The study of 8-story and 21-story slender, special moment resisting framed steel buildings (SMRF-SB) is presented. Buildings were designed according to the seismic provisions of Mexico's Federal District Code (RCDF) for a maximum story drift ratio close to the limiting drift Δ=1.2% established in the code for buildings designed according to what it is known as "the main body of the code". As buildings do not satisfy the limiting slenderness ratio H/L ≤2.5 established in RCDF for regular structures and other three requirements of structural regularity, then, the Qactor allowed in the code to reduce seismic forces for design purposes was affected by a 0.8 reduction factor, as established in RCDF (Q' irregular =0.8Qegular). Buildings were designed for the soft soil conditions of the lakebed region of Mexico City. Nonlinear dynamic analyses of representative frame models of subject structures were conducted. Several recorded and simulated accelerograms associated to the design spectra of RCDF for the lakebed region were used for the nonlinear dynamic analyses. Story drift ratios associated to the design according to RCDF were compared with peak dynamic story drift angles computed from nonlinear dynamic analyses. Structural yielding was studied and associated to hysteretic, deformation and strength demands. It can be concluded that although peak story ductility demands are within what it is assumed in the code, and the structural yielding is consistent with a weak-beam, strong-column failure mechanism, the peak dynamic story drift angles considerably surpassed the story drift limit established in the code. This condition has to be revised, particularly from a consistent seismic design methodology viewpoint, because underestimating design drift angles may cause: (1) very important damage to nonstructural elements and, (2) have a negative impact in the review of building separations to prevent a potential structural pounding.