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Frequently Asked Questions:
Strong Frame™ Ordinary Moment Frame
topGeneralWhy did you name your product an Ordinary Moment Frame (OMF)?
The name is specific to a type of steel frame and it follows the terminology used in building codes. Naming it otherwise might confuse a Designer who needs to know the type of frame -- Ordinary Moment Frame (OMF), Intermediate Moment Frame (IMF), or Special Moment Frame (SMF) -- for their calculations and building design.
What’s the difference between an Ordinary Steel Moment Frame (OMF) and a Special Steel Moment Frame (SMF)?
A steel frame designed and detailed as a Special Steel Moment Frame (SMF) must meet all the AISC 341 requirements for beams, columns, and connections. Since the SMF is more ductile than an OMF, ASCE 7-05 assigns it an R factor of 8.0 versus an R factor of 3.5 for an OMF.
Why specify the Strong Frame™ Ordinary Moment Frame instead of a site-built or prefabricated shearwall?
It provides higher capacities in a smaller wall space than a shearwall. The Strong Frame Moment Frame is not intended to replace all shearwalls but instead offers a solution where site-built or prefabricated shearwalls do not work due to lack of capacity or wall length. An additional benefit, over a site-built wall, is the security of a factory-built, quality component.
The Strong Frame Ordinary Moment Frame fits in a 2x6 wall -- why doesn't it fit in a 2x4 wall?
The flange width of the columns and beam help achieve the lateral strength of the frame. If the flanges were reduced to fit in a 2x4 wall, the column and beam depths would have to significantly increase to compensate for the loss of flange width. This would result in a larger wall area to fit the frame.
What are the costs and benefits of the Strong Frame Ordinary Moment Frame compared to a conventionally-fabricated ordinary moment frame?
The unit cost of a Strong Frame Ordinary Moment Frame may be more than a frame made by a local steel fabricator, however the following benefits will offset this cost difference:
- Fits within a 2x6 wall, eliminating the need for possible costly architectural modifications to “hide” the wider steel members used in ordinary moment frames.
- The ability to choose a solution from a catalog provides significant time savings for the Designer. This can save hours if not days required for the calculations and drawings of moment frames and their anchorage.
- No delays due to shop drawing production and review.
- Immediate internet, phone, and field support from the design phase to installation. (Call (800) 999-5099, send email to asksimpson@strongtie.com, or use this form.)
- May be installed by framers; no need to hire a steel erector.
- No field welding required, eliminating weld quality concerns, inspection costs and fire safety issues.
- Arrives unassembled to the job site, taking up less space in the site staging area.
- Comprehensive quality-control measures during production provide the designer and owner with security and peace of mind.
- Complete traceability of all steel components and inspected welds.
- 15/16"-diameter holes in the beam and column flanges and a 2"- or 3"-hole in the column web are pre-drilled for the installation of electrical and plumbing elements.
- Features pre-attached wood nailers designed for shear transfer eliminating additional labor and material costs.
topSystem LimitationsWhat are the height and weight limitations using the Strong Frame™ Ordinary Moment Frame in seismic design controlled projects?
Ordinary steel moment frames are permitted in Seismic Design Category (SDC) A, B and C without height or weight limitations. However, in SDC D or E, ordinary steel moment frames are limited in light-frame structures to a height of 35 feet with a maximum dead load of 35 psf at the roof or floor. In addition, the exterior wall dead load tributary to the frame shall not exceed 20 psf (ASCE 7-05 section 12.2.5.7).
Is it the building structure or the moment frame that is limited to 35 feet in height in SDC D & E?
The building structure is limited to 35 feet since the code states building height limitations not lateral-force resisting system height limitations. Structures with OMF lateral-force resisting systems do not have a height limit in SDC A-C, but building height and dead load limits do exist for structures in SDC D or higher (ASCE7-05 Table 12.2-1).
If my structure is located in SDC D or E and it is a one-story structure with brick veneer that exceeds 20 psf, can I still use the Strong Frame Ordinary Moment Frame?
