Inertial Interaction Research Articles

Performance of an advanced sand constitutive model in modelling soil and soil-structure interaction under seismic excitation

There is a growing number of available advanced soil constitutive models aimed at capturing soil cyclic behaviour and their subsequent use in seismic applications. Nevertheless, detailed validation studies of these soil constitutive models on benchmark experimental works including seismic soil-structure interaction are still rare. This work presents a short validation study of the seismic performance of an advanced elastoplastic sand constitutive model on a boundary value problem including kinematic and inertial soil-structure interaction. The results of the finite element numerical model for the free field and structural responses are compared with the experimental work on a group of piles analysed in a flexible soil container filled with dry sand and subjected to simplified seismic loading. In general, the comparisons show a satisfactory match between the results of the simulations and the experiments, with the exception of the numerical predictions of settlements. The computed results are discussed based on: i) the dominant stress-paths in soil; ii) parametric studies on the settlement evaluation; iii) the origin of the high frequency motion oscillations to simple sinusoidal input motions; all with respect to potential improvements in the formulation of the elastic behaviour of the constitutive model in the future.

3D Numerical Modeling of the Inertial and Kinematic Interactions of Inclined Pile Groups in Liquefiable Soils

3D Numerical Modeling of the Inertial and Kinematic Interactions of Inclined Pile Groups in Liquefiable Soils

Effects of multiple relaxation times in the annular flow of pulsatile electro-osmotic flow of a complex biological fluid: blood with low and high cholesterol

This study investigates the electro-osmotic flow of a biological fluid (blood with varying cholesterol levels) in annular flow to simulate a first approximation to arterial occlusion. The fluid´s rheology is characterized by a multi-modal convected Maxwell model equation. The charge density follows the Boltzmann distribution, governing the electrical field. Mathematically, this scenario can be modeled by the Poisson–Boltzmann partial differential equation. Assuming a small zeta potential (less than 25 mV) using the Debye–Huckel approximation and considering a pulsatile electrical field, analytical solutions are derived using the Fourier transform formalism. These solutions, expressed in terms of the modified Bessel function, provide transfer functions for axial velocity and volumetric flow as functions of material parameters represented by characteristic dimensionless numbers. This study further analyzes thermal, electric, inertial, viscoelastic, and various interactions within the plasma, hematocrit, hematocrit–cholesterol, and cholesterol–cholesterol as well as weight concentration through numerical simulations. Finally, the flow and rheology predictions are validated using experimental data on human blood with varying cholesterol levels. The obtained transfer functions reveal that the electric–thermal–viscoelastic effects and the multiple geometric relationships contribute to the dynamic response of the interactions between the input electrical field and output volumetric flow and shear stress functions, leading to and evolution of resonance curves. It is noteworthy that electro-osmotic flow in blood with pathologies associated with low and high cholesterol has been scarcely reported in the literature on rheology. Thus, this work represents a significant contribution to the field.

Non-linear behaviour of soil–pile interaction phenomena and its effect on the seismic response of OWT pile foundations. Validity range of a linear approach through non-degraded soil properties

The effect of non-linear and inelastic behaviour of the soil–pile interaction on the seismic response of offshore wind turbine pile foundations embedded in sandy soils is analysed. For this purpose, the responses obtained assuming three different Beam on Dynamic Winkler Foundation (BDWF) models are compared: a Plastic Non-Linear Model (PNLM), an Elastic Non-Linear Model (ENLM) and a simple elastic linear model with non-degraded properties of soil (NDLM). The influence of non-linearity and plasticity assumption is studied by evaluating the effects of the kinematic and inertial interaction within soil–pile interaction. Two soil stiffness levels are analysed: very loose and medium dense sand. The seismic response under ten earthquakes is computed in terms of mean envelopes of internal forces along the pile length. The non-linearity and inelastic influence of soil–pile interaction is quantified by means of relative differences with respect to the linear elastic model. Results show that the non-linear and inelastic models acquire relevance when the contribution of the inertial interaction dominates, leading to lower maximum responses than the linear elastic model. If the inertial interaction is not significantly activated, similar results between the three models are obtained, being the linear elastic model enough to reproduce the soil–pile dynamic interaction.

