Strength of Fiberglass/composite Repairs

Hands up all those who have seen a solid four inch square composite beam!

 

I refer everyone back to the original intent of the question. The OP wants to know if a glass repair can be as strong as full construction. There were two scenarios being considered, one was the butt to butt strength of a resin only rejoining and two was the necessity of interlacing the glass fibers.

It was not specified the solid or hollow construction, but either way, a butt to butt resin re-gluing will be inadequate.

However, for a truly strong repair, the typical techniques work very well and that involves getting as close as possible to the original interlaced layup of the cloth. A long tapered series of joins and a good final wrap that overlaps will give a repaired beam, either as a hollow tube or a a solid beam, something very close to the original construction. I don't think it will be as strong as the original without significant reconstruction, but it will be pretty close.

 

A hollow square fg "tube" would be a prime candidate for a "sleeve", far more robust, and solves a few construction problems.