Maximum span of laminated beam - Woodworking Talk - Woodworkers Forum
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post #1 of 30 Old 05-01-2019, 08:10 PM Thread Starter
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Maximum span of laminated beam

I'm helping a friend design (and build) a pergola. The only load on it will be the cross beams and runners, so it's not like theres a floor load or like that. We're hoping to have just four supported corners. the long span would be about 30'. Is there a laminated beam that can do that span, considering the load? (or lack thereof)
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post #2 of 30 Old 05-01-2019, 08:47 PM
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Go to a supplier of the beams with a sketch

You are only considering the static loads. What about the dynamic loads of many people moving about and their body weight? If I recall .... there's a 40 lbs per sq ft minimum for floor loads on decks:
https://www.google.com/search?client...oads+for+decks

Then an additional 10 lbs per sq ft for the deck material itself for a total of 50 lbs per sq ft.

As far as the 30 ft span, I'd use a center support which would not only make the beam size smaller, but would reduce the cost IF ... and that's a big IF you can even span 30 ft?
http://www.aitc-glulam.org/pdf/Capacity/DF_27.PDF

Better to have it "engineered" by someone in the business. JMO

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 #3 of 30 Old 05-01-2019, 09:01 PM
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Quote:
Originally Posted by Quickstep View Post
I'm helping a friend design (and build) a pergola. The only load on it will be the cross beams and runners, so it's not like theres a floor load or like that. We're hoping to have just four supported corners. the long span would be about 30'. Is there a laminated beam that can do that span, considering the load? (or lack thereof)
30' is a awful long span for wood. I believe I would use a steel beam and laminate wood over it.
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post #4 of 30 Old 05-01-2019, 10:00 PM
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This might help, I suspect even for the limited load you describe, that a 30' beam is going to be pretty large, and really heavy.

http://www.aitc-glulam.org/substitution.asp
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post #5 of 30 Old 05-01-2019, 10:39 PM
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Doesn't have to be a "Lam" at all...

Quote:
Originally Posted by Quickstep View Post
I'm helping a friend design (and build) a pergola. The only load on it will be the cross beams and runners, so it's not like theres a floor load or like that. We're hoping to have just four supported corners. the long span would be about 30'. Is there a laminated beam that can do that span, considering the load? (or lack thereof)
Spanning 30' feet is common practice with just simple green timbers...so a Lam has no issue at all spanning 30', 60', or even 90' and 120'...

Call your distributor for a "span chart" for the brand your seeking or reach-out to a professional that does timber framing and/or post and beam work like this...We do it all the time for a living...Nothing unusual about your span or the request....

Good Luck,

j

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post #6 of 30 Old 05-01-2019, 10:44 PM
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If your buddy is really set on only 4 posts then maybe some type of truss might be more appropriate, hopefully Jay will chime in, this sounds like it would be right up his alley.

Edit

Jay, you got in ahead of me.
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post #7 of 30 Old 05-01-2019, 11:29 PM
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Guys, it's a pergola .....

Quote:
Originally Posted by Quickstep View Post
I'm helping a friend design (and build) a pergola. The only load on it will be the cross beams and runners, so it's not like theres a floor load or like that. We're hoping to have just four supported corners. the long span would be about 30'. Is there a laminated beam that can do that span, considering the load? (or lack thereof)

I don't know why a 30 ft span is needed on a pergola, but if that's the case, it's gonna be expensive. The timbers or glu lams will be a major contributor to the cost. That's why I suggested having a center support to cut the span in half and reduce the size of the beams..... it's just more cost effective. Two more supports, probably less then $100.00 depending on the construction methods.


So why the 30 ft span?

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 #8 of 30 Old 05-01-2019, 11:42 PM
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Quote:
Originally Posted by woodnthings View Post
I don't know why a 30 ft span is needed on a pergola, but if that's the case, it's gonna be expensive. The timbers or glu lams will be a major contributor to the cost. That's why I suggested having a center support to cut the span in half and reduce the size of the beams..... it's just more cost effective. Two more supports, probably less then $100.00 depending on the construction methods.


So why the 30 ft span?
Well...I'll will take for the OP that the want 30' for the given aesthetics that I span 30' on many projects. Its stunning looking when done well...If you know what your doing...

As to cost, I would suggest that unless you actually do this work your guessing at best at what the cost is or...isn't.

