Replies

1. 
   Sphere | Jul 31, 2004 12:55am | #1

   LVL

    

   Spheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations. 

2. 
   BossHog | Jul 31, 2004 02:03am | #2

   Like Sphere said - LVL will carry more.

   Roughly twice as much.

   It varies some with the species and grade of 2X12, though.

   And there is no "standard" LVL. Every manufacturer publishes their own design values.

   We weren't selling cigarettes, we were selling an image. An image to young boys. - - rock-climber David Gurlitz on his Winston ads

3. 
   DanH | Jul 31, 2004 05:39am | #3

   Keep in mind that a 2x12 is actually l-1/2 x 11-3/8 or so, while the typical LVL is 1-3/4 by 11-3/8 exactly. So the LVL is actually thicker to begin with, and just as "deep". Plus the glue adds considerable strength to the LVL and it has no soft spots due to knots, etc.

1. 
   BossHog | Jul 31, 2004 01:32pm | #5

   "...the typical LVL is 1-3/4 by 11-3/8 exactly."

   Actually, they're 11 7/8 deep.Q: How does a woman know her husband's cheating?A: When he starts taking a shower twice a week.

1. 
   evetss | Jul 31, 2004 06:51pm | #6

   Thanks for all the info... the lvl is 1 3/4 thick, so that two of them together will be the 3 1/2 needed  and then you don't need that 1/2 plywood between as you do with the 2 x 12???  interesting

1. 
   gdavis62 | Jul 31, 2004 08:03pm | #7

   My supplier sells LVL at 11.25 and 11.875 depth.  All are 1.75 thick.

2. 
   Hooker | Jul 31, 2004 09:24pm | #8

   OK, we agree the LVL is stronger, but I was told at some point that the 1/2 spacer in a 2x12 header, if done correctly, will add considerably to the strength of the header.  Kind like making a truss mechanism using the nails as the "webs". Anyone agree or dispute?

   ADH Carpentry & Woodwok

1. 
   Sphere | Jul 31, 2004 09:36pm | #9

   I glue my ply spacer with PL...nail according to schedule..and yes maybe, a properly builtheader will ALMOST equal a LVL, BUT..it really boils down to loading (point loads, and modulus of elasticity) and the species and grade of the select stuctural members.

   I really put faith in SYP, with OSB as the filler..the downside is still the load , and the shrinkage, and the method of fabbbing it up.

   Given an open wallet..I'd take LVL. 

   Spheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations. 

2. 
   BossHog | Aug 01, 2004 01:27am | #11

   "I was told at some point that the 1/2 spacer in a 2x12 header, if done correctly, will add considerably to the strength of the header."

   I'd say that's a subject of much dispute.

   Personally, I think it makes little difference. It would greatly increase horizontal shear on the ends of a beam. But beams don't generally fail in horizontal shear.

   Also - To my knowledge, no one has ever done any testing of plywood in headers. (Or maybe I've just never seen any)

   And one final point - Unless I'm sorely mistaken, the NDS makes no allowances for design values of plywood in headers. If there are no published standards, then who decides how much value to give the plywood?

   Just my $.02 worth. You could probab;y start a thread on this and get a pretty good debate going.If builders built buildings the way programmers wrote programs, then the first woodpecker that came along would destroy civilization.

3. 
   gdavis62 | Aug 01, 2004 03:42am | #14

   If your 1/2" spacer is steel or carbon fiber maybe, but if it plain ol' plywood, or worse yet, OSB, your beam made with a 2-2x12 sandwich hasn't even as much strength as a solid-sawn member of the same species, at 3-1/2 x 11-1/4.

2. 
   DanH | Jul 31, 2004 09:52pm | #10

   Yeah, I knew it was some odd measurement, but couldn't remember the exact value.

2. 
   jonblakemore | Aug 01, 2004 01:37am | #12

   "Plus the glue adds considerable strength to the LVL"

   That is not true.  It is true that a good glue joint is stronger than the wood, but what that statement is referring to is the bond between the fibers.  As far as structural strength goes, glue has no appreciable value. 

   Jon Blakemore

1. 
   Lenny | Aug 01, 2004 01:50am | #13

   I heard somewhere from reasonably reliable sources that the strenth in a header comes from the 2-2x12's glued/nailed together primarily from the different orientation of the grain of each board.

   If so, would 2 pieces of 1x6 glued/nailed be stronger than a single 2x6?...on end, same length?

1. 
   DanH | Aug 01, 2004 03:54am | #15

   It would certainly reduce the average variation in strength between two random headers, and since headers must be designed to handle something on the order of a 3-sigma worst case, laminating would improve the design strength. This assumes, though, that the laminating process is "ideal" so that it doesn't impair the resistance to crush or roll.

1. 
   JohnSprung | Aug 03, 2004 04:00am | #18

   > a 3-sigma worst case,

   Is it sigma or delta?  Standard deviation?  It's been a long time since I've looked at statistics.

   -- J.S.

2. 
   DanH | Aug 03, 2004 04:30am | #19

   3-sigma is about the odds (pre 9/11 -- it's a lot worse now) that an airline would lose your luggage. It's 3 standard deviations out from the mean -- one in several thousand, IIRC. 6-sigma is about the odds that you'd die in a plane accident.

   When you're dealing with strength of materials, "average" strength isn't particularly useful. And "absolute minimum" strength isn't really achievable (especially in a material like wood). So you pick a number, say one in 10,000, and ask "What's the minimum strength that I can assume and have only one chance in 10,000 of being wrong?"

2. 
   Hooker | Aug 01, 2004 08:13pm | #16

   If so, would 2 pieces of 1x6 glued/nailed be stronger than a single 2x6?...on end, same length?

   This is what I was thinking.  The laminations of the material all providing their own structural properties.  Isn't the basic idea of LVL in the first place?

   ADH Carpentry & Woodwork

1. 
   Sphere | Aug 01, 2004 09:19pm | #17

   you would have to define "stronger" 

   yes, in one fashion, and no in another..stronger in shear? stronger in deflection ? stronger in compression?

   many ways to look at it. 

   Spheramid Enterprises Architectural Woodworks

   Repairs, Remodeling, Restorations. 

4. 
   DanH | Jul 31, 2004 05:44am | #4

   Just to add to that, when I resided my house about ten years back, I replaced two 2x14s over the double-wide garage door with two 11-3/8 LVLs. Even though the new members were less deep by 2 inches, this cut the sag in the middle of the door opening by about a factor of 4. (A small wedge in the center removed the sag completely.)