scholarly journals Seismic site response of layered saturated sand: comparison of finite element simulations with centrifuge test results

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Sparsha Sinduri Nagula ◽  
Yu-Wei Hwang ◽  
Shideh Dashti ◽  
Jürgen Grabe
Keyword(s):  
Finite Element ◽  
Seismic Response ◽  
Site Response ◽  
Numerical Results ◽  
Centrifuge Test ◽  
Test Results ◽  
Saturated Sand ◽  
Hypoplastic Model ◽  
Model Based ◽  
Seismic Site Response

AbstractA numerical model based on the finite element framework was developed to predict the seismic response of saturated sand under free-field conditions. The finite element framework used a non-linear coupled hypoplastic model based on the u-p formulation to simulate the behaviour of the saturated sand. The u-p coupled constitutive model was implemented as a user-defined routine in commercial ABAQUS explicit 6.14. Results of centrifuge experiments simulating seismic site response of a layered saturated sand system were used to validate the numerical results. The centrifuge test consisted of a three-layered saturated sand system subjected to one-dimensional seismic shaking at the base. The test set-up was equipped with accelerometers, pore pressure transducers, and LVDTs at various levels. Most of the constitutive models used to date for predicting the seismic response of saturated sands have underestimated volumetric strains even after choosing material parameters subjected to rigorous calibration measures. The hypoplastic model with intergranular strains calibrated against monotonic triaxial test results was able to effectively capture the volumetric strains, reasons for which are discussed in this paper. The comparison of the numerical results to centrifuge test data illustrates the capabilities of the developed u-p hypoplastic formulation to perform pore fluid analysis of saturated sand in ABAQUS explicit, which inherently lacks this feature.

Seismic response of sands in centrifuge tests

2008 ◽  
Vol 45 (4) ◽  
pp. 470-483 ◽  
Author(s):  
Mohammad H.T. Rayhani ◽  
M. Hesham El Naggar
Keyword(s):  
Shear Modulus ◽  
Seismic Response ◽  
Soil Structure ◽  
Site Response ◽  
Damping Ratio ◽  
Soil Structure Interaction ◽  
Response Analysis ◽  
Structure Interaction ◽  
Centrifuge Tests ◽  
Seismic Site Response

Seismic site response of sandy soils and seismic soil–structure interaction are investigated using an electrohydraulic earthquake simulator mounted on a centrifuge container at an 80g field. The results of testing uniform and layered loose to medium-dense sand models subjected to 13 simulated earthquakes on the centrifuge are presented. The variation of shear modulus and damping ratio with shear strain amplitude and confining pressure was evaluated and their effects on site response were assessed. The evaluated shear modulus and damping ratio agreed reasonably with laboratory tests and empirical relationships. Site response analysis using the measured shear wave velocity and estimated modulus reduction and damping ratio as input parameters produced good agreement with the measured site response. The effect of soil–structure interaction for structures situated on dry sand is also investigated. These tests have revealed many important insights with regard to the characteristics of seismic site response and seismic soil–structure behaviour. The tests showed that the seismic response of soil deposits, input motions, and overall behaviour of the structure are affected by soil stratification. The results showed that the seismic kinematic soil–structure interaction is not very significant for structures situated on loose sand.

scholarly journals Stress-independent parameters for stress-strain relationship and damping in nonlinear one-dimensional seismic site response analysis

2021 ◽  
Vol 15 (1) ◽  
pp. 14-29
Author(s):  
Nghiem Manh Hien
Keyword(s):  
Finite Element ◽  
Site Response ◽  
Computer Code ◽  
Site Response Analysis ◽  
Response Analysis ◽  
Ground Acceleration ◽  
Maximum Shear Strain ◽  
Seismic Site Response ◽  
Independent Parameters ◽  
Modulus Reduction

The modulus reduction and damping curves represent the nonlinear behavior of soil under cyclic load. In the literature, those curves were produced from lab tests of soil at particular confining stresses. This study developed a set of parameters that can be used to normalize the modulus reduction and damping curves to be stress-independent. The proposed formulations for the stress-independent parameters were implemented in the finite element code SRAP and validated through producing shear modulus reduction and damping curves that match the existed ones. Nonlinear 1D seismic site response analyses were conducted for centrifuge experiments to verify the developed computer code. Comparisons of the analysis results between SRAP and another computer code were presented in terms of maximum and minimum displacement, peak ground acceleration, maximum shear strain profiles, and response spectra. Keywords: backbone curve; hysteretic damping; dynamic soil model; stress-independent parameters; finite element method; nonlinear 1D seismic site response analysis.

scholarly journals Updating Stiffness and Hysteretic Damping Matrices Using Measured Modal Data

2018 ◽  
Vol 2018 ◽  
pp. 1-7 ◽  
Author(s):  
Jiashang Jiang ◽  
Yongxin Yuan
Keyword(s):  
Finite Element ◽  
Direct Method ◽  
Original Model ◽  
Numerical Results ◽  
Material Damping ◽  
Modal Data ◽  
Model Based ◽  
Hysteretic Damping ◽  
Vibration Modal ◽  
Damping Model

A new direct method for the finite element (FE) matrix updating problem in a hysteretic (or material) damping model based on measured incomplete vibration modal data is presented. With this method, the optimally approximated stiffness and hysteretic damping matrices can be easily constructed. The physical connectivity of the original model is preserved and the measured modal data are embedded in the updated model. The numerical results show that the proposed method works well.

scholarly journals A two-dimensional study on the weak-motion seismic response of the Aburra Valley, Medellin, Colombia

