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Built up vs. Dimensioned Headers ~ IRC

Brudgers,

LOL... this happens with engineers more often (percentage-wise of the respective practitioners) then building designers because the engineering profession has been much about how close they can dance the razor blade. (ie. How little factor of safety they can go and so on.) It isn't about how stout and massive you can build it. It is about how tiny of twigs you can go.

Any dumb-*** can build a bunker to survive a MOAB. It depends on how much money and how thick of walls and ceilings/roof.
 
Wonderful, you've managed to delude yourself into the belief that you are more competent than an engineer.
 
No. You made that assumption. General practice with Engineers is not about making buildings stronger but cheaper to build and use less material. Don't assume any meaning.
 
Don't have to be one to observe what they do.

This is just an observation of a pattern of activities of engineers in the building industry.
 
I've kind of seen the opposite with engineers.. they want to over-engineer things to the point no one can afford to build them.

I've never seen a field fabricated "glu lam" beam... it's values can be calculated.. but you would need to calculate each layer by species and strength.. and know something about the glue used. Reject it if it makes you happy.. :)
 
ASTM D2559 adhesives.

melamine formaldehyde resin

and in many cases:

Resorcinol-formaldehyde resin

There are a number of ASTM D2559 rated resins/glues. The importance is choosing a glue/resin that is rated to that level.

In a nail/glue-bonded built-up hybrid, I would spec the nailing schedule to meet the required fastening to keep each ply together. Then use glue resins like Gorilla Glue (polyurethane adhesive) might be used where application is combined with the nailing and exposure to water in minor otherwise Resorcinol-formaldehyde resin glue would be used.

Common glues used in plywood and may even be used in "Glulam" (product trade name) or Built-up beam where each ply is glue-bonded in addition to the nails (or in many cases, also just the glue).

I will usually specify nailing PLUS glue bonding on a typical built-up beam. The purpose for the glue-bonding is to create a fuller more uniform mechanics of each ply so each ply does not move independent of each other as much as it might with nails.
 
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In post 16 Phil did a good job or providing information from the NDS for wood construction.

He also points out that manufactured beams are stress tested following construction. An important part of the process. One that is seldom done for field glued up beams.

One point that has been glossed over is that the prescriptive beams have the plies vertical. Many manufactured beams - especially those in larger depths, have the plies horizontal. The nailing/gluing schedule is more important when the plies are horizontal.
 
Field Built-up beams have been done with the plies vertical and horizontal. Glulam (a product) is tested obviously for consistency and assurance for the load. However, a #1 grade lumber has been tested and basic built-up configurations have been tested. Even in regards to beam span and such, a 2x12 has a certain span under a load with a certain deflection. A built-up of 7 to 8 plies will perform similar if not better then a solid timber beam that is 12" x 12" mainly because the plies are consistent grade and therefore retain better modulus of elasticity and other critical factors that leads to a better strength beam. A solid timber beam that is 12 x 12 may look clear and perhaps be graded SS or #1 & BTR but a whole internal section in the middle can basically be about a good as #3 because it was not noticed or seen at the surface. Built-up's can be more consistent. Being all SS grade.

Solid Timber spans typically use lower spans for that very reason.

In general the best grade rating most any of today's fresh cut beams are rated to is basically #2.

The grade is important to have the correct modulus of elasticity and doing the beam sizing calcs.

So, it matters. A field built-up with the wood plies horizontal would typically be purely glue based and I would spec the same kinds of glue/resin used in glu-lam. I give the beam a more regular single grade calc and base the strength on the overall cross-section of the beam. As long as the glue is as strong if not stronger then the wood and work as a unit, all the better. The primary basis is that it isn't stress tested so I wouldn't calc it to the pre-engineered glu-lam load-span tables and such. I would calc it similar to a regular beam of that size. It will be as strong as a regular hewn beam OR built-up beam of a particular dimension. If the wood is #1 grade all the way through then it will have same or similar modulus of elasticity. I would size it with a factor of safety of 1.5 or 2.

The primary reason that plies are laid horizontally on glue-lams and really deep built-up beams (almost always glue-bonded versus nails) is beam depth. If the depth of beam required is 36" - you just aren't going to find a 2" x 36" lumber. So the field built Built-up would be built similar to a glue-lam in this nature. Just not with all the control environment and the sizing would be based on a solid beam/built-up of these dimensions versus glu-lam.
 
GluLams are not regularly used. I haven't had to spec out a Built-up beam of such dimensions and depth to require different ply orientation. Glues used would be the same kinds of glues used to plywood and glu-lams. More so when there is less use of nails to hold the pieces together. But then at a certain point, it often makes perfect sense to switch over to real Glu-Lam or use a Steel Beam. Just a point of thought.

If had to, the grades would all be the same grade and species. It makes it easier to spec out. Some consideration to grains per inch count would be considered and how well they fit together.
 
