Soil Foundation Structure Interaction Research Articles

Seismic performance of LNG tanks in deep soil site considering soil-foundation-structure interaction

The seismic performance of liquefied natural gas (LNG) tanks is significantly influenced by Soil-Foundation-Structure Interaction (SFSI). It is essential to investigate the effect of the SFSI on isolated LNG tank, particularly on a deep soil site. This study aims to examine the impact of the SFSI on the seismic performance of an isolated LNG tank located on the deep soil site. The impact of foundation type, pile length, and the frequency content on the primary seismic responses of the LNG tank were thoroughly examined in this study. These seismic responses include the acceleration of the outer tank, the height of the sloshing wave, and the shear force and bending moment of the inner tank. Additionally, the seismic force along the pile foundation, such as shear force, lateral displacement, and bending moment, was also analyzed. The results indicate that for isolated LNG tanks, it would be dangerous without considering the SFSI, while for the pile foundation, it may be beneficial when considering the SFSI. The pile foundation types did not considerably affect the seismic response of the isolated LNG tank in the deep soil site. Additionally, the seismic response appears to be highly sensitive to the frequency characteristics of the seismic excitation, especially the low-frequency content.

Soil-structure interaction effects on out-of-plane seismic response and damage of masonry buildings with shallow foundations

A significant amount of damage and casualties induced by several strong-motion earthquakes which recently stroke South-East Mediterranean area is due to the major seismic vulnerability of residential buildings. In small villages and mid-size towns, those buildings very often consist of two- to four-story, unreinforced masonry (URM) structures not designed for earthquake resistance, with direct foundations usually corresponding to an in-depth extension of load-bearing walls. For such structures, especially when founded on soft soils, site amplification and soil-foundation-structure interaction (SFSI) can significantly affect the seismic performance; conversely, such phenomena should be investigated through methods that allow a trade-off between accuracy and computational effort, hence encouraging their implementation in engineering practice. This paper provides a comprehensive updated description of the studies carried out in the last years by the authors, which are based on both linear and nonlinear, parametric, dynamic analyses of complete soil-foundation-structure (SFS) models representative of existing residential building configurations on different soils. Specifically, the parametric study investigated SFS models with different masonry types, aspect ratios, and code-conforming homogeneous and heterogeneous soil profiles. The methodology and analysis results allowed for reaching the following objectives: (i) predicting the elongation of the fundamental period and the variation of equivalent damping of the SFS system with respect to fixed-base conditions, through a simplified approach based on an equivalent simple oscillator; and (ii) estimating the probability of exceeding increasing damage levels associated with out-of-plane overturning of URM walls, through fragility functions that take into account SFS interaction. The effectiveness of these simplified tools was successfully validated against well-documented case studies, at the scales of both single instrumented buildings and urban area.

Pile Group Effect Modeling and Parametric Sensitivity Analysis of Scoured Pile Group Bridge Foundations in Sandy Soils under Lateral Loads

Scour can increase the earthquake-induced damage in pile group foundations. Quantifying the parameter sensitivity of the seismic performance for scoured pile group foundations is essential for the optimal design and retrofit of bridges located in seismic-prone regions. Such quantification requires numerical models that are computationally efficient and accurate in describing the mechanical behavior associated with the complex soil–foundation–structure interaction of these systems. This study proposes an efficient finite-element model (FEM) of pile groups based on a beam on the nonlinear Winkler foundation approach. This FEM uses asymmetric p-multipliers to describe the different soil resistance exerted on leading and trailing piles when applying cyclic lateral loads. The proposed FEM is validated by comparing the numerical response with the experimental measurements taken from a quasi-static test available in the literature and is used to perform an extensive parametric sensitivity analysis to quantify the response sensitivity to 11 structural and soil parameters. Tornado diagrams are employed to identify an importance ranking of these parameters on the seismic performance of scoured pile groups. The obtained results indicate that the proposed FEM is able to capture both the global and local structural responses of pile group foundations. The parametric sensitivity analysis shows that pile group foundations have considerable ductility capacity. Pile diameter and axial load ratio of piles are the most important parameters for the seismic performance of pile groups. Increasing the pile diameter is the most efficient approach to improve the seismic performance of a pile group when considering scour effects. The seismic performance of a scoured pile group deteriorates with increasing piles’ axial load ratio. For a deep pile group foundation, seismic performance is very little sensitive to pile length and relative density of sand. Based on the results of the parametric analysis, recommendations are proposed for the seismic design of pile group foundations with scour effects.

Soil–Structure Interaction Effects on a Regional Scale through Ground-Motion Simulations and Reduced Order Models: A Case Study from the 2008 Mw 5.4 Chino Hills Mainshock

ABSTRACT We demonstrate the effects of soil–structure interaction (SSI) for three idealized building typologies on a regional scale, using a simulated earthquake scenario of the 2008 Mw 5.4 Chino Hills mainshock in southern California as an example. All the three buildings lie on shallow foundations, and they are subject to three-component simulated ground motions. To carry out this task, we develop a reduced order model (ROM) for each building typology that accounts for the effects of SSI on the building system in the time domain. We specifically use ensemble Kalman inversion (EnKI) to extract the soil impedance values from fully coupled soil–foundation–structure interaction simulations; and we interpolate the EnKI results to derive analytical functions that span the range of applicability of the soil impedance model. We then verify our ROMs by comparing results to fully coupled soil–foundation–structure interaction simulations, also known as direct modeling methods. We finally populate the simulation grid across southern California with the verified building ROMs, and interpret the responses in the form of maps that represent urban-scale effects of SSI on the seismic demand parameters such as maximum displacement, acceleration, and interstory drift. We also identify areas where the effects of SSI, given the resonant characteristics of a specific building, the foundation typology, and the local site conditions, lead to higher seismic demand relative to the fixed-base response.

Evaluation of Soil–Foundation–Structure Interaction for Large Diameter Monopile Foundation Focusing on Lateral Cyclic Loading

In this study, the monotonic and cyclic behavior of an offshore wind turbine with a monopile foundation installed in a sand layer were evaluated in the centrifuge. A simplified offshore wind turbine was modeled, and the lateral load was applied to the tower under displacement control. The monotonic loading test evaluated ultimate lateral load capacity and bending moment profiles under different loading levels. During cyclic loading, variations of moment-rotation responses, cyclic stiffness, and bending moments along the pile were observed. The initial rotational stiffness of the monopile decreased as the loading level increased. In the fatigue limit state (FLS) and service limit state (SLS) loading conditions, no noticeable variation in stiffness was observed with the number of cycles. However, in the ultimate limit state (ULS), the stiffness of the monopile increased during the first few cycles, followed by a decreasing rate of increase, and reached a certain value. The loading rate had a weakening effect on the monopile–soil interaction, which was supported by the bending moments induced in the monopile.

Subsurface Explorations and Investigation of Foundation Performance for Distress Assessment of a Building

The serviceability limit of the foundation system plays an important role in the safe long-term performance of a building. Under governing load cases in service life, the building foundation system should satisfy the serviceability limit state, i.e., total and differential settlement criteria. This study investigated the distress of a building through foundation performance assessment incorporating the soil–foundation–structure interaction (SFSI) effects. A spatially variable soil model [zonewise, obtained from field observation and electrical resistivity tomography (ERT) study] was used to obtain the settlement of the foundation system. Engineering properties of the subsurface were estimated from the collected soil samples and field tests. ERT result shows the variability of the subsurface layer. A three-dimensional finite-element model of soil, foundations, and structures was developed to estimate the settlement demand of the foundation and structures. The numerical model includes the geometric variability of all the foundations of the building and subsurface variability. Settlement and bearing capacity demand of the foundations were estimated and compared with the standard provisions. Results obtained show that the building foundation system satisfies the serviceability limit of the foundation system under total settlement criteria. However, the differential settlement of the system exceeds the required limit despite considering the SFSI effects, and is one of the major causes of distress to the building. The main contributions of this study also include establishing the spatial variability of the soil layer through ERT and correlating it with the crack zone in the building.

Seismic (effect on) time history analysis for cable-stayed suspension hybrid bridge considering different geometrical configuration for far field earthquakes

To increase the maximum span of cable-stayed bridges, Uwe Starossek has developed a modified statical system. The basic idea of this new concept is the use of pairs of inclined pylon legs that spread out longitudinally from the foundation base or from the girder level. Spread-pylon cable-stayed bridge has distinct advantage like reduction of sag of cables and oscillation of cable during earthquake over traditional cable-stayed bridges. Spread-pylon also improves seismic performance of deck during strong ground motion. Here in this paper dynamic behaviour of cable stayed suspension Hybrid bridge with different structural configuration with seismic loading was studied. The primary aim , here, is to present response to Seismic effect on Cable stayed Bridges with different cable system taking under consideration SSI.It is evidently clear that Soil Foundation Structure Interaction relies greatly on various factors such as soil and its properties, manner and type of structure and/or its foundation.. In this paper , the emphasis is on the simplified model and foundation on piles. For the modelling author has used SAP2000 software. The study includes the response of the bridge modelled towards variation in the cable system under consideration of SSI. A bridge similar to that of Bridge at Ling Ding Strait China is taken as a reference and 6 models are created with variation in cable system ( ranging from original cable stayed bridge to suspension type, composite bridge and cable stayed suspension hybrid bridge). Soil modeling is done using the spring and dashpots ( Kelvin element) for simulation of SSI effects.The results observed that effects of SSI has a substantial impact on selection of system of cables and the pylon leg inclination for any Cable- Stayed- Suspension Hybrid Bridge(CSSHB)

