Crosswinds and bridge stability
The hypothesis that the bridge with minimal covering at the sides will be the least affected by crosswinds is proven to be true.
Building longer suspended bridges makes them more vulnerable to crosswinds and structural failures. An example is the Tacoma Bridge along State Route 16, which was opened on June 1, 1940 which collapsed 4 months later due to strong winds.
This science fair project can also be repeated with larger sized model bridges of materials (eg. aluminium, cast iron) to understand how the density and weight of the materials used to construct the bridge affects its ability to withstand high speed winds.
This experiment can also be repeated using varying wind speeds, or by simulating earthquakes.
Procedures for bridge construction - http://www.ehow.com/how-does_5300825_procedure-bridge-construction.html
Bridge - http://en.wikipedia.org/wiki/Bridge
Basic safety requirements