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.

 

[AELLC]

The detail needs some work - however the one king stud is not the only element resisting the wind bending. Read my post 11 MAR 10:54.

The problem is we don't have any rational method to prove this, by then why did the ICC come up with this standard to begin with?

Also, years ago, we demonstrated why one of 2 lightly loaded garage door trimmer studs doubled as a king stud to and existing king stud. That is, the 2 trimmers were 7' tall and the king stud was 9' tall.

 

[somewhatofanerd]

I did read it... and I am asking you to prove that those straps take the bending, shear, deflection requirements. And I also said that the wind pressures are forward pressures, and negative pressures.

The detail is wrong, it doesn't calculate, and the portal frame method was devised by hardware companies.

If you manage to work out the bending calc on the strap... please work out the shear on plywood in leeward wind force analysis.

Then, when that doesn't calc... figure out how the wind is getting resisted by the overstressed king stud with an approximate 12' trib.

 

[AELLC]

"I did read it... and I am asking you to prove that those straps take the bending, shear, deflection requirements. And I also said that the wind pressures are forward pressures, and negative pressures."

I already stated there is no rational method. Such is residential engineering, are you going to single-handedly change it?

"The detail is wrong, it doesn't calculate, and the portal frame method was devised by hardware companies."

It is based on a standard detail in the IRC. It is better than no detail at all for skinny garage shear walls.
Have you ever designed a detached RV garage with 12' ceiling?

 

[AELLC]

medeek,

You need to "mirror" the corrected version of your first (end jamb) detail so the middle jamb is symmetric.

 

[AELLC]

nerd,

I don't follow this:

"please work out the shear on plywood in leeward wind force analysis."

Can you describe another way or provide a sketch?

 

[somewhatofanerd]

"I already stated there is no rational method. Such is residential engineering, are you going to single-handedly change it?"

since the dawn of documented house building has at least 1 jack, 1 king been present. It is the norm.

The detail of 4 jack studs at minimum... should be one (1), at most (2) for a 4800# reaction. Each side of a garage opening should be the jack, and immediate to that the king. That is so normal wind pressures can transfer the load to the king, then to the diaphragm, through shear nailing of the two jack and king members.

The detail is so horrifically wrong it scares me that people would even comment on it, including myself.

Yes, hardware companies like Simpson, etc. came up with the portal frame method so they can sell straps and hold downs.

 

[AELLC]

nerd,

I doubt Simpson came up with this detail, because before it existed, I specified their wood Strong-Walls but the builder would never actually install them because he always claimed Simpson sent him the wrong size.

When the detail came out, I started using it and it was built per detail with no problems. Simpson sold 2 STHD14's but they would have sold those detail or no detail. They did sell 4 extra MSTC40's, however they were cheated out of a sale of 2 Simpson Strong-Walls.

Things are going to get busier for me in 2 months, but I doubt I would ask you for help because of your attitude. Perhaps you need to specialize in heavy steel construction, that would be more rational to design than residential.

 

[somewhatofanerd]

I can guarantee you that the portal frame in residential construction came out because it was first introduced by hardware companies.

Money is what drives this industry.

Why would I want to help you AELLC? I'm confused how my comments and your new business leads me to want to help you.

I know all to well residential design. The ridiculousness of some of these latest code standards, etc.

Let's get back to this thread... both details are not good, have way too much hardware, break basic structural engineering fundamentals, and would be shot down in a heart beat by any builder doing any volume.

Why in the world would you spec out a portal frame garage opening detail when you could get the same resistance from a few feet of regular wall? Do you really need it is my question? And when the windspeed get's higher... yes there is merit to stiffening the garage opening but I would never use that value to stabilize the home.

Then you start getting into other construction... i.e. block wall.

Either way, both details have major flaws. I also read your recommendation to pour a pad footing for a 4800# point load... lol

 

[medeek]

Both portal frame designs shown came from the IRC 2012 and I refer you to Figure 3.27 of "A Guide to the 2012 IRC Wood Wall Bracing Provisions" published jointly by the APA and the ICC. Directly under this figure I quote ," 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."

