Oregon State University

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Ph.D. Dissertation Defense – Qiang Li

Investigation of Drilled Shafts under Axial, Lateral, and Torsional Loading

Tuesday, November 21, 2017 1:45 PM - 4:30 PM

Investigation of Drilled Shafts under Axial, Lateral, and Torsional Loading

Student: Qiang Li 

Advisor: Armin W. Stuedlein 

Abstract: High-strength steel reinforcement and permanent steel casing may be used to mitigate the concreting concern owing to the use of large amount of steel reinforcement in drilled shaft foundations. However, the comparison of axial and lateral load transfer between drilled shafts with and without permanent steel casing and high-strength reinforcement has not been previously investigated, raising questions regarding the suitability of existing analytical approaches for the evaluation of axial and lateral load transfer. In addition, deep foundations may need to resist torsional loads, resulting from wind loading on traffic sign and signal pole structures, or seismic loading on curved or skewed bridges. However, the understanding of the actual resistance to torsion provided by deep foundation elements is not well established. Six full-scale test shafts with various composite cross-sections were instrumented and installed at the Oregon State University (OSU) Geotechnical Engineering Field Research Site to investigate the load transfer of drilled shafts under axial, lateral, and torsional loading. Empirical load transfer models (i.e., t-z, q-z, p-y, τ-Δ curves) were back-calculated, based on which reginal-specific axial and lateral load transfer models and general torsional load transfer models were proposed. The effects of permanent casing on axial load transfer were summarized 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 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. To facilitate the serviceability and ultimate limit state design of geometrically-variable deep foundations constructed in multi-layered soils, a torsional load transfer method was presented using a finite difference model (FDM) framework.

Kearney Hall (campus map)
Michelle McAllaster
michelle.mcallaster at oregonstate.edu
Sch of Civil/Constr Engr
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