Simplified Inelastic Design of Steel Girder Bridges

Past and present building and bridge specifications for inelastic design are discussed. The present inelastic bridge specifications apply only to compact girders and specify the mechanism method for satisfying the strength limit state. The theoretical inelastic behavior of noncompact girders subjected to moving loads is described. If these loads exceed the shakedown load, which is generally below the ultimate load predicted by the mechanism method, permanent deflections progressively increase without limit. New inelastic procedures are proposed for checking the strength and permanentdeflection limit states used in the LRFD bridge specifications. The strength check is based on the shakedown load and the permanent-deflection check is made by limiting positivebending stresses after yielding has occurred at interior supports and caused inelastic redistribution of moments. The proposed procedures apply to both compact and noncompact continuous-span girders and are much simpler than present procedures.