Transfer and Development Lengths and Prestress Losses in Ultra-High-Performance Concrete Beams

Results from a project that measured the transfer and development lengths and prestress losses of beams cast with ultra-high-performance concrete (UHPC) are presented. Seven beams measuring 6.5 x 12 x 18 ft were cast. The beams had compressive strengths that ranged from approximately 27 to 29 ksi. The results were compared with the calculated values derived from the AASHTO load and resistance factor design (AASHTO LRFD) bridge specifications, NCHRP Report 603, and the University of New South Wales design guidelines for prestressed UHPC beams. The research findings indicated that measured transfer and development lengths were shorter than those predicted with the use of the various design guidelines and recommendations developed for conventional concrete. However, measured transfer lengths correlated well with those predicted with NCHRP 603 (neglecting f'(d) limits) and University of New South Wales recommendations and guidelines. The AASHTO LRFD specifications overestimated transfer length, development length, and prestress losses (refined method) by approximately 50%. The data also showed that the contribution of creep and shrinkage in prestress losses was minimal.