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Special Moment Frame – Protected Zones

Strong Frame Special Moment Frame

Moment Frame Design Requirements and Assumptions

Protected Zones

According to the AISC 341-10 Section E3.5.c, the region at each end of the beam subjected to inelastic straining (plastic hinge formation) shall be designated as a Protected Zone. Each prequalified moment connection in AISC 358-16 has its own section on what is considered a Protected Zone. Figure 1 shows the requirements from the Los Angeles Department of Building and Safety (LADBS). A clear marking denoting the protected zone is required, as well as a sign prohibiting penetrations and welds to this zone as it would negatively affect the performance of the moment connection. AISC Code of Standard Practice for Steel Buildings and Bridges (ANSI / AISC 303-16) also has a similar requirement where the Fabricator shall permanently mark the protected zones designated in accordance with AISC 341. If markings are obscured in the eld after application of re protection, then it shall be re-marked.

Figure 2 shows the protected zone for an RBS connection, and Figure 3 shows the protected zone for a bolted flange plate moment connection. As can be seen in these examples, the protected zone encompasses the beam flange and the beam web, because this is the location where the expected inelastic deformation will occur. This means that during construction, the owner’s designated construction representative will have to confirm with the Mechanical, Electrical and Plumbing (MEP) trades that no penetrations will be made through the beam web at these locations. In addition, someone will have to physically mark these locations on each moment connection, as seen in Figures 4 and 5.

SMF Protected Zones, Figure 1 — LADBS Protected Zone Marking Requirements

Figure 1 — LADBS Protected Zone Marking Requirements

SMF Protected Zones, Figure 2 — Protected Zone for an RBS Moment Connection

Figure 2 — Protected Zone for an RBS Moment Connection

SMF Protected Zones, Figure 3 — Protected Zone for a Bolted Flange Plate Moment Connection

Figure 3 — Protected Zone for a Bolted Flange Plate Moment Connection

SMF Protected Zones, Figure 4 — Protected Zone Marking for an RBS Connection in the Field

Figure 4 — Protected Zone Marking for an RBS Connection in the Field

SMF Protected Zones, Figure 5 — Protected Zone Marking for an RBS Connection in the Field (Sprayed on Top of Fire Proofing)

Figure 5 — Protected Zone Marking for an RBS Connection in the Field (Sprayed on Top of Fire Proofing)

Strong Frame Special Moment Frame Protected Zone

Figure 1 (below) shows the protected zone for the Strong Frame SMF connection. Since the beam is not the yielding element, the protected zone only includes the elements in contact with the link at the beam flanges and shear tab at the beam web.

(a) T-Stub Links

(a) T-Stub Links

(b) End-Plate Links

(b) End-Plate Links

Figure 1 — Protected Zone for Strong Frame SMF Connection

Note:

  1. Protected zone included the following elements:
    • a. Link ange and link stem
    • b. BRP plates
    • c. Beam ange areas connected to the link stem
    • d. Column ange areas connected to the link ange
    • e. Shear tab and beam web at shear tab
    • f. Link-to-beam connection bolts
    • g. Link-to-column connection bolts
    • h. Shear tab-to-beam connection bolts
  2. No attachment shall be made to the protected zone.