Soil-structure Interaction Effects Research Articles

Influence of Soil Flexibility on Seismic Behavior of RC Buildings with Shear Wall

The seismic response of a structure is very complex owing to the behavior of soils during an earthquake. The importance of including the soil–structure interaction (SSI) effect in building frame analysis is quickly recognized, but the modeling of SSI is complicated. The present paper investigates the seismic response of a RC building incorporating soil–structure interaction. The research focuses on clayey soil conditions in situ, taking into account soft, medium, and hard soil. The SSI effect is accounted for by using a point spring element and a fixed support condition. For the study, a RC ground (G)+10-story building with a basement is considered with L-shape (L-SW) and T-shape (T-SW) shear walls resting on a raft foundation. To comprehend the different circumstances of the soil on the structure for comparison study, the responses of some parameters such as story drift, story displacement, and base shear are obtained. The findings of the study show that including SSI effects in the seismic design of multistory buildings is critical because it can result in a significant reduction in controlling design forces without compromising the structure’s safety. Moreover, assuming a fixed base can lead to a high overestimation of the structure design forces and seismic response. The aim of the present study is to obtain the behavior of the RC building under different soil conditions considering two types of shear walls.

Energy-Based Evaluation on Soil–Structure-Interaction-Related Damping of Inelastic Bridge Pier Structure Subjected to Pulse-like Velocity Ground Motion

This study proposed a procedure of using the energy method to evaluate the SSI-related damping effect when the soil–structure interaction (SSI) was considered in a bridge pier system, which can thus be deemed a soil–foundation–superstructure (SFS) inelastic system. Firstly, the SSI is implemented by adopting a discrete-time recursive filter approach as well as frequency-dependent foundation–soil impedance functions to solve for the external soil forces exerted onto the foundation. Then, by integrating such external soil forces into the motion equations of the SSI-based SFS system, the energy equations can be formulated during the ground motions. To demonstrate the proposed procedure, an implementation study involving a bridge pier was carried out, considering two earthquake recordings. The resultant energy quantities and SSI-related damping ratio shed light on how the aspects of earthquake characteristics affected the energy dissipation mechanism of the bridge pier SSI-based SFS system. This proposed procedure renders a promising solution for quantifying the soil role in the seismic energy dissipation of arbitrary single- and multiple-degree-of-freedom systems considering the SSI effect. The results obtained show that the SSI effect was suppressed when the SFS system underwent near-fault earthquakes, which illustrated that the stiffness and damping contribution from the soil was not pronounced. Furthermore, near-fault earthquakes with large incremental velocities may lead to a low SSI-related damping ratio (SSIDR).

Frequency-domain preliminary assessment of coupled site and SSI effects according to the Algerian seismic provisions

PurposeSeveral studies were made on paired site and soil–structure interaction (SSI) effects, but most of them were site specific. This paper aims to investigate the impact of SSI effects in conjunction with local soil condition effects on the seismic response of typical multistory low- to mid-rise–reinforced concrete (RC) buildings resting on Algerian regulatory design sites through a global explicit transfer function (TF).Design/methodology/approachA preliminary quantification of SSI effects associated with site effects is carried out through a frequency-domain solution based on the concept of rock-to-soil surface displacement TF performed for each design site category. It results from the combination of the TFs of structure, foundation and soil and reflects how seismic waves are amplified due to changes in the geological contrast between the rock and overlying soil deposits. As well, response modification factors, denoting displacement ratios of the building responses within the flexible and site-structure conditions with respect to the fixed-base one, are carried out.FindingsIn the context of Algerian seismic regulation, the study provides a clear vision of how and when site or SSI effects are expected to be influential, as opposed to the fixed-base hypothesis still retained by the current regulation. This helps engineers to be aware of the extent of the expected seismic damage.Research limitations/implicationsThe research applies to low- to mid-rise RC buildings within the Algerian seismic regulation, but it may also be expanded to other examples that fall under other seismic regulations.Practical implicationsThe response modification ratio is a quantitative approach to assessing response fluctuations. It draws attention to how the roof level drift varies depending on the condition. These results can be used as numerical parameters in structural seismic design when the structure is comparable because they provide useful information about how the two phenomena interact with the structure.Originality/valueThe study goes beyond particular situations dealing with site specific and offers effective indicators and quantitative evaluation of combined site and SSI effects according to the current national seismic provisions, where no indication about site or SSI effects exists.

