Continuous Multiple Garage Door Header

[waytsh]

I have noticed that home builders in my area are using a continuous LVL header for the entire length of garage wall with multiple doors. Does anyone know if this is a code requirement? I understand the need to maintain a continuous load path from endwall to endwall so that all the portal frames around the doors can be engaged but is this the typical method to accomplish this? The methods I see in the AWC documents seem to show breaking the header.

 

[dik]

I would hope that it would be designed for vertical as well as lateral loading.

Dik

 

[DaveAtkins]

I know of no code requirement that requires this. You get very little lateral resistance from a wall with large garage door openings, anyway.

DaveAtkins

 

[waytsh]

One of the builders mentioned it being a "requirement" which is why I am asking the question. When I catch up with him again I will ask where he heard that. I agree dik, I would hope the LVL is designed for the vertical load as well.

One other potential issue I see with this is the hinge that would be created at the pony wall when the wall is loaded out of plane. I would think you would need to have several continuous studs up to the first floor diaphragm unless the exterior sheathing and the interior drywall somehow prevents this.

 

[BridgeSmith]

I can see it being required by design, depending on the configuration. Something has to resist the wind load, so it has to have a continuous span either horizontally or vertically. If it can't span vertically for some reason (inadequate diaphragm resistance from the roof system, inadequate shear connection at the foundation, etc.), then the header would have to be continuous. The other case where it could be required by design is if the header is not adequate for vertical loads as a simple span.

 

[dhengr]

Waytsh:
Don’t ask him where he heard that…, those guys hear the grass grow, the paint dry and lots of my grampa showed me’s, this is the way we’ve always done it’s. Ask him to show you the code section that requires it, and if he can’t, tell him to at least learn to read the plans and specs. Do you (do they) really have portal frames (the pre-manuf’erd. moment frames) on each side of the doors? Those walls are still of pretty low value as shear walls because of the large openings. The door headers used to be simple span lumber or steel, until to could buy 30’ LVL’s of adequate cap’y. Whatever headers you use to do this, you still end up with problems with wind loads (loads perpendicular to the wall plane) at the large openings, and because of that hinge at the header issue. All that load has to be taken out to the door jambs where some full length studs exist.

 

[EngineeringEric]

If it is CS-PF portal frame or a garage portal frame then the header has to span over the wall panels (Braced wall panel). if they need three panels than it spans over the center and is continuous. These walls studs are then strapped to the LVL and act like moment transfer. not always required but they are sometimes.

this is the only time it is required as per residential (IRC) Chapter 6.

 

[waytsh]

I am going to use a CS-PF portal frame over three doors. I do have a 5'6" section of wall at one end of the wall which I was also going to use as a WSP. I'll clean up my drawing and post it.

EngineeringEric, as far as the strapping of the studs to make them continuous, this makes sense as this is the only way I can see some of these designs working. I don't think I could pack enough jack studs and king studs in my narrow section of wall to meet the requirements of Table R602.7(1) and Table R602.7.5. Is there a code or other reference that addresses this design? I would think that the straps making the portal frame would also need to be designed for the combined effect of the portal forces and then the out-of-plane sidewall pressures that would cause strong-axis bending in the studs.

 

[waytsh]

Here is the drawing I am sure you have all been waiting for breathlessly. I welcome any constructive input.

 

[NorthCivil]

What kind of constructive input are you looking for?

I don't think its the most efficient framing plan, but it might work.

If you are using the short wall sections as shearwalls, why dont they have proper hold-downs like the large wall section to the left? check your hold-downs and ensure your uplift works.

I dont think all those nails into the headers add any value.

all the lateral load has to travel through the top plates, through the short shearwall section above the headers, and past the headers into the shearwall below. follow the load path.

 

[waytsh]

I was basically wondering if anything jumps out to anyone as far as configuration. For instance, would a continuous header be better?

I am not using the short wall sections as shear walls, I am using them as portal frames legs. CS-PF to be exact. According to the IRC and other references this type of portal frame does not require hold downs. ...which is a good thing because I don't think I could fit both in the shot section of wall.

I know the framing is a little heavy. I can't bring myself to rely completely on the strapped studs for the out-of-plane loading so I threw a couple full king studs in each section.

 

[txeng91]

I don’t hate the detail, but there’s just no way to quantify your lateral resistance there. I think you need to justify your design with either the IRC prescriptive method, or through engineering analysis. I’m assuming your mixing methods because your lateral loads are too high for either the shearwall or the portal frames to take all the load themselves. I would say if the required length for the cs-pf method is just over what you need then see if counting the shearwall portion as WSP bracing will bring you up to the required length, I believe the IRC allows for this. If not, you could use the APA portal frame with holdowns along with the shearwall to get your required capacity. They actually have reported stiffness (which is greater than the IRC CS-PF) and shear values that you can quantify. The main issue with the detail your showing is that the shearwall has much greater stiffness than the portal frames, therefore will attract more load. The portal frames won’t deflect enough to provide their full potential of resistance.

