The requirements will depend on whose jurisdiiction the bridge is in. If it is only to support peds. and not at a school, it will likely be the city or the county and they may use the ICC or another Code depending on what part of the U.S. you are in. Pedestrian loading is likely to be 100 psf for LL.- a surcharge to account for children jumping as happened recently in South America.
If the ped. bridge is over a stream, it is necessary to provide anough clearance so that when the stream floods and debris comes down, it will not wash out. In addition there are wind forces and unbalanced loading to consider.
Stan Scholl, P.E.
Laguna Beach, CA