STATISTICAL-ANALYSIS OF SEISMIC BEHAVIOR OF STEEL FRAMES - INFLUENCE OF OVERSTRENGTH

The influence of structural overstrength on the seismic behaviour of s teel structures and on the assessment of the q-factor has been studied by means of a suitable procedure, based on the selection of a signifi cant set of homogeneous historical earthquakes and on the statistical analysis of the dynamic inelastic response of the structure to these a ccelerograms. Six schemes of steel frames, proportioned according to d ifferent design criteria and therefore with different amounts and dist ribution of overstrength, have been analysed. Three values of the beha viour factor have been considered for each one. The large number of re sults, obtained by more than 4800 dynamic analyses, has been elaborate d in a statistical way, providing damage level indexes which express t he probability of yielding and collapse and the plastic level reached, both for the single section and the whole frame. Interesting conclusi ons have been obtained. In particular, the effectiveness of the capaci ty design criteria in reducing the probability of collapse of frames h as been highlighted. Similar good results have been obtained even when the same overstrength is given to all columns, without any particular attention to its distribution, while the increment of the beam resist ance was not favourable in any case. Moreover, a very large improvemen t in safety has been obtained with just a little increase in the colum n strength over that supplied by the application of the capacity desig n criterion. The global behaviour appears thus connected to a new para meter herein defined and named ''effective behaviour factor'', which t akes into account the mean overstrength bath of beams and columns. Cop yright (C) 1996 Elsevier Science Ltd.