Effect of foundation embedment ratio in suppressing seismic-induced vibrations using optimum tuned mass damper

Tuned mass damper (TMD), which is used in structures to mitigate the dynamic responses caused by environmental loads, is tuned according to the dominant frequency of the structures. The dominant frequency of structure built on soil with low stiffness is significantly affected by the soil-structure interaction (SSI). In previous studies, only the surface foundation case is considered to investigate the design parameters of TMD considering SSI effects and the embedment depth of the foundation is neglected in these studies. Thus, this paper investigates the optimization of TMD for mitigation of responses of a high-rise building considering various depths of embedment and soil properties. The optimum parameters of TMD are investigated using five different optimization algorithms (i.e., simulated annealing, sequential quadratic programming, genetic algorithm, pattern search, and particle swarm optimization). The objective function minimizes the peak acceleration amplitude at the top of the structure. The effectiveness of optimum TMD is verified to use 20 near-fault pulse-like ground motions. The comparisons show that the embedment ratio of the foundation and the soil properties significantly affect the optimization of TMD.

Optimum tuned tandem mass dampers for suppressing seismic-induced vibrations considering soil-structure interaction

In recent studies, it has been stated that tuned tandem mass dampers (TTMD) will be a practical mechanical solution to reduce the dynamic responses of structures under seismic excitations. However, since TTMD is tuned based on the dominant frequency of the superstructure, ignoring the soil-structure interaction (SSI), it may cause a notable deterioration in the control performance of the control devices. Thus, a methodology for the optimum design of TTMD positioned on the top story of a high-rise building due to near-fault pulse-like ground motions considering potential SSI effects has been investigated in this paper. Firstly, the TTMD is located on the top story of a well-known 40-story shear building, and the equations of motion for soil-structure-TTMD interaction are derived. Based on the sequential quadratic programming (SQP), the tuning parameters of TTMD are then found for different support conditions in the frequency domain. The efficiency of SQP is also compared with two meta-heuristic algorithms (i.e., simulated annealing and pattern search algorithms). The effectiveness of optimum TTMD is tested using 30 near-fault pulse-like ground motions using time-domain analyses. Numerical results showed that the optimum TTMD is more effective in suppressing the maximum displacement and inter-story drift of the building, considering SSI. It is also found that the frequency content of the earthquake, as well as the pulse period of the earthquake and soil type, has a significant effect on the control performance of the TTMD.

Parameter design and performance evaluation of tuned mass damper (TMD) for seismic control of structure considering soil-structure interaction (SSI)

Tuned mass damper (TMD) is a practical tool for reducing structural vibration. The current TMD design often use the dynamic characteristics of structures with fixed base. However, in terms of resisting earthquakes especially when the soil-structure interaction (SSI) effect is prominent, the TMD designed for the fixed base situation behaves unfavorably and even amplifies the structural response. In this paper, a parameter design and performance evaluation of TMD for seismic control of structure considering SSI is studied. The contents include the SSI modeling, structural dynamic characteristic identification, and TMD parameter designing. A seismic SSI model that the soil is simulated by an accurate lumped parameter models (LPMs) is built firstly. A simple and practical method is then used to identify the structural dynamic characteristic of SSI model. The identified structural frequency is used to compute the parameters of TMD. Finally, two types of structures, three kinds of soils, and 100 ground motions are applied to comprehensively evaluate the TMD performance through the comparison with the fixed-ground-based design and optimization-algorithm-based design. The research shows the TMD designed by the proposed method can show a good performance and robustness.

