Behaviour of Deformed Steel Columns Exposed to Impact Load During Earthquakes: Experimental Study

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. The aim of this study was to investigate experimentally the behaviour of horizontally deformed columns (deformation as the result of earthquake loading) that are additionally subjected to vertical impact load. Steel columns with high slenderness ratio were considered in the study. In the experiment, impact load was generated by a steel sphere dropped onto a pad of technical clay, so as to simulate nearly plastic impact observed in the reality during earthquakes. The results of the experiment show that with the increase of the pre-deformation of a column (initial relative horizontal displacement between the base and the top) the value of the peak force acting on its top initially decreases and then shows the considerable increase trend. Moreover, with the increase of the pre-deformation, the peak horizontal displacement of the middle part of column substantially increases for all height drop values considered. The results indicate, however, that even the deformed column is still capable to carry substantial dynamic load before its failure due to stability loss.