Abstract
The results of a comprehensive parametric study on prestress losses in prestressed and partially prestressed high strength concrete beams are reported. Attention is focused on the influence of the partial prestressing ratio (from no prestressing to full prestressing) and the compressive strength of concrete, from 6 ksi (41 MPa) up to 10 ksi (69 MPa). Different beam cross sections, representing building and bridge girders with various spans and spacings, were studied. Additional parameters investigated include the strength and type of prestressing steel (stress-relieved of low-relaxation), the yield strength of reinforcing steel, the relative humidity of the environment and curing conditions (steam- or moist-curing). Time-dependent prestress losses were computed through an accurate time-step analysis procedure, which was implemented in a computer program. Conclusions and recommendations are drawn for use in design practice. The results are applicable to pretensioned as well as post-tensioned members. Proposed design recommendations are suggested to replace current lump sum design tables suggested in the AASHTO Specifications and the ACI 343R-88 report on analysis and design of reinforced concrete bridge structures.
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