Karamba model output

I’ve createad a Karamba model in Grasshopper using a series of lines that are converted into beam elements. However, when this plots in Rhino, these are beams with cross sections rather than surfaces, so it isn’t possible to export an stl file with the outputted Karamba model geometry. Does anyone know a way of saving this file in the stl format (so it can be 3D printed).

Thanks for any help!