A post-tensioned prestressed concrete beam is to carry an intermittent live load of 1000 lb/ft and superimposed dead load of 500 lb/ft, in addition to its own weight, on a 40 ft simple span. Normal-density concrete will be used with design strength f. = 6000 psi. It is estimated that, at the time of transfer, the concrete will have attained 70 percent of f., or 4200 psi. Time-dependent losses may be assumed to be 15 percent of the initial prestress, giving an effectiveness ratio of 0.85. Determine the required concrete dimensions, magnitude of prestress force, and eccentricity of the steel centroid based on ACI stress limitations for a Class U beam, as given in Sections 19.4 and 19.5.
A post-tensioned prestressed concrete beam is to carry an intermittent live load of 1000 lb/ft and superimposed dead load of 500 lb/ft, in addition to its own weight, on a 40 ft simple span. Normal-density concrete will be used with design strength f. = 6000 psi. It is estimated that, at the time of transfer, the concrete will have attained 70 percent of f., or 4200 psi. Time-dependent losses may be assumed to be 15 percent of the initial prestress, giving an effectiveness ratio of 0.85. Determine the required concrete dimensions, magnitude of prestress force, and eccentricity of the steel centroid based on ACI stress limitations for a Class U beam, as given in Sections 19.4 and 19.5.
Chapter2: Loads On Structures
Section: Chapter Questions
Problem 1P
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Transcribed Image Text:A post-tensioned prestressed concrete
beam is to carry an intermittent live load of 1000 lb/ft and superimposed dead load of 500 lb/ft,
in addition to its own weight, on a 40 ft simple span. Normal-density concrete will be used with
design strength f. = 6000 psi. It is estimated that, at the time of transfer, the concrete will have
attained 70 percent of f., or 4200 psi. Time-dependent losses may be assumed to be 15 percent
of the initial prestress, giving an effectiveness ratio of 0.85. Determine the required concrete
dimensions, magnitude of prestress force, and eccentricity of the steel centroid based on ACI
stress limitations for a Class U beam, as given in Sections 19.4 and 19.5.
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