Overview of Earthquake Resisting System Design and Retrofit Strategy for Bridges in Illinois

Abstract

An overview of an earthquake resisting system (ERS) strategy for the design and retrofit of bridges in Illinois is presented in the paper. Initial development of this ERS strategy by the Illinois Dept. of Transportation (IDOT) began in mid-2005. It was initially implemented in late 2006 and revised in late 2007 to reflect increased design accelerations adopted into the American Association of State Highway and Transportation Official’s bridge design code and a new seismic bridge design guide specification in mid-2007. The primary objective of IDOT’s ERS strategy is to prevent span loss. This is achieved through three levels or tiers of seismic structural redundancy, which allow for certain levels of damage at planned locations in bridges. Controlled damage at strategic locations in structures allows for the mitigation of seismic energy. Sacrificial or fuse-like connections between superstructures and substructures, conservative beam support lengths, and plastic hinging at planned locations in substructures are the primary areas of focus for Levels 1–3 of seismic structural redundancy, respectively, in Illinois’ developed ERS strategy.