Unbraced Length of Arch 1

[GoCyclones]

I am doing some preliminary design work for a building with Glu-Lam arches (this is more of a general question which could apply to steel as well). The member would be continuously laterally braced by the roof for buckling about its weak axis. But what would I use for an unbraced length for buckling about its strong axis? I have been unable to find any references with recommendations. Any help would be appreciated.

 

[youngstructural]

You seem to be trying to design this as a beam, but it is (presumably, depending on the geometry) a compressive arch. Note the same animal, and the member should not have a buckling failure mode about the strong axis.

You need to look up timber arch construction... I'll try to lay my hand on a design procedure.

If you have other specific questions, post again.

Good luck,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[GoCyclones]

Thanks YS. I am looking at it as a beam-column, since depending on the loading, it will be in both bending and compression. I guess it makes sense that it will not fail in buckling about its strong axis because of the arch shape, but I am looking to get a better understanding of why.

So that means if it is fully braced about the weak-axis, I can use the full allowable compressive stress for design (not reduced for column buckling/stability effects, i.e. Cp = 1.0 for NDS design)?

 

[JStephen]

Unfortunately, the typical building codes are set up around straight members, and you're on your own when it comes to anything curved.

There is an equation for buckling of circular rings under uniform compressive loading. Try Roark's Formulas for Stress and Strain, I believe it's in there. He might even have some information on buckling of arches, but I've not looked for it. For steel members, the buckling of a circular ring is usually not the controlling factor. Bending due to nonsymmetric loading is.

 

[msquared48]

If you are looking at a Tudor style Arch, as with a church, the 1966 Edition of the AITC "Timber Construction Manual" has a very detailed design example of this procedure. If you can get your hands on a copy, look at pages 4-33 to 4-69. The same or similar examples could also be in later versions too.

Mike McCann
MMC Engineering

 

[RARWOOD]

You need to throughly understand the design of curved glulam members to tackle this type of problem. You want to follow Mike McCain's advice and review the TCM.

 

[MiketheEngineer]

Also check with the manufacturer - they can be most helpful in providing the engineering you need.