arched joist design

A Gothic style arch... have you considered using 3/4" or 1/2" D.Fir strips laminated, not using LVL segments? Depending on the loads, you may want 6-10 laminations glued using a quality waterproof adhesive.

Dik

Douglas-Fir with 3/4" laminations can be laid up with a 12'-4" radous. As dik indicated by going to smaller laminations you may be able to achieve a lower radius. With Souther Pine 5/8" lamination you should be able to get down to about a 9' radius.

I would first analyze the arch following the methods given in the AITC Manual or by using a computer program. Then I would contact the LVL manufacturer for advice about using the LVL material.

The arch will experience axial load, bending moment and shear.
How that effects the LVL I am not sure. Probably what you will find is that if you cut a curve into an LVL, that it will viod the warranty.

However you might find the LVL works great. With glulam arches a major concern is radial tension or compression. Wood has vert low perpendicular to the grain allowable tension values.

RARSWC...

Where did you get information on radii for various species? I've designed many 'archrib' type frames and have set up spreadsheets for radial stresses and combined stresses and use RISA for analysis. Also set up spreadsheets for the various snow and wind loading conditions...

Dik

Just to clarify: Are you suggesting actually curving/bending the 3/4" d. fir strips, so I would be creating my own glulam? Or, are you suggesting cutting the radius out of 3/4" material and gluing them together. It seems to me the second option is just creating my own LVL, is it not?
Thanks?

Depending on your end conditions maybe your joist can be the classical compression only element.

What size LVL are you considering - how tall?? Say the height at the bearing is only 7'' but the middle is still 11 7/8.

Just analyze as a 1 3/4 x 7'' LVL and be conservative - bring it in at 75% or 80%. Check shear at ends

Making your own glulam.

Dik