Geotechnical Engineering Circular No. 9 Design, Analysis, and Testing of Laterally Loaded Deep Foundations that Support Transportation Facilities
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| 6. OTHER US-BASED SOURCES Included in the following section are basic summaries of various references which are considered important in the historic progression of lateral analysis for deep foundations. A full summary is not presented, but rather a brief, chronological summary of the salient concepts as introduced into the state of the practice. 6.1 BROMS (AB) As described in Section 6.5, the Broms method provides a means of estimating lateral capacity and deflection of deep foundation elements in homogeneous clay or sand with a level ground surface using the strength properties of the soil and the stiffness of the structural element. The linear load displacement method distinguishes between long and short piles using a ratio which employs the soil subgrade reaction modulus. Short piles are then analyzed fora failure mode commonly described as “fence-posting,” where the tip is not fixed and the entire element rotates. Long piles are assumed to have fixity at the tip and are assessed based on possible exceedance of the maximum moment (development of plastic hinge. 6.2 DAVISSON AND ROBINSON (1965) As stated previously, the main design concept presented by Davisson and Robinson (1965) is development of the point of fixity, as it relates to structural analysis using the equivalent cantilever method. This manual is only applicable to long piles as defined by the ratio presented by Broms (1964). It is referenced in AASHTO LRFD C (2014) as the recommended method for determining the depth to fixity for preliminary design. The limits for differentiating between long and short piles are not included in AASHTO. 272 6.3 REESE (1984, 1985) Documents FHWA-IP-84-11: Handbook on Design of Piles and Drilled Shafts Under Lateral Load Reese, 1984) and FHWA-IP-85-106: Behavior of Piles and Pile Groups under Lateral Load” (Reese 1985) present Broms method, but also recommend a method of using p-y curves to design laterally loaded piles. The method determines failure loads by iteration of increasing loads until the maximum bending moment is exceeded. At this point the allowable service loads are established by dividing the input loads by the desired safety factor. The allowable service loads are then input and deflection assessed. The concept of critical penetration is introduced, which has been adopted by some DOTs and is commonly called critical depth, as described in Section 3. The documents recommend significant interaction between the structural and geotechnical engineers during the design process, but do not define specific roles and responsibilities. Download 6.03 Mb. Share with your friends:
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