Shake table testing and computational framework for seismic response of utility-scale bucket foundation offshore wind turbines

Shake table testing was conducted to document the seismic response of a bucket foundation offshore wind turbine (OWT) system. Salient response of the system's soil-structure interaction effects is presented and discussed. Among the observed response characteristics, excess pore pressure fluctuation within and around the soil-bucket domain is thoroughly addressed, including the strong tendency for the soil dilation excursions driven by the induced cyclic strains. The experimental data is used to calibrate a numerical model with dynamic soil response simulated by a coupled solid-fluid formulation. The calibrated model is extended to investigate seismic response of a prototype utility-scale OWT, with and without added wind loading effects. Overall, the research outcomes indicate that: i) excess pore pressure fluctuations in the vicinity of the bucket play an important role in dictating the extent of potential permanent base rotation, ii) consideration should be given to wind loading that might further exacerbate this base rotation, and iii) it is of importance to model the turbine tower as a system of discrete masses rather than the simplified proposed for practice equivalent top mass idealization.

Seismic evaluation and reliability index of soft story buildings on flexible soils by using old and current seismic regulations in Mexico

A very important number of buildings with a flexible ground floor in Mexico City presented severe damages and collapses during the intraplate earthquake (Mw = 7.1) of September 19, 2017. The statistics of the damaged buildings showed that most of the collapsed structures were designed with a regulation in force in the late 70′s. As a response to the damages observed during this seismic event, the current version of the seismic regulation for Mexico City added a specific chapter for the analysis and design of structures with a flexible ground floor. This study assesses the seismic response of the existing buildings subjected to accelerograms recorded during the occurrence of this earthquake and the expected behavior of new structures designed with the current seismic regulations. To evaluate the methodology proposed in the code to design weak-story buildings, reliability indices of buildings designed with the regulation in force at the end of the 70′s and those obtained in buildings designed with the current regulation were determined. Soil-structure interaction played a very important role in the geographical distribution of the buildings with the greatest damage and also in areas that presented only slight damage. The soil-structure interaction was modeled as suggested in the current Mexican standards. The results show that the range of computed reliability indices in the structures built in the 70′s explain the collapses observed, and not in all cases, the current regulation leads to satisfactory values ​​of the reliability index, particularly when including the soil-structure interaction effects.

Effects of Uncertain Soil Parameters on Seismic Responses of Fixed Base and Base-Isolated Liquid Storage Tanks

ABSTRACT Effects of soil-structure interaction (SSI) on the seismic performance of cylindrical ground-supported liquid storage tanks are studied. The present study attempts to investigate the effects of uncertainties, associated with the critical soil parameters, on the seismic behavior of liquid storage tanks. Random multi-layered soil models coupled with the fixed base liquid storage tank are developed and analyzed. Further, the tank structure is considered base-isolated with lead rubber bearing and analyzed with the same set of soil models, to investigate the seismic behavior of base-isolated tank under uncertain soil condition. A set of three ground motions are selected from a large suite through a mean spectral matching scheme for investigating the effect of soil uncertainties on the seismic response. Distributions of the peak seismic response quantities observed herein show that the uncertainties in soil parameters critically affect the seismic responses of fixed base and base-isolated liquid storage tanks. Sloshing displacement of fixed base and base-isolated tanks is affected by both uncertainty in the soil parameters and ground motion characteristics. Nevertheless, for ground-supported tank, relatively larger dispersion or variability of base shear and overturning moment, as compared to that of the sloshing response, is observed.

The role of soil in structure response of a building damaged by the 26 December 2018 earthquake in Italy

