Creating the ropes for a suspension bridge

Problem description

A suspension bridge has many parallel ropes. The number is often to high to fiddle around and creating each single rope by hand. So we need some automation. The main problem on this is, the ropes have different lengths.

Base structure

The main suspension cable and the track are described as NURBS. The two pylons here are simply analytic cubes and simply works as placeholders.

The base layout of the structure. Simply NURBS

Creation process

Now create our master vertical suspender cable. It should be a little bit longer than the maximum distance between the track and the main suspension rope and aligned at the bottom with the track NURBS. Placed where the first vertical suspension rope should appear.

Created a vertical NURBS as a base Vertical Suspender Cable

Now create a Rotator inside a new Level and put in the MasterVerticalSuspenderRope and a Link of the track line into the Rotator. The ordering is important:

  1. MasterVerticalSuspenderRope
  2. link (track line)

No open the Spec tab of the attributes window on the Rotator. Set the rotation angles to zero. Increase the Count for the U direction to something like 24, depending on the numbers of ropes you wish. Move the translation to 1 and activate the construction. Now fine tune the translation so the last vertical ropes is at the wanted position shortly before the second pylon.

The 24 vertical suspender ropes created.

Now select the MasterVerticalSuspenderRope and activate the visibility in the rendering process and do test render. Same for the main suspension cable. Give the main cable a bigger radius than the small cables.


Duplicate the main suspension cable and add a NURBS (a polygonal is enough) to it and combine, so you have a closed NURBS. It must be a little bit higher than the vertical cables.

NURBS to create the cutting object.

Then simply extrude with hard edges. Then move it a little bit to the back so the top of the vertical ropes is just inside. Put the Extrude and the whole Rotator in a new Level. Set this Level to AND, the Extrude to Solid Surface and to inverted volume. Ready to render:

The final image.