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]

This is quite common; Prescriptive codes are created with maximums as these then determine the loads to which columns, lintels, jack posts (etc) and the foundations are designed.

You need a local Structural Engineer's help.

 

[Apexpredetor]

Thanks for the response CEL.

I wouldn't call myself a "structural" engineer, but I do have a great deal of experience in structural design and analysis I am a NY PE (Civil). I just don't have much experience in residential design. I could sit here and design a beam specific for the overhead door, but I know that we have prescriptive code in place that handles the vast majority of residential specification.

It appears that most people use LVL's in this scenario (keeps engineering costs down I assume, and transferrs liability to LVL manufacturere and sealer/stamper) but I was hoping for somebody to shed a little more light on the process or alternate methods. I am a PE and I do have experience in the analysis; not just a homeowner posting a question on here.


Thanks all. I appreciate the help.

 

[AELLC]

If you know your snow load, there should be online calculators for glulam beams. LVL's can be calculated by downloading their software from RedBuilt (free).

Here in Phoenix, most 16' headers with 2' max roof trib (gable end truss condition) are (2)-2x10 or (2)-2x12.

 

[Apexpredetor]

Thanks AELLC. MY condition would be the truss bearing side (I'm drawing a blank on the terminology here), with a fairly significant GSL (I need to check, but I think that it is 60-65psf).

I'm probably going to spec an LVL, but I really wanted to see if there were any other options (i.e. built up 2x12's won't make the 16 ft).

Thanks all

 

[AELLC]

LSL's have less in the way of properties, but may work. Parallams are useful for larger loads. Glulam may be cheaper than LVL and are definitely cheaper than Parallam.

Be aware of the recent discussions regarding LVL deflections, there may be inferior product made by other companies.

 

[boo1]

Typical local truss fabricator can supply the beam and engineering stamp.

 

[AELLC]

oops- try Weyerhauser for software, not RedBuilt

http://www.woodbywy.com/software/

 

[Apexpredetor]

I would expect the truss and LVL (or similar) manufacturer to stamp their product designs, but I will need to stamp the rest of the design (it is fairly simple design).

My real motivation here it to figure out how it is accomplished. Before composite materials was there not larger openings, or where they always steel?

Thanks again

 

[CELinOttawa]

They were nearly always steel back in the day, but Timber beams can work on those spans (timber properties were previously much more stiff, old growth forrest being a big part of the reason why)

I see a great deal of steel beams doing this in older houses.

 

[Apexpredetor]

Thanks. That's what I was thinking. Engineered beam for large openings, or multiple smaller openings.

Appreciate all the help.

 

[a2mfk]

I have never heard of a engineered lumber supplier providing any calcs or sealed drawings, you just specify what product you want on your drawing that is signed and sealed.

The tricky part of a garage is making the garage door walls/jambs work laterally and for in-plane shear, especially if the garage door(s) eat up most of the wall.

CELOttawa- Interesting comment about regional structural systems. I have never seen a steel beam used as a residential header in Florida, wood or CMU only. Rarely see steel at a house period, of course we also rarely have basements.

 

[AELLC]

Usually when there is a floor above the garage and then the wall up to the roof is load-bearing and snow loaded, then you have steel beam.

In fairly low-seismic areas like NY I understand in-plane lateral shear is not a big issue, assume 3-sided diaphragm but ignoring the stringent Code reqmts about diaphragm ratio and diaphragm deflection etc, as we mostly do here in Phoenix area.

 

[CELinOttawa]

a2mfk: Regional differences are as amazing as anything else I've seen in this business. New Zealand was a lovely country, and I absolutely fell in love with the PFC "Parallel Flange Channel". Think of our W-sections being a modern update to the I or S sections, and then think why hasn't that been done to channels? They have in Australia and New Zealand. Makes fastening much easier.

Actually New Zealand had fairly similar construction techniques to Canada, but was architecturally very different. Australia surprised me by having a great deal of residential load bearing masonry (clay brick). Haven't seen that in a building built in Canada since 1920.

 

[boo1]

a2mfk Bay County FL requires all truss plans and beams (outside the SBC code spans) to be stamped before permits are issued.

 

[msquared48]

More than likely, the size of the beam with those snow loads will not be stress governed, but deflection driven - I try to limit the vertical deflection to 1/4" or less for serviceability reasons under full snow load.

Mike McCann
MMC Engineering

 

[Archie264]

Apexpredetor,

I don't know of any practicing structural engineer who uses beam span tables. I'm not saying that they can't be useful but I am saying that if that's what you're relying on to proceed with caution. I wouldn't try to do civil or environmental engineering even though I work with people in those disciplines rather often. The problem would be, though, that I don't even know enough to know how much I don't know. I could get myself into trouble and not know it.

Some years back I reviewed drawings for some high-end residential structures. They had some very large and inefficient beam sizes, on the order of W10x54, maybe larger. Wondering why they used such a silly beam size I ran the numbers whereupon it became obvious: the designer apparently sized the beams from the moment capacity chart in the steel manual but didn't realize his beams were braced. I'm guessing the architect sized his own beams. The worst part was that this was a development so those beams sizes were repeated many times over. So, by saving a few hundred or a few thousand dollars by not hiring a structural engineer he cost many tens of thousands of dollars on inefficiently sized beams and unnecessarily-difficult installation labor.

But then, I suppose it could have been worse: he could have undersized them...

 

[CELinOttawa]

I try to keep the deflection of roof supporting structure to Span/360. I just never want to have someone come back on me as having "too soft" a beam. Besides, it is cheap insurance in case the builder uses cheap caulking.

 

[Archie264]

CELinOttawa,

Are you referring to live load deflection or total deflection?

 

[AELLC]

Span tables are utterly useless anyway because there is always at least one case of concentrated load or uneven distributed load.