Seismic stability of steel moment resisting frames with inelastic panel zones

This paper summarizes preliminary findings of nonlinear simulations aiming to quantify the seismic demands of codecompliant steel MRFs with variable panel zone targeted shear distortions, 𝛾!. The probability of beam fractures is explicitly considered in the modeling approach. In steel MRF designs with balanced beam-to-column connections (i.e., targeted 𝛾! = 15𝛾", where 𝛾" is the panel zone shear distortion at yield), the onset of local buckling in the steel beams does not occur prior to lateral drift demands of 4 to 5% rads, on average. For drift controlled MRFs, this slightly increases their collapse capacity relative to steel MRFs featuring elastic panel zones. This is because P-Delta effects mostly control the dynamic instability of steel MRFs in this case. The simulation results suggest that steel MRF designs with more balanced beam-to-column connections that conform to the current fabrication weld practice do not experience beam fractures at modest drift demands associated with a design-basis earthquake. Moreover, the likelihood of residual story drift ratios along the steel MRF height reduces by 70% relative to steel MRFs that mostly concentrate their inelastic deformations in steel beams.