Simplified BNWF model for nonlinear seismic response analysis of offshore piles with nonlinear input ground motion analysis

2005 ◽  
Vol 42 (2) ◽  
pp. 365-380 ◽  
Author(s):  
M Hesham El Naggar ◽  
Mohsen Ali Shayanfar ◽  
Mehrdad Kimiaei ◽  
Ali Akbar Aghakouchak
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Motion Analysis ◽  
Nonlinear Response ◽  
Free Field ◽  
Response Analysis ◽  
Winkler Foundation ◽  
Offshore Platforms ◽  
Nonlinear Seismic Response ◽  
Offshore Piles

The seismic response of pile-supported offshore structures is strongly affected by the nonlinear behavior of the supporting piles. Nonlinear response of the pile foundation is the most important source of potential nonlinearity in the dynamic response of offshore platforms to earthquake excitations. It is often necessary to perform a dynamic analysis of offshore platforms that accounts for soil nonlinearity, discontinuity conditions at pile–soil interfaces, energy dissipation through soil radiation damping, and structural nonlinear behaviors of piles. In this paper, an attempt is made to develop an inexpensive and practical procedure, compatible with readily available structural analysis software, for estimating the lateral response of flexible piles embedded in layered soil deposits subjected to seismic loading. In the proposed model a beam on nonlinear Winkler foundation (BNWF) approach, consisting of simple nonlinear springs, dashpots, and contact elements, is used. This model was incorporated into a finite element program, ANSYS, which was used to compute the response of laterally excited piles. A nonlinear approach was used for seismic free-field ground motion analysis. The computed responses compared well with the centrifuge test results. This paper deals with the effects of free-field ground motion analysis on nonlinear seismic behavior of embedded piles. Different parts of a BNWF model, together with quantitative and qualitative findings and conclusions for dynamic nonlinear response of offshore piles, are discussed and addressed in detail.Key words: nonlinear, seismic response, offshore piles, seismic pile–soil interaction, BNWF models.

Effects of Structural Material Damping on Nonlinear Seismic Response of Offshore Piles

2008 ◽  
Author(s):  
Mehrdad Kimiaei
Keyword(s):  
Structural Material ◽  
Nonlinear Response ◽  
Free Field ◽  
Winkler Foundation ◽  
Offshore Platforms ◽  
Material Damping ◽  
Nonlinear Seismic Response ◽  
Lateral Response ◽  
Foundation Model ◽  
Offshore Piles

Nonlinear response of pile foundations is the most important part of potential nonlinear response of pile supported offshore platforms to seismic excitations. Soil nonlinearity, soil radiation damping and structural material damping are the main sources of energy dissipation in seismic behavior of offshore piles. In this study, a practical BNWF (Beam on Nonlinear Winkler foundation) model is used to compute the nonlinear lateral response of piles, embedded in layered soil deposits, subjected to seismic loading. The results of equivalent linear and nonlinear earthquake free field ground motion analyses are used as the input excitations at support nodes of the model. Sensitivity of the pile seismic responses to structural material damping ratios are discussed and addressed in this paper. Numerical results are compared with centrifuge test results.

The Effects of Free Field Ground Motion Analysis on Seismic Response of Offshore Piles

2005 ◽  
Author(s):  
Mehrdad Kimiaei ◽  
Mohsen Ali Shayandar ◽  
M. Hesham El Naggar ◽  
Ali Akbar Aghakouchak
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Free Field ◽  
Nonlinear Behavior ◽  
Winkler Foundation ◽  
Main Concern ◽  
Offshore Platforms ◽  
Seismic Excitations ◽  
Earthquake Design ◽  
Offshore Piles

Nonlinear response of piles is the most important source of potentially nonlinear behavior of pile-supported offshore platforms due to earthquake excitations. Earthquake design of offshore platforms is one of the main parts in offshore platforms design on which seismic soil pile structure interaction could be the main concern. In this paper, seismic response of offshore piles embedded in layered soil deposits is determined using a BNWF model (Beam on Nonlinear Winkler Foundation). Results of the free field ground motion analyses using equivalent-linear or nonlinear approaches are applied as input seismic excitations to the support nodes of BNWF model. Sensitivity of the results to input ground motions are discussed and addressed in this paper. Computed responses are also compared with centrifuge test results.

