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SUMMARY: 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.

SUMMARY: The work is devoted to the evaluation of the influence of link configuration on seismic performances of Moment Resisting Frames-Eccentrically Braced Frames dual systems (MRF-EBF dual systems) designed by means of Theory of Plastic Mechanism Control (TPMC). As it is known TPMC assures the development of a collapse mechanism of global type, therefore, the seismic performances evaluated by means of IDA analyses, are affected only by the structural scheme configuration. However, in this paper only a 5 bays structure with 4, 6 and 8 storeys are reported, so that, the work configures as a preliminary evaluation. Additional analyses on different structural schemes with different number of bays will be the natural development of the work herein presented.

SUMMARY: In this paper the experimental results of two beam-column composite connections (one welded and the other bolted) tested under cyclic loading are presented and discussed. The two full-scale specimens were designed as sub-assemblages of a frame to localize the damage at the end of the composite beam in respect of the capacity design, therefore the joint contributed to the deformability of the system essentially in the elastic field. The detail in the area around the column were realized according to the provisions of Eurocode 8 to assure the strength hierarchy by the local mechanisms of the concrete slab. The results highlight the main role of the composite beam in terms of  ductility; the rotational capacity and an “equivalent” plastic hinge length are evaluated.

SUMMARY: The nonlinear seismic response of eccentrically braced frames is strongly correlated to the cyclic response of links, i.e. the dissipative members of this structural type. In this paper, a simple but refined link model recently proposed by the authors is used to assess the effectiveness of some common and simpler models in which the effect of the isotropic hardening is not taken into account explicitly. The comparison is carried out by comparing the dynamic response of 12 multi-storey eccentrically braced frames designed as per Eurocode 8. The structures are characterised by different number of storeys and link lengths. The investigation considers both global and local response parameters. The results show which model gives the best estimate of the ultimate response of the frames. It is also shown that the major differences between the responses predicted by the models are recorded for systems with long links.

This is the complete No 1-2, 2016

Abstracts of the single papers can be found in the Archives under April 2016