Dynamic performance of axially and rotationally restrained steel columns under fire

Abstract

Columns in real buildings are normally axially and rotationally restrained by adjacent members. This paper investigates the dynamic performance of axially and rotationally restrained steel columns under fire via parametric analysis. Investigated parameters include the axial restraint stiffness, rotational restraint stiffness, column slenderness and load ratio. An explicit dynamic solver is employed to analyse the considered columns up to total failure. The numerical model is validated through comparing the results against those of a plane steel frame model which has been verified by means of experimental and analytical work. The results of the column model match well with those of the whole model of steel frame. Results show that the behaviour of restrained steel columns under fire may be quasi-static up to total failure or be with severe dynamic effects during buckling, depending on the restraint condition, load ratio and column slenderness. It is found that static analysis may significantly underestimate the maximum displacement for the case of dynamic buckling of columns under fire, and the maximum displacement of that case may even be larger than the final displacement of gradually removing the heated column. Axial restraint stiffness, rotational restraint stiffness and load ratio have significant effects on both the critical temperature and the initiation of dynamic effects. In this regard, dynamic buckling tends to occur with small axial and rotational restraint stiffness and a large load ratio. However, the performance of columns is found to be relatively insensitive to rotational stiffness ratio beyond a specific threshold value.