Shakedown Limit State of Compact Steel Girder Bridges

Using current American Association of State Highway and Transportation Officials (AASHTO) allowable stress or load‐factor bridge‐rating methods, many of the nation's bridges are deficient in their load‐carrying capacities. These evaluation methods are direct extensions of their respective design procedures and are inherently conservative for many of the bridges in existence. Recently, reliability‐based procedures have been developed to better estimate actual site‐specific bridge‐loading and resistance characteristics. For compact bridges, the ultimate limit state for these procedures is the formation of a flexural hinge. However, slab‐on‐steel girder bridges are highly redundant structures and show a large reserve capacity in the postelastic range. This paper presents models that extend these reliability‐based procedures to analyze bridge systems for inelastic ultimate limit states. A system‐shakedown limit state is presented where, after some initial inelastic deformations, the deflections stabilize and future loadings are resisted by pure elastic action. An example bridge is analyzed for the first hinge, shakedown, and plastic‐collapse limit states to illustrate the system models.