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 nailing is shown correctly except 7/16" shtg gets 10d not 8d, but it is lacking rebar specific to the STHD14's - are you sure you need this dtl? It is generally a high shear detail where the ratio of shear wall height to width exceeds the Code allowable of 3.5:1

 

[msquared48]

I would add one more MSTC40 strap at the same side of the wall but at the right end of the shear wall to join the two discontinuous studs above and below the LVL on which the LVL bears.

Mike McCann
MMC Engineering

 

[AELLC]

Good catch MMC I missed that -

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.

 

[medeek]

The IRC for PFH portal frame calls out 8D nails:

http://publicecodes.cyberregs.com/icod/irc/2012/icod_irc_2012_6_par047.htm

 

[AELLC]

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.

 

[medeek]

The number of trimmer studs is controlled by the length of the span carried by the header. Maybe only nail the outer two perimeter studs at 3" o/c and the rest at 12 or 6?

 

[AELLC]

That must be a horribly loaded header to get (4)-2x6T. Are you certain of your design method?
Nail the rest of the trimmers at 12" oc

 

[AELLC]

I get 12,300 lbs of dead and floor live to max out (4)-2x6T (SPF-S#2) 12' high.

 

[AELLC]

Also, wth a heavily loaded situation, you need a larger square footing there, not just the 20" wide wall footing.

 

[medeek]

Agreed, the concentrated force at the bearing point of the studs will want to punch through and a spread footing is likely.

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.

 

[medeek]

Ok, made a mistake, not sure how to edit a post once its posted. The vertical force on the trimmer group is actually 1/4 of the 19,348 lbs which is only 4837 lbs. Ok, so we are a little over designed here.

How are you coming up with that 12,300 lbs?

 

[AELLC]

The species, grade and especially height of the trimmers affect its capacity. You didn't show all that in your post above.

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.

 

[AELLC]

It is a better idea to use nominal stated width of window or door plus 6" for all your header designs.

 

[AELLC]

I am assuming this is a normal garage door 7 or 8' high, and this detail doesn't have the normal king studs for wind pressure normal to the garage door, so (3)-2x6T would be more than adequate. That (4) just doesn't look right.

 

[medeek]

I'm unfamiliar with the king studs for wind pressure do you have an example of this. You're right 3 trimmers is more than adequate, I'll adjust the detail accordingly.

 

[AELLC]

This detail doesn't have king studs but the straps and plywood seem to provide the equivalent - but it is impossible to calculate rationally, but the Plans Checkers here don't seem to pick at that.

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.

 

[AELLC]

This detail doesn't have king studs but the straps and plywood seem to provide the equivalent - but it is impossible to calculate rationally, but the Plans Checkers here don't seem to pick at that.

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.

 

[medeek]

I purchased the 2005 Sample problems. I could not find one for the 2012 NDS.

 

[AELLC]

No problem, it doesn't matter to be a few years behind for your NDS standards. I believe the only big thing new in the NDS 2012 was a change in SP allowable stresses, but I don't have a copy.