Analysis and Design of Steel Tubular Pile Foundations Embedded in Typical Soils

Download or read book Analysis and Design of Steel Tubular Pile Foundations Embedded in Typical Soils written by Zeinab Bayati and published by . This book was released on 2022 with total page 261 pages. Available in PDF, EPUB and Kindle. Book excerpt: Piles should sustain the axial loads transmitted from the supported structure without failing in bearing capacity and/or undergoing structural damage, as well as limit excessive settlements. This is verified by examining the stability (strength) and serviceability (e.g. permissible settlements) of the pile foundation. Classical design frameworks (e.g. the AASHTO LRFD specifications) only address the pile design at the strength limit state, and the pile serviceability is typically checked after determining the design bearing capacity. Therefore, a more comprehensive and practical design framework is required to account simultaneously for the strength and serviceability limit states. An analysis approach based on predicting the load-settlement response can facilitate the incorporation of both strength and serviceability limit states in the routine design of axially loaded pile foundations. The research presented in this dissertation aimed at investigating the strength and serviceability limit states for the analysis and design of axially loaded steel tubular piles. The research was conducted over three major phases of study. The first phase investigated the stability of a pile having tubular steel square section. The model considered buckling of an axially loaded pile entrenched in a continuous medium. Three-dimensional finite element analyses were conducted by modelling partially embedded piles in typical clayey and sandy soils. Three-dimensional analyses were necessary in order to account for the influence of the surrounding soil elastic medium. In order to model the pile section as closely as possible to reality, no particular restrains were imposed on the pile tip. The influence of the pile head restraint, as well as lateral soil support, on the stability of a pile was investigated. Moreover, the effect of the pile-soil interface stiffness on the value of critical buckling load (Pcr) was brought to light for design purposes. The second phase of the study verified the stability of the pile-soil system against failure by considering the nonlinearity of the surrounding soil medium. The serviceability of the pilesoil system was also examined at this stage by means of the pile load-settlement relation in order to certify satisfactory control of the allowable deformations. The objectives of the second phase of the study were met through conducting two levels of analyses: (1) Continuum medium-based finite element analyses, and (2) one-dimensional load transfer analyses. The first level of analyses involved using two- and three-dimensional finite element simulations, that incorporated classical elasto-plastic (Drucker-Prager and Mohr-Coulomb), and nonlinear elastic (Duncan-Chang and Hyperbolic) soil models. The properties of such soils are generally obtained from lab tests. In this context, a new modelling strategy was proposed for the elasto-plastic analysis of steel tubular section piles having sharp corners embedded in a granular (sandy) soil medium. The second level of analyses introduced an approach based on the simultaneous use of the load transfer and finite element analysis methods. In this framework, an elasto-plastic finite element approach was implemented in order to conduct nonlinear finite element analyses with the load-settlement response curve of axially loaded single piles. This was achieved via the nonlinear pile-soil stress-displacement curves along the pile shaft (t-z curve) and a tip (qz curve). The plasticity algorithm considered strain hardening through the pile-soil interaction (t-z and q-z) curves. The load transfer analysis showed a significantly improved characterization for the pile load-settlement behavior compared to field test results. The computation of pile settlement was also improved by reproducing the interaction curves for both pile shaft and pile tip via the use of the so-called “Sublayer” or “Overlay” method. Finally, the third phase aimed at providing a practical design framework accounting simultaneously for the pile strength and serviceability limit states. The design framework accounts for the stability (buckling) of the pile section and can be extended to the design of different types of deep foundations such as steel tubular and concrete piles.