Yes, provided the brick veneer does not extend above a wall height of 35 feet and the roof dead load does not exceed 20 psf. Ordinary steel moment frames are permitted in one story structures up to 65 feet in height if the wall weight does not exceed 20 psf at a height of 35 feet above the base or higher (ASCE 7-05 12.2.5.6).
topDesign (General)How are the loads for the Strong Frame™ Ordinary Moment Frame determined?
Load capacities are calculated using the International Building Code reference standards along with Design Guides from AISC. Design of the beam and column elements are in conformance with AISC 360. The beam to column connection design is per AISC 341 and AISC Design Guide #4 and #16. The base plate connection is calculated per the second edition of the AISC Design Guide #1.
Is there an Evaluation Report for the Strong Frame Ordinary Moment Frame?
Yes, Strong Frame ordinary moment frames are now code-listed under the 2006 and 2009 IRC/ IBC (IAPMO ES ER-164). After a rigorous review by a nationally-recognized structural engineering firm contracted through IAPMO ES, the code listing includes 368 standard frame models and anchorage solutions.
I have a project where I want to specify the Strong Frame Ordinary Moment Frame. Where can I get the calculation packages and drawings for a specific frame?
What if I have a loading condition that exceeds or is different from the Strong Frame Ordinary Moment Frame catalog limits?
Frames with loading conditions that are not covered by the Strong Frame Ordinary Moment Frame catalog, may be analyzed using the Simpson Strong-Tie Strong Frame Ordinary Moment Frame Selector Software (click here to download a free copy). If you prefer, you may fill out the OMF Alternate Loading Worksheet and email it to asksimpson@strongtie.com. We'll evaluate your specific loading condition and provide a response within 2 working days whenever possible.
Is beam bracing required on the Strong Frame Ordinary Moment Frame?
No, the beams were designed as unbraced and the AISC 341-05 (Seismic provisions) do not have additional beam bracing requirements beyond that required in the AISC 360-05 Specifications.
Is beam bracing required for a Special Steel Moment Frame (SMF) if there is an evaluation report for the SMF connection?
Yes, a special moment frame beam must be braced per the AISC Seismic Provisions (AISC 341). A code report for a moment frame connection is not the same as a code report for the moment frame assembly. Unless the entire frame has been tested without beam bracing and accepted by AISC or an Evaluation Agency, the beam must be braced for the load and stiffness as required by Appendix 6 (Equation A-6-7 and Equation A-6-8) of AISC 360.
topDesign of Structural Systems with the Strong Frame™ Ordinary Moment FrameDo all shearwalls, parallel to an OMF in the same story, have to be designed with an R factor of 3.5?
No, only the shearwalls along the same wall line as the OMF need to be designed for an R=3.5. Shearwalls parallel to the OMF, but not in the same wall line, may use an R=6.5 if the structure meets all of the following requirements from ASCE7-05 12.2.3.2:
- Occupancy category I or II building [see Table 1-1 in ASCE 7-05 or Table 1604.5 in the 2006 IBC]
- 2 stories or less in height, and
- Light-frame construction or flexible diaphragms are used.
If I use the Strong Frame Ordinary Moment Frame on the first story and I have a wood shearwall directly above on the 2nd story, what R factor do I use for seismic design of the various structural elements?
The wood shearwall would be designed with an R = 6.5 and the OMF would be designed with an R = 3.5. ASCE 7-05 Section 12.2.3.1 addresses R, Cd and Ωo values used in seismic design with vertical combinations of lateral-force resisting systems. It requires that the R factor for any story must not exceed the lowest value of R that is used in the same direction at any story above that story.
If I use the Strong Frame Ordinary Moment Frame on the first story and I have a wood shearwall directly above on the 2nd story, do I design the shearwall connections and the Moment Frame using the load combinations that include the overstrength factor, Ωo ?
The shearwall connections are designed for the same force as the shearwall, that is, without the overstrength factor (ASCE7-05 Section 12.3.3.).
The Moment Frame is designed using the load combinations that include the overstrength factor,
Ωo, or the maximum load that the system (e.g., shearwall above) can deliver.
What R factor do I use for the diaphragm when I use an OMF?
