site made glum or I beam strength - Woodworking Talk - Woodworkers Forum
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post #1 of 23 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 23 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 23 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 23 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)

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post #5 of 23 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 23 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 23 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 23 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 23 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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post #10 of 23 Old 09-23-2020, 03:43 AM Thread Starter
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I would love to do it all traditionally but I just don't have the time or the quality and availability of wood at a price that we can afford. Also the Moroccan climate is so harsh that timber moves all over the place so it needs to me installed very quickly..... or prefabbed. We get 20 degree changes in temperature night and day and everything can be dripping with dew at 8am and bone dry with pumping sun 10.30.... can be very tricky and hard work.

Thanks for the advice.... were trying as hard as possible to not use concrete and steel so an I beam in timber, ply or OSB would be the easiest way to go or a Glulam but i would need avoid formaldehyde resin. No snow loading.

I am assuming making a Glulam onsite is not particularly difficult as long as I get a good covering of glue and apply good clamping pressure with a few quality mechanical fixings along the way oh and obviously spread the joints well away from each other?

Any advice on constructing these onsite?

Many thanks,

Anthony
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post #11 of 23 Old 09-23-2020, 09:09 AM
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The two ways to DIY a beam ......

You can laminate the pieces in a vertical stack like books, OR you can laminate them on their faces like how you store LP records label to label.


The first method is called "glulam" and uses 2" thick by 3" or greater widths.
The second method is called "microlam" and may use plywood, or LVL, and uses thin veneers.
https://architecturesideas.com/2019/...Glulam-Timbers


https://www.thebalancesmb.com/what-i...-glulam-845106
"A glue-laminated timber is an engineered wood product, meaning it is made from wood but is machined and assembled to precise specifications to create a predictable, dimensionally stable building material. Other common engineered wood products include plywood, oriented strandboard (OSB), and laminated veneer lumber (LVL). A glulam beam looks like a stack of 2 x 4s (or larger lumber) glued together on their broadsides. This is in contrast to other engineered members, such as LVL (laminated veneer lumber) and Microlam beams, which look like very thick plywood, with very thin layers of wood glued together to form a thicker mass."

Which method would you use onsite with your available wood types?
I'm guessing glulam because of the ease of milling or sawing them to thickness and width. You may have access to wider and thinner material, but less likely in my opinion.

Here's a method of making a glulam on site:

A warning about using a nail gun to secure the pieces. The nail gun will NOT draw the pieces together like screws. Clamps or screws will be necessary to squeeze the layers together as well as glue and then nails.
This video uses clamps and applies a generous amount of glue, working one layer at a time:
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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; 09-23-2020 at 09:26 AM.
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post #12 of 23 Old 09-23-2020, 09:24 AM
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Another option would be to sandwich a piece of 1/4" flat steel between two pieces of solid wood. The wood would prevent the metal from deflecting and the steel would prevent the wood from sagging.
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post #13 of 23 Old 09-25-2020, 05:42 AM Thread Starter
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Thanks Steve and woodnthings. Its given some confidence that I can solve this onsite. I probably need a spec from a structural engineer as we have severe wind loadings from the south seasonally and extreme temperature differences.

Thanks again A
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post #14 of 23 Old 09-25-2020, 09:32 AM
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Woodnthings gives a nice description of glulam and microlam (or laminated veneer lumber--LVL) beams.

A glulam beam will be much stronger and stiffer than the same pieces of wood just stacked on top of each other. For this to work, the gluelines must be rigid so the wood pieces can't slide past each other, even minutely and slowly, under load. In industry this is always done with glue intended for structural applications, not just any glue. The PVA or aliphatic resin glues that carpenters and cabinet shops use will not resist long term stress without slippage. They are not intended for structural applications. Industrial laminated beams use phenolic resins--possibly some urea formaldehyde resins outside the US--which cure to rigid gluelines which withstand shear stress indefinitely without slippage. Resorcinol glue is the best substitute outside a factory. There are caulk type construction adhesives that would be second best, especially if clamping pressure is applied with wood screws.

A microlam beam is entirely different. If you glue several wood pieces together side by side, there is no shear stress on the glue lines between them when the composite beam is loaded. The beam deflection calculation (the bending moment) for the composite beam is the simple sum of the calculations using the bending moments of the individual beams. The individual beams will bend in unison with out without the glue. There are some buckling considerations when the plys are very thin compared to the beam depth, and gluing it all together will make it easier to work with.

A microlam type beam made of OSB or plywood will not be as strong or stiff as a properly glued glulam beam made of solid wood and the same size because the OSB or plywood is not as strong or stiff as solid wood as the long grain structure of the wood has been disrupted in those board products. True microlam beams have the grain in all the individual plies aligned, not criss crossed as in plywood.

I did a lot of beam deflection calculations when I worked in the window industry. Window mullion calculations are simple because they just consider short duration wind load rather than combinations of short term and long term live and dead loads. There are some odd combinations of distributed loads and concentrated loads in mullion configurations put together for aesthetics.

For a small project like yours there are handbooks of standard wood frame construction. In the US they are in imperial units, but you should be able to find metric versions.
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post #15 of 23 Old 09-25-2020, 12:12 PM
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Antho - when you finally get a direction to proceed in, could you share
a few photos of your project and after it is installed ?
sounds like a fun project .

.
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post #16 of 23 Old 09-26-2020, 08:22 AM Thread Starter
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Will do John....
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post #17 of 23 Old 09-26-2020, 08:24 AM Thread Starter
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Hi all, So much great info here.... really appreciate it. Ill post some photos to this thread once we get into the construction.
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post #18 of 23 Old 09-26-2020, 06:46 PM
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re mixing steel-timber elements in a sandwich - too much work for too little gain
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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 #19 of 23 Old 09-26-2020, 07:05 PM
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Agreed

Quote:
Originally Posted by kiwi_outdoors View Post
re mixing steel-timber elements in a sandwich - too much work for too little gain

You need to drill bolt holes all the way through all 3 pieces and then you have exposed bolts heads and nuts. Lots of work and won't look good.... JMO. I've used 3 - 2 X 12's with plywood spacers on garage door headers with a 9 ft spans and 6" walls.



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; 09-26-2020 at 07:10 PM.
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post #20 of 23 Old 09-27-2020, 05:15 AM Thread Starter
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Yes agreed on the timber steel sandwich.... not a bad solution but not the most beautiful unless I was going for an industrial look. Looks like were decided on Glulam as its best looking most flexible and strongest solution. Ill be following the videos you posted and get a set of calcs from an engineer for the beams and wind loadings.

Is that a client job or your own garage?
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