Equivalent fundamental period of bridge piers on caisson foundations from dynamic centrifuge testing

Dynamic soil-structure interaction is typically decomposed in kinematic and inertial effects. Inertial interaction generally results in an increase in the fundamental period and damping of the system, which, for slender structures, corresponds to a decrease of the inertial forces transmitted to the superstructure. Relations to estimate the period increase are mainly available in the literature for shallow foundations.In this paper, the fundamental period of bridge piers on compliant caisson foundations was obtained from dynamic centrifuge tests. A rigid and a flexible bridge pier were subjected to trains of sinusoidal waves and real ground motions. The interpretation of the experimental results permitted to (i) evaluate the increase of period with respect to fixed-base conditions; (ii) assess the dependency of the compliant-base period on the motion intensity. The second aspect sheds light on the role played by non-linearity of soil behaviour and emphasises the importance of performing preliminary soil response analyses.

Analysis of seismic response of a large-scale isolated LNG tank considering dynamic soil-pile interaction

Seismic safety is a critical issue for liquefied natural gas (LNG) tanks. It is essential to investigate the effect of the isolation system on the seismic response of LNG tanks, considering dynamic soil-pile interaction, especially for tanks located in the deep soil site. This study aims to quantitatively evaluate the effects of isolation system (e.g., lead-core rubber bearings) on various aspects of a large LNG tank located on a deep soil site under horizontal bi-directional seismic action. Specifically, the evaluation includes outer tank acceleration, inner tank base shear, overturning moment, and pile force distribution. The findings demonstrate that the isolation system can effectively minimize the transfer of inertial interaction from the superstructure to the pile foundation, optimize the internal force distribution within the pile foundation, mitigate the pile group effect, and enhance the safety margin of the structure. Moreover, the isolation system can effectively suppress the transmission of seismic energy in medium and high frequencies, but amplify it in the low-frequency domain. Consequently, it is recommended that it is needed to avoid the site's natural frequency in the design of seismic isolation bearings for LNG tanks.

Effects of kinematic and inertial interaction on seismic responses of pile-structure system in liquefiable and non-liquefiable deposits

Numerical simulation models for pile group-superstructure in liquefiable and non-liquefiable sites were established. The validity and reliability of the numerical model are verified by the shaking table test results. Based on the cross-correlation analysis of superstructure acceleration-pile bending moment and soil displacement-pile bending moment obtained from the tests, the coupling law of kinematic and inertial interaction and its influence on pile failure modes were discussed combined with the numerical simulation results. The results shown that the effect of kinematic interaction on piles were greater than that of inertial interaction in both types of sites, but coupling mechanisms of kinematic and inertial interaction were different. For the liquefiable site scenario, the middle part of piles was prone to bending failure and the kinematic interaction was the main reason for it. For the non-liquefiable site scenario, the inertial interaction had an obvious influence on the pile failure occurred at the pile top. The results of parameter analysis shown that the mass of the superstructure was the most important parameter of inertial interaction in the liquefiable site. Parameters of inertial interaction would affect the vibration of the superstructure in the non-liquefiable site, but the influence on pile bending moments was not obvious.

Dynamic Soil-Structure Interaction Through 2-D Site-Specific Response Analysis

Seismic response of structures involved soil-structure-interaction (SSI) that need to consider both inertial and kinematic interaction. Many underground SSI has been developed such as modelling the structures and soils as continuum with seismic load simplified as pseudo-static or static equivalent. More recent and more realistic SSI model consider non-linear time-history analysis in the form of 2-D site-specific response analysis (SSRA), in which both inertial and kinematic interaction in combination with non-linear soil model, as well as time-history ground-motions are simulated. This paper presents simplified pseudo-static soil-structure interaction finite-element (FE) response of underground box-station structure under prescribed maximum strain displacement as resulted from 1-D site-specific response analysis under various ground-motions characteristics of subduction and shallow crustal earthquakes. More complex model of SSI system of basement is also presented. This basement SSI model incorporates non-linear time-history analysis with dynamic soil properties considered through 2-D SSRA simulating seismic wave propagation from reference base-rock to ground surface. Various base-rock seismic ground-motions are simulated from results of de-aggregation analysis from probabilistic seismic hazard analysis considering both subduction and shallow crustal earthquakes scaled at various ground-motion periods. The analysis adopts dynamic soil model with non-linear modulus and damping using FLAC computer program.

