserved.