Structure-foundation System Research Articles

Pseudo-damage simulation and CNN deep learning for damage identification of submerged structure-foundation systems

Autonomous damage identification of submerged structure-foundation systems is challenging due to the difficulty of acquiring damage-induced system responses for training deep learning models. In this study, a novel approach integrating pseudo-damage simulation and convolutional neural network (CNN) deep learning is proposed for damage identification in the submerged structure-foundation system. Pseudo-damage simulation is a technique to generate equivalent damage conditions in inaccessible submerged sub-systems for training deep learning models. The following approaches are implemented to achieve the objective. Firstly, a scheme of pseudo-damage simulation for 1-D CNN deep learning is designed for the caisson-foundation system. Secondly, a vibration monitoring method using pseudo-wave-impulse excitations is designed for the caisson-foundation system. Thirdly, 1-D CNN models are trained for individual caisson units to predict the location and size of foundation damage by vibration signals out of a series of pseudo-damage cases. The 1-D CNN models demonstrate accurate performance in handling untrained scenarios. Experimental results validate the effectiveness of the proposed approach in achieving high accuracy for identification of the foundation damage.

Uncertainty and Latin Hypercube Sampling in Geotechnical Earthquake Engineering

A soil–foundation–structure system (SFSS) often exhibits different responses compared to a fixed-base structure when subjected to earthquake ground motion. Both kinematic and inertial soil–foundation–structure interactions can significantly influence the structural performance of buildings. Numerous parameters within an SFSS affect its overall response, introducing inherent uncertainty into the solution. Performing time history analyses, even for a linear elastic coupled SFSS, requires considerable computational effort. To reduce the computational cost without compromising accuracy, the use of the Latin Hypercube Sampling (LHS) technique is proposed herein. Sampling techniques are rarely employed in soil–foundation–structure interaction analyses, yet they are highly beneficial. These methodologies allow analyses determined by sampling to be conducted using commercial codes designed for deterministic analyses, without requiring any modifications. The advantage is that the number of analyses determined by the sampling size is significantly reduced as compared to considering all combinations of input parameters. After identifying the important samples, one can evaluate the seismic demand of selected soil–foundation–bridge pier systems using finite element numerical software. This paper indicates that LHS reduces computational effort by 60%, whereas structural response components (translation, rocking) show distinct trends for different systems.

Comparative Analysis of Foundation Systems in Expansive Soil: A Three-Dimensional Model Approach to Moisture Diffusion and Volume Changes

This study compares the performance of various foundation systems in expansive soils, such as mats, granular anchor piles, and concrete piles. Expansive soils experience volumetric changes due to moisture fluctuations, which can lead to structural damage. Abaqus software, in conjunction with the SCV approach, is used to analyze soil-foundation interactions. A custom subroutine enhances simulation accuracy by incorporating empirical data on unsaturated clay behavior, matric suction, and variations in effective stress. The method’s accuracy is validated by comparing simulation results to field and laboratory experiments. The findings indicate that increasing the applied load on mats decreases overall heave but increases the differential heave. Additionally, higher soil permeability dereases the differential heave of mats. Granular anchor piles outperform concrete piles by more than 50% in highly expansive soils, suggesting a preference for these foundations. This study provides insights into the behavior of expansive soils, which will assist engineers in designing resilient foundation systems for structures.

CNN-Based Damage Identification of Submerged Structure-Foundation System Using Vibration Data

This study presents a convolutional neural network (CNN) deep learning approach for identifying damage in submerged structure-foundation systems using vibration data. Firstly, foundation damage in a lab-scale caisson-foundation system is simulated to measure time-history responses. Singular value decomposition (SVD) responses are derived from the time-history responses. Secondly, the 1-D CNN deep learning model is trained using both the time-history responses and SVD responses. Finally, the trained CNN models are implemented to evaluate the foundation damage under conditions of noise contamination and partially untrained data. The experimental results demonstrate the effectiveness of CNN models for damage identification and highlight the comparative strengths of time-history and SVD data. The CNN model trained using SVD data outperforms the other model when under noise contamination conditions, while the CNN model trained using time-history data maintains better accuracy in partially untrained data conditions. Integrating both types of data enhances the accuracy of damage classification.

Study on seismic response of liquefiable soil-pile group considering pile cap and soil contact

In this paper, based on the centrifuge test of liquefied soil-pile foundation system, a numerical model of liquefied soil-pile foundation-structure system is modelled by using OpenSees platform. In the simulation model, the friction effect between liquefied ground and low pile cap is considered, and the method of establishing virtual nodes is used to deal with the non-linear contact between liquefiable soil and low pile cap. The rationality and effectiveness of the numerical simulation method adopted in this paper has been verified and evaluated by comparing with the results of centrifuge experiments. A typical liquefaction soil-pile integrated finite element model is modelled using validated numerical simulation methods. The law of seismic response of the pile foundation system with different embedding depths of pile cap, different contact modes between the pile cap and saturated sand, and the thickness of the overlying saturated loose sand layer are discussed. The results show that the pile cap and pile foundation in the high pile cap system show higher seismic response characteristics than the other three low pile cap system conditions; Under the condition of different contact modes between the pile cap and the surrounding saturated sand, the peak bending moment and residual displacement of the pile foundation calculated by the bond contact are larger than calculated by the friction contact, and the deformation of pile is more significant. By comparing the working conditions of different thicknesses of overlying saturated loose sand layer, it is found that the degree of liquefaction in shallow soils is less affected by thickness of the saturated loose sand. As the thickness of saturated loose sand layer increases, the peak bending moment and residual displacement at the top of the pile also gradually increase. The change of peak bending moment at the soil interface is more obvious.

Topology Optimization based Integrated Design of Structure-Foundation System

This study introduces a novel topology optimization method with the goal of achieving an integrated design for offshore infrastructure. A key feature of this method is its capability to eliminate artificial boundaries between the design of the above-ground support structure and underlying soil foundation, thus facilitating a more efficient and effective design solution. In contrast to traditional stress-based topology optimization methods, the proposed approach combines limit analysis with density-based topology optimization techniques. Formulated as a volume minimization task, it targets the structure’s bearing capacity, ensuring that the external force applied is precisely matches the bearing capacity of the system obtained in the design. Furthermore, it is demonstrated that the proposed method exhibits favorable convergence properties within a prescribed number of iterations, indicating a steady progression towards an optimized solution.

Reliability of pile foundations in the Arctic zone of the Russian Federation (Tomsk)

One of the main problems associated with the operation of building structures in permafrost conditions, is the deformation of support systems due to changes in soil geometric parameters. The methods used today for assessing the health of buildings and support systems are not universal. One of the important indicators during the buildings operation, which allows us to determine the health of the permafrost soil–pile foundation–structure system, is the vibrational amplitude of the supporting structure.Purpose: The aim of this work is to conduct a comprehensive analysis of the pile foundation reliability in the Arctic zone of the Russian Federation.Methodology/approach: Modern monitoring and remote sensing technologies are used to collect the real-time data. Numerical modeling was carried out to assess long-term trends in changes in meteorological parameters and their impact on pile foundations. New methods and technologies are developed to improve the stability of pile structures in permafrost conditions and permanently frozen soil.Practical implications: The obtained results can be used in design and operation of buildings in permafrost conditions. Moreover, these results can be used to develop new technologies and equipment for improving the performance in the oil and gas and other industries relating to engineering structures in the Arctic zone of Russia.

A negative stiffness dynamic base absorber for seismic retrofitting of residential buildings

In this study, a negative stiffness-based passive vibration absorber is developed and implemented as a seismic retrofitting measure for typical reinforced concrete (RC) residential buildings. The device, namely, the extended KDamper for retrofitting (EKD-R), is introduced at the base of the structure, between the foundation level and the first story of the building. The design of the EKD-R device and the selection of its properties are undertaken by incorporating a harmony search (HS) algorithm that provides optimized parameters for the mechanism, following constraints and limitations imposed by the examined structural system. Nonlinearities due to the plastic behavior of the structural members and soil–structure interaction (SSI) effects are modeled and taken into consideration during the process. Subsequently, a realistic case study of a benchmark three-story RC building is examined, and the performance of the EKD-R system is assessed. The building superstructure is designed according to Eurocodes. The structure–foundation system, along with the EKD-R, is explicitly modeled using finite elements (FE) that may realistically capture structural nonlinearities and SSI effects. The HS algorithm is employed, and optimized EKD-R components are obtained and implemented in the benchmark structure. Finally, a series of recorded real ground motions are selected, and nonlinear time-history dynamic analyses are conducted aiming to assess the behavior of the controlled system. Results indicate the beneficial role of the novel dynamic absorber, hence rendering the concept a compelling seismic retrofitting technology.

Fragility curves for existing reinforced concrete buildings, including soil–structure interaction and site amplification effects

SSI and site amplification effects are investigated as influences on the seismic fragility of existing reinforced concrete moment-resisting frame and dual frame-wall system buildings supported on shallow foundations without interconnecting beams. We build upon a holistic methodology that accounts for site amplification and soil–foundation–structure interaction effects using a modular approach. We calculate fragility curves based on nonlinear dynamic analyses for various building structural typologies and geometries, infill conditions, code provisions, and soil profile materials and dynamic characteristics. We demonstrate that site amplification during earthquakes may significantly increase the fragility of the soil–foundation–structure system, which is reflected in its vulnerability. Moreover, SSI is especially prevalent for buildings on soft soil profiles and might modify their fragility. We propose a modular method to include site amplification and/or soil–structure interaction effects in a large-scale earthquake vulnerability assessment using fragility modifiers, which we express using an easy-to-code equation form.

Seismic Interaction of Adjacent Structures on Liquefiable Soils: Insight from Centrifuge and Numerical Modeling

In urban environments, structures are often built in close proximity to each other. Seismic coupling and structure-soil-structure interaction (SSSI) are known to affect system accelerations, settlement, and tilt with consequential impact on structural damage. Yet, the extent and nature of these interactions are poorly understood, particularly on ground susceptible to liquefaction. In this paper, we use dynamic centrifuge and numerical modeling of isolated and neighboring, similar and dissimilar, shallow-founded structures on layered, level, saturated, and liquefiable soils to provide insight into (1) the mechanisms of SSSI; and (2) the relative influence of key parameters on system performance. Fully-coupled, nonlinear finite-element analyses of the centrifuge experiments indicated that in addition to a comprehensive calibration of the soil constitutive model parameters, use of higher-order elements and a sufficiently large domain size in three dimensions (3D) were critical ingredients to predicting the general trends in system response compared to centrifuge recordings. A limited numerical sensitivity analysis was performed subsequently. The results identified the key parameters affecting SSSI as spacing between the two foundations (S) in relation to their width (W) as well as the contact stress and geometry of the neighboring foundation-structure system. SSSI slightly decreased the permanent settlement of structures at the expense of a notable increase in their permanent tilt, particularly when S≤W. The foundation’s spectral accelerations were observed to amplify at shorter periods when near a taller and heavier building at S≤W/3, which was attributed to the added confinement. Increasing the uniform thickness of the critical liquefiable layer increased both adjacent structures’ permanent settlement, while not affecting their residual tilt or SSSI. Importantly, the impact of SSSI on foundation tilt and accelerations remained significant for building spacings exceeding 2.5W. The results point to the importance of considering the impact of SSSI on structure’s key engineering demand parameters and the urgent need for improved guidelines when assessing and treating liquefaction in urban settings.

On the finite element modeling of a particular shallow foundation system for soft soil

The presentation deals with an investigation on the static and dynamic behavior of a five floors reinforced concrete building supported by a shallow foundation system, called SNSF (Spider Net System Footing). The present study concentrates on the linear static under permanent and life vertical loads and on the free vibrations of the upper structure and the foundations. The study based on performing 3D solid finite elements includes the soil underneath (one layer of 2 m and an additional layer of 9 m). Several aspects are investigated like: the structural analysis of the SNSF foundation compared to a simpler raft foundation and the soil-foundation interaction of the soil and the structurefoundation system on the first frequencies and modes of vibration.

A practical method for seismic response analysis of nonlinear soil-structure interaction systems

Soil–structure interaction (SSI) plays an important role in the analysis of seismic structural responses. This study significantly extends an efficient linear SSI analysis method presented previously by the authors and co-workers to realistic nonlinear SSI systems, that is, systems with nonlinear soil, nonlinear structures, and flexible foundations (e.g. single- or multiple-pile foundations). The flexible foundations lying on half-space nonlinear soil are represented by frequency-dependent compliance functions that are fitted numerically instead of obtained by closed-form solution. These functions are then transferred to the time domain using the discrete-time recursive filtering method. A non-iterative algorithm is applied to guarantee the boundary conditions between soil and structure, that is, the displacement continuity and force equilibrium between them. The proposed method is implemented on an open-source FE software framework, called OpenSees. The accuracy and efficiency of the extended coupling method are investigated in detail through the seismic response analyses of typical soil–foundation–structure systems while considering the cases of linear or nonlinear soil, linear or nonlinear structures, and single- or multiple-pile foundations. Results show that the extended coupling method is significantly faster than the traditional FE method and provides acceptably accurate solutions for SSI systems with linear or low-to-moderate nonlinear soil. The paper provides a method for fast evaluation of nonlinear SSI effects in seismic structural response analysis.

Direct Method for Generating Floor Response Spectra considering Soil–Structure Interaction

ABSTRACT A methodology is developed for generating floor response spectra (FRS) considering the effect of dynamic soil–structure interaction (SSI) based on the substructure technique and a recently-developed direct spectra-to-spectra method. Dynamic stiffness matrix of a three-dimensional structure with a rigid foundation subject to three translational and three rotational base excitations is derived, and is expressed in terms of the modal information of the structure. A transfer matrix, depending on the dynamic stiffness matrices of the structure-foundation system and generalized soil springs, is developed to modify the tri-directional response spectra at the foundation level of free-field (FIRS) in soil medium. The modified response spectra, called foundation level input response spectra (FLIRS), are used as the input to the fixed-base structure to generate FRS using the direct spectra-to-spectra method. Numerical examples of a reactor building and a service building in nuclear power plants demonstrate the accuracy and efficiency of the proposed method. FRS with % and % Non-Exceedance Probability (NEP) given by the proposed method agree well with the FRS obtained from a large number of time history analyses. Furthermore, the effect of SSI on FRS is studied, the physical meaning, and the advantages of the proposed method are highlighted.

Effects of Stratification on Soil–Foundation–Structure Interaction: Centrifugal Observation and Numerical Simulation

It is essential to reduce structural damages caused by earthquakes in severe conditions, such as layered ground, especially when a soft soil layer is close to the surface. In this study, the kinematic and inertial interactions, two mechanisms of soil–foundation–structure interaction (SFSI), of different soil–foundation–structure systems (SFS) were investigated on uniform and layered grounds. Two layered soil profiles composed of a low stiffness layer laid over another were prepared in an equivalent shear beam container. Nine centrifuge experiments were carried out for three structures located on the surface of each ground and exposed to the Hachinohe earthquake while increasing the peak acceleration of the input motion. Numerical simulations were performed to simulate the centrifuge tests. It was found that roof motion (RM) of the tall structure increased in layered profile even though the free-field motion (FFM) decreased compared to homogeneous ground. The appearance of a soft layer beneath structures modifies the SFS system’s stiffness that causes kinematic and inertial interactions to alter to those on uniform soil profile.

Fragility curve modifiers for reinforced concrete dual buildings, including nonlinear site effects and soil–structure interaction

We investigate the influence of soil–structure interaction (SSI) and nonlinear soil behavior on the seismic fragility of reinforced concrete (RC) dual (frame + shear wall) buildings resting on shallow foundations. This article includes a holistic methodology to account for nonlinear soil behavior and soil–foundation–structure interaction in a modular way. Using nonlinear dynamic analyses, we derive fragility curves for a wide set of building typologies and soil profiles, showing that soil behavior during strong shaking significantly affects the vulnerability of the soil–foundation–structure system. The influence of SSI is pronounced mostly for soft soil profiles, varying in a building-specific way. Post-processing of our results evolves into a set of fragility modifiers that enable risk analysts to massively account for soil-related and/or SSI effects in large-scale risk assessments.

Robustness of simplified analysis methods for rocking structures on compliant soil

SummaryRecognizing the beneficial effect of nonlinear soil–foundation response has led to a novel design concept, termed ‘rocking isolation’. The analysis and design of such rocking structures require nonlinear dynamic time history analyses. Analyzing the entire soil–foundation–structure system is computationally demanding, impeding the application of rocking isolation in practice. Therefore, there is an urgent need to develop efficient simplified analysis methods. This paper assesses the robustness of two simplified analysis methods, using (i) a nonlinear and (ii) a bilinear rocking stiffness combined with linear viscous damping. The robustness of the simplified methods is assessed by (i) one‐to‐one comparison with a benchmark finite element (FE) analysis using a selection of ground motions and (ii) statistical comparison of probability distributions of response quantities, which characterize the time history response of rocking systems. A bridge pier (assumed rigid) supported on a square foundation, lying on a stiff clay stratum, is used as an illustrative example. Nonlinear dynamic FE time history analysis serves as a benchmark. Both methods yield reasonably accurate predictions of the maximum rotation θmax. Their stochastic comparison with respect to the empirical cumulative distribution function of θmax reveals that the nonlinear and the bilinear methods are not biased. Thus, both can be used to estimate probabilities of exceeding a certain threshold value of θ. Developed in this paper, the bilinear method is much easier to calibrate than the nonlinear, offering similar performance.

A Procedure for 3D Seismic Simulation from Rupture to Structures by Coupling SEM and FEM

ABSTRACTThis article aims at numerically simulating the 3D seismic wave propagation from rupture to structures. A two-step method coupling the spectral element method (SEM) and the finite-element method (FEM) is proposed based on the domain reduction method to simultaneously simulate the seismic wave propagation in large-scale regions and analyze the dynamic behavior of structures in local sites. First, the concept of the proposed two-step method is illustrated. In the first step, the seismic wave propagation of the entire area, involving the source, propagation media, and local region of interest, is simulated using the SEM. In the second step, the dynamic analysis of structure-foundation system with local geological and topographical conditions is implemented using the FEM in a fine mesh based on the results in the first step. Subsequently, the FEM grid size is evaluated to match the SEM results, and the proposed SEM–FEM procedure is verified using both point-source and finite-fault model in a layered flat model. Finally, two analysis examples are presented using the proposed procedure. The analysis results show that the proposed SEM–FEM procedure can well consider the effects of local geological and topographical conditions on synthesized ground motions and can be applied to the rupture-to-structure simulations in earthquake engineering.

Reliability assessment of the physical modeling of liquefaction-induced effects on shallow foundations considering nonuniformity in the centrifuge model

Abstract Physical modeling has been widely used to simulate geotechnical earthquake engineering-related problems and to validate finite element numerical models. In both cases, the model ground is usually considered to have uniform soil properties. However, the model ground is prone to spatial nonuniformity and may affect engineering judgment based on physical modeling. This paper presents a reliability assessment of the physical modeling of liquefaction-induced effects on shallow foundations considering the spatial variability in the centrifuge model. Two-dimensional (2D) finite element simulations with the PM4Sand (version 3.1) elastoplastic soil constitutive model are performed for a sufficient number of stochastic realizations. The nonuniformity in the centrifuge model is implemented with stochastic realizations of the overburden and energy-corrected, equivalent clean sand, SPT (N1)60cs values using a spatially correlated Gaussian random field. The reliability of the centrifuge model test is assessed based on the stochastic average settlement and tilt of the foundation-structure system. The implications of the nonuniformity in the centrifuge model on the liquefaction extent of the ground and spectral displacement of the foundation are also investigated.

Seismic Performance of Steel Structure-Foundation Systems Designed According to Eurocode 8 Provisions: The Case of Near-Fault Seismic Motions

The seismic performance of steel structure-foundation systems subjected to near-fault earthquakes was assessed on the basis of response results from nonlinear time-history seismic analyses. The structural results included the maximum values for residual interstory drift ratios, base shears, and overturning moments of the steel structures, as well as the maximum values for residual settlement and tilting of the foundations. In order to reveal the influence of soil-building-interaction on the aforementioned response results, the steel building-foundation systems were designed according to Eurocode 8 provisions, assuming initially fixed and then compliant base conditions. It was concluded that for the case of near-fault seismic motions, good seismic performance of steel building-foundation hybrid systems designed according to European Codes was not guaranteed. A particular thing to note for these systems under near-fault seismic motions was that the seismic performance of the steel structure was most likely unacceptable, while one of the foundations was always acceptable.

The new foundation system of the Basilica di Collemaggio's transept

In the seismic retrofitting of historical churches, the realisation of new foundations of collapsed elements represents an important aspect for the interaction with both the underground pre-existing structures and the new structural elements to be rebuilt. For the specific case study of the Basilica di Collemaggio, after an accurate geometrical survey and onsite geotechnical tests, a specific mixed structure foundation system is proposed in order to fulfil the seismicsafety requirements and the Cultural Heritage Office's conservation prescriptions. Nonlinear analyses are performed considering the interaction between the soil and the foundation system, together with the new couple of main pillars and the triumphal arch. The analyses are aimed to verify the capabilities of the new foundation system to bear the transversal seismic actions. The analyses are also completed by some experimental tests on micropiles, which represent the main underground-to-elevation connection elements.