The R factor for diaphragm design shall be the least value of any of the systems utilized in the same direction so the diaphragm design shall use R=3.5.
Do the Strong Frame Ordinary Moment Frame capacities still apply if I use an R factor of 3 per ASCE7-05 Table 12.2-1 Row H?
Yes.
topCollector DesignOn the Strong Frame™ Ordinary Moment Frame load tables, there is a “Top Plate to Nailer Connection” column with fastener quantities. Were those calculated with an overstrength factor, as required in SDC C through F, assuming the top plate is acting as a collector?
No, since many times the field installed top plate will only be acting as a direct shear transfer element. The fastener quantity provides a capacity that exceeds the maximum allowable shear load. For those cases, in SDC C through F, where the designer needs to design this connection with an overstrength factor then additional fasteners shall be specified using the appropriate overstrength factor (2.5 for structures with flexible diaphragms). Refer to ASCE7-05 Section 12.10.2.1.
On the Strong Frame Ordinary Moment Frame load tables, in the “Top Plate to Nailer Connection” column, can we use 1/4" diameter x 3" long SDS screws instead of the 1/4" diameter x 3.5" screws?
Yes, provided the Designer considers the load reduction due to the shorter screw length (280 lbs vs. 340 lbs per C-2009 Connector Catalog at a load duration =1.00). Additional SDS screws may need to be specified. As a minimum, it is recommended that SDS screws be spaced at 16" on center maximum.
What is the in-plane shear capacity of the countersunk 5/8" diameter bolts on the double 2x beam top nailer?
This connection was tested and found to be slightly lower than a calculated value. The ASD capacity is 2000 lbs per bolt with no increase permitted for load duration. The 9-inch-deep beams have 10 bolts total along the length of the top nailer whereas the 12-inch-deep beams have 14 bolts total.
If I design a field installed 2x6 top plate as a collector for the overstrength force and determine that it is not adequate, what options do I have?
A thicker top plate is one solution (e.g., a 3x instead of a 2x). See detail 5/SF3 (PDF) (page 61 in the C-SF10 Strong Frame Ordinary Moment Frame catalog) for other possible collector configurations.
topConnections to the Strong Frame™ Ordinary Moment FrameHow do I detail uplift connections to the Strong Frame Ordinary Moment Frame beam?
If the roof rafters or trusses bear directly on the top-beam nailer plates, then hurricane ties such as the H2.5A or the H10 can be used similar to their attachment to wall top plates.
If the moment frame is on the lower story and a post/stud uplift force must be transferred from the upper story, then a continuous strap can connect the upper story wall studs to wood blocking placed within the OMF steel beam web. This blocking may be attached to the steel beam web with Quik Drive™ TB screws, PDPH powder-actuated fasteners or A307 machine bolts. For more information, see details 1/SF3 (PDF), 2/SF3 (PDF) and 14/SF3 (PDF) (pages 60 and 65 in the C-SF10 Strong Frame Ordinary Moment Frame catalog) or on the downloadable detail sheets.
For end wall uplift conditions, one can use vertical straps directly attached from the upper post/stud to the moment frame column wood nailer below. See details 3/SF3 and 4/SF3 (PDF) (page 60 in the C-SF09 Strong Frame Ordinary Moment Frame catalog).
How do I transfer load from a cold-formed steel (CFS) framed structure into the Strong Frame Ordinary Moment Frame?
The Designer can remove the OMF wood nailers and attach cold-formed steel studs or tracks to the steel beam or column directly using screws, powder-actuated fasteners or by welding. Refer to detail 11/SF3 (PDF) (page 63 in the C-SF10 Strong Frame Ordinary Moment Frame catalog) for welding and fastening limitations.
If the wood nailers remain on the steel beam of the moment frame, steel straps can be used similar to detail 7/SF3 (PDF) (page 61 in the C-SF10 Strong Frame Ordinary Moment Frame catalog). Note that wood strap values are listed in the C-2009 Wood Construction Connectors catalog and CFS strap values are listed in the C-CFS10 Cold-Formed Steel Construction Connectors catalog. Alternatively a cold-formed steel track can be attached to the wood nailers using Simpson Strong-Tie® SDS wood screws.
