site made glum or I beam strength - Woodworking Talk - Woodworkers Forum
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post #1 of 9 Old 09-10-2020, 02:27 PM Thread Starter
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site made glum or I beam strength

Hi All,

I need to span a beam on a timber cabin about 5M internally with a 1.6m exterior cantilever carrying a mono pitch roof made of 150mm joists plus insulation, OSB and decorative boards.

Whats stronger making one continuous I beam from OSB or PLY into 150mm plates across the the entire 13m width of the property then cladding that with 20mm boards or making up a Gluelam beam onsite from 150x 50 timbers?

What depth would I need to make them? I assume adding a double PL/OSB I would give it a lot more strength ?

I would prefer to avoid the toxic chemicals involved in making a GLUlam.,

Advice and help needed....

Many thanks

Anthony
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post #2 of 9 Old 09-10-2020, 04:33 PM
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you need a structural engineer to advise you.


the actual roof weight is a major factor.

add climate conditions. HI does not have a lot of snow load, CO does.


the load carrying capacity, deformity, etc etc depends on the materials and the moment of inertia for the actual shape.
the supplier of professional made products can provide that kind of info, doing homespun stuff and making wild axx guesses it not recommended.
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post #3 of 9 Old 09-10-2020, 04:42 PM Thread Starter
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Thanks Tom... Unfortunately being in Morocco i don't have access to a local engineer with the experience as almost everything is in concrete and masonry.

I feel very confident building whats needed on site with the correct spec but doing the calcs myself..... hmmm

Im in the desert so very hot day time, can be cool at night and gets very high winds with the roof pitch facing towards storms off the sea. luckily we don't have to meet dogmatic regulations but obviously it must work.

Any engineers on here?
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post #4 of 9 Old 09-10-2020, 10:53 PM
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I made a scale model house in high school

It was 1/4" to the foot if I recall and all the studs and joists were cut to scale and glued on with Elmer's white glue. When they were finished
the teacher asked who would be willing to stand on the roof of theirs to see how strong it was. I may have been the only volunteer, but it withstood my 157 lbs gently applied.



I am suggesting even if you could find a structural engineer OR a supplier of glue lams or trusses who would calculate the loads for you and then spec out your beam, I would make a scale model of the vertical supports and span them with beams of different construction made to scale of course. You may learn quite a bit from doing this and it should be fun also. Video the loading to failure keeping track of the amount of weight you add on.




The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 09-10-2020 at 10:58 PM.
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post #5 of 9 Old 09-11-2020, 07:01 AM
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You are going to need VERY accurate measurements if you are to gain from using scale model.


George
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post #6 of 9 Old 09-11-2020, 09:11 AM
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You might gain "knowledge" ......

Quote:
Originally Posted by GeorgeC View Post
You are going to need VERY accurate measurements if you are to gain from using scale model.
George

I doubt you could use any direct calculations from a scale model, rather just knowledge if there are major differences in failures using the different construction methods. Who would have thought the popsicle bridge in the video above would have supported over 800 lbs?


There are trusses like that bridge that were not proposed by the OP which may be a possible solution?


The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #7 of 9 Old 09-13-2020, 11:28 AM Thread Starter
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Ill just copy the girls design half way through.... ha ha ....fun Video.

Yes because the quality of the glue they used and the way the popsicles were stuck together would make a massive difference to the strength. Hard to replicate that from model to site a great test in principal though.
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post #8 of 9 Old 09-13-2020, 09:41 PM
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Quote:
Originally Posted by Antho View Post
Hi All,

I need to span a beam on a timber cabin about 5M internally with a 1.6m exterior cantilever carrying a mono pitch roof made of 150mm joists plus insulation, OSB and decorative boards.

Whats stronger making one continuous I beam from OSB or PLY into 150mm plates across the the entire 13m width of the property then cladding that with 20mm boards or making up a Gluelam beam onsite from 150x 50 timbers?

What depth would I need to make them? I assume adding a double PL/OSB I would give it a lot more strength ?

I would prefer to avoid the toxic chemicals involved in making a GLUlam.,

Advice and help needed....

Many thanks

Anthony
your options wander all over the place. Pick what you want, then figure out the particulars of the solution. And please be clear on the load regimes and tributary width (which you did not explicitly state). I'm a registered structural engineer - but just reading your question makes my head hurt.

Retired engineer-bureaucrat in Oakland, CA. Been working with wood since the 1960's. From the 50's if you count the scrap woodpile on the farm!
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post #9 of 9 Old 09-13-2020, 11:05 PM
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Quote:
Originally Posted by Antho View Post
Hi All,

I need to span a beam on a timber cabin about 5M internally with a 1.6m exterior cantilever carrying a mono pitch roof made of 150mm joists plus insulation, OSB and decorative boards.

Whats stronger making one continuous I beam from OSB or PLY into 150mm plates across the the entire 13m width of the property then cladding that with 20mm boards or making up a Gluelam beam onsite from 150x 50 timbers?

What depth would I need to make them? I assume adding a double PL/OSB I would give it a lot more strength ?

I would prefer to avoid the toxic chemicals involved in making a GLUlam.,

Advice and help needed....

Many thanks

Anthony
I don't care much for modern methods of construction. They make beams out of OSB and you see it deteriorating just from humidity. No longer than the span is I could either use a laminated beam or an 8" steel I Beam. The steel beam would probably be cheaper. If you live somewhere without snow or ice you could get away with a doubled 2x12.
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