2002 ◽  
Vol 35 (1) ◽  
pp. 17-41 ◽  
Author(s):  
Brian M. Adams ◽  
Juan Diego Jaramillo
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Seismic Response ◽  
Site Response ◽  
Poor Correlation ◽  
Two Dimensional ◽  
Specific Detail ◽  
One Dimensional ◽  
Finite Element Software ◽  
Element Method

A two-dimensional elastic finite-element method is used to investigate the weak-motion seismic response of the Aburra Valley of Medellin, Colombia. A vertically propagating anti- plane SH Ricker wavelet is used to study the response of the valley for frequencies up to 5 Hz. The Aburra Valley is very large and geologically diverse. The -1200-metre-deep and -15- kilometre-wide valley is covered by a variable layer of soft soils averaging some 30 metres deep. The soils are mainly residual, alluvial or debris-flow deposits. The valley also contains a network of 24 strong-motion seismic recorders. A 49,900-element mesh of a cross-sectional model through the southern end of Medellin is analysed using the finite-element software package, Archimedes. The results are presented in both time and frequency domains. A similar one-dimensional finite-element method is used for comparison. It is found that while amplification often occurs at frequencies defined by a one-dimensional analysis, the level of amplification is often highly dependent on multi-dimensional effects. Local irregularities in the stratigraphy and topography at some sites have a significant effect on the seismic response. Site response may also be influenced strongly by sub-valley structures up to a few kilometres across, yet the influence of the valley as a whole is small. Poor correlation between modelling results and recorded data is probably due to a lack of site-specific detail within the model, and the limiting two-dimensional nature of the analysis.

Modal Testing and Finite Element Analysis of a Battery Rack for Seismic Applications

2005 ◽  
Vol 48 (1) ◽  
pp. 94-102 ◽  
Author(s):  
Elzbieta Berak
Keyword(s):  
Finite Element Analysis ◽  
Finite Element ◽  
Numerical Results ◽  
Test Method ◽  
Modal Testing ◽  
Test Results ◽  
Element Analysis ◽  
Resonance Search ◽  
Qualification Testing ◽  
Sine Sweep

One of the most challenging aspects of reliability testing in the telecommunication industry is earthquake resistance testing. Cabinet systems, battery racks, equipment racks, and distribution frames are considered compliant with Network Equipment-Building System (NEBSTM) criteria for surviving earthquake conditions if test results indicate (1) the maximum deflection of the top of the structure does not exceed 7.6 cm (3 in.), (2) there are no permanent deformations or structural damage, and (3) the equipment or batteries remain functional (as defined in NEBS Requirements: Physical Protection, Specification GR-73 Issue 2). Based on seismic test results of a large population of telecom enclosures, it is accepted that a system always passes the seismic test if its fundamental natural frequency is at least 6 Hz. It is costly to produce and configure enclosures and conduct seismic qualification testing. To minimize the risk of telecom system failure, a modal finite element analysis (FEA) of the system should first be performed. Numerical results of the FEA should then be verified with experimental resonance search data generated by modal testing or sine sweep testing, combined with static pull testing where applicable. The resonance search results will determine the need for seismic testing (seismic analysis) prior to seismic qualification testing. This paper elaborates on key aspects of the static pull test method supported by the test results for a cabinet framework and a configured cabinet relative to the seismic test results. The paper also discusses sine sweep testing of a battery cabinet and results of two modal test methods used on the corresponding battery rack. Finally, this paper describes modal FEA of the same battery rack anchored to a concrete pad supported by a polystyrene plastic foam sheet and explains the correlation of the numerical results with the experimental modal analysis results. The correlated model serves as the baseline model for analyzing other battery racks and equipment cabinets configured with batteries.

Prediction of Tread Pattern Wear by an Explicit Finite Element Model3

2007 ◽  
Vol 35 (4) ◽  
pp. 276-299 ◽  
Author(s):  
J. C. Cho ◽  
B. C. Jung
Keyword(s):  
Finite Element ◽  
Wear Rate ◽  
Tangential Stress ◽  
Rate Equation ◽  
Constitutive Equations ◽  
Slip Velocity ◽  
Test Results ◽  
Explicit Finite Element ◽  
Driving Condition ◽  
Driving Conditions

Abstract Tread pattern wear is predicted by using an explicit finite element model (FEM) and compared with the indoor drum test results under a set of actual driving conditions. One pattern is used to determine the wear rate equation, which is composed of slip velocity and tangential stress under a single driving condition. Two other patterns with the same size (225/45ZR17) and profile are used to be simulated and compared with the indoor wear test results under the actual driving conditions. As a study on the rubber wear rate equation, trial wear rates are assumed by several constitutive equations and each trial wear rate is integrated along time to yield the total accumulated wear under a selected single cornering condition. The trial constitutive equations are defined by independently varying each exponent of slip velocity and tangential stress. The integrated results are compared with the indoor test results, and the best matching constitutive equation for wear is selected for the following wear simulation of two other patterns under actual driving conditions. Tens of thousands of driving conditions of a tire are categorized into a small number of simplified conditions by a suggested simplification procedure which considers the driving condition frequency and weighting function. Both of these simplified conditions and the original actual conditions are tested on the indoor drum test machines. The two results can be regarded to be in good agreement if the deviation that exists in the data is mainly due to the difference in the test velocity. Therefore, the simplification procedure is justified. By applying the selected wear rate equation and the simplified driving conditions to the explicit FEM simulation, the simulated wear results for the two patterns show good match with the actual indoor wear results.

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