Portal Frame Nailing Patterns
Portal Frame Nailing Patterns
(OP)
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.






RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
Mike McCann
MMC Engineering
RE: Portal Frame Nailing Patterns
The original detail had only 2 trimmer studs and called out 2 rows (staggered) of 10d nails @ 2" o.c. (not 3") everywhere, considerably less nails because less rows of nails.
RE: Portal Frame Nailing Patterns
http://publicecodes.cyberregs.com/icod/irc/2012/ic...
RE: Portal Frame Nailing Patterns
The version I have is older, and has 2 straps as MMC mentioned. I see that this new version only has 1 strap.
The new version does only show 2 trimmer studs, I think 4 is actually going to make this weaker and if you do use 4 then use only 2 rows not 4 rows of nailing.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
Nail the rest of the trimmers at 12" oc
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
Here are the specs:
28 ft. wide garage with 12/12 attic roof with 14 ft. span attic.
30 psf snow load
10 psf dead load
10 psf ceiling dead load
I know the dead loads are a little high but I'm trying to be conservative.
30 psf attic live load
Gives:
28ft x (30 psf + 10 psf (1.4) + 10 psf) + 14ft x 30 psf = 1,934.8 plf
The actual span of the garage door is 9 ft. but if we go center to center of the trimmer stud groups its more like 10 ft.
1,934.8 plf x 10ft = 19,348 lbs
Each side of the beam is then -> 9,674 lbs
Your telling me my capacity is 12,300 lbs so my stress index is 1.27 which is nice to have that reserve strength.
RE: Portal Frame Nailing Patterns
How are you coming up with that 12,300 lbs?
RE: Portal Frame Nailing Patterns
I use Excel for all my calcs and the formulas are all based on IBC, but I use just the basic load (alternate) combinations, not the newest "difficult to compute" ones. It is legal though.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
With a normal detail, whether a large window or a garage door, the king studs are designed for wind pressure normal to the door or window, no axial load, so for a 9' door you have pressure in psf x 4.5' resulting in a uniform wind load in plf putting the king stud(s) in strong-axis bending, no axial, with the bending allowable multiplied times the wind duration factor allowable if you are using ASD.
There is a guide to all this here:
http://www.awc.org/standards/nds.php
I recommend you getting the Wood Solved Problems publication, I get the sense you are a residential designer but not as familiar with wood as a structural engineer would be.
RE: Portal Frame Nailing Patterns
With a normal detail, whether a large window or a garage door, the king studs are designed for wind pressure normal to the door or window, no axial load, so for a 9' door you have pressure in psf x 4.5' resulting in a uniform wind load in plf putting the king stud(s) in strong-axis bending, no axial, with the bending allowable multiplied times the wind duration factor allowable if you are using ASD.
There is a guide to all this here:
http://www.awc.org/standards/nds.php
I recommend you getting the Wood Solved Problems publication, I get the sense you are a residential designer but not as familiar with wood as a structural engineer would be.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
Everyone is more than welcome to take a look at the full planset I drew up here:
http://design.medeek.com/plansets/garages/GARAGE48...
I'm sure there is plenty wrong with it as it is my first "real" planset that I've put out there. I've tried to make sure everything is compliant with the IRC 2012, so look at it through those lenses. Normally, most designers don't include full framing plans with their designs but my intent with this one was to provide a planset for the lowest common denominator, basically someone with zero framing or building experience.
What I really ought to do is pay to have a structural engineer go through the entire planset and run all the calcs and tell me what needs adjustment or fixing based on my basic design parameters.
RE: Portal Frame Nailing Patterns
The footing is easy, if you just assume 1500 psf allowable brg pressure. You will come up with either A 30" square or 36" square depending on your exact gravity load there, don't include self-weight of footing (too conservative).
Make the footing 12" thick, bearing at depth dictated by your local Bldg Dept to get it below frost line (or 18" if you live in the desert), 3-#4 ea way for the 30" sq and 4-#4 ea way for the 36" sq.
Those rebar schemes are very common and I don't bother showing calcs for the rebar and concrete shear, no one else does, it seems (for residential).
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
You are in a pretty sketchy area as far as licensing is concerned and practicing outside your area of expertise.
If you have interest and the chops you should absolutely be learning under an experienced PE, and I would follow your own advice:
RE: Portal Frame Nailing Patterns
It is up to the bldg. dept to determine if it needs gravity and/or lateral calcs by a licensed PE or SE. A licensed ME would not meet that criteria - it needs to be licensed PE in Civil Engineering or a Structural Engineer.
I imagine this is very common in all the USA states.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
I agree.
RE: Portal Frame Nailing Patterns
Check to see if Civil PE's can stamp low-rise structures in your state, or if there are any single-family house exclusions. That route may be easier for you.
RE: Portal Frame Nailing Patterns
Basic Wind Speed: 100 mph
Seismic: A,B,C,D0 (still looking at D1 and D2 to see if its worth the hassle)
Wind Exp.: C
Assume Flat Building Site
Roof Snow Load: 30 psf (Pf and not Pg)
Floor Loads: 40 psf
Stair Loads: 100 psf
Earth Pressure: 30 pcf
Soil Capacity: 1,500 psf
Ultimately, the local climate/geography/energy code will probably determine if the planset needs further engineering and modifications but that is beyond my scope.
However, after working with the IRC for a few months I find that some of its methods are either too restrictive or do not give enough direction. Hence, I have questions, that I have brought to this forum. As I mentioned above I have recently arranged for a full review of each planset by an experienced structural engineer since it will give me an education in residential structural engineering and also some piece of mind that I am not leaving anything to chance.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
We helped you for some stuff but you can't really justify us checking everything. You initially overlooked the spot footing reqm't as I mentioned above, so be real careful.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
It also has way too many nails, hardware, and wood to make it desirable to build.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
I corrected medeek regarding the nailing in my posts above.
This is based on a standard IRC detail that I also use frequently, so why are you so doubtful of it?
RE: Portal Frame Nailing Patterns
please do the calc on 12' trib king stud at 90 mph.. 100mph, etc.
It's not just that... but how does the load really get to the king anyway? And if those straps take it (remember leeward is also a consideration) what is the bending, shear, deflection on providing face nails normal to wind?
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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?
RE: Portal Frame Nailing Patterns
You need to "mirror" the corrected version of your first (end jamb) detail so the middle jamb is symmetric.
RE: Portal Frame Nailing Patterns
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?
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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
RE: Portal Frame Nailing Patterns
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. .."
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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.)
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
Link
Take a look at the Dropped Header Design Guide (Figure 3)
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
Option 1
Option 2
The original AutoCAD drawing and two options are here:
AutoCAD Drawings
RE: Portal Frame Nailing Patterns
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).
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
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?
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
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?
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns
"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.
RE: Portal Frame Nailing Patterns
Who mandates that requirement? Got a link?
RE: Portal Frame Nailing Patterns
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.
RE: Portal Frame Nailing Patterns
I suppose anything can happen. Did the walls have sheathing?
RE: Portal Frame Nailing Patterns
RE: Portal Frame Nailing Patterns