Evaluation of the Inertial and Kinematic Interactions Effects on the Seismic Behavior of Single Piles Embedded in Sand Using Different Theoretical Approaches

Evaluation of the Inertial and Kinematic Interactions Effects on the Seismic Behavior of Single Piles Embedded in Sand Using Different Theoretical Approaches

Influence of seabed profile on the seismic response of monopile-supported offshore wind turbines including dynamic soil-structure interaction

In this article, the seismic response of four different Offshore Wind Turbines (OWTs) from 5 to 15 MW, founded on monopiles embedded in homogeneous and non-homogeneous soil profiles with equivalent shear-wave velocities from 100 to 300 m/s is analysed. Two types of variable soil profiles with a semi-parabolic variation of the shear-wave velocity as depth increases are considered. The system seismic response under ten different accelerograms is computed through a finite element substructuring model in frequency domain. The foundation behaviour is obtained by a continuum model including kinematic and inertial interaction. Several models, in addition to that of rigid base condition, are considered to determine the influence of soil-structure interaction (SSI), as well as the contribution of each kinematic interaction (KI) factor. The seismic response of the OWTs is obtained in terms of maximum shear forces and bending moments at mudline level, as well as the acceleration amplification factor at hub level. It is found that the maximum response is produced when SSI is considered, including both the inertial and kinematic interaction. The differences arising due to the soil profile definition are shown to be mainly related to the rotational KI factor, which significantly affects the second vibration mode of the system. The largest responses are obtained for the homogeneous equivalent profile.

How do tall buildings affect seismic earth pressures on their basement walls?

The construction of tall buildings has recently undergone exponential growth in major cities, creating new challenges in earthquake engineering and design. For instance, existing analytical procedures for evaluating seismic lateral earth pressures on basement walls connected to these buildings typically ignore the inertia and dynamic properties of the superstructure. The inertial forces from a tall superstructure may cause additional displacements and rotations in its basement, affecting the distribution and magnitude of seismic lateral earth pressures. These additional soil-basement-structure-interaction (SBSI) effects are currently not well understood. Hence, the applicability and reliability of existing procedures to the basements of tall buildings remain questionable. In this paper, we use an experimental-numerical approach to provide insight into how the lateral resisting system of tall superstructures may impact the magnitude and distribution of seismic earth pressures on basement walls buried in dry sand and gravel. Numerical simulations are first validated in 3D using a prior centrifuge experiment that included a simplified model of a 42-story, high-rise structure in medium-dense, dry sand. Then, the numerical tool is used to perform 156 2D, nonlinear simulations of more realistic buildings and basements, ground motion characteristics, and sandy and gravely soil profiles. Nonlinear numerical simulations successfully capture the building's inertial and kinematic seismic interactions with the basement and an adjacent underground structure. The subsequent numerical sensitivity study showed that inertial forces from the dynamic lateral movements of the tall superstructure increase the total lateral earth pressures on the basement walls. This increase is particularly notable in the top two-thirds of the basement wall, and it can be approximated by a trapezoidal distribution. These effects and reliability of existing analytical procedures are shown to be highly sensitive to the building's modal frequencies in relation to the frequency content of the input motion as well as the stiffness of the structure-basement system with regard to the underlying soil. The results highlight the importance of considering the building's dynamic properties and inertia in evaluating seismic earth pressures on basement walls to avoid unsafe estimations or the need for overdesign.

