scholarly journals OPTIMIZATION OF EFFECTIVE STRAIN COEFFICIENT FOR NONLINEAR SITE RESPONSE ESTIMATION BY EQUIVALENT-LINEAR SIMULATION

2019 ◽  
Vol 84 (760) ◽  
pp. 781-791
Author(s):  
Hiroaki SATO ◽  
Sadanori HIGASHI ◽  
Yoshiaki SHIBA ◽  
Hiroyuki FUJIWARA ◽  
Takashi KUNUGI
Keyword(s):  
Site Response ◽  
Effective Strain ◽  
Nonlinear Site Response ◽  
Equivalent Linear ◽  
Strain Coefficient

Comparison of Equivalent Linear and Nonlinear Site Response Analysis Results and Model to Estimate Maximum Shear Strain

2016 ◽  
Vol 32 (3) ◽  
pp. 1867-1887 ◽  
Author(s):  
Brian Carlton ◽  
Kohji Tokimatsu
Keyword(s):  
Shear Strain ◽  
Site Response ◽  
Response Spectrum ◽  
Peak Ground Velocity ◽  
Site Response Analysis ◽  
Response Analysis ◽  
Ground Acceleration ◽  
Maximum Shear Strain ◽  
Nonlinear Site Response ◽  
Equivalent Linear

We compared the results of equivalent linear (ELA) and nonlinear site response analyses (NLA) and found that the differences between the values of the peak ground acceleration ( PGA), peak ground velocity ( PGV), Arias intensity ( I a), significant duration ( D5–75), and response spectrum for periods between 0.025 s and 2 s predicted by each method are non-negligible for maximum shear strain values predicted by ELA ( γ max, ELA) greater than 0.04% to 1.0%. As γ max, ELA increases, ELA in general predict smaller shear strain and D5–75 values, and larger PGA, PGV, I a, mean period, and response spectral values for periods less than 0.1 s and periods near the natural site period than NLA. To help researchers and practitioners decide when to use ELA and/or NLA, we developed a model to estimate γ max, ELA before conducting a site response analysis.

Bounding surface models in site response analysis: comparison with the equivalent linear approach

2021 ◽  
Author(s):  
Tony Fierro ◽  
Massimina Castiglia ◽  
Filippo Santucci de Magistris
Keyword(s):  
Site Response ◽  
Soil Column ◽  
Strong Motion ◽  
Nonlinear Behaviour ◽  
Bounding Surface ◽  
Nonlinear Site Response ◽  
Linear Approach ◽  
Equivalent Linear ◽  
Non Linear ◽  
Soil Behaviour

<p>A reliable prediction of the response of a soil column subjected to earthquake excitation is a basic although challenging achievement in geotechnical earthquake engineering problems.</p><p>A critical step is the analysis type selection. Nowadays, the equivalent linear approach is extremely widespread, mainly for its low computational demand and for its suitability to simulate soil behaviour up to the medium-strain level. However, this approach approximates the hysteresis loop exhibited by soils during a load cycle through an average shear modulus and damping ratio. Consequently, the nonlinear approach would more adequately describe the real soil behaviour, but it requires a large amount of data to be correctly calibrated that is not always available.</p><p>To address the differences by using these approaches, a comparison between the surficial acceleration response spectra of a single-layered 20 m-thick soil column of Messina Gravels (gravel and sand with occasionally silty levels) underlain by a rigid bedrock, subjected to strong-motion recordings, is presented.</p><p>The software STRATA was used for the equivalent linear analyses. The nonlinear site response analyses were performed with the OpenSees framework, while the bounding surface-based SANISAND constitutive model was selected to reproduce the soil nonlinear behaviour.</p><p>A single column in 3D space with periodic boundaries to simulate 1D conditions was considered. The input excitation was applied at the base nodes of the column and the parameters to be assigned to the model were obtained from Gorini (2019).</p><p>For both analysis methods, linear elastic analyses were performed by applying a 0.3g sine sweep with frequencies up to 30 Hz. The obtained results were interpreted in terms of acceleration transfer function and a satisfactory congruence was achieved.</p><p>The non-linear behaviour of the soil was triggered by applying three accelerograms from strong-motion events (Kobe, Kocaeli and Chi-Chi), downloaded from the PEER database. As results, for periods higher than 1.5 s neglectable amplification effects are observed, so a good accordance is highlighted between equivalent linear and nonlinear analyses. For the period range 0.3-1.5 s, amplification occurs but it is still correctly caught by both the approaches. Strong differences are, instead, observed in the lower periods range, up to 0.3 s, where the equivalent linear approach returns essentially similar spectral accelerations as those of the input motions, while nonlinear analysis highlights amplification and eventually deamplification effects.</p><p>In conclusion, it appears that the soil non-linearity should be carefully evaluated for high-seismicity areas because the equivalent linear method tends to underestimate the response, assuming a stiffer behaviour. This was clear for a single-layered soil column and it becomes certainly more complex for stratified soil deposits. To this end, the non-linear approach appears more appropriate to avoid underpredictions of the input motion to be applied for design purposes, but a high effort should be made to properly characterize the soil for the calibration of the selected nonlinear model as well.</p>

Simulation-based site amplification model for shallow bedrock sites in Korea

2021 ◽  
pp. 875529302098198
Author(s):  
Muhammad Aaqib ◽  
Duhee Park ◽  
Muhammad Bilal Adeel ◽  
Youssef M A Hashash ◽  
Okan Ilhan
Keyword(s):  
Linear Models ◽  
Site Response ◽  
Site Amplification ◽  
One Dimensional ◽  
Nonlinear Component ◽  
Nonlinear Site Response ◽  
Simulation Based ◽  
Linear And Nonlinear ◽  
Input Motion ◽  
Nonlinear Components

A new simulation-based site amplification model for shallow sites with thickness less than 30 m in Korea is developed. The site amplification model consists of linear and nonlinear components that are developed from one-dimensional linear and nonlinear site response analyses. A suite of measured shear wave velocity profiles is used to develop corresponding randomized profiles. A VS30 scaled linear amplification model and a model dependent on both VS30 and site period are developed. The proposed linear models compare well with the amplification equations developed for the western United States (WUS) at short periods but show a distinct curved bump between 0.1 and 0.5 s that corresponds to the range of site natural periods of shallow sites. The response at periods longer than 0.5 s is demonstrated to be lower than those of the WUS models. The functional form widely used in both WUS and central and eastern North America (CENA), for the nonlinear component of the site amplification model, is employed in this study. The slope of the proposed nonlinear component with respect to the input motion intensity is demonstrated to be higher than those of both the WUS and CENA models, particularly for soft sites with VS30 < 300 m/s and at periods shorter than 0.2 s. The nonlinear component deviates from the models for generic sites even at low ground motion intensities. The comparisons highlight the uniqueness of the amplification characteristics of shallow sites that a generic site amplification model is unable to capture.

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