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Author Topic: Strength of different kinds of beams?  (Read 8839 times)

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Offline Furby

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Strength of different kinds of beams?
« on: October 12, 2004, 09:49:42 PM »
I know there has been a lot of talk on different beam sizes, types, and strength. Which is strongest?

A dimensional beam cut from one log.
An LVL.
A glue lam (pieces stacked and glued).
Simply spiking several 2x's together.

Or am I just fishing in the dark for something that is more "use specific"???

Offline etat

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Re: Strength of different kinds of beams?
« Reply #1 on: October 12, 2004, 10:59:29 PM »
Somewhere I've got a old old steel square and framing book that has a table with the strengths of different types of wood, and sizes of wood beams and how much weight they will support for a given span.   If ya want I could try to find it tomorrow somewheres.  

They tell me a properly sized glue lam beam out of 2/4's or 2/6's is really strong. I've seen em cover some really long spans and I know they're really strong but it just makes me nervous all them boards glued together.  I would think they would be more stable than a beam made out of real wood though.

I would not try to duplicate the process by nailing two by fours together.  All that glue and pressure when they put em together helps keep them beams stiff and tight.

My personal favorite is a 10 inch steel I beam with 2/10's bolted to both sides of the webbing.  I spanned two 24 foot sections in my house with these.   I didn't have a engineer here to advise me, just duplicated what I a have seen.  

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Online beenthere

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Re: Strength of different kinds of beams?
« Reply #2 on: October 13, 2004, 12:08:53 AM »
IMO, The LVL (laminated veneer lumber) would likely be the strongest, provided the veneer used in the tension side of the beam was straight-grained.

The glue-lam likely the next strongest, as the glue will keep the individual laminations from sliding past each other under load. Careful selection of high grade laminations in the tension side will also increase the strength.

The nailed laminations would be the weaker, compared to the above.  The nails allow more 'sliding' of the laminations under load.

Because trees don't grow without limbs, the dimensional beam (sawn timber) could be the weakest of them all, but that is only an assumption. It would depend a whole lot on the number, size, and distribution of strength-reducing characteristics.  In the first three, these characters can be randomly distributed, so they don't have as much effect on the strength as when they are in a single sawn beam.

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Offline Timber_Framer

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Re: Strength of different kinds of beams?
« Reply #3 on: October 13, 2004, 09:23:16 AM »
I tend to agree with beenthereI've worked with all of the material he mentioned and can attest to the strength of LVLs and to their weight! All that glue is DanG heavy!
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Offline Jeff

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Re: Strength of different kinds of beams?
« Reply #4 on: October 13, 2004, 05:13:01 PM »
How about a little help from Don P's beam calculator? It wont answer the question but gives a chance to show it off. :)

http://www.forestryforum.com/members/donp/LogBeamCalculator.htm
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Online beenthere

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Re: Strength of different kinds of beams?
« Reply #5 on: October 13, 2004, 06:10:16 PM »
Jeff
Don P's beam calculator answers the other question regards white pine and red pine. Both have the same values in the calculator for the 4 stress grades listed for the two species.

The trick is to get the material graded.  

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Offline Timber_Framer

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Re: Strength of different kinds of beams?
« Reply #6 on: October 14, 2004, 09:58:35 AM »
Nice tool that calculator is...thanks
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Offline ARKANSAWYER

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Re: Strength of different kinds of beams?
« Reply #7 on: October 14, 2004, 03:05:01 PM »
Just a note for you guys who like glued timbers.  Most do not take water or humid conditions well.   Also during a fire they do not sag or groan when about to fail.  They will "melt" and bust at about half the temp of a solid wood beam.   We do not know the life span of the glue but, solid wood timbers have been in buildings for hundards of years.  Time will tell but me I like real wood after all I own the sawmill.
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Offline beetle

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Re: Strength of different kinds of beams?
« Reply #8 on: October 14, 2004, 03:11:12 PM »
There are several old commercial buildings around my area that  burned many years ago, they were rebuilt at some time and them old chared timbers are still in em holding the structure up. Try that with todays technology?
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Online Jim_Rogers

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Re: Strength of different kinds of beams?
« Reply #10 on: October 15, 2004, 07:54:45 AM »
Don P:
Thanks for posting all the links to some really useful calculators.
I hope others will find them as useful as I have.
Jim Rogers
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Offline slowzuki

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Re: Strength of different kinds of beams?
« Reply #11 on: October 18, 2004, 01:05:25 PM »
Arkan sawyer,  this simply isn't true with modern gluelams.  Most now use thermoset glues that can't melt.  I have investigate many gluelam fires and the industry has submited them to fire testing.  Heavy timber is assigned 45 min rating as either gluelam or sawn timber.