Computation of irreversible seismic displacements of rock wedges: an application to dam abutment safety assessment

The paper discusses a method to assess the seismic performance of rock wedges in contact with arch-dam abutments based on the Newmark displacement approach, conveniently modified to include all possible three-dimensional failure mechanisms and forces transmitted by the structure. Under rigid-block and no-rotations assumptions, the method allows to consider the three components of the seismic input, the progressive detachment of the block from the supporting discontinuity planes, the possible recover of the contact, and the temporary complete detachment of the block from the rock mass. In addition to gravitational and seismic inertial actions, static and dynamic forces exerted at the dam-wedge contact, including those related to the inertial interaction with the reservoir, are included in the analyses.A case study is presented, referred to the seismic verification of the Ridracoli arch-gravity dam (Italy), founded on a marly-arenaceous formation. In particular, the right abutment is thoroughly investigated against wedge sliding involving bedding planes of particularly poor resistance. The results in terms of maximum wedge displacements are compared with the corresponding factor of safety obtained with a limit equilibrium approach, indicating that even a wedge resulting unstable with limit equilibrium analyses shows relatively small displacements at the end of the seismic excitement.

Electric-field-mediated morpho-dynamic evolution in drop–drop coalescence phenomena in the inertio-capillary regime

When two drops collide, they may either exhibit complete coalescence or selectively generate secondary drops, depending on their relative sizes and physical properties, as dictated by a decisive interplay of the viscous, capillary, inertia and gravity effects. Electric field, however, is known to induce distinctive alterations in the topological evolution of the interfaces post-collision, by influencing a two-way nonlinear coupling between electro-mechanics and fluid flow as mediated by a topologically intriguing interfacial deformation. While prior studies primarily focused on the viscous-dominated regime of the resulting electro-coalescence dynamics, several non-intuitive features of the underlying morpho-dynamic evolution over the intertio-capillary regime have thus far remained unaddressed. In this study, we computationally investigate electrically modulated coalescence dynamics along with secondary drop formation mechanisms in the inertio-capillary regime, probing the interactions of two unequal-sized drops subjected to a uniform electric field. Our results bring out an explicit mapping between the observed topological evolution as a function of the respective initial sizes of the parent drops as well as their pertinent electro-physical property ratios. These findings establish electric-field-mediated exclusive controllability of the observed topological features, as well as the critical conditions leading to the transition from partial to complete coalescence phenomena. In a coalescence cascade, an electric field is further shown to orchestrate the numbers of successive stages of coalescence before complete collapse. However, an increase of the numbers of cascade stages with the electric field strength and parent droplet size ratio is non-perpetual, and the same is demonstrated to continue until only a threshold number of cascade stages is reached. These illustrations offer significant insights into leveraging the interplay of electrical, inertial and capillary-driven interactions for controllable drop manipulation via multi-drop interactions for a variety of applications ranging from chemical processing to emulsion technology.

Validation of earthquake analysis methodology of a suction-caisson foundation-structure through model testing

Suction caissons are one of the most widely used foundation solutions for subsea structures and wind farms. Seismic response of subsea structures is however seldom documented properly, often just treated as a foundation capacity issue applying a quasi-static acceleration and not considering the inertial interaction between the structure and the soil. The more relevant tasks to document are the motions of the unit and the response of the externally connected flowlines and equipment/systems on the unit.Based on a case study located in the Shah Deniz field in the Caspian Sea, model centrifuge tests and numerical modelling were carried out to validate the global response of a 4-caisson supported manifold structure subject to seismic motions in soft clay. The centrifuge tests were carried out at 58 g at the centre for geotechnical modelling at UC Davis. To simulate the soil-structure interaction, a series of non-linear springs defined by kinematic hardening models were used in analyses with the ABAQUS software. This development includes the algorithms for determining the required model parameters. A very good agreement between recorded response from the centrifuge test and calculated response from the FE-analyses was achieved.The development and validation of the soil model presented in this paper is an improvement in design methodology for caisson foundations subjected to earthquake loading. The non-linear soil springs are well suited to incorporate in more detailed structural analyses where an accurate representation of the foundation response is required. The paper also briefly describes how the subsequent earthquake design analyses were performed for the Shah Deniz manifold structures making use of the validated soil spring model and the added value it gave to the project.

