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Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Soils. Bradley Fleming, Sri Sritharan , & JinWei Huang Iowa State University Kanthasamy Muraleetharan & Gerald Miller Oklahoma University. Modeling Techniques. Finite Element ( OpenSees )
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Understanding and Improving the Seismic Behavior of Pile Foundations in Soft Soils Bradley Fleming, Sri Sritharan, & JinWei Huang Iowa State University KanthasamyMuraleetharan & Gerald Miller Oklahoma University
Modeling Techniques • Finite Element (OpenSees) • Detailed 3D analysis • Used to understand complex interactions between • pile and improved soil • improved soil and unimproved soil • p-y Analysis Method (LPILE) • Simple 2D analysis • Attractive for engineers in industry • Account for improved soil of limited width by applying modification factors to p-y relationships
OpenSees Finite Element Model • Soil “Island” (OpenSeesPL soil mesh generation) • 10.3 m long, 5.15 m wide, and 7.62 m high • 3,450 nodes • 2,492 soilelements • Pile (forceBeamColumn) • 7.23 m total length • 34 beam elements • 5.3 m embedded length • Non-linear fiber section (half of pile) P Clay Sand Contact Elements (BeamContact3D) Soil Elements (SSPbrick) ClaySand • PressureIndependMultiYield•PressureDependMultiYield •Gmax = 3250 kN/m2•Gmax = 1.0E+5 kN/m2 • c = 30.5 kN/m2 •φ = 37 deg. • γsat =1.8 ton/m3• γsat =2.0 ton/m3 Soil m1 Pile slave r m2
Pile Head Responses of Full-Scale Test and FEM Unimproved Pile Improved Pile
Effective Length • Attenuation of stresses in soil layer Guo and Lee (2001) or 0.05
Equivalent Rigidity • R – Equivalent rigidity (analogous to AE for axially loaded member) • Leff - Length of uniform soil layer • ki – Equivalent stiffness of the p-y curve • S - Stiffness of spring Improved Soil Unimproved Soil
p-y Modification Factors JinWei Huang (2011)
Global Response Comparisons (Centrifuge) JinWei Huang (2011)
Global Response Comparisons (Centrifuge) JinWei Huang (2011)
Global Response Comparisons (Centrifuge) JinWei Huang (2011)
Field & LPILE Global Responses JinWei Huang (2011)
Field & LPILE Test Local Responses JinWei Huang (2011)
Conclusions • Both LPILE and OpenSees closely resembles centrifuge and field behavior • OpenSees is an effective analysis tool but requires specialized knowledge and involves high computation costs • LPILE is an attractive tool for engineers and has flexibility to modify p-y curves • The proposed method for modifying p-y curves does well in characterizing the behavior of piles in improved soil of limited width