CONTINUING INVESTIGATION OF STRAND SLIPPAGE IN 24 INCH OCTAGONAL PRESTRESSED CONCRETE PILES

The objective of the current research is to investigate the problem of excessive slippage in prestressed piles. From the measurements taken in the field, it is apparent that the problem of excessive initial strand slip is not limited to the 24 inch octagonal piles. The problem is independent of pile shape and size. The slippage is evident in piles of different manufacturers in different states in the Southeast. Excessive slippage was found in both the top and bottom of the cross-section of the piles, although the top portion of the cross-section generally exhibited higher initial slip. This leads to the conclusion that the problem is considerably more widespread and systematic than what was originally reported. Several preventive measures can be adopted to reduce the excessive strand slippage observed. These preventive measures include: a) use of higher strength concrete, b) gradual release of prestress, with an optimal release sequence, c) assess the condition of the strands prior to installation to insure lack of contamination by oils, d) proper concrete mix design to reduce the "Top Bar Effects", e) use of minimum vibration to insure consolidation. The strand slippage measured at the three prestressed plants in the Southeast is considerably higher than the allowable slippage and is expected to have deleterious effects on the pile performance. If the strand slip theory is adopted, the strand development length increases substantially due to the excessive strand slippage. The ultimate strength of the pile is reduced in the development length region making the safety of the pile questionable. Protection against cracking is very important for the installation and durability of prestressed piles. However, for piles that exhibit excessive and eccentric slippage, cracking is possible during lifting, transportation, and installation. Such results suggest that the strand slippage measurements must be made mandatory for all pile manufacturers. Piles that exhibit strand slippage more that the allowable should be rejected.

  • Corporate Authors:

    University of South Carolina, Columbia

    Department of Civil and Environmental Engineering, 300 South Main Street
    Columbia, SC  United States  29208

    South Carolina Department of Transportation

    P.O. Box 191
    Columbia, SC  United States  29202

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Authors:
    • Petrou, M F
    • Joiner, W S
  • Publication Date: 1996-5

Language

  • English

Media Info

  • Features: Appendices; Figures; References; Tables;
  • Pagination: 152 p.

Subject/Index Terms

Filing Info

  • Accession Number: 00725535
  • Record Type: Publication
  • Report/Paper Numbers: Final Report, FHWA-SC-96-04
  • Contract Numbers: SPR 573
  • Files: TRIS, USDOT, STATEDOT
  • Created Date: Sep 6 1996 12:00AM