Some of the most frequently seen truss structures are bridges.
Strong and easy to build, truss bridges appear in a variety of shapes
and sizes, depending on their use. A common type of truss bridge,
called a Warren truss, is shown in Figure 4 with a photo of a real
railroad bridge. The volume above the deck (the surface along
which vehicles pass) was kept clear in this example by using constraints to limit the movement of the free joints to vertical planes.
The initial guess to generate this bridge was created automatically from thirty user-specified points (the loads and anchors),
shown in Figure 3. From this description of the problem, the system
automatically added 22 free joints (one above each load point) and
connected each of these to their eight nearest neighbors, resulting in
a problem with 228 variables (22 free points and 163 beams)