 

[KootK]

I can't bring myself to rely completely on the strapped studs for the out-of-plane loading so I threw a couple full king studs in each section.

Imagine me sending you a great big e-hug as you read this. Thank goodness there are still engineers practicing who a) possess fundamental structural intuition and b) refuse to set it aside.

Does anyone know if this is a code requirement?

It had better not be because it's a foolish detailing practice.

One other potential issue I see with this is the hinge that would be created at the pony wall when the wall is loaded out of plane.

Exactly. I see four "needs" for vertical framing that is flexurally continuous:

1) Gravity stability for axial loads in the wall system. I'm kinda big on gravity stability... yeah. Granted, if this is an end wall with minimal trib, it may not be a big deal.

2) Gravity stability for compression side flexural stresses in the beam, particularly as the beam passes over intermediate supports.

3) Out of plane wind load as you've pointed out.

4) Stability of the "moment frame" beam column joints themselves. It is critically important with these things that the joints don't just roll the heck over under lateral demand. We tend to take these things for granted in steel and concrete systems because there is usually gobs of joint stabilization. Not so here. Not even close really.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[JLNJ]

You need some out-of-plane stability for when my grandmother runs into the door jamb with her car.

A very real possibility, but I haven't seen it as a load case in the IRC or the IBC.

 

[BridgeSmith]

Grandmother? Teenage sons hit more often and at higher speeds.

 

[Tmoose]

3/8" thick steel plate "sheathing" on each interior and exterior wall, passing from the top plate, over the LVL, and half way down each short wall.
Predrilled and countersunk for deck screws 6 inch on centers.

Just kidding, but maybe setting the LVL and all 4 wall back an extra inch or so for 2 layers of 1/2 inch sheathing inside and out as described with staggered joints to make box beams vertically, and horizontally.

With doubled 2X4s above the doors I might be able to skip the LVL altogether.

 

[waytsh]

Sorry I have been MIA guys. I am back in the saddle and I see a lot of good comments here. Haha, glad I am not alone in some of my thinking KootK! JLNJ and HotRod, I have two teenage drivers in the house so now you have just given me one more thing to worry about that I hadn't even considered. Maybe I should invest in some nice big bollards on each side of the door.

Let me back up and explain some of my thoughts as to how I got to this layout. First of all I should note that I am working with 2015 IRC. To get in the ballpark I started with the prescriptive method and Table R602.10.3(1) which found that for a CS-WSP & CS-PF system I would need 12.33' of braced wall section. According to IRC these two systems are allowed to be used together on the same wall. I should note that I agree with txeng91's comments on this topic. My CS-WSP is 5.5' in length and after I throw in a couple of king studs my CS-PF wall sections will each be 2'-3" in width. Table R602.10.5 allows for the contributing length of CS-PF to be 1.5 x Actual. This would give me 15.6' of effective braced wall section.

On top of all of this I do plan to add a couple kickers to each header if it doesn't check out for the weak axis bending (maybe even if it does). I think after I have done all of this I should be good and more detailed calculations should reflect this. I understand that it may be a little excessive but several extra kings studs and some kickers seem like a little extra material going a long way.

My final concern is the anchorage of the wall for uplift from the roof trusses. I will have about 4.5 kips of uplift on the walls between the doors. The anchors are checking out fine but I am a little uncertain how to verify the sill plate connection to the studs. Just standard pullout values from NDS or do you typically consider the contribution from the 7/16" sheathing nailed to it as well?

Thanks for all the contributions!

 

[charliealphabravo]

Not every problem can be solved in the plane of a 2x4 wall. It may be better to dedicate additional space and not expect the same system to resolve vertical, lateral, out-of-plane, and impact loads.

 

[BridgeSmith]

"Not every problem can be solved in the plane of a 2x4 wall."

Maybe not every problem, but in residential construction, many common loading conditions can be handled adequately. It may require some extra 2x4s and some carefully designed reinforcement, but it generally can be done. In this case, individual header beams, adequately sized, attached to enough king studs to carry the out-of-plane loads to a diaphragm above and the foundation below, seems to be a feasible solution.

 

[BridgeSmith]

"Maybe I should invest in some nice big bollards on each side of the door."

Just make 'em park outside. Cars are made to outside, power tools and plywood, not so much. I never take up my valuable garage space with cars, unless I'm working on them.