How Much Would an Unusual Beam Bend?

Depends on the weight of the sign. Is the triangle apex pointing up or down? Point down for strength. It sounds like it would be ok as long as the sign is not too heavy.

When calculating wood, it's not cut and dry like steel. Wood has many imperfections, and each piece of wood is unique. One small knot, or fracture in the grain of the wood can cause it to act in strange ways.

What is the weight of the sign?

What type of wood are you using for the beam?

Are you attaching the sign with two attachment points on the beam, or one on the tip of the beam?

I'm assuming this sign will hang over the heads of the customers and pedestrians walking down the sidewalk, so certain precautions should be taken to avoid a lawsuit. I would think a 4" Dia, 4' long triangular style beam should be ok for an average sign, and the amount of bending should be negligible. But this will depend on the sign you intend to hang on it. I wouldn't hand a 1/2" thick 36"x36" hunk of plate steel on it. But a nice Di-Bond sign, or plastic/fiberglass sign should be fine.

Generally I would figure out what will support the sign then at least double it.

The type of wood it crucial, crucial, also you need to have it treated correctly for UV. I made the error with white oak one time and completely ruined my project (porch glider), because of UV.

I've seem some basic strengths of materials for wood, where was that?? Oh yea, some excerpts here, strongest wood material red oak, followed closely by white oak, then hickory.. but there are too many variables to predict stain and breaking point.

Good Luck

Laby

Sorry, but you have too little info here to get a good evaluation by a structural engineer, whose business it is to calculate what you wish to learn. Go find one in the yellow pages, show him the actual objects you wish to use, and pay for about an hour of his time to calculate things like moments of inertia, stress distribution, and lifetime maintenance requirements.

As an alternative, construct a full-size replica of the set-up and load it with at least three times your expected design load. If it does not break or distort, go with it.

But even in the replica, Its quite hard to replicate the exact grain structure of the wood... thats why you need to triple the load to err on the safe side.

Yes, Carver is correct in saying there is too little information to provide an actual analysis of your project, from an engineering perspective.

But on the other hand, Your just hanging a sign right? Ther is no harm in complete overkill, just make all the extras look perty. Just DONT under build it.

A picture(s) worth?

American Wood councils span tables, calculators etc..

To even begin to answer your question, one would need to know whether the 3' long dimension is intended to be horizontal or vertical when installed. One would also need to know the weight of the sign, and details about the consrtuction of the beam. (I doubt it's a single piece of wood). Are you only interested in the deflection of the sign, or also the strength of the assembly. The building the assembly is attached to will also influence the amount of deflection. If it is attached (for example) to wood siding, the siding will flex and contribute to deflection of the sign. You might also want to consider wind loads. Once more details are known or assumed, the calculations are simple. Because there is an element of safety involved, you won't find many on this web site who ore willing to make assumptions about your problem.