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Special Moment Frame — Anchorage Design

Strong Frame Special Moment Frame

Moment Frame Design Requirements and Assumptions

Anchorage Design

Anchorage to Concrete

In addition to the steel frame design, Simpson Strong-Tie also offers anchorage design. We have two solutions for anchorage of the column bases to concrete:

  1. MFSL — The MSFL anchorage assembly comes with a preattached shear lug, so no field-bent ties or hairpins are required for shear capacity (see Figure 1).
  2. MFAB — The MFAB assembly requires field-installed ties or hairpins, but also provides higher shear capacity depending on the amount of reinforcing provided (see Figure 2).
SMF Anchorage Design, Figure 1 — MFSL Anchorage Assembly

Figure 1 — MFSL Anchorage Assembly
Patent 833,626,7B2

SMF Anchorage Design, Figure 2 — MFAB Anchorage Assembly

Figure 2 — MFAB Anchorage Assembly

Anchorage Design Notes

The steel-strength calculations for anchor shear and anchor tension are per ACI 318-11 (2012 IBC) and ACI 318-14 (2015 IBC). Tension and shear anchorage are designed as follows:

Element

Anchor rod steel strength in tension
Anchor breakout strength in tension
Anchor pullout strength in tension
Anchor rod steel strength in shear
Embedded plate bending strength
Concrete shear strength — shear lug
Concrete shear strength — tied anchorage

2012 IBC Code Section

ACI 318-11, D.5.1
ACI 318-11, D.5.2
ACI 318-11, D.5.3
ACI 318-11, D.6.1
AISC Chapter F
AISC Design Guide 1
ACI 318, Chapter 10

2015 IBC Code Section

ACI 318-14, 17.4.1
ACI 318-14, 17.4.2
ACI 318-14, 17.4.3
ACI 318-14, 17.5.1
AISC Chapter F
AISC Design Guide 1
ACI 318, Chapter 10

Anchorage designs are based on LRFD loads. For designs under the 2012 IBC, tension anchorage for seismic loads complies with ACI 318 Appendix D. The design strength is governed by the maximum tension that can be transmitted to the anchors by the frame capacity or the maximum tension obtained from design loads combinations that include E, with E increased by ΩO. (Section D.3.3.4.3 with modi cations contained in 2012 IBC section 1908.1.16.)

For designs under the 2015 IBC, tension anchorage for seismic loads complies with ACI 318-14 Chapter 17. The design strength is governed by the maximum tension that can be transmitted to the anchors by the frame capacity or the maximum tension obtained from design loads combinations that include E, with E increased by ΩO. (Section 17.2.3.4.3 with modi cations contained in 2015 IBC section 1908.1.16.)

For strength calculation, strength reduction factors in tension are based on:

  • Seismic Design Category, φseismic = 0.75
  • Crack/Uncrack Concrete factor, φconc = 0.70

Strength reduction factor in shear included:

  • Grout pad reduction factor = 0.8

Simpson Strong-Tie Strong Frame Anchorage design calculates anchor bolt shear and tension interaction above the concrete using the AISC 360 bolt interaction equation. However, for capacity within the concrete, anchorage designs are based on anchor embedment into the foundation for tension, while shear design is based on the resistance within the curb or slab. The Designer must consider shear and tension interaction of the concrete if failure surfaces overlap. If this failure mode occurs, we recommend providing supplemental reinforcing to transfer the shear forces into the concrete. Where a greater end distance is required, the Designer should specify this on their plans. Additional studs can be specified to increase this end distance.

Calculations for the anchorage are provided and typically assume a cracked concrete design based on ACI 318 with no supplementary reinforcing and a centered square pad. Alternate design and detailing of anchorage can be specified by the Designer as well.

Inspection Requirements

Since the entire Simpson Strong-Tie® Strong Frame special moment frame can be field bolted, no field welding is required. Welding for the frames is performed on the premises of a fabricator registered and approved in accordance with 2012 IBC Section 1702.2.5.5. Special inspections prescribed in IBC Section 1704 are not required for approved fabricators. Nevertheless, all Strong Frame special moment frames are inspected by a certified third-party welding inspector. For the Yield-Link® stem-to-flange complete joint penetration (CJP) weld, 100% UT is performed with no reduction in sampling rate. Third-party certified bolting inspection is also provided for the pretensioned bolts between the link stem-to-beam flange connections. On top of the code inspection requirements, Simpson Strong-Tie also provides link smoothness measurements and link tensile assurance testing as part of our strict quality-control program. Welding and bolting inspection documents as well as bolt pre-installation testing records can be obtained from Simpson Strong-Tie at the request of the Project Designer or by scanning the QR code on the frame at the jobsite.

Even though the Strong Frame can be field bolted and all field bolting is specified as snug tight, the latest IBC code references AISC 360 and AISC 341 for bolting inspection requirements. AISC requires inspection prior to, during and after bolting similar to welding inspections, although not much is required during snug-tight bolt installation.

In addition to field-bolting inspection, different building jurisdictions might have base plate grouting inspection requirements. Please consult with your project building jurisdiction about this requirement.

Frame Inspection

Simpson Strong-Tie Strong Frame special moment frames have had all required special inspections performed and are built in a factory environment under strict quality-control measures and third-party independent inspection protocols as required under AISC 341, AWS D1.1 and AWS D1.8.

All factory welds for the Strong Frame special moment frame are third-party inspected; some of the inspections are noted in the table on the right.

SMF Anchorage Design, Bullet Chart

In addition to welding, structural ASTM A325 as well as F2280 Twisted-off Type (TC) high-strength bolts are lot tested and stored under requirements of the Research Council on Structural Connections (RCSC). Bolting of the SMF Yield-Link structural fuse to the beam flanges are observed and documented by an independent third-party certified bolting inspector.

Special Moment Frame QR Code Label

Special Moment Frame QR Code Label

Lot Inspection for Tension Controlled Bolts DTI Washers

The structural fastener assembly lots are randomly sampled. The samples are tested to the pre-installation verification requirements for pretension bolts conform with AISC Steel Construction Manual 14th Edition. Where used, the Certificate of Conformance for DTI washers can be found at strongtie.com/strongframe and listed by hardware kit lot number. The lot number is located on the beam and on the hardware box.

Bolting and welding inspection reports and material certifications for any individual frame are available by contacting Simpson Strong-Tie with the work order number listed on the frame stickers or by scanning the QR code on the Strong Frame moment frames and entering the work order number.

Special Moment Frame Label

Special Moment Frame Label

During the frame installation, some special inspections might be necessary depending on jurisdictional requirement; please contact your project’s building department for specific requirements. In the table below are some of the inspections that may be required:

Special Moment Frame Bullet List (2)