The Designer is responsible for designing these connections for the appropriate load combinations of the Code.
topAnchoragePage 18 of C-SF10 Strong Frame Ordinary Moment Frame catalog indicates your shear lugs are designed per AISC Design Guide #1 and not ACI 318-05 Appendix D, is this code compliant?
ACI 318-05 Section D2.2, states that Appendix D applies to cast-in-place anchors and post-installed anchors and is not applicable for “Specialty inserts, through bolts, multiple anchors connected to a single steel plate at the embedded end of the anchors, adhesive or grouted anchors, and direct anchors such as powder- or pneumatic-actuated nails or bolts.”
Therefore since this type of connection is not addressed by ACI 318-05 Appendix D, the OMFSL shear lug design follows the procedure outlined in AISC Design Guide #1 with the exception that the concrete bearing of the shear lug is based on ACI 318.
Are the footings sized for compression and uplift loads assuming a certain soil pressure?
No. The footing design (size and reinforcing) must be determined by the Designer based on the project loads, specific geometry and allowable soil bearing pressure. The footing dimensions, shown on page 39 in the C-SF10 Strong Frame Ordinary Moment Frame catalog are the minimum required for the anchorage of the moment frame anchor bolts to the concrete foundation.
However, in the wall bracing portion of the website, footings were sized based on the assumptions stated in General Notes – Prescriptive Wall Bracing. If these assumptions are met and footing sizes (including grade beam and reinforcing) are provided as shown in Foundation Design – Solutions for Footing and Grade Beam, then the foundation sizes are adequate for both bearing and uplift.
All the solutions shown in the engineering section of the C-SF10 Strong Frame Ordinary Moment Frame catalog are for concrete foundations. What about masonry foundation solutions?
Engineered solutions for masonry foundations are not currently available from Simpson Strong-Tie. However the C-SF10 Strong Frame Ordinary Moment Frame catalog does provide the tension and shear reactions of each frame for use by the Designer to design alternate foundations. Prescriptive solutions for masonry foundations are provided in the wall bracing portion of the website.
I have additional wind uplift that must transfer through the Strong Frame Ordinary Moment Frame to the foundation. This increases the tension requirements on the anchorage. How do I verify that an OMFSL or OMFAB anchorage assembly has enough capacity for the combined tension due to the lateral uplift and my additional wind uplift?
Design for additional uplift may be accommodate by using the detailed tension anchorage design method. Tension Anchorage table 1.2 (page 39 in the C-SF10 Strong Frame Ordinary Moment Frame catalog) provides tension capacities for a range of anchor embedments and footing sizes. Per footnote 6 of the table, the requirements for anchor rod strength include 4,000 lbs. of additional uplift for wind solutions
Can I do my own anchorage design?
Yes, a Designer is permitted to design and detail their own anchorage solution.
Can I recess the Strong Frame columns below the concrete surface?
Yes, see details 6/SF2, 7/SF2 and 8/SF2 (PDF) (page 59 in the C-SF10 Strong Frame Ordinary Moment Frame catalog) for additional information. Please note that these details do not consider moisture protection of the columns.
topModifications and Field CorrectionsAre there pre-drilled holes in the Strong Frame™ Ordinary Moment Frame for electrical and plumbing needs? Can more holes be drilled through the beam? What size and where?
Yes, the frame has several pre-drilled 15/16" diameter holes in the beam and column flanges and one 2" or 3" diameter hole in the column web. Additional holes for 5/8" diameter bolts may be added to the flanges and 1" diameter holes may be added to the column webs per detail 12/SF3 (PDF) (page 64 in the C-SF10 Strong Frame Ordinary Moment Frame catalog) and in the installation detail sheets available for download.
Can I weld to the steel beam or steel column?
Yes, subject to the weld area limitations shown on 11/SF3 (PDF) (page 63 in the C-SF10 Strong Frame Ordinary Moment Frame catalog) and the installation detail sheets. Weld design shall be by the Designer.
May post-installed anchors be used to secure the base plate without non-shrink grout?
Yes, provided the column bases are set level to the correct elevation with full bearing on the concrete or masonry.
