Towards Performance Based Design of Drilled Shafts-Article

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The study proposes a performance-based approach to drilled-shaft design that considers both load capacity and settlement while meeting Load and Resistance Factor Design (LRFD) requirements. It addresses a limitation of the commonly used Osterberg-cell (O-cell) load test: a single cell typically measures the full response of either side resistance or end bearing, but not both. This makes it difficult to construct a complete top load–displacement curve and assess resistance at a target settlement.<br /><br />Using load-test and site data for 24 drilled shafts from the DSHAFT database, the author developed a procedure to reconstruct the full curve by combining measured O-cell responses with analytical estimates and, where needed, extrapolations. The procedure covers three test scenarios: side resistance reaches its maximum first (Case A), end bearing reaches its maximum first (Case B), or neither component reaches its maximum during testing (Case C). Examples show how the method can estimate equivalent top loads at specified displacement limits.<br /><br />The reconstructed curves allow designers to select shaft resistance based on acceptable settlement rather than relying solely on a strength-based failure criterion. The approach may improve design economy and reliability, and it has been used to support preliminary LRFD resistance-factor calibration. However, the procedure’s uncertainty is difficult to assess because tests that independently measure both side resistance and end bearing are scarce. Further validation with such tests is recommended.

Keywords

drilled-shaft design

load-displacement curve

Osterberg-cell

load test reconstruction

side resistance

end bearing

settlement

LRFD

DSHAFT database

resistance factor calibration