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Abstract

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, š¯›¾!. 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 š¯›¾! = 15š¯›¾", where š¯›¾" 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.

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