My anchor rods shifted during concrete placement and now the column base plate does not fit over the anchor rods. What should I do?
Depending on the amount of misalignment, there are several options:
topInspectionWhat special inspections are required for the Strong Frame™ Ordinary Moment Frames?
Inspection requirements are no different than for any other ordinary steel moment frame. The designer must designate what inspections are required in accordance with the code, based on building occupancy, concrete strength, requirements of the local building official, and other considerations. For cases where high strength bolts require inspection, Certificates of Conformity for material verification of high-strength bolts, nuts, and washers, and pre-installation verification of fastener assemblies may be obtained on this website at Lot Control for Structural Fastener Assemblies.
Can you clarify the requirements for pretension of bolts in the beam to column connection?
AISC 341 (Seismic Provisions) applies to seismic load resisting systems that use a value of R greater than 3. When ordinary steel moment frames are designed with an R equal to 3.5 then, in accordance with AISC 341 Section 7.2, all bolts are required to be pretensioned high strength bolts. For designs resisting only wind loads, using an R of 3 or less, or meeting the exceptions of IBC Section 1613.1 (which need not be designed to resist the effects of earthquake loads) snug-tight joints are permitted.
Are the supplied DTI (Direct Tension Indicator) bolt washers required to be installed on all Strong Frame Ordinary Moment Frames?
We recommend that the DTIs be installed in all conditions, as the orange silicone that squirts out makes it easy to verify that the bolts are tight. If the DTI washers are not used, the designer must specify an alternate method to verify the bolts are tight and to provide inspection of the bolt installation when required. Additional hardened washers may be required for pretensioned joints, depending on the pretensioning method that is used. Please see Bolt-Tightening Requirements (page 15 in the C-SF10 Strong Frame Ordinary Moment Frame catalog) for detailed information on use of DTI washers and bolt tightening requirements.
topCustom Sizes and SoftwareWill additional sizes of Strong Frame Ordinary Moment Frames be available?
We have added 16-foot tall columns as well as 14-foot, 18-foot and 20-foot wide beams, resulting in a total of 368 frame models. See allowable loads (for 8', 9', 10', 12', 14', 16', 18', or 19' nominal heights) and anchorage solutions.
Can Strong Frame Ordinary Moment Frames be stacked?
Currently the Strong Frame Ordinary Moment Frames are intended for installation on concrete. However, Designers may be able to design their own custom stacked application to fit their project needs. Please contact Simpson Strong-Tie for more information.
Do you offer custom sizes, 2 bay solutions or 2 story applications?
We now offer frames in custom sizes manufactured to your size specifications. Using our standard column and beam sections, we offer frames in clear-opening widths ranging from 6’-0” to 20’-4” and clear-opening heights ranging from 6’-0” to 19’-10-1/2”. Two bay and 2 story applications are being considered. Please contact Simpson Strong-Tie for status or sign up to be notified of Strong Frame news by email.
Do you have a program to help choose the frames and their corresponding anchorage?
We have developed the Simpson Strong-Tie Strong Frame Ordinary Moment Frame Selector Software (click here to download a free copy) that offers the following features:
- Requires only minimal input to help Designers quickly select an appropriate Strong Frame ordinary moment frame.
- In addition to our 368 standard frame sizes, the software can analyze and design frames with custom opening dimensions.
- Easy-to-use input screen with drop-down buttons makes it easy to input design information and loads.
- Software can accommodate uniform, partial uniform, and point loads placed anywhere along the span of the beam.
- Provides output in a concise format, as well as an option for detailed output.
- Provides anchorage design for the selected frame.
topOrdering a Strong Frame Ordinary Moment FrameWhat is the approximate lead time for a Strong Frame Ordinary Moment Frame that is in inventory?
The suggested lead time for a frame that is in stock is approximately 1 to 2 weeks.
What is the approximate lead time for a Strong Frame Ordinary Moment Frame that is not in inventory?
The suggested lead time for a frame that is not in stock is approximately 6 weeks.
What is the price of a Strong Frame Ordinary Moment Frame?
Contact Simpson Strong-Tie or your local representative for pricing information.
