BEAM LIMITATIONS AISC STANDARDS BASIC INFORMATION


Beams shall satisfy the following limitations:

(1) Beams shall be rolled wide-flange or built-up I-shaped members conforming to the requirements of Section 2.3 of AISC.

(2) Beam depth is limited to W36 (W920) for rolled shapes. Depth of built-up sections shall not exceed the depth permitted for rolled wide-flange shapes.

(3) Beam weight is limited to 300 lbs/ft (447 kg/m).

(4) Beam flange thickness is limited to 13/4 in. (44.5 mm).

(5) The clear span-to-depth ratio of the beam shall be limited as follows:
(a) For SMF systems, 7 or greater.
(b) For IMF systems, 5 or greater.

(6) Width-thickness ratios for the flanges and web of the beam shall conform to the limits of the AISC Seismic Provisions. When determining the width-thickness ratio of the flange, the value of bf shall not be taken as less than the flange width at the ends of the center two-thirds of the reduced section provided that gravity loads do not shift the location of the plastic hinge a significant distance from the center of the reduced beam section.

(7) Lateral bracing of beams shall be provided as follows:
(a) For SMF systems, in conformance with Section 9.8 of the AISC Seismic Provisions. Supplemental lateral bracing shall be provided at the reduced section in conformance with Section 9.8 of the AISC Seismic Provisions for lateral bracing provided adjacent to the plastic hinges.

References to the tested assembly in Section 9.8 of the AISC Seismic Provisions do not apply. When supplemental lateral bracing is provided, attachment of supplemental lateral bracing to the beam shall be located no greater than d/2 beyond the end of the reduced beam section farthest from the face of the column, where d is the depth of the beam.

No attachment of lateral bracing shall be made to the beam in the region extending from the face of the column to end of the reduced section farthest from the face of the column. (b) For IMF systems, in conformance with Section 10.8 of the AISC Seismic Provisions.

Exception: For both systems, where the beam supports a concrete structural slab that is connected between the protected zones with welded shear connectors spaced a maximum of 12 in. (300 mm) on center, supplemental top and bottom flange bracing at the reduced section is not required.

(8) The protected zone consists of the portion of beam between the face of the column and the end of the reduced beam section cut farthest from the face of the column.

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