Quasi-Static Cyclic Testing of Hybrid Posttensioned Bridge Column Supported on a Monopile Foundation

In this research, a low-damage posttensioned rocking solution referred to as dissipative controlled rocking (DCR) connection is proposed for bridge columns supported on monopile foundations. The DCR connection is a low-damage system that replaces the plastic hinge mechanism in a column and aims to minimize and potentially eliminate the repair time and costs after an earthquake. A DCR bridge system combines unbonded posttensioning and replaceable dissipaters to provide self-centering and energy absorption capabilities, respectively. Current research on DCR column systems has focused on the performance of bridge bents founded on a fixed foundation, neglecting soil damping effects. In this research, a one-third scaled bent supported on a monopile with passive soil resistance was tested under quasi-static cyclic loading to validate the lateral seismic response of a DCR bridge bent with the contribution of the soil–foundation–structure interaction. When developing the details for the DCR connection, particular emphasis was made on utilizing conventional construction materials and forms for a low-damage bent that yields a similar construction cost to a monolithic joint. Nevertheless, the proposed DCR connection can be easily and quickly repaired or replaced after a significant seismic event. The performance of the bent was compared against a benchmark structure with an emulative connection type that resembles a monolithic cast-in-place joint. Results from testing suggest a greater performance of the low-damage DCR column. The dynamic response of the DCR column built on a flexible foundation differed from that of a fixed-base structure, which is primarily due to the energy dissipation capability of the flexibly supported structure. Flexibility in the soil foundation increased the structural period of the structure and reduced the seismic response of the DCR column. Damage to the DCR bent was limited to concrete crushing at the rocking interface, which proved to be easily repairable. In contrast, the bent with an emulative connection developed plastic hinging at the bottom of the column, which was nonrepairable.

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.

Soil–Foundation–Structure Interaction of Inelastic Structural Systems on Unsaturated Soil Layers

Recently, progress has been made toward understanding the seismic response of structures placed on unsaturated soil layers. A missing link, however, involves the influence and assessment of the underlying soil saturation conditions on the expected superstructure seismic demands. Simplified soil–structure interaction procedures that can be used to predict superstructure seismic demands have not been explicitly extended to incorporate the influence of unsaturated soil on the system response. In this paper, results from a series of six centrifuge tests are compared. In each test, an inelastic single-degree-of-freedom physical model was shallowly embedded in a sandy silt with a distinct water table elevation or a completely dry soil condition. The soil-structure system was subjected to a series of earthquake motions. The response of the system was evaluated to assess the influence of the soil saturation condition on the seismic response. Specifically, a conventional analytical procedure for predicting the influence of inertial interaction on the seismic response of the structure was extended to consider the water table elevation and underlying soil saturation condition and evaluated for its reliability. Analytical flexible-base modal parameters were compared with those determined from experimental results to judge the potential of the analytical procedure to be used in practice. Experimental results suggest that as the water table elevation was lowered from the fully saturated condition, both the flexible-base system period and damping ratio reduced. Therefore, the system behaved stiffer in the unsaturated soil compared with the dry and fully saturated conditions. The stiffer response reduced the seismically induced foundation settlements and rotations but amplified superstructure seismic demands in the form of accelerations, flexural drifts, and bending strains.

Effects of the anchor bolts and soil flexibility on the seismic response of cylindrical steel liquid storage tanks

