ABSTRACT
This work is related to the protection envisaged by Eurocode 8 with regard to accidental torsional effects for Concentrically Braced Steel Frames in seismic zones. According to Eurocode 8, apart from the natural eccentricity, it is mandatory to consider an additional eccentricity. This takes into account unwanted accidental torsional effects, not otherwise considered in the analysis, due to the spatial variation of the seismic motion or the uncertainties in locating the Center of Mass or the Center of Stiffness. The last depends on the statistical dispersion of the material physical characteristics and of the elements cross-sections. Within this framework, a six-floor building with regularity in plan has been designed for the 1995 draft of Eurocode 8; the structure is of the concentrically braced type. Two different position in plan of the bracing systems have been considered in order to achieve different ratios of the traslational periods to the torsional one. The building has been analyzed in the non-linear range for two different distribution of the accidental eccentricity along the height of the building. The results obtained from the time histories non-linear analyses are compared with those predicted by the design.