So your "cost effective" is not true at all...not by a long shot!!!...since the parameters of the project have already been shared as being...30'

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post #9 of 30 Old 05-02-2019, 12:00 AM
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Cost effective by cutting the length in half?

Quote:
Originally Posted by Jay C. White Cloud View Post
Well...I'll will take for the OP that the want 30' for the given aesthetics that I span 30' on many projects. Its stunning looking when done well...If you know what your doing...

As to cost, I would suggest that unless you actually do this work your guessing at best at what the cost is or...isn't.

So your "cost effective" is not true at all...not by a long shot!!!...since the parameters of the project have already been shared as being...30'

So, you don't think two 15 ft beams will be less expensive than one 30 ft? We do not know if the 30ft span is a "locked in" requirement? .... we are just assuming. That's why I asked "Why a 30ft span?" If you are buying beams "over the counter" as opposed to having access to a sawmill, probably the cost will be greater, you agree? There are a lot of unknowns here before we start the bickering. I'm sure you have all the answers, as always.
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post #10 of 30 Old 05-02-2019, 12:05 AM
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Another issue is cross winds. That is a lot of stress on four posts. I doubt if it would hold up to a severe storm. What is the width of this structure?
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post #11 of 30 Old 05-02-2019, 12:43 AM
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Quote:
Originally Posted by woodnthings View Post
So, you don't think two 15 ft beams will be less expensive than one 30 ft? We do not know if the 30ft span is a "locked in" requirement? .... we are just assuming. That's why I asked "Why a 30ft span?" If you are buying beams "over the counter" as opposed to having access to a sawmill, probably the cost will be greater, you agree? There are a lot of unknowns here before we start the bickering. I'm sure you have all the answers, as always.
First, we are off topic already, and the post thread hasn't even got started...This is just not why I come here...so unless the OP (Quickstep) asks me a specific question, you and Steve can be the "experts" you both seem to want to be on this post thread too...

Respectfully Woodnthings...I'm not the one that posted first and immediately offered the advise of changing the OP's goal set...that would be you...

As to "all the answers"...not at all, but often I do have more experience that you do. I won't apologize for that or the 40 years worth of working experience to get it. I don't post an "opinion" on ever conversation like some here, only the ones I think I can actually be helpful on and actually have reputable experience in...Maybe it would be nice if others tried that???

The project parameters are a 30' span...That's the help being sought out...not suggestions to change it...At least not until the OP asks for alternate suggestions that is...???

Your not going to ever try to purchase 30 foot beam "over the counter," that is a silly to use as a comparative. Its going to be spec'd specific for most major project and if a DIYer is doing it they will seek the guidance that Quickstep has. An alternative to the 30' laminated beam seems the only likely germane and aesthetically matching alternative...not added posts, less span distance or steel...

So, no...a 15' beam is not always (quite often actually) the most cost effective method at all...and why we often eliminate posts where we can...unless following a design spec., historical context, or aesthetic mandate...

The BF (board footage) may be less for the given 15' beam, plus the cost for hardware or joinery to connect it to another 15' beam...PLUS the point load cost of the plinth assembly under the added post...PLUS!!!...the BF of the post now added to the cost, and the time/cost of cutting the joinery to now connect this to the two short beams...and most likely (if well built and designed) the added cost of a corbel assembly...I could add more but the point is made...

Skill set of the OP (without some help) is the only primary mitigating condition of any note in all this that would remotely give me pause on approaching this as an actual timber frame...or...the OP just not liking that look (some don't) or want to take the time?

The project parameters are as posted by the OP, that being...30'...that is the help that is being sought out, at least until the OP chooses to change it, so that's where our help is best offered...I'm done Quickstep...take the advise that best fits your needs...I'll help if you want it? If not, good luck and I look forward to seeing photos of the project...

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Last edited by Jay C. White Cloud; 05-02-2019 at 12:49 AM.
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post #12 of 30 Old 05-02-2019, 12:47 AM
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Originally Posted by Steve Neul View Post
Another issue is cross winds. That is a lot of stress on four posts. I doubt if it would hold up to a severe storm. What is the width of this structure?
Width, is give already if it a true pergola...30'...since most (not all) of these structures are typically (historically) square in geometry...

"Cross winds" (aka uplift) is not an issue at all for four posts...IF...its designed properly...and sized accordingly...