When cylindrical tanks are subjected to strong seismic excitations, the main characteristic that they present is the partial uplifting of the base plate due to the hydrodynamic pressure on the tank walls. This partial base uplifting occurs in both unanchored and anchored tanks, and can provoke several types of failure. A comprehensive analysis of the tank base uplifting implies considering different non-linearity mechanisms. This paper presents a simple and efficient model that takes into consideration the effects produced at the tank base (i.e., uplifting and rocking), as well as, the soil flexibility and the nonlinear effects at anchor system. A comprehensive analysis of the soil–foundation–structure interaction effects, in conjunction with the influence of the convective part of the fluid, was carried out for three anchored cylindrical steel tanks subjected to lateral seismic loads. First, a sinusoidal ground motion was applied to the tanks and the response was discussed for a better understanding of the model capabilities and the soil–foundation–structure interaction. Later, a 3D dynamic analysis was carried out and the effect of considering or not considering the convective component was evaluated. Three seismic ground motion and four different soil flexibilities were considered. Finally, a sensitivity analysis considering different number of anchor bolts in addition to the soil–foundation–structure interaction was performed for the slender tank. The non-linear simplified model proposed in this study was able to obtain a good estimate for the rocking resistance, the anchor bolt effects (considering post-yielding and gap opening/closing at the tank–foundation interface), soil flexibility and the stress distribution on the tank walls. The obtained results allow a better understanding of the seismic response of anchored tanks and shows that the soil–foundation–structure interaction reduces critical response parameters. However, the energy dissipation caused by the anchoring system is low, therefore, response modified factor is not expected in thin walled cylindrical liquid storage tanks. Finally, a certain minimum number of anchors is required to avoid failure due to buckling or excessive uplift. These results can motivates possible modifications in current seismic design codes, where energy dissipation technologies could be considered explicitly as a very promising alternative.

Analyse the effect of Soil Structure Interaction on Seismic Response of Building Cluster by Variation in Soil and Building Properties

The seismic response of a building is dependent on the foundation flexibility, soil properties as well as the interaction between the soil and structure. The frequency and amplitude of the seismic response depends on the soil properties. For simpler calculations, the soil is usually assumed to be rigid which is unrealistic mostly. The buildings are designed on basis of idealized conditions taking fixed base or on Winkler foundations. Until recently, the efforts to ascertain the effect of Soil-Foundation-Structure Interaction (SFSI) on the response of structure have been limited. This study aims at investigating the nature of soil-structure interaction and investigate the effect on the response of building owing to variation in soil stiffness, depth of foundation and building mass ratio using numerical method. The analysis shows that the response of building cluster decreases with increase in soil stiffness. Heterogeneous cluster proved better during earthquake than homogenous cluster. The results indicated that the soil and building properties have major influence on the dynamic response of building cluster and thus may be given due consideration during design and seismic analysis.

Impacts of Pile Foundation Arrangement on Seismic Response of LNG Tanks Considering Soil–Foundation–Structure Interaction

AbstractLiquefied natural gas (LNG) is cleaner and cheaper for power generation than traditional energy sources. Many tanks that store LNG are located in coastal areas with less favorable geotechni...

Non‐linear dynamic analysis of buildings founded on piles: Simplified modelling strategies for soil‐foundation‐structure interaction

AbstractThe paper investigates the problem of Soil‐Foundation‐Structure Interaction (SFSI) for buildings supported on piles through the comparative analysis between the fixed base and the compliant base assumptions. The structure, a nine‐storey residential building (with or without infills), is modelled in non‐linear regime while the piled foundation is idealized by means of independent lumped parameters models, either linear or non‐linear. In this last case, the soil‐foundation system is replaced by an assembly of viscous‐dampers, fictitious masses and non‐linear springs modelled according to the classical Bouc‐Wen formulation, so as to account for the hysteretic behaviour of the foundation. A detailed calibration procedure for both linear and non‐linear foundation models is also presented and discussed. Two different natural soil deposits are considered, a pyroclastic deposit and a deep layer of lacustrine clay. The results undertaken in the context of a probabilistic analysis show that SFSI may lead to a significant reduction of the seismic demand in infilled buildings at low and intermediate earthquake intensity levels. Conversely, at higher intensity earthquakes the seismic demand is not affected by the non‐linear springs. It is shown that a proper modelling of radiation mechanism at foundation level is crucial for a reliable and sustainable prediction of SFSI effects.

Experimental and computational assessment of shear beams as earthquake resilient measure for double-column piers supported by pile-group

The double-column pier with energy dissipation members is an effective way for achieving the seismic resilience of bridges. However, there is short of shaking table tests to assess the impacts of the energy dissipation member on the seismic response and soil-foundation-structure interaction (SFSI) of the double-column pier. Therefore, this paper aims to evaluate the effects of the shear beams on the seismic response of the double-column pier supported by the pile-group in the mixed soil, rather than the cable-stayed bridge model. Two types of double-column piers-one is a conventional double-column pier, and the other is a new double-column pier with shear beams-were built and studied in a 1/70-scale cable-stayed bridge model using shaking table tests. The dynamic characteristics, seismic responses, and SFSI effects between two types of double-column piers were compared under different earthquake waves. Test results revealed that the shear beams significantly decreased the reinforcement strain and the bending moment of the double-column pier. The SFSI effects on the double-column pier with shear beams are more significant than the double-column pier. Also, the computational model developed in OpenSees could reproduce the seismic responses of the double-column piers with and without shear beams and detect the seismic response variations induced by the shear beams. The shear beam was earlier yielding than the column and dissipated the earthquake input energy so that the column could remain elastic under the El Centro with 1.4 g. Consequently, the effects of the shear beam on mitigating the seismic damage and enhancing the seismic resilience of the double-column pier were validated.

