Experimental study on the behaviour of steel columns under seismic-induced axial impact load

It has been observed during major earthquakes that the so called soft-storey failure of an upper floor of a structure results in large impact load acting on structural members of the lower storeys. It may further lead to progressive collapse of the whole structure substantially intensifying human and material losses. Therefore, the aim of this paper is to investigate experimentally the behaviour of columns under bending (observed during an earthquake) that are additionally subjected to an axial plastic impact load. Steel columns with high slenderness ratio were considered in the study. In the experiment, impact load was created by a weight that was dropped onto the top of the column and stayed on it. The weight with the shape of a ball was made of clay so as to simulate more plastic impact. The results of the experiment show that the value of the permanent horizontal deformation of the column observed after impact depends much on the initial relative displacement between the base and the top of the column. As the initial displacement increases the values of the permanent deformation increases significantly indicating the significant reduction in the critical buckling force. The results obtained in the study can be utilized at the design stage of the structures in order to enhance their seismic resistance. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)