It is true they don't sag as much before failure but it is normally due to heavier loading engineers are allowed to place on gluelams because their strength is more predicable.

Ken

Quote
Just a note for you guys who like glued timbers.  Most do not take water or humid conditions well.   Also during a fire they do not sag or groan when about to fail.  They will "melt" and bust at about half the temp of a solid wood beam.   We do not know the life span of the glue but, solid wood timbers have been in buildings for hundards of years.  Time will tell but me I like real wood after all I own the sawmill.
ARKANSAWYER


Offline IndyIan

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Re: Strength of different kinds of beams?
« Reply #12 on: October 19, 2004, 09:37:27 AM »
Depending on what your application is sometimes getting away from wood altogether could be best.  We used a steel I-beam to cross a 28' span for our garage.  It was cheaper and needed less depth than a glue lam beam.  Also we do have some glue lam headers and the scraps after they have been left outside for a few months are not doing to well, they are starting to fall apart...  Not real confidence inspiring.

The main advantage of glue lams is their stiffness though,  they flex very little and since most construction codes are based on maximum deflection at a load instead of ultimate strength you can use a properly sized glue lam beam instead of over built steel beams or solid wood.

Ian

Offline slowzuki

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Re: Strength of different kinds of beams?
« Reply #13 on: October 20, 2004, 06:10:22 AM »
I find this really interesting as the glulam's I've worked with have been insensitive to water...  I'll take back what I said :-X  The older gluelams I've seen have used organic based binders but all the newer ones have been 2 part glues that can't melt, they only char or burn.  They also aren't water soluble.


Quote
glue lam beam.  Also we do have some glue lam headers and the scraps after they have been left outside for a few months are not doing to well, they are starting to fall apart...  Not real confidence inspiring.



Offline slowzuki

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Re: Strength of different kinds of beams?
« Reply #14 on: October 20, 2004, 07:48:30 AM »
I have a piece of an answer!  :P   According to the Canadian Wood Council, all graded glulams in Canada are required to use glues suitable for outdoor, exposed use.  Apparently this is not the case in the US.

This would explain some of the differences ;D

Quote
I find this really interesting as the glulam's I've worked with have been insensitive to water...  I'll take back what I said :-X  The older gluelams I've seen have used organic based binders but all the newer ones have been 2 part glues that can't melt, they only char or burn.  They also aren't water soluble.




Online beenthere

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Re: Strength of different kinds of beams?
« Reply #15 on: October 20, 2004, 09:22:21 AM »
I don't think it is any different in the US. The glues won't melt.

IMO, if leaving glued material exposed to the weather (outside), the wood veneer, flakes, or chips get wet, swell, and come apart. But I doubt the glue changes. Even with exterior glue, wood needs to be protected. Leaving an engineered wood I-joist or glue-lam exposed to the weather, isn't much of a test of its intended design or usefulness, IMO. (Sorry Indylan, but couldn't let this alone   :) .  No offense intended to you, for sure)

Remember back in the days of SYP plywood (I do  ;) ). Great stuff if kept dry, and exterior glue didn't keep it flat if not kept dry.
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Offline slowzuki

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Re: Strength of different kinds of beams?
« Reply #16 on: October 21, 2004, 09:01:31 AM »
Many timber frame arbor type architectural things with no roof.  Some are varnished, some aren't.  They don't fall apart.

I have some 3/8" exterior grade plywood that has been unprotected for well, over 30 years.  It is weathered but no delamination, swelling or warping.

Also have some 1/2" interior stuff that got wet for about a couple of months and it is garbage now.

Offline Timber_Framer

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Re: Strength of different kinds of beams?
« Reply #17 on: October 21, 2004, 09:59:58 AM »
The last I worked with lams (2"x16") was just over a year ago and while they are no longer exposed to weather I feel they would hold up just fine. I can't remember the specs but I do remember how long it took my new worm drive to cut em!
"If people concentrated on the really important things in life, there'd be a shortage of fishing poles."

Offline beav

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Re: Strength of different kinds of beams?
« Reply #18 on: October 22, 2004, 11:48:06 PM »
   I think real wood tastes best, but I know my porkypine buddies like the glued-up stuff best :D

Offline Timber_Framer

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Re: Strength of different kinds of beams?
« Reply #19 on: October 23, 2004, 08:46:37 AM »
 :D Yup, we were just checking deer stands this last week and my dads plywood deck has a nice big porky hole right in the center! Glad I used tongue and groove ;)
"If people concentrated on the really important things in life, there'd be a shortage of fishing poles."


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