Adding material to existing steel stringer bridges has been commonly used as a strengthening method. For simple-span bridges, addition of material can include coverplating, creating composite action with the deck, or increasing transverse stiffness of the existing diaphragm system. For simple-span bridges, these methods may increase live-load ratings by as much as 30%, depending on span length. Continuous stringer bridges behave differently when stiffened because of the way stiffening affects the distribution of stress. Because continuous bridges are indeterminate in the transverse direction as well, selective longitudinal stiffening of the stringers and its effect on the whole structural system should be carefully evaluated. In some cases, addition of material to continuous stringers may be detrimental at unstiffened locations. If properly designed, selective longitudinal stiffening can be beneficial in strengthening other locations in the bridge by changing the stress distribution throughout the bridge. Fatigue-critical details associated with stiffening an existing stringer should be checked, because of possible detrimental effects.
Abstract