evaluating the ductility of x-braced frames which are braced in two middle adjacent spans

in this study, for evaluating ductility of ordinary concentrically braced frames (ocbfs) and special concentrically braced frames (scbfs) which are x- braced in two adjacent middle spans, 16 steel ordinary concentrically braced frames and 16 special concentrically braced frames are studied. the results confirm that, although most of ordinary concentrically braced frames, which are x-braced, cannot experience the corresponding target displacement, but because of their high designing force level expected ductility can be obtained. also results confirm that the response modification factor of scbfs which is proposed by iranian seismic design code (2800 standard forth edition), r=5.5, is more logical than asce's one, r=6. according to the results, the response modification factor of 5 is proposed for special concentrically braced frames, which have an analytical period of more than one second (frames more than 10 stories).