Inertial and kinematic interactions of bridge‐pile group subjected to liquefaction induced lateral spreading: Large‐scale shaking table experiments

AbstractThis paper investigates the seismic bridge‐pile‐soil system failure mechanisms due to liquefaction‐induced lateral spreading. Two large‐scale shaking table tests were performed on pile groups with and without bridges in sloped liquefiable soils overlain by soil crust. The systems were subjected to a weak earthquake signal (Tabas 0.05 g) and a strong earthquake signal (Tabas 0.3 g). Their responses were recorded in terms of excess pore pressure, acceleration, and displacement time histories. The piles seismic failure mode and mechanism are described based on the obtained results. In addition, the inertial and kinematic interaction effects on the piles’ deflection were evaluated. The results demonstrated that the bridge had no significant effect on the seismic response of the pile‐soil system under weak earthquakes. Meanwhile, the test model without a bridge experienced more significant soil lateral displacement, and the saturated sand exhibited dilatant behavior, and amplified the acceleration peak response during the strong earthquake. Moreover, the liquefaction‐induced lateral spreading moved the vulnerable position of the pile group bridge system from the pier bottom to the pile head, which changed the failure mode of the pile head. The results also revealed that, compared with weak earthquake excitation, the kinematic effect was significantly enhanced, and the inertia effect was weakened during strong earthquakes. Moreover, the pile curvature during both weak and strong earthquakes was inversely proportional to the bridge inertial load.

A probabilistic study on impedances and kinematic response factors of square pile groups in homogeneous soils

The complexity of the Soil-Structure Interaction (SSI) problem is mainly due to difficulties related to the modelling of the soil-foundation behaviour, which is not only frequency-dependent, but is also largely influenced by uncertainties related to soil properties and stratigraphic conditions. According to a sub-structuring scheme for the analysis of SSI problems, a deterministic approach is usually adopted for the analysis of the soil-foundation system assuming properties and geotechnical models based on the expert judgment, despite the fact that uncertainties related to the intrinsic variability of soil parameters are widely recognised and confirmed by experimental campaigns and laboratory tests.This paper presents a probabilistic study on the dynamic behaviour of square pile group foundations in homogeneous soils, focusing on the effects of the uncertainties related to (i) the frequency-dependent impedance functions and (ii) the kinematic response factors. Above quantities are required to define compliant restraints for the modelling of the soil-foundation system in performing inertial soil-structure interaction analysis, and for the definition of the foundation input motion starting from the free-field motion. Square pile groups are considered, and uncertainties are described through probabilistic distributions of parameters governing the soil-foundation dynamic response. The probabilistic analyses are performed through a numerical model developed by the Authors and some results are presented to show and discuss the variability of the results. In addition, a sensitivity analysis is performed to assess the influence of each variable uncertainty on the system response. Overall, response quantities are found to be very sensitive to shear wave velocity, although soil density and pile elastic modulus may often play a significant role.

Combined Effects of Liquefaction-Induced Lateral Spreading and Superstructure Inertial Loads on Pile Foundations

Pile foundations in sloping or gently sloped liquefiable soils are often subjected to a combination of inertial and lateral spreading loads. Current design codes vary significantly in terms of the methods used to analyze and design piles that are subjected to combined loading. The results from a full-scale shake table test on a 0.25-m-diameter reinforced concrete pile in gently sloping ground are used in this study to back-calculate the inertial loads, the kinematic loads, and the interaction between inertial and kinematic loads during seismic loading. It was found that large pile strains developed after liquefaction was triggered. The maximum pile strains (and curvatures) at shallow depths within the nonliquefiable crust were correlated with maximum inertial loads in the upslope direction that were resisted by a crust load applied in the downslope direction, indicating an out-of-phase interaction. The maximum pile strains (and curvatures) at deeper locations below the loose liquefiable sand were correlated with the maximum inertial loads in the downslope direction but without any resistance or driving load from the crust (i.e., no lateral spreading load during peak downslope inertial cycles). The lack of crust load during the downslope inertial cycles was attributed to the pile head outrunning the crust displacement, causing the pile to be pushed into a gap that had formed on the downslope front of the pile. The findings of this study contribute a data point to a wide range of inertial and kinematic interaction factors proposed by other studies and highlight the site- and project-dependency of interactions between inertial and kinematic loads.

