Finding the right shape:
You can experiment with the shape of your design by trying different options in the West Point Bridge Designer Computer Aided Design (CAD) program.The CAD program can be downloaded from the Internet as freeware and is male ware free.
West Point Bridge Designer Link: http://bridgecontest.usma.edu/download.htm
A new bridge design with a span of 16m and no piers works very well to determine the rough shape of your bridge.
Faults of West Point Bridge Designer CAD program:
a) The competition loading harness does not fit through the sidewall of the bridge at the middle because of the placing of the joints in the CAD program at the level plane. That means you cannot use the design exactly as it is in the CAD program and have to adapt your design for the real bridge.
b)The software of the CAD program does not allow the structure to "sit" on supports beyond the abutments and the designer must make sure that at least 50mm of each side of the real structure is flat from the level plane downwards.
c)The bridge will only exhibit how it will perform if the truck used to represent a dynamic load on the CAD design is stopped in the middle of the bridge and the members in tension and compression are examined whilst there is a static force acting on the CAD design.
d)Double members in CAD can only be represented as members with double the material size thus a steel beam of 160mm must be changed to a steel beam of 320mm for the structure to behave realistically under test conditions.
