In addition, Deb and Gulati illustrated that there existed
multiple different topologies with almost equal overall weight in
truss-structure design problems as the members in the ground
structure increase. In other words, they suggest that the resulting
solution of truss-structure optimization design problems becomes
‘‘multi-modal’’ with large number of truss members. Recently
another bio-inspired computation method, two-stage ant colony
optimization (ACO) scheme, was proposed by Luh and Lin [11] for
optimal design truss structures. Compared with the results derived
by Deb and Gulati [3], two-stage ant algorithm was observed to find
truss structures superior to one-stage genetic algorithms.