Assessment of the Soil Structure Inertial Interaction Effect on the Behavior Coefficient Using Simplified Methods

This study aims to assess the effect of the Soil Structure inertial Interaction (SSI) on the behavior coefficient (R). For this purpose, R was estimated with and without SSI. The pushover N2 method and its extension SSI-N2 method were applied to the plain Reinforced Concrete (RC) frame structures. For calculating the SSI effect on R, four shear wave velocities Vs, representing rocky soil, firm soil, loose soil, and very loose soil, with three soil damping ratios ζg% for each soil type were considered. The estimated values of R using the N2 method were 4.1, 4.97, 5.75, and 6.96 for rocky soil, firm soil, loose soil, and very loose soil respectively. For the SSI-N2 method, R values were in the range of 3.67-3.97 for rocky soil, 4-4.69 for firm soil, 4.01-5.09 for loose soil, and 4.14-5.81 for very loose soil. In the Algerian code, R was kept constant for each soil type, and its value is 3.5 and 5 with and without infill masonry respectively. Soil shear wave velocity and the soil damping ratio must be taken into account in calculating R. The redundancy, overstrength, and ductility reduction coefficients were determined by taking into account the SSI. The SSI effect can change the values of R, so it must be taken into account when calculating R.

Seismic fragility of tall buildings considering soil structure interaction (SSI) effects

Soil Structure Interaction (SSI) effects have been extensively studied for low-rise buildings, while less contributions considered tall buildings. In this regard, 3D numerical simulations were herein performed to evaluate the seismic performance of a 20-floor building founded on pile foundation. SSI effects have been studied with a probabilistic-based approach in order to develop analytical fragility curves. Opensees was applied to perform non-linear dynamic analyses in order to consider soil hysteresis and plasticity that cause non-linear mechanisms in the ground and are responsible for structural damage. The principal findings consist of considering both the cases where SSI helps reducing the vulnerability of the system and the mechanisms of site amplification that are driven by SSI effects (kinematic and inertial interaction). In particular, the developed fragility curves show the role of the mutual interaction of the soil and of the structure (in terms of period elongation, lateral deflections, roof accelerations and floor drifts). Therefore, neglecting the role of SSI was shown to be responsible of the increase of the vulnerability of the entire system (soil-foundation-superstructure).

Assessment of Turbulent Mixing Associated With Eddy‐Wave Coupling Based on Autonomous Observations From the Arctic Canada Basin

AbstractInteraction between mesoscale eddies and near‐inertial internal waves can contribute to enhanced turbulence mixing but quantitative knowledge from in situ observations is still lacking. This study reveals how eddy/near‐inertial wave interactions (ENIs) can affect the variability of turbulent mixing in the ice‐covered Canada Basin of the Arctic Ocean. We use data from five Ice‐Tethered Profiler with Velocity (ITP‐V) systems that autonomously obtained vertical profiles of horizontal velocity as well as temperature and salinity, which enabled quantification of ENI‐caused turbulent mixing using a fine‐scale parameterization. From the ITP‐V observations in 2013–2015, 67 anticyclones were detected, of which 90% had a deep core at 150–250 m depth. The remaining eddies had a shallow core, typically embedded in the Pacific Summer Water (PSW). Just over one third of the eddies showed evidence of ENI with enhanced near‐inertial internal wave amplitude (NIW) near the eddy cores. For these ENI cases, the parameterized turbulence dissipation rate was O (10−10–10−8 W kg−1), the larger estimates being several orders of magnitude greater than the background level. For the deep eddies, the ENI process can largely be accounted for by the classical theory, NIWs are trapped inside the negative relative vorticity core of anticyclones. For one shallow eddy, the NIW signal was greatest below the core. We postulate that a vertically elongated system of NIWs cannot be constrained vertically within such small‐cored eddies. It is also interpreted that the wave enhancement below the core was supported by the isopycnal slope near the PSW through its geostrophic shear.