The seismic behaviour of steel moment-resisting frames with stiffening braces

摘要

The present paper deals with the seismic behaviour of steel struc- tures which are designed in the attempt of exploiting the dual characteristics of moment resisting frames (MRFs ) and concentri- cally braced frames (CBFs) as lateral force resisting systems. Three prototype frames are studied within the context of Eurocode 8 (EC8) provisions; these are MRFs which are traditionally designed, against ultimate seismic actions (ULS), without checking ser- viceability limit state rules (SLS-interstory drift limits). To fulfill these requirements concentrical braces are inserted in the frames, which are not considered in the collapse resistance of the structural system. The non-linear behaviour of these systems under ultimate seismic environment is studied and compared to the one of the unbraced MRFs. The influence of second order effects is also inves- tigated.