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post #13 of 30 Old 05-02-2019, 01:33 AM
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I would suggest that you find a local licensed, bonded, insured and experienced contractor that can help you out.

If you want to do the work yourself, then at least contract with a local licensed structural engineer to produce the necessary construction drawings. Every state has licensed structural engineers. They will have P.E. (Professional Engineer) after their name. Here is a link to finding a structural engineer in California https://www.seaoc.org/page/find_a_se

I suggest that you find a Structural Engineer that is a sole owner of their company. They are going to be more reasonable in cost and responsive in results than some engineering firm that has multiple engineers on staff with lots of overhead cost. The structural engineer that I have hired for multiple projects, works with his father and grandfather who are both licensed structural engineers.

You should be able to specify your requirements to the structural engineer and get complete engineering drawings. The drawings can be submitted to get a building permit (if you need one). The drawings should be detailed enough for you to construct the structure, if you have some basic construction experience. You will also be able to take the drawings to your local lumber yard and they will provide you all the specified materials as a package.

There is a lot more that goes into engineering a sound structure than just the span. The geographical location makes a big difference. Is your pergola being designed for a snow load? earthquake? high winds? etc. What about the footers for the four posts? It may cost you $1000 for the Structural Engineering drawings, but it is probably cheaper than being sued when your 30' pergola falls on someone and injures them.

Eric
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post #14 of 30 Old 05-02-2019, 03:06 AM
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Another issue is weight .....

You will need either a fork lift, crane or a band of hearty workers to move any structural member 30 ft in length. The last steel I beam I placed into my garage addition weighed 1300 lbs and I used a tractor with forks to lift it the 11 ft onto the support posts. I have used steel beams in 7 different locations during the 2 remodels and the garage addition and getting them into place was always a challenge. The pergola will probably be much closer to grade than in my situation.

Just letting you know in advance.

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 #15 of 30 Old 05-02-2019, 07:05 AM
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check you local codes. where once we could build about anything with little more than a permit, now requires engineered drawings and inspections. often your code enforcement officer can aid in what you need to do. you are right to seek out information.


fwiw, I believe your plan is very do-able if done correctly. a laminated beam will easily span you distance - but doesn't have a nice look unless you are painting it. a wooden beam will have to be larger in thicknesses to accomplish the same span, but will look nicer.


when I built my house I installed a 4" x 12" x 50' lam, 3 of us put in place.
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post #16 of 30 Old 05-02-2019, 08:25 AM
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Is there a drawing? The pictures I'm looking at don't have a long support beam, they have beams connecting the corner posts.
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post #17 of 30 Old 05-02-2019, 08:28 AM
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Quote:
Originally Posted by Jay C. White Cloud View Post
Width, is give already if it a true pergola...30'...since most (not all) of these structures are typically (historically) square in geometry...

"Cross winds" (aka uplift) is not an issue at all for four posts...IF...its designed properly...and sized accordingly...
The width could be anything, is why I asked. The structure may be better off structurally and aesthetically with more posts and perhaps trusses instead of a 30' beam. It sounds like quickstep is just in the beginning stages of the design so he is the one asking for opinions.

I don't see uplift as a problem with a pergola, it's direct cross winds. In the right direction it could be sufficient to break off only four posts.
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post #18 of 30 Old 05-02-2019, 12:29 PM
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Looking for long beams online I stumbled across this rendering of a structure that would seem to fit in the 30' range, interesting concept:
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post #19 of 30 Old 05-02-2019, 12:48 PM Thread Starter
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Is there a drawing? The pictures I'm looking at don't have a long support beam, they have beams connecting the corner posts.
Thanks for supplying the drawing. That's pretty much what we're trying to design and the beams I'm talking about will connect the four corner posts. The long dimension is about 30', the short dimension is about 20'. The reason we're trying to avoid posts in-between is that the pergola is over a stone patio which we don't want to cut to dig footers.
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post #20 of 30 Old 05-02-2019, 01:31 PM
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long VS short dimension?

Is the shape a rectangle? With the short dimension is 20 ft and the long dimension 30 ft? So, my bad, the only "load" is the additional structure.
Honestly, I would use sawmill beams and the rough sawn look will add to the character. Search out a local sawyer ... Craig's List or the



https://woodmizer.com/us/Services/Find-a-Local-Sawyer


site has listings of owners who saw privately. They may also sell their lumber

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; 05-02-2019 at 02:44 PM.
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