Local soil conditions can significantly modify the seismic motion expected on the soil surface. In most cases, the indications concerning the influence of the underlying soil provided by the in-force European and Italian Building Codes underestimate the real seismic amplification effects. For this reason, numerical analyses of the local seismic response (LSR) have been encouraged to estimate the soil filtering effects. These analyses are generally performed in free-field conditions, ignoring the presence of superstructures and, therefore, the effects of dynamic soil-structure interaction (DSSI). Moreover, many studies on DSSI are characterised by a sophisticated modelling of the structure and an approximate modelling of the soil (using springs and dashpots at the foundation level); while others are characterised by a sophisticated modelling of the soil and an approximate modelling of the structure (considered as a simple linear elastic structure or a single degree of freedom system). This paper presents a set of finite element method (FEM) analyses on a fully-coupled soil-structure system for a reinforced concrete building located in Fleri (Catania, Italy). The building, designed for gravity loads only, was severely damaged during the 26 December 2018 earthquake. The soil was modelled considering an equivalent visco-elastic behaviour, while the structure was modelled assuming both the visco-elastic and visco-inelastic behaviours. The comparison made between the results of the FEM analyses and the observed damage is valuable. • Soil filtering phenomena are a key aspect for structure seismic response. • FEM modelling of the soil cannot ignore the dynamic properties of the bedrock. • Modelling of the structures should be performed in the inelastic range. • Earthquake damage is not necessarily a "physical" process for vulnerable buildings. • FEM analyses of DSSI must be encouraged for all buildings.

Application of Soil Structure Interaction on Building with Basement using Nonlinear Soil Springs

In a typical building design, the interaction between building and surrounding soils is often ignored. Since soil is deformable and has limited capacity to resist loads, this interaction, called soil-structure interaction (SSI), could alter building responses, especially during earthquake loadings for buildings with significant basement depths. In this study, a 10-story reinforced concrete building with 3-level basement was used to evaluate the effects of SSI on building during earthquakes. Dynamic time response analyses were performed using earthquake time histories scaled to a design response spectrum for a Surabaya, Indonesia, location. Soil responses during earthquakes were modeled using nonlinear hysteresis normal and elastic-perfectly plastic frictional soil springs, developed using the hardening soil with small strain stiffness model. Depth-varying ground motions were also applied along the basement depth. The results show inconclusive SSI effects, where some of the time histories produce greater base shears and inter-story drifts when SSI is considered, while others show the opposite results.

The Effect of Soil Liquefaction and Lateral Spreading to the Seismic Vulnerability of RC Frame Buildings Considering SSI

ABSTRACT Evidence of past earthquakes highlighted the seismic vulnerability to buildings due to soil liquefaction and lateral spreading phenomena. Damage to buildings on a liquefiable site, especially on a gently sloping site, can be severe. The liquefied soil can undergo permanent lateral ground displacements as large as several meters in some cases, which can be severely disastrous to buildings. Recent physical tests and effective stress analyses of nonlinear dynamic soil-structure interaction (SSI) proved that simplified empirical processes are often improper for evaluating liquefaction-induced building settlements. A better understanding of the SSI effects is also essential in cases where the underlying soil is susceptible to liquefaction. In this respect, the interaction of the earthquake excitation and ground failure (i.e. soil liquefaction and lateral spreading) for buildings considering SSI is investigated herein. Typical low-code reinforced concrete (RC) frame buildings of different heights with shallow spread footings on liquefiable level-ground or sloping soils subjected to ground shaking are considered. The direct SSI approach is implemented. Predictive relationships are established between the maximum normalized differential displacements (horizontal or settlement) and the permanent ground displacement (PGD) vector at the level of foundation for low-code RC frame buildings with shallow spread footings on soils with high liquefaction potential subjected to ground shaking. Finally, vulnerability is expressed in terms of fragility and vulnerability curves as well as in terms of fragility surfaces as a function of two intensity measures.

Seismic response of a stilted mid–story isolated structure in mountainous areas based on variable parameters soil–structure–interaction effect

Many mountainous areas in the world are vulnerable to earthquakes. The geology of mountainous areas is complicated, the terrain fluctuates wildly, and the dynamic characteristics differ from those of flat areas. The soil–structure-interaction (SSI) effect has rarely been considered in studies of mountain structures. Theoretical research on SSI in mountainous areas lags behind engineering applications. It is suggested that SSI should be considered in mountainous areas. In this study, three mountain structure models were established: a stilted mid–story isolated structure without SSI effect, a stilted mid–story isolated structure with traditional SSI effect and a stilted mid–story isolated structure with variable parameters SSI effect. The earthquakes were input in the direction of down and transverse slopes. The results indicate that the seismic response of the stilted mid–story structure with SSI effect is larger than that of the stilted mid–story structure without SSI effect in mountainous areas. The seismic response of the stilted mid–story structure with variable parameters SSI effect in mountainous areas is more accurate and reliable. The seismic response is significantly affected by the changes of soil stiffness and damping. The maximum stress values of the three structures appear at the stilted short columns and the ends of the connected beams. As the soil softens, the seismic response of the stilted mid–story isolated structure with SSI effect in mountainous areas increases. When earthquakes are input in the transverse slope direction, the soil twists, aggravating structural torsion.

