Supplemental system retrofit considerations for braced steel bridge piers

Braced piers of steel truss bridges having braces with latticed built-up cross-sections may suffer significant damage during earthquakes due to the buckling, rapid strength degradation, and fracture of the braces. One retrofit alternative for such a bridge pier is to supplement the existing structural system with a system of energy dissipation devices (or structural fuses) that will yield and dissipate energy prior to existing brace buckling. These devices depend on the global shear displacements of the pier to yield and dissipate energy. However, relatively tall and slender bridge piers are also subject to large overturning displacements. This paper investigates and quantifies the effectiveness of using supplemental systems relying on devices used to control pier shear displacements to retrofit braced steel bridge piers, including the effect of overturning displacements on the effective ductility of such systems. A closed form equation for the total ductility of the retrofit pier, as a function of the shear displacement ductility, is derived and expressed graphically. A simple preliminary design procedure that incorporates these effects is proposed and an example design is presented.