Accession Number : AD0650329

Title :   EFFECTS OF LONG-TIME LOADS ON PRESTRESSED CONCRETE BEAMS.

Descriptive Note : Technical rept.,

Corporate Author : NAVAL CIVIL ENGINEERING LAB PORT HUENEME CALIF

Personal Author(s) : Breckenridge,R. A. ; Valent,P. J. ; Bugg,S. L.

Report Date : MAR 1967

Pagination or Media Count : 49

Abstract : Thirty post-tensioned concrete beams were loaded for 10 to 12 years, and changes in deflections, prestressing forces, and concrete strains were recorded. All of the beams were simply supported on a 40-foot span. Twenty-two of the beams were straight and had an I cross-section. Eight of these were prestressed with cables. The other fourteen were prestressed with high-strength steel bars, and eight of these beams were grouted after being post-tensioned. The twenty-two I-beams were subjected to loads varying in magnitude from dead load only to dead load plus 1.5 design live load. Eight of the beams had a gabled shape with a hollow-box cross section and were post-tensioned with wires running straight through. Six of these beams were uniformly loaded with concrete weights to provide four different loading conditions. The beams with no live loads continued to deflect upward for about 1 year. Their total camber was about 2.1 times their initial camber due to prestressing. The loaded beams continued to deflect downward for several years. In 6 1/2 years the I-beams had undergone about 94% of their total deflection due to live loads, and the hollow-box beams had reached their maximum. The maximum midpoint deflections due to live loads were from 2.2 to 2.8 times the initial deflections due to those loads. Loss of prestress was a function of the magnitude of the sustained loads. It was highest for beams with no live loads, reaching its maximum of 24% in 7 years.

Descriptors :   (*BEAMS(STRUCTURAL), *CONCRETE), (*CONSTRUCTION MATERIALS, *LOAD DISTRIBUTION), DEFLECTION, STEEL, RODS, STRAIN(MECHANICS), LOADS(FORCES), CRACKS, STRAIN(MECHANICS)

Subject Categories : Structural Engineering and Building Technology
      Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE