Kinematic Interaction Research Articles

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.

Kinematic pile-soil interaction using a rigorous two-parameter foundation model

The response of a single pile to vertically incident shear waves embedded in a homogenous visco-elastic soil layer of finite thickness is considered. In order to study the influence of the soil shear, the pile-soil interaction is modelled using a rigorous analytical elastic continuum model recently proposed by the first author that translates into a two-parameter Pasternak-type mechanical model with a viscose component to account for energy dissipation. The viscose behavior is represented by a bed of dashpots each arranged in parallel with an elastic spring. The elastic part of the model has two distinct important features. Primarily, its second elastic parameter directly represents the soil shear, which is missing in the classical beam-on-dynamic-Winkler foundation model. Secondly, the model is provided with fully-established parameters that are known down to a single coefficient determined through a calibration process with the help of the finite element method. These unique model parameters adjusted for the static pile response are used in the dynamic analysis. The second model parameter is used to study the influence of the soil shear on the pile response in terms of the various kinematic factors. The parametric study shows in general that the soil shear influence increases with decreasing pile-soil stiffness ratio over a wide range of frequency and pile slenderness ratios. It has been particularly observed that neglecting the soil shear can excessively overestimate the pile response, especially of reinforced concrete piles in soils of wide ranging stiffness among other effects.

Excitation Spectrum in an Ensemble of Hubbard Bosons

An approach that makes it possible to correctly derive equations describing the Bose–Einstein condensation and the spectrum of elementary excitations in the ensemble of Hubbard bosons in the strong correlation regime (U gg {text{|}}{{t}_{{fm}}}{text{|}}) has been developed in the atomic representation using the Dyson method with the introduced indefinite metric. The kinematic Dyson interaction caused by the properties of the commutation relations of dynamic variables plays an important role in such a system. An effective Hamiltonian has been obtained using the operator form of perturbation theory at finite U values. It has been shown that the properties of the ensemble of Hubbard bosons have been determined by the kinematic interaction, correlated hopping, and the attraction between Hubbard bosons. Numerical calculations have demonstrated the effect of these interactions on the characteristics of the energy spectrum of excitations of the ensemble of Hubbard bosons and on the dependence of the density of condensate particles on the density of bosons in the system.

Vision-Kinematics Interaction for Robotic-Assisted Bronchoscopy Navigation.

Endobronchial intervention is increasingly used as a minimally invasive means for the treatment of pulmonary diseases. In order to acquire the position of bronchoscopy, vision-based localization approaches are clinically preferable but are sensitive to visual variations. The static nature of pre-operative planning makes mapping of intraoperative anatomical features challenging for learning-based methods using visual features alone. In this work, we propose a robust navigation framework based on Vision Kinematic Interaction (VKI) for monocular bronchoscopic videos. To address visual-imbalance between the virtual and real views of bronchoscopy images, a Visual Similarity Network (VSN) is proposed to extract domain-invariant features to represent the lumen structure from endoscopic views, as well as domain-specific features to characterize the surface texture and visual artefacts. To improve the robustness of online estimation of camera pose, we also introduce a Kinematic Refinement Network (KRN) that allows progressive refinement of camera pose estimation based on network prediction and robot control signals. The accuracy of camera localization is validated on phantom and porcine lung datasets from a robotically controlled endobronchial intervention system, with both quantitative and qualitative results demonstrating the performance of the techniques. Results show that the features extracted by the proposed method can preserve the structural information of small airways in the presence of large visual variations along with the much-improved camera localization accuracy. The absolute trajectory errors (ATE) on phantom data and porcine data are 8.01 mm and 8.62 mm respectively.

The Filtering Effect of Pile Foundations in Clay

This paper reports the results of a series of centrifuge experiments exploring the dynamic response of pile foundations. The model tested in a centrifuge at 50g consisted of an isolated pile and two pile groups embedded in a kaolin clay, subjected to a sequence of quasi-sinusoidal waves with different amplitudes and frequencies. The results are back-analyzed through a two-step procedure. First, a one-dimensional ground response analysis is performed, in which the small-strain shear modulus is evaluated using data from air hammer tests, while a literature model is used to account for nonlinearity of soil behavior. Second, a three-dimensional finite-element analysis of the model foundations is carried out using the mobilized soil damping ratio and shear modulus determined from the previous step. The aforementioned procedure allowed to reproduce satisfactorily the response of the model foundations tested in the centrifuge, showing that the response of these models is strongly affected by the inertial oscillation of the cap connecting piles necessary to accommodate the measurement devices and to rigidly connect the piles’ heads of the groups. The same numerical model was then adopted to evaluate the change of seismic motion due to pure kinematic interaction effects by setting the pile cap mass equal to zero. This allowed to check the prediction capability of simplified methods of analysis for the evaluation of the base excitation of pile-supported structures. In addition, a number of issues related to the execution of centrifuge tests aimed at investigating the kinematic interaction between pile and soil are highlighted and discussed.

Measurements of low-mode asymmetries in the areal density of laser-direct-drive deuterium-tritium cryogenic implosions on OMEGA using neutron spectroscopy.

Areal density is one of the key parameters that determines the confinement time in inertial confinement fusion experiments, and low-mode asymmetries in the compressed fuel are detrimental to the implosion performance. The energy spectra from the scattering of the primary deuterium-tritium (DT) neutrons off the compressed cold fuel assembly are used to investigate low-mode nonuniformities in direct-drive cryogenic DT implosions at the Omega Laser Facility. For spherically symmetric implosions, the shape of the energy spectrum is primarily determined by the elastic and inelastic scattering cross sections for both neutron-deuterium and neutron-tritium kinematic interactions. Two highly collimated lines of sight, which are positioned at nearly orthogonal locations around the OMEGA target chamber, record the neutron time-of-flight signal in the current mode. An evolutionary algorithm is being used to extract a model-independent energy spectrum of the scattered neutrons from the experimental neutron time-of-flight data and is used to infer the modal spatial variations (l = 1) in the areal density. Experimental observations of the low-mode variations of the cold-fuel assembly (ρL0 + ρL1) show good agreement with a recently developed model, indicating a departure from the spherical symmetry of the compressed DT fuel assembly. Another key signature that has been observed in the presence of a low-mode variation is the broadening of the kinematic end-point due to the anisotropy of the dense fuel conditions.

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).

Seismic evaluation of frictional FRP piles in saturated sands using shaking table tests

This manuscript presents results of two shaking table tests that were used to characterize seismic performance of Fibre-Reinforced Polymers (FRP) pile groups in saturated sand. A laminar shear box with a dimension of 1.0 m × 1.0 m and a depth of 1.0 m was employed to contain the soil medium and allow the soil to respond in the same fashion as the free field. Two types of composite group piles (2 × 2) made of Carbon FRP (CFRP) and Glass FRP (GFRP) along with a series of Aluminum model piles were manufactured and embedded as frictional piles within the soil. The pile-soil models were subjected to acceleration time histories adopted from the 2010 Val-des-Bois Earthquake in Canada and the 1995 Kobe Earthquake. The foundation motions recorded along the model piles showed significantly higher levels of excitation compared to the accelerations recorded within the soil at the same level. This was attributed to strong interaction between the soil and the foundation, and higher flexural stiffness of the model piles. Pile material was also found to influence the seismic response of pile caps and its superstructure through kinematic soil-pile interaction and possible rocking motion. The aluminum pile cap experienced significantly higher acceleration response compared to the FRP piles. Among the FRP piles, GFRP piles were shown to provide slightly better performance and could be an appropriate alternative piling material for frictional traditional piles especially in liquefiable soils.

Kinematic seismic response of end-bearing piles to S-waves

In this paper we revisit the problem of modelling analytically the kinematic interaction between a single pile and its surrounding soil under the action of seismic shear waves, by means of a Tajimi-type continuum elastodynamic model in three dimensions. The model provides the steady-state kinematic response of a cylindrical end-bearing pile embedded in a homogeneous viscoelastic soil layer, subjected to vertically propagating harmonic S-waves. Results of the model are first validated against the results of numerical simulations, and the results of an existing, approximate solution. Accordingly, we employ the model in a parametric study, where we investigate the sensitivity of the seismic response of piles to certain key problem parameters, including pile slenderness, soil-pile relative stiffness, excitation frequency and fixity conditions at the pile head. The solution yields closed-form expressions for pile deformations and for the soil resistance developing on the pile, that do not require introducing fitting coefficients.

Nonlinear steel strains in cracked RC beams based on bond-stress profiles

Steel–concrete bond is instrumental in transferring tensile forces to the concrete via the bond stresses, whose values and distribution along a steel bar vary with the level of the load applied to the reinforcement. To study the profile of the strains in the reinforcement, the variation of the bond-stress distribution is considered and the bond stresses are introduced according to Model Code 2010. The transfer length where the bond stresses are active is shown to be a function of the slip in the cracked sections. This slip can be evaluated from the concrete strains based on the plane-section hypothesis to take care of the strain compatibility between the concrete and the reinforcement. The equilibrium of the internal forces, the constitutive laws of the materials and the bond stress-slip law make it possible to model the kinematic interaction between the concrete and the reinforcement. An iterative algorithm is proposed to calculate the steel strains, and the effectiveness of the numerical procedure is checked against the test data coming from simply-supported RC beams tested in this research project or available in the literature. The results show that the nonlinear evolution of steel–concrete slip close to the cracks may increase the transfer length of the bond stresses by 50% under increasing loads, and the steel strains by up to 90% along the bonded length. As a result, the steel-strain profile becomes a slightly-nonlinear function of the load, which is also markedly affected by the crack pattern.

Dynamic response of pile embedded in unsaturated soil under SH waves considering effect of superstructure

Soil is usually treated as one-phase or two-phase media in previous soil-pile dynamic studies. However, the air inside the soil pores can induce strong matrix suction to the skeletons, which would significantly affect the propagation of the shear horizontal waves within the soil. In addition, the superstructure's effect on the soil-pile system's dynamic response is often neglected. This can result in the underestimation of the dynamic impedance of a pile, which would further lead to the overdesign of the pile dimensions. In this study, a novel unsaturated soil–pile–superstructure model induced by vertically propagating shear horizontal waves is established to investigate the seismic performance of a pile under the influence of superstructures. The analytical solutions of the kinematic amplification and interaction factors (IU and AU, respectively) are derived using the Laplace transform and variable separation method. The developed solution is verified by comparing results from the hybrid boundary element method and the dynamic Winkler model in previous studies. Based on the obtained solutions, a parametric study is conducted to investigate the effects of pile and soil properties on the system's seismic response. The main conclusions can be drawn as follows: (1) When 0.2 < a0 (normalized frequency) < 0.7, IU and AU decrease with the increase of soil water saturation. This trend becomes extremely evident when the saturation is above 0.95. (2) Resonance appears at 0 < a0 < 0.7, and the resonance frequency decreases with the increase of the superstructure mass. (3) The vibration of the free-field soil has a non-negligible effect on reducing the system's seismic response.

Defensive or competitive Autonomous Vehicles: Which one interacts safely and efficiently with pedestrians?

The emergence of Autonomous Vehicles (AVs) could provoke unexpected challenges in urban traffic environments. One such crucial challenge is the conflicts between pedestrians and AVs, particularly on unsignalized mid-block crosswalks (UMC), where pedestrians are exposed to the AV flow. This study investigates the efficiency and safety performance of a UMC in the presence of both AVs and pedestrians considering the diversities in their behaviors. Through empirical analyses, two pedestrians’ crossing decision models are built and four groups of speed profiles are classified. Meanwhile, based on previous literature, defensive and competitive driving strategies are assumed for AVs. The simulation is implemented on an agent-based framework that can dynamically reproduce the kinematic interactions between pedestrians and vehicles. Results indicated that with a reasonable safety margin (2.5 s), percentages of low post encroachment time events for competitive AVs with different pedestrian types are smaller than defensive AVs with differences of 0.2% to 2.9%. The average delays of competitive AVs for all pedestrian types are smaller than defensive AVs with a maximum estimated difference of 39 s. Moreover, the analysis showed that lowering the speed limit may reduce the crash rate of competitive AV up to 0%. It is also found that the pedestrians who make reckless crossing decisions and change their speed drastically during the crossing process are more likely to incur crashes with competitive AVs. Therefore, if pedestrian behaviors can be regulated reasonably, competitive AVs with appropriate parameter settings are most suitable for UMC in the future.

Seismic resonant metamaterials for the protection of an elastic-plastic SDOF system against vertically propagating seismic shear waves (SH) in nonlinear soil

The paper explores the key mechanisms that govern the dynamic interaction between resonant metamaterials (consisting of multiple unit cells embedded in the soil, with horizontally vibrating internal masses) and an existing nonlinear structure on nonlinear soil. Elastic behavior of the soil and of the SDOF system, representing the structure, is also investigated for comparison. The Real-ESSI Simulator is employed to develop in-plane (2D) finite element (FE) models, and an extensive parametric analysis is conducted to evaluate the influence of key parameters on the protective efficiency of resonant metamaterials. Both artificial and real ground motions are used as seismic excitation, vertically propagated through the soil as shear waves (SH), employing the Domain Reduction Method (DRM). Two protective mechanisms are identified. The first mechanism is related to the inertial interaction of the metamaterials with the surrounding soil, namely, it is the out-of-phase resonant oscillation of the internal metamaterial masses with respect to the soil at periods close to the natural period of the structure. The maximum reduction in structural response is achieved when the resonant period of the metamaterials is equal or a bit larger than the effective period of the structure. The second mechanism is related to the kinematic interaction of the metamaterials with the surrounding soil, namely, the presence of empty unit cells (no internal masses) in the soil next to the structure creates a protective “shadow” zone. This kinematic interaction mechanism becomes effective when the wavelength of the incoming seismic waves is comparable to the size of the metamaterials, and at the same time, the period of the waves is close to the natural period of the structure. When both soil and structural nonlinearities are considered, the effect of metamaterials remains always beneficial, and their action is localized, making them practically harmless to neighboring structures.

Evaluation of dynamic soil-structure interaction effects in buildings with underground stories using 1 g physical experimentation in a transparent shear laminar box

This article presents a study of the Dynamic Soil-Structure Interaction (DSSI) using physical reduced–scale models of a building under different configurations of above-ground and underground stories. Each model was tested in a laminar shear box with a transparent front side. This characteristic of the device makes it possible to visualize the soil particles during the test and acquire data from the soil-structure interaction in a direct and spatially continuous way. A shaking table, an array of 3 high–speed and high–resolution cameras and a tactile dynamic pressure sensor were used. Ricker wavelets, with a wide range of frequencies and amplitudes, were used to evaluate the transfer functions in the system and the seismic response of model. Kinematic interaction effects were evaluated using the Digital Image Correlation (DIC) technique. It is verified that the experimental system allows a detailed tracking of the dynamic interaction between the building and the surrounding soil. The results show the direct relationship between the frequency content of the input wavelet and the dynamic pressure distribution acting on the underground levels, and the increase of the building’s first vibrating period. In addition, it was found that the distribution and magnitude of the lateral soil thrust is dominated by the superstructure vibration, and not the ground movement. This relationship becomes more important as the slenderness of the building increases, i.e., as the rocking mode of vibration becomes more significant. Additionally, in the case of buildings with basements, our results suggest that the combination of the increased confinement, the interaction of the foundation in terms of motion compatibility and the vibrations transferred from the superstructure to the ground produces an invariable reduction in effective base motion, suggesting that neglecting the effects of DSSI would be a conservative assumption.

Diver tracking in unknown structured clutter background using a force-based GM-PHD filter

This paper considers the problem of tracking multiple human divers using a high-resolution 2D active sonar. The proposed solution can handle the real-world challenges of a time-varying number of targets, complex correlated diver dynamics affected by external factors (e.g., water current, activities of neighbouring divers and the intent of the divers themselves), and unknown spatial non-homogeneous clutter intensity due to the complex non-stationary underwater environment with structured clutter. The proposed algorithm uses the probability hypothesis density (PHD) filter with a novel force-based diver state evolution model, along with a log-Gaussian Cox process (LGCP) model for a global clutter spatial intensity estimation.In addition, the posterior Cramér-Rao lower bound (PCRLB), which quantifies the best possible accuracy in the presence of kinematic interactions among targets in an uncertain underwater structured environment, is derived as the benchmark for performance evaluation. Simulation results demonstrate the improved performance of the proposed method over the standard PHD filter.

A Soil-Pile Response under Coupled Static-Dynamic Loadings in Terms of Kinematic Interaction

Abstract Although the axial aptitude and pile load transfer under static loading have been extensively documented, the dynamic axial reaction, on the other hand, requires further investigation. During a seismic event, the pile load applied may increase, while the soil load carrying capacity may decrease due to the shaking, resulting in additional settlement. The researchers concentrated their efforts on determining the cause of extensive damage to the piles after the seismic event. Such failures were linked to discontinuities in the subsoil due to abrupt differences in soil stiffness, and so actions were called kinematic impact of the earthquake on piles depending on the outcomes of laboratory tests and other numerical analyses. In this research, numerical modeling is used to explore the kinematic forces created in a single pile erected in two sand layers under two different conditions (dry and saturated states). Based on the obtained results from the physical model, the maximum bending moment was observed at a depth around 200 mm below the ground surface in the loose sand layer, then these values gradually reduced until it becomes negative in the dense sand layer. It has been demonstrated that this modeling may be used to predict how a pile foundation would respond to “kinematic” loading generated by ground movements during a seismic event. Consequently, the current findings could be used in the design and construction of bored aluminum or steel piles in Al-Karbala soil.

