State Street Bridge: CFRP Composite Seismic Rehabilitation and Specifications

摘要

The State Street Bridge in Salt Lake City, was designed and built in 1965 according to the 1961 AASHO Specifications but the design did not consider earthquake-induced forces or displacements since wind loads governed the design. The bridge consists of four bents, each of which has four reinforced concrete columns and a bent cap supporting composite welded girders; the bents are supported on cast-in-place concrete piles and pile caps. A vulnerability analysis of the bridge was conducted and it was determined that the bridge had deficiencies in: (a) confinement of the column lap splice regions, (b) confinement of column plastic hinge zones, and (c) shear capacity of columns and cap beam-column joints. A seismic retrofit design was performed using Carbon Fiber Reinforced Polymer (CFRP) composites, which was implemented during the summer of 2000 and 2001 while the bridge was in service. The paper describes the design of the CFRP composite, which in addition to column jacketing, implemented a new "ankle wrap" for improving joint shear strength, and a new "U-strap" for improving anchorage of column bars; other rehabilitation measures included hinge restrainers. The paper also describes the specifications developed especially for the CFRP composite column jackets and the CFRP composite bent wrap; these included provisions for materials, minimum initial properties, required constructed thickness including an environmental durability reduction factor, surface preparation and finish coat requirements, as well as quality control and quality assurance provisions which included sampling and testing.