Portal Frame Nailing Patterns

[medeek]

Due to the overwhelmingly positive feedback I received on my questions about the foundation/driveway question I thought I might post up one other item that has been bugging me for a while. I drew up this portal frame detail to show the nailing pattern per code so that a person with little or no construction experience could properly nail off the OSB so that it is structurally sound. However, with all those nails the whole thing looks like swiss cheese to me. Any ideas on the "correct" nailing pattern. I am trying to comply with the IRC 2012 nailing requirements for this type of portal frame.

 

[medeek]

The raised header would require a second smaller header:

Link

Take a look at the Dropped Header Design Guide (Figure 3)

 

[Archie264]

medeek,

What they're showing as a "low header" in Figure 3 just seems like a piece of lumber added in to generally hold the little wall extension/soffit/what-have-you in place. The only purpose I could see it having is to maybe provide a little bit of wind resistance, though not much. And while it shows up in the sketch the article doesn't seem to address it, unless I missed it. Overall, to me that still seems like a better way to build it.

 

[AELLC]

" Note, that when using the Method CS-PF, a continous header across both openings is not permitted. In the figure above, one header spans the double portal frame and the header for the single portal frame bears on the the left side on additional jack studs. This is how a double opening with Method CS-PF should be fabricated"

1) I don't understand all that. Why isn't a continuous header OK?

2) You have a fairly substantial wall on the left, why don't you design it as the only shear wall OR combined w/ only one garage portal frame? Otherwise I think the Builder is going question the sanity of what you are now showing. It is too complicated and so many studs, you might as well make it out of solid wood.

3) If you can't do (2) then hire an engineer.

 

[medeek]

I've sketched up Option 1 and Option 2. With both options I've added an additional king stud between the portal frames for both wind resistance and due to construction issues. If there is only one king stud it will be impossible to nail through the king stud into the LVL header for both headers. Ignore the nailing pattern, rebar, holddowns for now lets just look at the wood framing.

I'm actually thinking option 1 is simpler to frame up and unless the pony wall gets above four feet in height I don't see a reason to go to option 2.

I've had someone also ask me about mid span block. Correct me if I'm wrong but with a garage wall that is not laterally braced on the interior its studs would be more susceptible to torsional buckling especially with walls that are taller (ie. 10ft, 12ft) than your standard 8 ft. wall. Hence, the mid span blocking.

 

[medeek]

These images are a bit hard to discern. View the larger images here:

Option 1

Option 2

The original AutoCAD drawing and two options are here:

AutoCAD Drawings

 

[AELLC]

You never go to Option 2 with wood...that is used occasionally in light-gage steel.

Problem is, I think you need at least 2 king studs whenever you have 2 adjacent doors. That was the gist of an opinion I got from someone else more familiar with the IRC detail. That IRC detail was intended only for situations with one door only, no other door adjacent (to prevent the pushing in or out of the wall with wind pressure in either direction).

 

[XR250]

@AELLC.

As you said, I would just use the wall at the left. If you try to combine it with the portal frame, it will take all the load anyway as it will be significantly stiffer than the frame.

I would like to see some testing on these portal frames as far as deflection goes. It it likely that other forms of stability will take over once this thing deflects such as three sided building action.

 

[AELLC]

"It likely that other forms of stability will take over once this thing deflects such as three sided building action."

I have used this detail for many detached garages, especially RV-type where the ceiling is 10'-12' high, and the usual IBC rules for 3-sided buildings can't be satisfied, i.e. the ratio of the roof diaphragm was out of allowable. However this was for very low seismic.

In the past, whenever I tried to specify Simpson Strong-wall, the builder would find a way not to be able to install them and I would end up doing a field fix similar to the IRC detail.

 

[somewhatofanerd]

http://files.engineering.com/getfil...b-44ab-49b9-ab62-80df9492f031&file=WALL_1.jpg

Wall with half the lumber (likely less), 25% hardware, stronger in both the normal direction to wind as well as shearwall *calculated* capacity.

The attachment is what would be expected by a builder. Not in the format shown, but that type of analysis.

What type of capacity do you think a Doug_Fir_#2 stud has in axial, 10' tall?

 

[AELLC]

You could also do a segmented analysis to also include the wall between the ordinary door and the first garage door.

 

[somewhatofanerd]

.... or a perforated analysis of the left side, or ignore the entire wall all together if conditions allowed (which would be silly since so much good wall exists). This is a prime example of how software, lumber companies, and hardware companies are making an impact, and not in a good way.

 

[Archie264]

Somewhat,

I don't see any reason why that system you showed couldn't be built with the garage door beams (i.e. "headers") directly underneath the joists. Am I missing something?

 

[somewhatofanerd]

Archie,

It can. It's just extending the header past the jack stud which is unnecessary. It is detailed like that to try and justify a nailing pattern around an opening and throw in some straps and call it a stiff portal frame. Like others have said, that opening will always deflect more then the solid framed wall so it doesn't add anything except a lot of lumber and hardware.

The only downside to moving the header up is then you are hanging the cripples. The bottom plate can act as support I suppose. Certainly do not want to throw an *additional* header in.

 

[medeek]

The secondary header is recommended by the APA to help keep the cripple portion hanging from the main header stiff. I'm assuming you would still use strap holddowns at the garage doors?

 

[AELLC]

@nerd:
"The only downside to moving the header up is then you are hanging the cripples. The bottom plate can act as support I suppose. Certainly do not want to throw an *additional* header in."


If the garage door uses the torsion spring helper system, you need a substantial header at the very top of the garage door.

@ medeek:
"I'm assuming you would still use strap holddowns at the garage doors?"


Technically you don't need hold downs, but here it is a reqm't to at least provide LSTHD8's to prevent damage if a strong windstorm occurs during construction when all the dead load isn't in place yet. As far as the finished structure goes, a strong wind in the direction toward an opened door could cause a net uplift condition if the dead load is small.

 

[somewhatofanerd]

"Technically you don't need hold downs, but here it is a reqm't to at least provide LSTHD8's to prevent damage if a strong windstorm occurs during construction when all the dead load isn't in place yet. As far as the finished structure goes, a strong wind in the direction toward an opened door could cause a net uplift condition if the dead load is small."

Who mandates that requirement? Got a link?

 

[AELLC]

@nerd:

It is mandated for the entire Maricopa County, Arizona - it overrides local town and city codes.

I could not actually find a link online. But we locals are very familiar, it is a word of mouth thing too. It will always be red-flagged at any plans check if omitted.

The jambs also need 1/2" plywood nailed 8d @ 6:12" oc, and we add: "NOT A SHEAR WALL".

It came about relatively recently because a very large subdivision under construction suffered extreme damage during one of our famous "monsoon" events - we call it a micro-burst thunderstorm, and downflow winds cause approx. 100 mph horizontal winds moving radially outward in a relatively small area. The garage walls were lifted a bit and then racked severely, resulting in huge lawsuit. None of the garage door jambs had hold downs, because they were about 18" wide and worthless as ordinary shear walls.

 

[somewhatofanerd]

interesting... I assume *not a shear wall* is so you limit the number of letters to the building department

I suppose anything can happen. Did the walls have sheathing?

 

[AELLC]

Don't know. I doubt it because we use California one coat stucco here (it rarely rains), and only custom homes get full plywood to eliminate that wavy apperance when the sun's rays are nearly parallel to the wall.

 

[AELLC]

Did Medeek ever get around to getting an opinion from a local SE? I hate unfinished sagas.