Another type of bridge, a cantilever truss, is shown in Figure 1.
As with the bridge shown in Figure 7, the cantilever bridge was
constrained to have no material above the deck, and the joints were
further constrained to move in vertical planes only. However, the
addition of a third set of anchor joints in the middle of the span has
significantly influenced the final design of this problem. This bridge
is shown with a real bridge of the same design: the Homestead High
Level Bridge in Pittsburgh, Pennsylvania.
The bridge in Figure 8 was generated with the same starting point
and the same objective function as that in Figure 1, but without
the “clear deck” and vertical-plane constraints. Removal of these
constraints has allowed the structure to converge to a significantly
different solution, called a through-deck geometry.