RickAstoria said:
GluLams are not regularly used. I haven't had to spec out a Built-up beam of such dimensions and depth to require different ply orientation. Glues used would be the same kinds of glues used to plywood and glu-lams. More so when there is less use of nails to hold the pieces together. But then at a certain point, it often makes perfect sense to switch over to real Glu-Lam or use a Steel Beam. Just a point of thought.If had to, the grades would all be the same grade and species. It makes it easier to spec out. Some consideration to grains per inch count would be considered and how well they fit together.
Click to expand...
Coming soon to the Darwin awards:

Building Designer specs thermoset adhesive for exempt building.

http://www.gp.com/chemical/products.asp?rc=1&kw=&bs=71%7Cplywood%7C62%7Chardwood%20plywood&dc=3%7Cwood%20adhesives
 
RickAstoria said:
Glues used would be the same kinds of glues used to plywood and glu-lams. If had to, the grades would all be the same grade and species. It makes it easier to spec out. Some consideration to grains per inch count would be considered and how well they fit together.But then at a certain point, it often makes perfect sense to switch over to real Glu-Lam or use a Steel Beam.
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I can think of few better arguments for leaving the design and construction of built up beams to the professionals. (One better argument would be that they have much more insurance coverage.)
 
Another good reason in my book is a registered design professional has had to at least take a test to prove some degree of competence in his/her field. Folks without any type of license, if they are really good enough to design so many things, would probably have a license so they didn't have to limit their practice so greatly.

And, I as a code official, if I take an unlicensed persons calcs and miss that they are wrong, my head is on chopping block big time (and it should be). If the licensed design professional screws it up I have someone standing in front of me when the shots are fired.

Besides brick doors are hard to open.
 
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texas transplant, the State of Texas doesn't have any regulations for a design professional. Archtects and engineers, interior designers... yes, but someone who draws up residential plans.....no requirements for the State of Texas.

Am I correct on this?
 
Mule,

Your description is basically right. However, if it gets outside the prescriptive methods and tables of the code, I do not allow just anyone to decide what a beam size should be etc. Under the code I have the right to require a Texas Engineer to do plans. We have a planned community here that has some very large homes and when it gets to big, the contractors understand why I want an Engineer on the job. Besides I haven't met one of our home designers or draftsmen or whatever they go by, that wants to try. Pre-engineered products like the imfamous Glu-Lams, above, etc. we accept as long as its a tested and engineered product. But if I am going to accept a 4-2x12 beam, with layers of plywood glued and nailed inbetween them for additional strength, 30 foot long with a large load on it, to be field built, there is going to be a licensed professional engineer with his seal on a plan. Then we will make sure the framer puts it together exactly that way.

I feel that if it is outside the prescriptive measures I have the right to require a licensed engineer. :)
 
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tt, totally agree, the aggravating thing is that when I have is when w plan submited, doesn't even come close to the perscriptive of the code, reject the paln and require an engineer, and get the same plans back with no changes...just an engineers seal!

2X6 #2 SYP flat roof pergola spanning 26 feet with 2X4 for lattice on the top. The perimeter header is 2X12's, not even a header. a 2X12 is on each side of a 4X4 so we have a 4" gap between the 2X12's. Oh did I mention the 2X12's are spanning 26' also?

Got an engineers seal!!!!

Still not accepting it! Just because I have a seal doesn't make it right!!!
 
Mule,

I agree and when it looks wrong and has a seal, I ask for more back up on why its right. And I have had engineers show me how little I know on in a few instances, but I do sleep well at night (Daddy raised me well enough to know I ain't always gonna be right). But If I am going to screw it up I would rather be shown that I am wrong on paper, than find out five years later I approved something that got killed someone just because a piece of paper showed up with a seal on it.
 
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A built-up beam of conventional ply layout will operate the same as a solid hewn lumber of the grade that the lumber ply would be. This means the same formulas would be use. The only issues with built-up is that additional calculations and assurance measures needs to take place so each ply works uniform with each other. I am already aware of those considerations.

Some states exempts certain buildings under engineer's law. That is important to understand under legal parameters. Exemption is an exception (sometimes called an exception) to the licensing requirement to engage in making plans and specifications.

First and foremost, by virtue of the commanding power of "Standard of Reasonable Care" - any requirement required of a licensed professional becomes a requirement also to an unlicensed professional. The commanding rule is - the standard of reasonable care for any particular work is REQUIRED by all persons to meet when performing such work. By law, the standard of care for properly designing a built-up beam applies to everyone that designs a beam. The license stamp irrelevent. The standard of care required by a licensed pilot also applies to an unlicensed pilot. Otherwise, they committ what the courts call - NEGLIGENCE. This is part of Tort law and applies to me as much as any other person. There is no legal recognition for discriminating between licensed and unlicensed person in these laws. Whether you have a license or not is another case in regards to other laws.

So, if I design a truss or built-up beam, I am required by law to perform the work to the same standard of care as it would for any other person including engineers and the highest level of standard prevails. In Oregon, I work under an exemption.
 
Mule said:
tt, totally agree, the aggravating thing is that when I have is when w plan submited, doesn't even come close to the perscriptive of the code, reject the paln and require an engineer, and get the same plans back with no changes...just an engineers seal!2X6 #2 SYP flat roof pergola spanning 26 feet with 2X4 for lattice on the top. The perimeter header is 2X12's, not even a header. a 2X12 is on each side of a 4X4 so we have a 4" gap between the 2X12's. Oh did I mention the 2X12's are spanning 26' also?

Got an engineers seal!!!!

Still not accepting it! Just because I have a seal doesn't make it right!!!
Click to expand...
And what would be the loading on that pergola roof? If I recall my engineering courses, we were always trying to find the closest number to failure. Because the prescriptive is a cookbook handbook, I believe there is an element of safety built in which is greater than that which would be found many times if the numbers are run. So, it could be that the engineered number yields a lesser member than the prescriptive.
 
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