You can't have two double portal frames next to each other. You basically use single portal frames adjacent to each other, and one of your garage door openings can be a double portal frame as shown in the full framing for this wall below:

If my details are that flawed then what does that say about the IRC wall bracing provisions?

I also quote from page 167 of the Wall Bracing Guide, "The tension strap provisions are meant to address the problem of a structural hinge created over a door or window header that can result in the header bulging in or out due to wind loads blowing directly against the wall, or even differential moisture conditions. .."

 

[medeek]

I think what is confusing everyone is my 4 trimmers under the portal frames, this should probably be reduced to (3) or even (2) trimmers to make it more in line with actual capacities. I would probably reduce to (3) since I like to be conservative.

 

[somewhatofanerd]

"I think what is confusing everyone is my 4 trimmers under the portal frames, this should probably be reduced to (3) or even (2) trimmers to make it more in line with actual capacities. I would probably reduce to (3) since I like to be conservative."

No Medeek... that is not what is confusing. The detail of specifying something like above is the problem and the inherent fact that it was obtained from the IRC as *OK* is the problem.

The detail has disregarded every fundamental aspect of wall construction and relies on hardware to make up for it... which it doesn't.

 

[medeek]

Before I understood portal frames the old school way I would have framed these door is a couple of trimmers and then a king stud on each end of the header. The problem with this method is the lateral resistance is weak and hence the use of the portal frame method. However, I can see your problem with the pony wall hinging and only having straps to resist this effect. So what is the correct solution?

 

[XR250]

I like to push the header up the plate to eliminate the additional joint. Then backframe the remainder of the opening. This also allows the use of a 1000 lb. strap in lieu of the 4000 lb. strap req'd by the IRC.

 

[Archie264]

>>>However, I can see your problem with the pony wall hinging and only having straps to resist this effect. So what is the correct solution?<<<

medeek,

I'm only commenting on that question; I have not followed the rest of the discussion. Generally speaking it is better to raise the height of the beam so that the members it carries frame directly onto it as opposed to the load being transferred by way of "stilts" that can rotate. Then hang your pony wall, soffit, etc. below that. To exaggerate the point it's analogous to the difference between carrying a loaded serving tray on the palm of your hand versus balancing it on the end of a walking stick, ala a circus performer.

Now, again, that's generally speaking. If that causes your columns to become too long to function adequately, well, that's a different problem so the whole system needs to be considered.

At the end of the day for many residential applications it may not make much difference but it some cases it could and it's just generally a better way to do things.

 

[Archie264]

Excel,

Our posts crossed in the mail. You said in much fewer words what I was trying to say and you backed yours up with numbers. Medeek, listen to Excel. (And the others.)

 

[medeek]

The more I think about it the more I'm liking the portal frame with the beams moved up to the bottom of the double plate and then just framing below to fill the gap. With the pony wall on top it seems to me that you are taking a tried and true method of post and beam construction and introducing a complication that only serves to weaken the structure. What you gain laterally in one direction you are loosing in the other direction.

Why would the IRC promote this type of construction when it could be avoided.

I'm going to drop all the notes and rework this one framing drawing in AutoCAD real quick and post it back to the board for further discussion, when I get a minute on my lunch hour. I think this discussion has been very worthwhile for all involved.

 

[boo1]

Why dont you tie the STHD14 to the footing with rebar? The 2' concrete kneewall sectoin looks weak.

 

[medeek]

Rebar not shown for clarity

 

[somewhatofanerd]

If you raise the header and frame a pony wall underneath... you have a weak point in your wall under the header. Then what? Put another header in?

There is a reason why a header is above the opening, framed with (2) jack studs (required for your loading conditions assuming SPF #2 or something similar) and (1) king stud.

Throw every single thought of a calculation out the window, and picture, in your head, how that wall would behave when a 100 mph gust hits it straight on. What is the stiffest part of the wall (full height stud - hint)? And where would you want that stiffness? How does the garage door (the actual door when closed) transfer the head on wind load into the wall? By what method? Once you realize that, you will realize how to frame the wall and it is *exactly* the conventional way of framing an opening.

 

[Archie264]

Why would raising the header to underneath the joists eliminate the king stud?