An analytical study of precast, prestressed concrete girder spans using 0.7 in. strand

It has been proposed that 0.7 in. (17.8 mm) diameter prestressing strand be permitted for use in bridge girders. If 0.6 in. (15.2 mm) diameter strand is replaced on a one-to-one basis with 0.7 in. strand, the pretensioning force can be increased by 35%. When designs use 0.7 in. strands as well as high concrete strengths, longer-span prestressed concrete girders may be achieved. An extensive analytical study is presented to assess the maximum girder span lengths that can be achieved when using 0.6 and 0.7 in. strands. A parametric design study with 584 cases was conducted to examine the influence of girder shape and size on the potential benefits of using 0.7 in. strands. A detailed finite element analysis of some of the longer spans achieved was also conducted. The impacts of using 0.7 in. strands on end-region detailing requirements, prestress transfer, and handling and erection stability of long-span girders were examined. Girder span increases of up to 22% were achieved using 0.7 in. strand in place of 0.6 in. strand. The larger pretension forces affected end-region detailing and increased congestion, though all resulting requirements were constructible. The longer spans affected girder stability calculations, and some girder types required a wider top flange to meet stability-related limit states.