Kinematic response of vertical and batter pile groups in non‐linear soft soil

AbstractThis paper presents a comprehensive numerical study on kinematic response of vertical and batter pile groups in soft soil, where soil non‐linearity, batter angle, pile spacing and excitation frequency are related to pile‐cap displacements, rotations, maximum pile moments, shear forces and axial forces. The finite element model is constructed in OpenSees MP, and parallel computing is utilized for a better (faster) performance. Results reveal that soil non‐linearity has a profound impact on the kinematic interaction. Increasing batter angle decreases horizontal displacements but increases rotations. Batter pile groups yield lower spectral accelerations compared to vertical pile groups. For high , the spectral accelerations of the pile‐cap may be lower compared to the spectral acceleration of the seismic input motion. Estimation using non‐linear interaction factors conservatively estimates pile‐cap displacements and rotations, while roughly captures the effects with respect to batter angle and frequency content within the specified framework.

Transverse seismic response of end‐bearing pipe piles to S‐waves

AbstractThis paper presents a method for the seismic analysis of open‐ended pipe piles subjected to vertically propagating S‐waves, that considers kinematic interaction between the pipe pile and its external and internal soil. Following the presentation of the elastodynamic continuum model, which is based on the assumptions of linear elastic soil response and uniform soil conditions, we employ the derived solution to investigate the sensitivity of the seismic response of pipe piles to certain key problem parameters, such as pile slenderness or the relative stiffness of the pipe pile compared to its surrounding soil. We demonstrate that the bending stiffness of pipe piles is governing their seismic response, and that thin‐walled pipe piles offer the best material usage versus seismic performance ratio. The presented solution offers a low‐cost alternative to complex numerical simulations for preliminary seismic design purposes, such as the selection of optimal pipe pile section geometry.

Strain Signals Governed by Frictional‐Elastoplastic Interaction of the Upper Plate and Shallow Subduction Megathrust Interface Over Seismic Cycles

AbstractThe behavior of the shallow portion of the subduction zone, which generates the largest earthquakes and devastating tsunamis, is still insufficiently constrained. Monitoring only a fraction of a single megathrust earthquake cycle and the offshore location of the source of these earthquakes are the foremost reasons for the insufficient understanding. The frictional‐elastoplastic interaction between the megathrust interface and its overlying wedge causes variable surface strain signals such that the wedge strain patterns may reveal the mechanical state of the interface. To contribute to this understanding, we employ Seismotectonic Scale Modeling and simplify elastoplastic megathrust subduction to generate hundreds of analog seismic cycles at a laboratory scale and monitor the surface strain signals over the model's forearc across high to low temporal resolutions. We establish two compressional and critical wedge configurations to explore the mechanical and kinematic interaction between the shallow wedge and the interface. Our results demonstrate that this interaction can partition the wedge into different segments such that the anelastic extensional segment overlays the seismogenic zone at depth. Moreover, the different segments of the wedge may switch their state from compression/extension to extension/compression domains. We highlight that a more segmented upper plate represents megathrust subduction that generates more characteristic and periodic events. Additionally, the strain time series reveals that the strain state may remain quasi‐stable over a few seismic cycles in the coastal zone and then switch to the opposite mode. These observations are crucial for evaluating earthquake‐related morphotectonic markers and short‐term interseismic time series of the coastal regions.

Corrigendum to “Influence of the sloping ground conditions and the subsequent shaking events on the pile group response subjected to kinematic interactions for a liquefiable sloping ground”[Soil Dyn. Earthq. Eng. 152 (2022) 107036

Corrigendum to “Influence of the sloping ground conditions and the subsequent shaking events on the pile group response subjected to kinematic interactions for a liquefiable sloping ground”[Soil Dyn. Earthq. Eng. 152 (2022) 107036