Location:;Highway 101 north of Santa Barbara, CA;Description:;The Arroyo Quemado Bridge, constructed in 1916, is an historic twin arch concrete structure, carrying the two southbound lanes of Highway 101. In 1999, Buckland & Taylor Ltd. won awards from both CELSOC and ACEC for their seismic retrofit of this bridge. ;Total Length including Approach spans: 125 m (411 ft);Main Span: Twin 33 m (109 ft) arch spans;Tower Height: Center tower 27 m (89 ft);Owner and Client:;State of California;Scope of Work:;The scope of work included assessment of the seismic performance of the structure in its current condition, evaluation of several retrofit strategies and preparation of the final detailed retrofit design. Constraints on the seismic strategy included respect for the historic and aesthetic qualities of the structure as well as the need to minimize environmental impact on the site. The final retrofit strategy was to keep the existing unretrofitted arch ribs essentially elastic by providing enhanced lateral and longitudinal restraint to the structure. This was achieved through the addition of piled restraints at the abutments, infill shear walls and tiedowns at the towers and a structural deck overlay. High ductility demands in some of the approach bents and spandrel columns were addressed by the provision of confinement.