Influence of over-strength on the seismic behaviour of steel frames

A procedure, based on the analysis of the dynamic inelastic response of the structure to a significant set of homogeneous historical earthquakes, has been adopted to examine the influence of structural over-strength on the seismic behaviour of steel structures. Six schemes, proportioned with different values of behaviour factor q and different amount and distribution of over-strength, have been analysed. The great deal of results, obtained by more than 4800 dynamic analyses, has been statistically elaborated, providing local and global damage indexes which express the probability of yielding and collapse. Both the use of the capacity design criterion and the adoption of uniform column over-strength prove to be effective in reducing the probability of collapse, while the increment of the beam resistance resultes not favourable. The global behaviour appears thus connected to a new parameter, named effective behaviour factor, which takes into account the mean over-strength of beams and columns.