The Efects of Long-Time Loads on Prestressed Concrete Hollow-Box Beams
Abstract
Tests were conducted on prestressed concrete hollow-box beams under loads of various magnitudes. Prestressed concrete beams suffer from certain time-dependent changes. They lose part of their initial prestress, their deflection increases, and the concrete shrinks and creeps. To obtain information on prestressed concrete hollow-box beams, 8 such beams were loaded for 4-1/2 years and changes in deflections, concrete strains, and prestressing forces were recorded. The beams were 42 ft. long, 33 in. deep, and 18 in. wide. They were simply supported on a 40-ft. span and uniformly loaded with concrete weights. Four different loading conditions were used. The loaded beams had an additional time-dependent deflection during the 28 days following loading approximately equal to the immediate elastic deflection at the time of loading. The beams with no live load continued to deflect upward. Measurements showed that the time-dependent strains in the concrete were greater than the immediate strains due to normal working stresses. The prestressing force data indicates that the unloaded beams experience a greater reduction of prestress than the loaded beams, that the first-year prestressing losses can be as high as 13%, and that in 4-1/2 years they can be as high as 22%.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 21, 1961
- Accession Number
- AD0267468
Entities
People
- R. A. Breckenridge
Organizations
- Naval Facilities Engineering Service Center