Seismic retrofit of bridge steel truss pier anchorage connections

In assessments of the seismic adequacy of existing steel bridges, the anchorage of steel truss piers to their foundations often has insufficient strength to resist seismic demands. Many other non-ductile failure locations may also exist along the seismic load path that cannot provide adequate seismic performance. Although strengthening is an option, this approach may only transfer damage to another location. An alternative solution could be to release the anchorage connection, allowing development of a rocking bridge pier system. The retrofit solution proposed here, allows this rocking mechanism to develop, but complements it by adding passive energy dissipation devices across the anchorage interface to control the rocking response. Specially detailed, hysteretic energy dissipating elements (unbonded braces) act as ductile structural "fuses" in this application. An inherent re-centering capability is also possible. This paper investigates the dynamic characteristics of the above proposed controlled rocking/energy dissipation system with focus on design implications. Non-linear response history analyses presented here demonstrate the effectiveness and potential benefits of the proposed retrofit solution.