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Barrel Vault Trusses

Barrel Vault Trusses

Barrel Vault Trusses

(OP)
The problem with this type of truss is the webs get messy or at least hard to predicate because of the interplay between the vault and the pitched roof above it. In an effort to better understand this type of roof/ceiling configuration I've created the matrix below:





High Res. PDF copy here:


http://design.medeek.com/resources/truss/BARREL_VAULT/BARRELVAULT_STUDY1.pdf


I am trying to predict the max. height of the vault given a specific roof pitch and and vault width to span ratio. Perhaps I am recreating the wheel and some architect, truss designer or truss engineer has devised a method to create the perfect barrel vault given a roof pitch and other criteria.


I would be interested in what other opinions are on this matter.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Barrel Vault Trusses

(OP)
Using a typical Barrel Vault 8/7+4 or 8/7+2 configuration I come up with the following triangulations. I'm sure there are other methods of configuring these webs but for the purposes of the plugin I think these solutions will suffice:



High Resolution PDF copy here:

http://design.medeek.com/resources/truss/BARREL_VA...

The goal with triangulation, in my opinion, is to make sure the panel length is more or less equalized for both top and bottom chords.

Based on this matrix I've been able to come up with a simple algorithm for the triangulation of this truss type. I'll admit the barrel vault truss is one handsome devil.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Barrel Vault Trusses

I've had some luck with making trusses out of sections of 2x12 and ripping them to a radius. But it tends to be expensive, and people usually don't want to pay for it.

RE: Barrel Vault Trusses

(OP)
I wouldn't suggest trying to fabricate these by hand, too much work and too much to go wrong. The typical client who requests a truss like this will probably care little about the price, it will be all about the look.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Barrel Vault Trusses

I'm not talking about making trusses by hand. I worked for 30 years in the building component business. I've designed about any kind of truss you can imagine.

RE: Barrel Vault Trusses

(OP)
I've noticed, examining some other barrel vault truss drawings, that the bottom chord segment at the top of the barrel vault is often shorter than the rest of the segments that make up the curved bottom chord. Is there any particular reason for this? I would prefer to arrange these segments so they are as similar in length as possible to better approximate the arc of the vault.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Barrel Vault Trusses

I have no idea why that segment should be shorter.

Maybe some of the guys designing the trusses aren't good with geometry & trig.

RE: Barrel Vault Trusses

(OP)

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Barrel Vault Trusses

I'm just trying to picture what a sheetrocker would do with that barrel vault. winky smile

Mike Halloran
Pembroke Pines, FL, USA

RE: Barrel Vault Trusses

(OP)
Two layers of 1/4" gypsum would probably be the way to go. Time consuming and expensive job.

A confused student is a good student.
Nathaniel P. Wilkerson, PE
www.medeek.com

RE: Barrel Vault Trusses

Why not take a flexible, continuous length of 1-by material, the same width as the bottom chord segmental members, and smoothly bend and fasten it into place under the bottom chord? Then you would at lease have a smoothly curving surface to work towards with the finished ceilings.
Dave

Thaidavid

RE: Barrel Vault Trusses

A batten is one way to smooth the curve, but it will still warp with time, and move when the gypsum is screwed to it.
I'd be inclined to use something wider than 2x4s as the bottom chords, maybe join them as an assembly and bandsaw the radius around an actual pin.
Then, instead of trying to laminate gypsum into a cylinder, I'd have some 1x stock milled with cove and bead edges, and plank the inside of the vault with them and a little glue.
Amd if I were going to that much trouble to make a nice smooth strong vault, I'd just varnish the wood instead of hiding it behind sheetrock.
... but that's me, and I don't have money for building custom homes anyway.

Mike Halloran
Pembroke Pines, FL, USA

RE: Barrel Vault Trusses

I'd give them a square box/tray or scissor vault at the bottom chords and let the framer fill in the barrel w/plywood gusset-nailer and battens. Too much to go wrong without a field modification. It rarely ends the why the designer thought it would -too many pretty pictures and not enough brains.

______________
MAP

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