United States Department of Transportation
i
Implementation of AASHTO LRFD Design Specifications for Driven Piles
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2013-11-01
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[PDF-1.24 MB]
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Abstract:This report is intended to provide a technical resource for highway engineers responsible for the development of Load and Resistance Factor Design (LRFD) specifications for driven piles based on the 2012 AASHTO LRFD Bridge Design Specifications. It addresses many of the issues and problems that highway agencies face in implementing LRFD design for driven piles. First, the report describes the AASHTO LRFD design limit states for driven piles, the design information obtained by addressing these limit states, and the overall design process needed to address them. Next, the report describes with examples the design procedure required to address all the strength limit states for the axial compression resistance of a single pile: geotechnical, drivability, and structural. These limit states are considered to determine the maximum factored axial compression load that can be applied to the top of a pile, Qfmax. The geotechnical strength limit state is addressed by using both static analysis methods (e.g., the β-method) and field analysis methods (e.g., wave equation analysis) to determine the pile nominal bearing resistance at various depths and the pile length, L, needed to support a given factored axial compression load applied to the top of a pile, Qf. For the field analysis methods, a new procedure to improve the agreement between the pile lengths estimated in the design and finalized in the field is presented. The advantages of static load tests and accounting for setup are demonstrated. Drivability analysis using wave equation analysis is employed to estimate the maximum length a pile can be safely driven to without damage, Lmax. Safe drivability is addressed in the design by keeping the pile length less than or equal to Lmax. The report also discusses addressing the drivability and structural limit states by fitting to local ASD practices. The design results obtained from addressing the three strength limit states for a single pile (geotechnical, structural, drivability) include a Qf vs. depth curve and pile bearing resistance vs. depth curves up to Qfmax and Lmax. These results are summarized in a design chart that can be used by the foundation designers to optimize and finalize LRFD design for a pile group, such as obtaining pile length and required field bearing resistance. The report presents and solves a comprehensive LRFD Design Example problem to demonstrate the development and application of design charts using static and field analysis methods. Finally, the report describes how to ensure that all LRFD design limit states for driven piles are met in the field during construction.
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Content Notes:This report is issued by the FHWA Resource Center as a deployment aid to help highway agencies develop LRFD-based design specifications for driven piles that explicitly cover LRFD limit states, estimated pile length and maximum supported load, drivability analysis, setup, and load tests. Also, design charts are presented as an effective way to communicate design results. This report is intended to reinforce and support the design guidance provided by the AASHTO and FHWA technical references cited herein.
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