Hi, I have the structure below which, under solicitations, is bending a bit towards the direction of the red arrows.
Pipes are 40mm diameter.
I was thinking about moulding two half pipes composed mostly of several layers of unidirectional carbon tape and then glue with mma the half pipe to the existing pipes (along the orange lines).
The layup I am thinking is 10x layers of 50mm wide 650gm2 carbon unidirectional tape, alternated with some 50mm wide plain carbon tape.

What do you think about the idea and the layup schedule?

Also, maybe adding a 2 mm pvc core in between would help? I am just worried that the shear force could cause the two carbon frames to slip on the pvc core, so maybe a not cored layup would be better?

If you add plates to the marked plane on both sides of the structure, and bolt them every few inches the stiffness should improve quite much. if you only find shorter plates you might just cover the middle area around the thinnest section.