2205A.3 Modifications to AISC 341
Add Section D1.6 as follows:
- Diagonal bracing members comply with Section D1.1 for moderately ductile members.
- Each diagonal bracing member resists no more than 30 percent of the diaphragm shear at each line of resistance.
- Diagonal bracing members shall not support gravity loads other than self-weight.
- The slenderness ratio (KL/r) of diagonal bracing members shall not exceed , except tension-only bracing.
- The load effect required for collectors using the load combinations stipulated in the applicable building code.
Modify Section D2.6c(b)(ii) as follows:
(ii) the moment calculated using the load combinations of the applicable building code, including the amplified seismic load, provided the connection or other mechanism within the column base is designed to have the ductility necessary to accommodate the column base rotation resulting from the design story drift.
Add Section F1.4c as follows:
4c. Multi-tiered braced frames: Braced frames configured with two or more tiers of bracing between diaphragm levels or locations of out-of-plane support shall comply with the additional requirements of Section F2.4e.
Modify Section F2.3 Exception (2)(a) as follows:
(a) The maximum of the forces determined using load combination stipulated by the applicable building code including the amplified seismic load, applied to the building frame model in which all compression braces have been removed and those determined with no compression braces removed per D1.4a(2).
Modify Section F2.4a by adding the following:
Where each framing bay on a line of resistance does not have opposing diagonal braces within the same column bay, then the collector forces along that line shall be designed considering the redistribution of seismic forces to other bays as a result of the post-buckled redistribution of loads using the analysis requirements of Section F2.3. The collector shall not be designed for a load less than that stipulated by the applicable building code.
The required strength of the collector need not exceed the forces determined using load combination stipulated by the applicable building code, including the amplified seismic load, applied to the building model in which all compression braces have been removed.
Add Section F2.4e as follows:
4c. Multi-tiered braced frames: Braced frames configured with two or more tiers of bracing between diaphragm levels or locations of out-of-plane support shall comply with the additional requirements of this section:
- Braces shall be used in symmetrical pairs at every tier level.
- Horizontal beams at intermediate tier levels for V- and inverted V-brace configurations shall have out-of-plane strength, stiffness, and beam-to-column connections adequate to resist torsional moments arising from brace buckling when braces are designed to buckle out-of-plane.
- Columns shall be restrained against rotation about their longitudinal axis at each intermediate tier level and shall resist out-of-plane bending moments due to second-order effects, geometric imperfections, and out-of-plane brace buckling.