Analytical approach for seismic analysis of onshore wind turbines considering soil-structure interaction

The aim of this study is to present an efficient analytical approach, based on a combination of transfer matrix formulations and modal superposition, to perform seismic response analysis of onshore wind turbines (WT) incorporating the effects of soil-structure interaction (SSI). The WT tower and rotor-nacelle assembly (RNA) are idealised as a segmented Timoshenko beam-column and lumped mass, respectively. SSI is taken into account using elastic springs at the bottom of the tower to model soil flexibility. The mass of the foundation is also considered in the mathematical model as a lumped mass at the base of the tower. As the serviceability limit state tends to be the governing design condition for WTs, the soil behaviour is idealised as linear-elastic with equivalent linear stiffness. Firstly, natural frequencies and mode shapes of the WT are obtained using the transfer matrix method (TMM), which is based on analytically-calculated state vectors of beam-column members, and state vectors of joints at the top and bottom of the tower. The entire vibrating structure is simplified into an equivalent single-degree-of-freedom (SDOF) system using mode shapes calculated from TMM. The seismic responses are derived using the Newmark-Beta method and modal superposition. The application of TMM for free vibration analysis is validated with reference to results from existing literature. Additionally, the accuracy of the method for calculation of seismic responses is verified using finite-element software. Three different ground models are considered, namely stratum over half-space, stratum over rigid base, and elastic half-space; and the effect of each on the free vibration and seismic responses are examined in terms of displacement and base shear time-histories of the WT with varying foundation geometries. The effects of varying soil properties on the natural frequencies and seismic responses of the WT are also investigated. Finally, the dynamic responses of the model subjected to different seismic time-histories are presented comparatively, to highlight the significant effects of the frequency content of ground motion records.

The optimum design of particle tuned mass damper for structural seismic control considering soil-structure interaction

Particle tuned mass damper has received considerable attention on mitigating structural seismic responses recently. However, soil-structure interaction effects have not been considered for the optimization design of particle tuned mass damper in the previous studies yet, which may play significant roles in particle tuned mass damper’s effectiveness. This paper investigates the seismic control performance of particle tuned mass damper for tall buildings considering SSI effects. A 40-story benchmark structure is adopted as the primary structure, and different soil conditions including soft, medium, dense soil, and the fixed-base case are considered. Based on the Cuckoo Search algorithm, an optimum design approach for the particle tuned mass damper implemented in SSI system under earthquake excitations is proposed, and the optimum parameters of particle tuned mass damper are obtained from the optimum design process. The optimum results indicate that the optimized particle tuned mass damper can effectively decrease the displacement response without the increase of peak acceleration, and the reduction rates could exceed 30% in some cases. Compared with other soil type cases, under soft soil condition, the optimum parameters of particle tuned mass damper are especially different, and the mitigation effects of the optimized particle tuned mass damper on maximum displacement weaken. Hence, it is necessary to consider the SSI effects for particle tuned mass damper’s seismic design. Furthermore, the interaction effects between the primary structure and particle tuned mass damper in SSI system are also evaluated through energy analysis. The results show that considering SSI effects, the optimized particle tuned mass damper device dissipates the overwhelming majority of the input energy, and it greatly decreases the structural energy, displaying excellent energy dissipation performance on seismic vibration control of structure.