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.

Numerical simulation of the seismic response and soil\u2013structure interaction for a monitored masonry school building damaged by the 2016 Central Italy earthquake

Despite significant research advances on the seismic response analysis, there is still an urgent need for validation of numerical simulation methods for prediction of earthquake response and damage. In this respect, seismic monitoring networks and proper modelling can further support validation studies, allowing more realistic simulations of what earthquakes can produce. This paper discusses the seismic response of the “Pietro Capuzi” school in Visso, a village located in the Marche region (Italy) that was severely damaged by the 2016–2017 Central Italy earthquake sequence. The school was a two-story masonry structure founded on simple enlargements of its load-bearing walls, partially embedded in the alluvial loose soils of the Nera river. The structure was monitored as a strategic building by the Italian Seismic Observatory of Structures (OSS), which provided acceleration records under both ambient noise and the three mainshocks of the seismic sequence. The evolution of the damage pattern following each one of the three mainshocks was provided by on-site survey integrated by OSS data. Data on the dynamic soil properties was available from the seismic microzonation study of the Visso village and proved useful in the development of a reliable geotechnical model of the subsoil. The equivalent frame (EF) approach was adopted to simulate the nonlinear response of the school building through both fixed-base and compliant-base models, to assess the likely influence of soil–structure interaction on the building performance. The ambient noise records allowed for an accurate calibration of the soil–structure model. The seismic response of the masonry building to the whole sequence of the three mainshocks was then simulated by nonlinear time history analyses by using the horizontal accelerations recorded at the underground floor as input motions. Numerical results are validated against the evidence on structural response in terms of both incremental damage and global shear force–displacement relationships. The comparisons are satisfactory, corroborating the reliability of the compliant-base approach as applied to the EF model and its computational efficiency to simulate the soil–foundation–structure interaction in the case of masonry buildings.

NHERI@UTexas Experimental Facility With Large-Scale Mobile Shakers for Field Studies

The Natural Hazards Engineering Research Infrastructure (NHERI) experimental facility at the University of Texas (NHERI@UTexas) is funded by the National Science Foundation (NSF). NHERI@UTexas contributes unique, large-scale, hydraulically-controllable mobile shakers and associated instrumentation to study and develop novel, in-situ testing methods that can be used to evaluate the needs of existing infrastructure as well as optimize the design of future infrastructure. The ability to test existing infrastructure under actual field conditions bridges the gap in the transformative tools needed for the next frontier of resilient and sustainable natural-hazards research. Further, these unique facilities are available to any NSF-funded research. The field shakers and support equipment are described. Examples of on-going and future projects in three key areas of investigation that NHERI@UTexas is targeting are presented. These examples includes: (1) performing more accurate 2D/3D subsurface geotechnical imaging up larger depths, (2) characterizing liquefaction resistance and nonlinear dynamic behavior in situ soils, and (3) developing in-situ methods nondestructive soil-foundation-structure interaction (SFSI) studies.

Structural inertial interaction effects on foundation behavior

The effect of inertial interaction of a superstructure with the soil must be understood to evaluate soil–foundation–structure interaction (SFSI) problems. Inertial interaction causes period lengthening and damping increasing and affects the foundation behavior, rocking and swaying motions. This effect is also significant in systems that induce foundation-yielding behaviors during earthquakes, such as rocking foundation. This study evaluates the structural inertial interaction effects on the foundation behavior through an analytical calculation to obtain the natural frequencies of the foundation's rocking and swaying motions. Dynamic centrifuge tests were also conducted to evaluate the variations in natural frequencies of an SFSI system on the rocking foundation. Test results demonstrate that the natural frequency of foundation motion is close to that of structural motion as far as foundation yielding behaviors are concerned. From strong seismic data, with free-field motion as the input motion, a reasonable natural period of the structure is identified. However, the structural natural period is considered abnormal when the foundation motion is used as the input motion. This phenomenon should be considered in future SFSI studies.

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.