Analysis and Design for Inelastic Structural Response of Extended Pile Shaft Foundations in Laterally Spreading Ground During Earthquakes
- ISBN-10
- 1267402628
- ISBN-13
- 9781267402622
- Language
- English
- Published
- 2012
- Author
- Arash Khosravifar
Description
Experiences from past earthquakes have shown that lateral spreading associated with liquefaction of cohesionless soils can be a cause of severe damage to bridge foundations. Large diameter extended pile shafts can be an effective bridge foundation choice for areas subjected to lateral spreading because they offer greater stiffness and strength relative to the magnitude of lateral spreading loads that can develop against them. A limited degree of plastic hinging below the ground surface may be allowable in design of extended pile shafts. Issues for design for extended pile shafts include: (a) how to estimate the demands due to superstructure inertia and lateral spreading in liquefied soils, and (b) how to combine these two loads in estimating the local and global inelastic demands on the structure. Studies of the response of pile foundations and pile-supported structures in liquefiable soils using physical models, numerical models, and case studies have provided the basis for a number of design recommendations. The guidance is, however, quite varied regarding how lateral spreading and superstructure inertial loads should be combined in design. To answer the above questions a series of Nonlinear Dynamic Finite Element Analyses (NDA) have been performed to investigate inelastic response of extended pile shafts subjected to liquefaction-induced lateral spreading, covering a range of soil, pile, and ground motion conditions. The results of NDA were first used to show that combined effects of lateral spreading and superstructure inertia produce larger demands than are produced by either loading case alone, such that the combined demand cannot be enveloped by analyzing the two load cases separately. The results were then used to evaluate current equivalent static analysis (ESA) method (Caltrans, 2008), with the relatively poor agreement illustrating the limitations of methods that do not combine the two loads. The results of NDA parametric study were then used to develop and calibrate an ESA procedure. The ESA procedure addresses both the nonliquefaction and liquefaction cases, and includes criteria that identify conditions which tend to produce excessive demands or collapse conditions. Finally, a series of three-dimensional (3D) Nonlinear Dynamic Finite Element Analyses (NDA) were performed to examine inelastic behavior of large diameter extended pile shafts subjected to earthquake shaking and liquefaction-induced lateral spreading. The purpose of these analyses was to evaluate the differences between 2D and 3D simulations, understand the source of any differences, and evaluate whether those differences would affect design recommendations for Equivalent Static Analysis (ESA).
