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TECHNICAL PRESENTATION TOPIC – LRFD FOR MICROPILES (1 PDH)
Speaker: Jonathan Bennett, PE, D.GE
Load and Resistance Factor Design (LRFD) is the predominant design method utilized today for reinforced concrete and structural steel, and is the primary focus of the AASHTO LRFD Bridge Design Specifications. Historically, micropile design has been performed mainly with Allowable Stress Design (ASD) methodologies, and most of the micropile design manuals and specifications in existence prior to 2008 were based on ASD.
In light of this history of ASD design methodologies, and in spite of the widespread use of LRFD in general structural design disciplines, there have been a number of questions and a great deal of confusion regarding the proper use and implementation of LRFD design methodologies for micropiles. The author, as part of a DFI / ADSC Joint Micropile Committee initiative, developed a presentation in response to these questions and issues which covers the fundamentals of LRFD as it applies to micropiles, and provides an illuminating comparison with ASD methodology.
This paper is a formalized and updated snapshot of the current State of Practice of LRFD for Micropile Design based on the most current information and design codes relevant to micropiles. It will describe the fundamentals of Load and Resistance Factor Design (LRFD), demonstrate micropile design and testing utilizing LRFD, compare the results with historical ASD design, point out the limitations of current LRFD practice relative to micropiles, and finally map out the path forward with regard to proper implementation of LRFD as a true reliability based design methodology for the design of micropiles.