On the behaviour of concentrically braced frames subjected to seismic loading

This paper deals with the causes and the development of weak storey mechanisms in concentrically braced frames subjected to seismic action. In order to investigate this phenomenon, different braced frames were designed in accordance with Eurocode provisions. The design parameters and the obtained structures are presented in the paper Later the results of a comprehensive nonlinear time history analysis carried out with various accelerograms are shown emphasizing the presence of weak storeys. The connection between the behaviour of the brace and the occurrence of the weak storey is investigated. It is described how the plastic deformation of the diagonals and the development of the weak storey are related. A theoretical influence of the brace deformation on the modal response of the braced frames is introduced and also proven by means of signal processing of the displacement time series of the numerical experiments. In the last chapter a possible redesign method is introduced to rule out the occurrence of weak stories.