THE SEISMIC BEHAVIOR OF STEEL MOMENT-RESISTING FRAMES WITH STIFFENINGBRACES

The present paper deals with the seismic behaviour of steel structures which are designed in the attempt of exploiting the dual characterist ics of moment resisting frames (MRFs) and concentrically 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 action s (ULS), without checking serviceability limit state rules (SLS-inters tory drift limits). To fulfill these requirements concentrical braces are inserted in the frames, which are not considered in the collapse r esistance 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 investigated. (C) 1998 Elsevier Science Ltd, All rights reserved .