Shear Exhilaration

This webinar provides a top-to-bottom overview of lateral design for wood-framed structures with a focus on shear walls. As a result of this training, participants will understand load path continuity and shear wall performance, including design methodologies for shear walls. Examples from post-disaster evaluations illustrate common failure modes, and methods and outcomes of various designs of wood structural panel shear walls are compared. Participants will also be introduced to installation considerations that may affect performance and how to address these issues proactively. The force transfer around openings (FTAO) method is covered as well.

Force Transfer Around Openings (FTAO) Design Examples

Access a PDF of the design examples referenced in the webinar by clicking the DOWNLOAD button below.
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Note: This course is approved by AIA (1 HSW/LU) and ICC (0.10 CEU). Do not navigate to YouTube if you require a certificate. A downloadable certificate of completion is available only when this webinar is viewed on this webpage in entirety, after completing a brief questionnaire.

 
Approximate length: 63 minutes.

 

Webinar Participant Questions and Answers

Are there any strategies to use FTAO around openings that go to the floor (doors)? Why is the Diekmann method not applicable to walls with doors?

Presently there are no strategies to address FTAO around door openings using the Diekmann method as this analysis requires wood structural panels both above and below the openings. Typically, you would design an FTAO section on one side of a door opening. If an additional shear wall is needed you can use another FTAO, segmented, or perforated shear wall. The collectors (typically top plates) can transfer the shear load over the door to the shear walls on either side.

I'm a bit confused about the diaphragm loads. In the SDPWS tables it gives allowable diaphragm loads in PLF. So, to check if your diaphragm is acceptable, you need to check the PLF at each shear wall? If one shear wall exceeds the unblocked diaphragm loads, do you have to upgrade the whole diaphragm to a blocked diaphragm?

The unit shear force in the diaphragm and the unit shear force in the shear walls may or may not be the same. It’s a function of how many shear walls resist the diaphragm forces and a function of the depth of the diaphragm, as well as the length of the shear walls. For example, a full-depth unblocked diaphragm can transfer, say, 180 plf into a wall that is half the length of the diaphragm, so shear wall force would be 180 plf * 2 = 360 plf. The load transfer into the wall would need to be sufficiently detailed; that would include collectors and the rest of the lateral force resisting system. The wall loads of 360 plf would probably require a blocked shear wall; however, it does not mean the diaphragm needs to be designed for this high of a unit shear. The original diaphragm shear of 180 plf could be resolved with an unblocked diaphragm. This simple example is assuming that there are not stacked shear wall loads on top of the example wall.

Can anchor bolts with washers be considered hold-downs?

No, anchor bolts with washers will not provide the uplift capacity. Hold-downs are attached to the chord of the shear wall, or studs at the ends of the wall sections, to provide a direct load path into the wall system. Some common details are provided in American Wood Council Wood Frame Construction Manual,Figure 3.8a and 3.8b. A view-only version is also available on their web page.

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Can the hold-down forces be adjusted for the effect of applied dead load on wall?

Yes, the hold-down forces can be adjusted for the effects of the dead load of the structure. For simplicity, dead load was not considered in the examples presented in the presentation.

What if walls exceed 10 feet?

As these are engineered design, the height of the wall is not limited in SDPWS. The only reference we had to a 10-foot height would have been in SDPWS table 4.3.3.4, which lists shear capacity adjustment factors for 8-foot and 10-foot walls. Other wall heights can be calculated using equation (4.3-5).

What method is best suited for walls with different sized openings at different elevations?

Each wall is unique in determining which option is best, as all methods have pros and cons. FTAO does work with different sized openings, although the APA FTAO Calculator has a limitation requiring the maximum size opening that may be input.

Does the aspect ratio for the pier segment include or omit the length of the hold-down post?

The aspect ratio includes the hold-down post.

In the FTAO example with the door opening, is there any way to use the wall pier (to the left of the door in the example)?

You could mix methods and include this wall pier as a segmented section or, quite often, the area to the left of a door opening can become part of another FTAO section.

Where can I download the calculator?

You can download the APA Force Transfer Around Opening Calculator at https://www.apawood.org/ftao.

Can you move strapping outside of the flange?

Strapping could be moved outside the flange; we recommend oversizing your window dimension 2 to 3 inches to accommodate for actual strap location.

Does SDPWS specify a diameter for nails (in lieu of penny size), or is that up to the designer?

The Nominal Unit Shear Table specifies common nail sizes. Footnote 1 of this table references SDPWS Appendix A, where nail dimensions for common, box, and sinker nails can be found.

When will there be an example of a multi-story FTAO shear wall?

Not at this time.

You mentioned that you need to transfer the uplift forces past the floor cavity. Do you need to span the cavity with a full panel?

No, the wood structural panel does not need to span the floor cavity. It is only one of several options to transfer the uplift and lateral loads between stories. The designer could also choose to lap first and second story wall sheathing at a common engineered wood rim board, or they could use a system of straps for uplift and connections for lateral loads.

Additional design guidance can be found in:

You mentioned that FTAO requires strapping around the openings. Does this strapping need to extend the full length of the wall?

The straps only need to be long enough to allow for the full development of the tension load. The required strapping is dependent on the calculated internal tension and compression forces of the wall system and is put in place to aid in the resistance of the tension forces through the thickness of the wall at the corners of the openings.

I’m concerned how FTAO strapping can interfere with window installation and over nailing with sheathing, siding and trim fasteners. Is this a concern, or is there a way to address this?

One item to note is that sheathing edge fasteners can be omitted when they coincide with strap locations, assuming the strap nailing is at a closer nail spacing than the panel edge nailing.

Strapping can be installed on the interior face of studs to prevent conflict with window and siding installation. If the strapping is installed on the interior side, special detailing is required in that the blocking should be the full depth of the wall studs so that the strap can be installed to the blocking with the required fasteners.

Also, the nailing pattern from the sheathing into the blocking should be the same nailing as what is specified by the strap manufacturer. Some builders prefer this approach, as it allows the strapping to be installed under cover and not on the exterior from scaffolding.

Can you use staples in shear walls?

Yes, but it isn’t a one-to-one substitution. The tables that I have referenced are based on common nails. To use an alternate fastener, like a staple, you would need to refer to IBC Table 2306.3(1) for allowable shear values for wood structural panels utilizing staples, or the manufacturer’s code report for an alternate fastening schedule to achieve the required strength.