Seismic Provisions (SidePlate PLUS)
I. Moment Frame Protected Zones
The AISC Seismic Provisions (ANSI/AISC 341) prohibit certain attachments in the protected zone for all Special and Intermediate Moment Frame applications. A protected zone (PZ) occurs where the beam or column is subject to inelastic strain and a plastic hinge forms or, more simply, the element bends and buckles under high seismic loads. For the SidePlate connection there are protected zones on the beam and on the side plate. The protected zone locations are illustrated in Figure E9 below.
SidePlate Welded OSHPD
Figure E9 - SidePlate Connection Protected Zones
NOTE: It is acceptable to weld to the face of the side plates outside of the protected zone provided that connections do not interfere with the fabrication and erection of the system.
II. Span to Depth
Each SidePlate connection type and application has a unique span to depth limit. The hinge-to-hinge span of the beam can be approximated by the following equation (final span to depth calculations are done by SidePlate connection design software and provided in the calculation package):
The ratio of the hinge-to-hinge span of the beam, Lh, to beam depth, d, shall be limited to:
SidePlate PLUS SMF (IAPMO): 3.5 or greater.
SidePlate PLUS SMF (AISC): 4.0 or greater.
SidePlate PLUS IMF: 3 or greater.
SidePlate Welded OSHPD: 5.0 or greater.
III. Lateral Bracing of Beams
The engineer of record shall provide lateral bracing of the frame beam bottom flange in accordance with the latest AISC Seismic Provisions. The distance of unbraced length can be calculated from the ends of the side plates, as they provide lateral bracing of the beam, unless otherwise prohibited by local jurisdiction.
Beams should be laterally braced at a distance not to exceed:
Figure E10 - SidePlate Moment Frame Beam with Lateral Bracing
The requirements for lateral bracing are based off of testing, as discussed in this section of the Commentary on the Seismic Provisions for Structural Steel Buildings (341). Supplemental top and bottom flange bracing at the expected hinge is not required for SidePlate because it is provided by the side plates.
Lateral bracing of the bottom beam flange may not be possible in some rare cases, such as large openings. In those instances, the engineer may consider torsional bracing such as built-up sections, or adding supplemental gravity columns between floors.
NOTE: For projects under California’s OSHPD jurisdiction, unbraced length must be measured from the centerline of each column.
IV. LATERAL JOINT BRACING
Although AISC 341 requires lateral joint bracing at the top and bottom of beams in Special Moment Frames (SMF), these requirements do not apply to the SidePlate connection. Since there is a physical gap between the beam and the column, the load path does not use continuity plates at the joint, and localized buckling of the column is very unlikely. Additionally, the connection of the side plate to the column flanges provides additional stability at the joint. As a result, the SidePlate connection may be considered braced at the joint by simply providing a perpendicular beam shear tab connection within the joint region. At locations where no perpendicular framing occurs, the effects of a multi-story unbraced column should be considered, especially in weak axis bending and buckling outside of the SidePlate connection joint region.
V. Collectors and Chords
In some configurations of moment frames, the load path for chords, collectors, or other axially loaded members will need to pass through perpendicular to the SidePlate connection. Coordination of drags will be similar to the coordination of cantilevers and will rely on the configuration of the engineer’s details.
In Plane / Parallel
Unless the detailing will conflict with the SidePlate connection, there is no need for coordination.
Out of Plane / Perpendicular
Out of plane or perpendicular drag connections forces are included in the SidePlate PLUS connection design. In order for the SidePlate PLUS connections to be designed adequately for these conditions, drag/chord beam sizes and design level forces perpendicular to any SidePlate Connection will need to be provided with the preferred type of detailing (whether it be through a shear tab, top flange welded, or another mechanism). Please contact your SidePlate Engineer to discuss these options.