Header Span Table Questions

[Apexpredetor]

Good Morning All,

I'm from NY (PE-Civil). I am doing some design on my own attached garage and I am a bit stumped on my garage header as far as prescriptive code is concerned. IT doesn't appear that the prescriptive code accounts for openings larger enough for the 16' doors? Must these be an engineered beam, or spec's by LVL/Glulam, etc...

Thanks all for the help.

 

[CELinOttawa]

Hi Archie: Total deflection. This is as per the recommendation of CWC Wood Design Manual, but note that NBCC permits it under live load.

I will vary from this if the job is clearly going to be able to sustain more movement, but rarely. The number one complaint one hears these days about all the McMansions is the lively floors and crappy roofs. I want our work to stand firm.

 

[AELLC]

Defections of long header beams over sliding patio doors needs to be looked at carefully.

Also, longer header beams where exterior wall is stucco. A beam w/ L/360 total may be adequate for a 16' span, but create a problem with a 35' span.

 

[CELinOttawa]

We aren't talking about a 35' span, nor are we talking about stucco. Have I missed something?

 

[KootK]

I'm am the unicorn. I'm an SE and I'm happy to use span tables every chance that I get. Headers, masonry walls, precast planks... you name it. I'm pretty sure that I only make money on the stuff that I don't design.

Back in the day, the vast majority of garage roofs were gable end roofs with the truss bearing on the walls not containing the 16' door. They were often constructed with 3-2x10 and, while likely not kosher by the numbers, seem to have been serviceable. Who knows, maybe the roof framing held up the header somehow.

Even in NY lateral will be an issue for the wall segments either side of the door. Think hurricane.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[AELLC]

Sorry, CEL, don't get cross.
I was just suggesting additional considerations in a general sense for application in any other project.
It was implied, but you are right, it did sound a bit like I was contradicting you.

 

[AELLC]

KootK,

Yes you are generally correct, but I now do so many custom, wood constructed houses, for me it has become quicker overall to use my Excel workbook to churn out all my designs. The way it is set up, it makes it easier to just run the uniform loaded beams along with the beams with complex loading.

I am not saying everyone should be able to do this, I am saying it as advice for someone wanting to streamline the design process.

I use to submit a sheet or two with tabulated beam designs, ie B3, B7, B8 are 2-2x6 and B2, B13 are 2-2x8, etc, which was fine, but the way I set up my Excel shows 4 beam designs per sheet and showing simple uniform load desiogns along with the more complicated case works a bit better for me.

 

[AELLC]

Speaking of roof framing holding up the header, when I was working at a small consulting company located on residential street in an older neighborhood in Phoenix, and old house with a stick-framed roof and brick exterior walls was being demolished across the street, so we all took a break to check it out.

The demolition contractor started knocking down the right elevation wall (the house was rectangular in plan, longer in the left-right direction than the front to back direction), but leaving the roof. He got about 1/3 of the way into the house as he was knocking down the front and back walls alternatively, all the time the roof was cantilevering and sagging, then finally the unsupported roof collapsed. It made a more efficient demo because he didn't waste any time thrashing at the roof.

 

[XR250]

I always design Garage Door headers at L/600 as even a small sag in the header is very apparent when you drive up to the house (at least to me anyhow). Also, don't forget about out-of-plane loads. You have to have enough king studs and enough attachment to the structure to resist the in/out wind pressure.

 

[CELinOttawa]

Not cross, it is a good extra bit of info... Frankly I very strongly oppose anything that is too long to put up with a SPAN/360 total deflection. In terms of TOTAL deflection, you can't get much better in non-commercial construction. You need steel all the way to foundations, and very good foundations. Each case is different, but if the requirements are too strict the performance is rarely there.

 

[AELLC]

The usual header for 8' setback hip roof around here is a 3-1/8"x10-1/2" glulam (dead=22 psf, live=20 psf reduced for pitch, non-snow), and that yields about L/360 total. I haven't heard of any problems.

Years ago, before plans check, the tract home builders were always insisting the headers be 2-2x10, and those did sag a little.

 

[AELLC]

oops - I meant to say 16' garage door headers.

ps - for 8' plate height tract house, always 2 jack studs and 2 king studs, whether 2x4 or 2x6. If I took the time to design the kings per IBC 2012, the king probably wouldn't calculate, but I am of the opinion that the 2 lightly loaded jack studs, being just 1' short of the wall top plate, stiffen up the king studs considerably.

 

[Archie264]

KootK

I guess I wasn't thinking of things like lintels, precast planks, etc. Yes, I use tables for the likes of them too, as well as for metal decking, bar joists, and sometimes other types of joists as well. But I never use span tables for beams or girders. For such as that I always want some type of documentation of what loads I applied to it and what unbraced length I used. I.e., I would like to be able to check my files and quickly see whether the member in question carries a point load, a line load, does it carry a masonry veneer, etc. If it's guaranteed to include none of that then sure, a table will work, but I'd still rather have the full documentation. And yes, I have Excel spreadsheets and other software to help speed the process along.

What scares me, though, is the thought of people consulting span tables without considering all of the loads or circumstances that may apply. Just my opinion.