APPRAISAL OF SEISMIC DESIGN CRITERIA FOR CONCENTRIC BRACING STEEL STRUCTURES ACCORDING TO ITALIAN AND EUROPEAN CODES

The critical review of design methods provided by the Italian codes for constructions NTC2008, in agreement with the European seismic code (EC8), for steel Concentrically Braced Frames (CBF) with X and chevron (or inverted V) diagonals, has the aim at providing more efficient design criteria able to ensure adequate safety levels under seism. As reference case studies, common structural configurations of CBF are designed according to NTC2008, by both Linear Static and Dynamic analyses. The purpose is identifying the weaknesses in the design criteria, with particular reference to both the applicability of the proposed procedures and the actual possibility to size braces and connected structural members, like beams and columns. The critical issues in the design process are evidenced. A discussion on the obtained results has allowed to point out the pros and cons of the current design approach and to propose some enhanced design criteria.