Perp Frames torquing

Hello! I'm starting using Grasshopper and I don't seem to understand almost any discussion about the same issue, so I hope you can tell me a solution to my problem.

Here is what I have. I'm creating a curved roof and it has a reticule so it's basically a truss structure. Each curve of this reticule generates 2 rectangular pipes above it, and here is where the problem begins... For some reason there are some curves (the ones at Y-axis in the image below) that are torquing at some points, making this 2 pipes going in the X axis instead of the Z axis.

I would like to have all the pipes in the same direction (z axis) or at least in perpendicular to the surface of the roof.

Thank you.