Curved Glulam Beams 1

[smik]

I am looking for some information on designing and specifying curved glulam beams. The particular case that I am looking at is for roof construction of 20' span w/ a 50' radius and a high snow load.
Can anyone point me in the direction of some good design examples or curved glulam information?

 

[Kenbob]

First stop is to read AITC 's Timber Construction Manual, 4th edition (Publisher - Wiley Interscience)Chapter 5, sections 5.11 Curved Members and 5.12 Curved Beams. These chapters lay out the basic design paramaters and considerations and give you a couple of design examples to follow along.

The discussion in AITC however does avoid mention of one consequence of using a curved beam and that is the thrust created at the ends of the beam as it deflects or "flattens". Similar tendencies may be observed when using scisssors trusses. The effect this has on the structure depends alot on the ability of the bearing support to resist and/or tolerate thrust.

Your beam has a "rise" of about 12.125" at the center. Under an approximate 1" downward vertical deflection at the center, each end bearing of the beam would move outward about 0.10" if the bearing was on a horizontal "roller" or frictionless vertical support.

If the beam is for a bridge and supported on a pier, often one end of the beam will be designed to accomodate the thrust by use of a sliding type bearing on top of the pier. If the beam is supported on an elevated wall and is in many cases used to "braced" the wall. i.e., connected so that it moves with the wall, the wall design must accept this movement. The amount of movement can be contolled by minimizing the vertical deflection of the beam or altering other design parameters.