Maximum span of laminated beam - Page 2 - Woodworking Talk - Woodworkers Forum
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post #21 of 30 Old 05-02-2019, 01:53 PM
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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.

O.k. I understand better now. I had thought that there would be one long beam.
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post #22 of 30 Old 05-02-2019, 02:01 PM
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You might not like the appearance of the pergola without center legs. It would be more like this.
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post #23 of 30 Old 05-02-2019, 02:17 PM
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Some guys will do anything to prove a point, think the proportions would be more like this:
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post #24 of 30 Old 05-02-2019, 05:59 PM
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Some guys will do anything to prove a point, think the proportions would be more like this:
I agree it didn't come out very good. The photoshop software was acting up and I couldn't fix it without starting over.
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post #25 of 30 Old 05-02-2019, 06:47 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:
Hi Frank,

Good guess...

That was a second concept draft when it went to the State of Wisconsin on behalf of the Farmers Market Group of Menomonie, Wisconsin for its pre PE approval. It has been slowly moving toward the first page on Google Images when folks look for Pavilions, Pergola, and related structures...

This Pavilion does indeed spans ~30' wide between posts (37' drip edge to drip edge of eave) Then 20' between bay posts. This is approximate as its built in metric. Total length is over 147'. There are photo of the progress at:

Menomonie Farmers Market Pavilion.

One bay area is the size of Quicksteps proposed Pergola project...

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post #26 of 30 Old 05-02-2019, 06:50 PM
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Quote:
Originally Posted by Quickstep View Post
...That's pretty much what we're trying to design and the beams I'm talking about will connect the four corner posts...
Again, totally plausible and not unusual at all to span these distances...

Quote:
Originally Posted by Quickstep View Post
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.
That is not only a plausible reason, but also a common one as well when doing a "retro" design for pre-existing work that now is to be covered...

I can offer that your idea of four post are more than achievable, yet you can also set intermittent plinth stones directly on the patios surface as well between the primary corners if that does appeal to your design aesthetic? There are several ways of doing this if interested...

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post #27 of 30 Old 05-03-2019, 12:20 PM
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Quickstep -

be aware that the pavilion design is actually a truss construction - which is not the same as a beam supported only at the ends - and the forever spans idea is not applicable to the pergola design.

first you need to determine the dead load on the span. those 20 ft 'shade rails' will have weight - probably not the nominal ?x2 type framing - the aesthetics of a structure that large may need ?x3 or ?x4 rails. they will have measurable weight. a 20' span will require 10"-12" depth.

any intent to grow vines on the pergola? with age vine stems can get quite large. stems+leaves+rain will add more weight.

the glued up lam beam is a solution - the local box store will not carry xx" by 32 ft framing lumber.
a wood clad steel beam is also a solution - the cladding needs to be well thought out & executed or water will get to the steel - causing rust on the beam and stains on the stones.

regardless, a structure of this size with the mass supported, you really should get a structural engineer to check the design. the beam people will help size things - but they may not sell you one without a sealed drawing.
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post #28 of 30 Old 05-03-2019, 02:21 PM
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On any structure that people are going to be in, on or under it is always a good idea to to have the plans approved. Recently there was a terrible accident very close to home where a deck collapsed at a wedding reception, several people were seriously injured. This was a commercial establishment and the liability investigation is still ongoing, needless to say the wedding was not the joyous occasion they had hoped for.

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post #29 of 30 Old 05-05-2019, 12:31 AM
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Maximum span of laminated beam

Maximum span is up to manufacturer, but realistically speaking there are limits. For example I've never seen specs suitable for bridging some of the mouths holding forth on WWT under their loads.
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post #30 of 30 Old 05-10-2019, 01:04 AM
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Hiring an engineer is the rightest, bestest comment here. Do it. You need a proper structural system, including foundations.

Oh yeah, once you exit the realm of “nominal lumber” the price accelerates for every inch in every dimension faster than the inches add up — due to the rarity of ever larger timbers.
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