Optimum parameters for adjacent frames coupled by fluid viscous dampers considering soil-structure interaction

In this paper, the optimum conditions which ensure that the resulting minimum base shear force and minimum roof displacement for two adjacent frame structures interconnected by fluid viscous dampers, including soil-structure interaction (SSI) effects under seismic excitation were presented. A two-dimensional (2D) finite element analysis was carried out with the Taguchi method. As non-reflecting boundaries, viscous boundary conditions were used on the edges of finite soil region. An optimization study was carried out for four parameters such as soil type, height ratio of the frames, damping coefficient of viscous damper, and the location of the viscous damper each with four levels. The optimum conditions which minimize maximum roof displacements and the maximum base shear forces have been obtained. The most affecting parameter on the system response was found to be soil type. It was also found that the sufficient damping coefficient of the viscous damper is equal to 1x105 N.s/m for minimum response. The minimum system response can be achieved by using only one damper. It can be drawn that the Taguchi method can be used with the finite element (FE) method for determining optimum conditions of a soil-structure system for minimum system response.

3D Soil Structure Interaction Effects on the Seismic Behavior of Single Span Historical Masonry Bridge

3D Soil Structure Interaction Effects on the Seismic Behavior of Single Span Historical Masonry Bridge

Modal analysis and extraction method for the frame structure considering soil-structure interaction effect

For a soil-structure interaction (SSI) system, the direct method can analyze the dynamic characteristics of the arbitrary complicated soil deposits. However, to determine the radiation damping effect on the structural dynamic characteristics, the complex modal analysis using the direct method needs to calculate many complex modes for obtaining the few exact structural modes due to a large number of soil degrees of freedom. The needed structural modes among a large amount of soil modes are difficult to be extracted. In this paper, a new complex modal analysis method using sequential eigenvalue-shift is developed for the calculation of the modal parameters of the frame structure under SSI effect. Accordingly, a new index of the local modal mass ratio is proposed to quickly and accurately extract the structural modes from many combinations of modes from structures and soil. Several comprehensive examples are presented to validate the proposed method, and the influence of artificial boundary on the natural frequency, mode and modal damping ratio of the structure is investigated.

Shaking table test study of nuclear power plant model considering soil-structure interaction effect

The influence analysis of site condition is fundamental to the seismic design of nuclear power plants. In this paper, a series of shaking table tests were performed to investigate the Soil-Structure Interaction (SSI) effect on the seismic response of nuclear power structures. An AP1000 nuclear power plant was taken as the objective structure, lead rubber bearings (LRBs) were used as the isolators and Shanghai silty clay was selected as the model soil. Test results show that (1) The soil has different effects on the dynamic characteristics of isolated and non-isolated model structures. (2) During the shaking table test, the foundation edge is subject to the highest soil pressure, and a contact surface separation between the foundation and the soil begins to occur under the seismic-margin earthquake (SME) seismic input level. (3) Both for the rigid and soil foundation, seismic isolation bearings can effectively reduce the acceleration response of the superstructure. (4) For the non-isolated model, the SSI effect significantly amplifies the seismic response at the bottom floor of the structure in the low frequency range, and an obvious rocking behavior occurs at the operating basis earthquake (OBE) seismic input level. (5) For the isolated model, the SSI effect reduces the hysteresis capacity of the seismic isolation system and amplifies the seismic response at the bottom floor, especially in the vertical direction. The site condition and the use of an isolation system have a significant impact on the seismic response of a nuclear power structure. Therefore, in the design and safety assessment of nuclear power plants, the influences of soil characteristics and isolation equipment in the soil-structure interaction system should be fully considered.

Seismic behaviour of elevated liquid storage tanks by considering the different soil types using MATLAB software

For a structure the soil structure interaction (SSI) is the connection between the super structure and the foundation. In this paper, the seismic responses of liquid storage elevated tank with SSI and without SSI effects are considered and effects were analysed. The consequences of SSI on peak seismic responses of tank like displacement, overturning moments are discussed. Furthermore, the impacts of different factors such as slenderness ratio and time period of liquid tank staging on the seismic performance of the raised tank are investigated. From the study it is observed that the soft soil is prone to overturning moment of water storage tank and also found that as the slenderness increases, the overturning moment decreases gradually irrespective of soil type and time period of the staging.