Abstract

The so called soft-storey failure is one of the most typical types of damage induced in buildings as the result of earthquake excitation. It has been observed during ground motions that the failure of an upper soft storey of a structure results in large vertical impact load acting on the lower floors. If the resistance of the structural members of the lower storeys is not sufficient it may further lead to progressive collapse of the whole building substantially intensifying material damages as well as human loses. The main aim of the dissertation is to study the behaviour of steel columns that experience horizontal deformations due to earthquake forces and are additionally subjected to vertical impact load (the effect of the soft-storey failure during ground motion). Furthermore, the response of a multi-storey steel frame building that suffers from a soft-storey failure under real earthquake excitation is also investigated in details. First, the horizontal stiffness degradation of deformed building steel columns subjected to vertical impact has been investigated. Then, the experimental investigation focused on the behaviour of models of deformed steel columns that are additionally subjected to vertical impact load, by dropping the steel sphere from different heights onto the top of the models, has been carried out. The detailed numerical investigation concerning the behaviour of a model of deformed steel column that is additionally subjected to vertical impact load has been studied in the next part of this dissertation. The geometric nonlinearity (large strain analysis) as well as the elasto-plastic material behaviour with the strain rate effect have been considered in the analysis. The accuracy of the numerical model of the specimen has been confirmed by comparing the results of the numerical analysis with the experimental results. Finally, the detailed, nonlinear, three-dimensional numerical analysis using FEM, focused on the behaviour of multi-storey steel frame building that suffers from a soft-storey failure under ground motion excitation, has been conducted. The geometric nonlinearity due to impact and the second order effects as well as the elasto-plastic material behaviour with the strain rate effect have been considered in the numerical analysis.

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