A Practical Model for Nonlinear Seismic Response Analysis of Jacket Type Fixed Offshore Platforms

2006 ◽  
Author(s):  
Mehrdad Kimiaei ◽  
Ali Akbar Aghakouchak ◽  
Mohsen Ali Shayanfar ◽  
M. Hesham El Naggar
Keyword(s):  
Seismic Response ◽  
Response Analysis ◽  
Winkler Foundation ◽  
Offshore Platforms ◽  
Seismic Response Analysis ◽  
Practical Procedure ◽  
Nonlinear Seismic Response ◽  
Lateral Response ◽  
Proposed Model ◽  
Soil Structures

Offshore platforms in seismically active areas should be designed to survive severe earthquake excitations with no global structural failure. In seismic design of offshore platforms, it is often necessary to perform a dynamic analysis that accounts for nonlinear pile soil structures interaction effects. This paper summarizes an inexpensive and practical procedure compatible with readily available structural analysis software (ANSYS) for estimating the nonlinear lateral response of fixed offshore platforms resting on flexible piles subjected to seismic loading. In the proposed model, piles and jacket members are modeled using BNWF (Beam on Nonlinear Winkler Foundation) and FE (Finite Element) approaches respectively in an integrated model. In this paper, nonlinear seismic response analysis of an existing sample offshore platform has been performed and sensitivity of the results to the model main parameters is investigated.

scholarly journals Study on the influence of seafloor soft soil layer on seismic ground motion

2020 ◽  
Author(s):  
Jingyan Lan ◽  
Juan Liu ◽  
Xing Song
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Sea Water ◽  
Response Spectrum ◽  
Soft Soil ◽  
Free Field ◽  
Soil Layer ◽  
Response Analysis ◽  
Peak Acceleration ◽  
Seismic Response Analysis

Abstract. In the complex medium system of sea area, the overlying sea water and the surface soft soil have a significant impact on the seafloor ground motion, which brings great seismic risk to the safety of offshore engineering structures. In this paper, four sets of typical free field models are constructed and established, which are land model, land model with surface soft soil, sea model and sea model with surface soft soil. The dynamic finite difference method is used to carry out two-dimensional seismic response analysis of typical free field based on the input forms about P and SV wave. By comparing the seismic response analysis results of four groups of calculation models, the effects of overlying seawater and soft soil on peak acceleration and acceleration response spectrum are studied. The results show that when SV wave is input, the peak acceleration and response spectrum of the surface of soft soil on the surface and the seabed surface can be amplified, while the overlying sea water can significantly reduce the ground motion. When P wave is used, the effect of overlying seawater and soft soil on peak acceleration and response spectrum of surface and seabed can be ignored. The peak acceleration decreases first and then increases from the bottom to the surface, and the difference of peak acceleration calculated by four free field models is not obvious. The results show that the overlying sea water and the surface soft soil layer have little effect on the peak acceleration of ground motion below the surface.

Inelastic Seismic Response of Extended Pile-Shaft-Supported Bridge Structures

2004 ◽  
Vol 20 (4) ◽  
pp. 1057-1080 ◽  
Author(s):  
T. C. Hutchinson ◽  
Y. H. Chai ◽  
R. W. Boulanger ◽  
I. M. Idriss
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Performance Measures ◽  
Soil Profile ◽  
Site Response ◽  
Free Field ◽  
Winkler Foundation ◽  
Dynamic Analyses ◽  
Inelastic Seismic Response ◽  
Motion Characteristics

Nonlinear static and dynamic analyses were used to evaluate the inelastic seismic response of bridge and viaduct structures supported on extended cast-in-drilled-hole (CIDH) pile shafts. The nonlinear dynamic analyses used a beam-on-nonlinear-Winkler foundation (BNWF) framework to model the soil-pile interaction, nonlinear fiber beam-column elements to model the reinforced concrete sections, and one-dimensional site response analyses for the free-field soil profile response. The study included consideration of ground motion characteristics, site response, lateral soil resistance, structural parameters, geometric nonlinearity (P-Δ effects), and performance measures. Results described herein focus on how the ground motion characteristics and variations in structural configurations affect the performance measures important for evaluating the inelastic seismic response of these structures. Presented results focus on a representative dense soil profile and thus are not widely applicable to dramatically different soil sites.

scholarly journals Study on the influence of the seafloor soft soil layer on seismic ground motion

2021 ◽  
Vol 21 (2) ◽  
pp. 577-585
Author(s):  
Jingyan Lan ◽  
Juan Liu ◽  
Xing Song
Keyword(s):  
Seismic Response ◽  
Ground Motion ◽  
Response Spectrum ◽  
Soft Soil ◽  
Free Field ◽  
Soil Layer ◽  
P Wave ◽  
Response Analysis ◽  
Peak Acceleration ◽  
Seismic Response Analysis

