C-12.412.4 column-beam relationship limitations

The requirements for the Strong Frame connection are similar to those of other prequalified SMF connections. $M_{p r}$, however, is calculated based on the probable maximum tensile strength of the Links, $M_{p r}=P_{r \text {-link }}\left(d+t_{\text {stem }}\right)$, where $P_{r \text {-link }}$ is the probable maximum tensile strength of the Link calculated as the product of the yield area, the specified minimum tensile strength, $F_{u}$, and the ratio of the expected tensile strength to the specified minimum tensile strength, $R_{t}$. When Links are fabricated from ASTM A572/A572M Grade 50 (Grade 345) plate material, this approach results in a $23 \%$ higher estimate of demand than what would be calculated if an approach equivalent to that of other SMF connections was used (Equation 2.4-1). Basing connection demand on the section properties and the expected tensile strength is used in numerous places in the design procedure and produces similarly higher demands when compared to typical SMF requirements. This is consistent with the overall goal of keeping nearly all inelastic demand in the replaceable Yield-Link elements and creating little if any inelastic demand in the members. Using this higher demand also applies to the evaluation of panel zone strength, which for the Strong Frame connection is done in accordance with the AISC Specification rather than the AISC Seismic Provisions. One effect of this requirement is the use of the AISC Specification $\phi=$ 0.90 rather than the AISC Seismic Provisions $\phi_{v}=1.00$ (AISC Seismic Provisions Section E3.6e), in conjunction with nominal resistance, $R_{n}$, calculated in accordance with AISC Specification Section J10.6. Adding to the differences in how $M_{p r}$ is calculated results in panel zone shear demands approximately $26 \%$ higher than would be calculated if typical SMF design methodologies were used.