Effects of High Strength Steel Bars and Steel Casing on the Response of Drilled Shafts

The amount of steel reinforcement in drilled shaft foundations has increased over the past several decades to account for anticipated seismic hazards. Increased reinforcement may lead to a higher frequency of anomalies within shafts due to the increased difficulty for concrete to flow through reduced clearance between the reinforcement. High-strength steel reinforcement and permanent steel casing may be used to mitigate this concern. However, use of a lower steel area my serve to reduce flexural stiffness, and depending on the method of construction, steel casing may result in reduced axial load transfer to the surrounding soil. Thus, existing analytical approaches need to be evaluated for modern construction methods, and new approaches developed if necessary to ensure desired performance criteria are met. Four full-scale instrumented test shafts with various composite cross-sections were constructed to investigate load transfer under axial and lateral loads and the effect of high strength steel reinforcement and steel casing. Empirical, region-specific axial and lateral load transfer models were proposed for use with drilled shafts constructed in the Willamette Valley. The effects of permanent casing on axial load transfer were determined, and synthesized with existing observations to provide an up-to-date reference on the reductions expected based on construction sequencing and installation methods. The lateral responses of the test drilled shaft foundations indicated that the high-strength reinforcement could be used without detriment to the lateral performance; and that the shafts with permanent steel casing responded in a more resilient manner than uncased shafts at the same nominal diameter due to their significantly greater flexural rigidity.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 281p

Subject/Index Terms

Filing Info

  • Accession Number: 01659806
  • Record Type: Publication
  • Report/Paper Numbers: FHWA -OR -18- 09, SPR 765
  • Files: TRIS, ATRI, USDOT, STATEDOT
  • Created Date: Feb 1 2018 2:21PM