Abstract. In the complex medium system of the sea area, the overlying seawater and the surface soft soil have a significant impact on the seafloor ground motion, which brings great seismic risk to the safety of offshore-engineering structures. In this paper, four sets of typical free-field models are constructed and established, comprising a land model, land model with surface soft soil, sea model and sea model with surface soft soil. The dynamic finite-difference method is used to carry out two-dimensional seismic response analysis of a typical free field based on the input forms of P and SV waves. By comparing the seismic response analysis results of four groups of calculation models, the effects of overlying seawater and soft soil on the peak acceleration and acceleration response spectrum are studied. The results show that when an SV wave is input, the peak acceleration and response spectrum of the surface of soft soil on the surface and the seabed surface can be amplified, while the overlying seawater can significantly reduce the ground motion. When the P wave is used, the effect of overlying seawater and soft soil on the peak acceleration and response spectrum of the surface and seabed can be ignored. The peak acceleration decreases first and then increases from the bottom to the surface, and the difference of peak acceleration calculated by four free-field models is not obvious. The results show that the overlying seawater and the surface soft soil layer have little effect on the peak acceleration of ground motion below the surface.

Sensitivity analysis of geotechnical site conditions effect on the seismic response of a saturated inhomogeneous poroviscoelastic soil profile

2018 ◽  
Vol 15 (6) ◽  
pp. 661-677 ◽  
Author(s):  
Toufiq Ouzandja ◽  
Mohamed Hadid
Keyword(s):  
Soil Properties ◽  
Seismic Response ◽  
Pore Water ◽  
Soil Profile ◽  
Water Saturation ◽  
Free Field ◽  
Response Spectra ◽  
Response Analysis ◽  
Content Type ◽  
Linear And Nonlinear

Purpose This paper aims to present the investigation of the linear and nonlinear seismic site response of a saturated inhomogeneous poroviscoelastic soil profile for different soil properties, such as pore-water saturation, non-cohesive fines content FC, permeability k, porosity n and coefficient of uniformity Cu. Design/methodology/approach The inhomogeneous soil profile is idealized as a multi-layered saturated poroviscoelastic medium and is characterized by the Biot’s theory, with a shear modulus varying continuously with depth according to the Wichtmann’s model. Seismic response analysis has been evaluated through a computational model, which is based on the exact stiffness matrix method formulated in the frequency domain assuming that the incoming seismic waves consist of inclined P-SV waves. Findings Unlike the horizontal seismic response, the results indicate that the vertical one is strongly affected by the pore water saturation. Moreover, in the case of fully saturated soil profile, the same vertical response spectra are found for the two cases of soil behavior, linear and nonlinear. Originality/value This research is a detailed study of the geotechnical soil properties effect on the bi-directional seismic response of saturated inhomogeneous poroviscoelastic soil profile, which has not been treated before; the results are presented in terms of the peak acceleration ratio, as well as the free-field response spectra and the spectral ratio (V/H).

Nonstationary Probabilistic Seismic Response Analysis of Nonlinear Soil Profile under Bidirectional Dynamic Loading

2012 ◽  
Vol 193-194 ◽  
pp. 949-953
Author(s):  
Xiao Dong Pan ◽  
Jia En Zhong ◽  
Chao Chao He
Keyword(s):  
Spectral Density ◽  
Seismic Response ◽  
Ground Motion ◽  
Power Spectral Density ◽  
Soil Profile ◽  
Response Analysis ◽  
Time Varying ◽  
Seismic Response Analysis ◽  
Dynamic Reliability ◽  
Power Spectral

In this paper, according to the characteristics of near-fault earthquakes, combined with the strong ground motion attenuation law in China, the nonstationary power spectrum of bidirectional ground motion input is obtained through random vibration analysis. By introducing the pseudo excitation algorithm, the evolutionary power spectral density (PSD) of acceleration at the engineering bedrock is handled as the nonstationary pseudo input, and the Hardin-Drnevich hyperbolic model is utilized to take into account the nonlinearity of soil layer. On this basis, finite element method in the time domain and frequency domain are used for seismic response analysis of soil profile. Values including various time-varying power spectral density of the dynamic response, time varying RMS and time-dependent reliability at different threshold can be obtained by calculating, which provides a basis for the analysis of the foundation dynamic reliability assessment.

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