TRANSFER AND DEVELOPMENT LENGTH AND PRESTRESS LOSSES IN ULTRA-HIGH PERFORMANCE CONCRETE BEAMS

摘要

Results from a project that measured the transfer and development length and prestress lossesof beams cast with ultra-high performance concrete (UHPC) are presented. Seven beamsmeasuring 6.5 in. by 12 in. by 18 ft. were cast. The beams had compressive strengths thatranged from approximately 27 ksi to 29 ksi. The results are compared with the calculatedvalues derived from the American Association of State Highway and TransportationOfficials' Load and Resistance Factor Design (AASHTO LRFD) bridge designspecifications, National Cooperative Highway Research Program (NCHRP) Report 603, andthe University of New South Wales' (UNSW) design guidelines for prestressed UHPCbeams. The research findings indicate that measured transfer and development lengths areshorter than those predicted using the various design guidelines and recommendationsdeveloped for conventional concrete and high-strength concrete. However, measuredtransfer lengths correlate well with those predicted using the NCHRP 603 (neglecting f'climitations) and the University of New South Wales recommendations and guidelines. TheAASHTO LRFD specifications overestimated transfer length and development length andprestress losses (refined method) by approximately 50 percent. The data also show that thecontribution of creep and shrinkage in prestress losses is minimal.