SSI Effects Research Articles

Dynamic analysis of an offshore wind turbine under random wind and wave excitation with soil-structure interaction and blade tower coupling

This study investigates the dynamic response of a 5 MW offshore wind turbine with monopile foundation subjected to wind and wave actions. The work includes dynamic interaction between the monopile and the underlying soil subjected to realistic offshore random wind and wave loading modeled using Von karman spectrum and Pierson Moskowitz spectrum respectively. The study also incorporates the effect of blade tower coupling in the analysis. The offshore wind turbine tower is modeled herein as a multi-degree of freedom system (MDOF) and it comprises of a rotor blade system, a nacelle, and a flexible tower. The mass of the rotor, blade, and nacelle are lumped at the top of the tower for simplicity. Separately, the effect of the rotation of blades has also been incorporated in the work. The rotational effect of the blades is taken into account considering shape filters using von Karman spectrum. The soil-structure interaction effect at the foundation level is modeled using equivalent spring-dashpot model for embedded foundations. The results are studied in time as well as frequency domain for both wind and wave loading. It has been observed that soil structure interaction effect greatly alters the response of the offshore wind turbine structure not only in the parked condition but also in operational conditions when blade tower coupling is also included. The effect of blade tower coupling and SSI on the response of the structure are observed more coherently in the case of wave induced loading.

Effect of Soil Saturation On Seismic Performance of A Structure: A Numerical Approach

The aim of this study is to investigate the impact of soil saturation on the seismic performance of a structure when subjected to earthquake-induced vibration. More specifically, this paper examines the effect of the soil saturation level taking into account of soil-structure interaction (SSI) on the structural response. For this purpose, a two dimensional (2D) finite element model was developed with Mohr-Coulomb failure criterion under plane-strain conditions using geotechnical finite element code PLAXIS. To emphasize SSI problems in civil engineering applications, mechanical behavior and various saturation levels of the local soil condition is examined using a numerical model. As can seen from the analysis results, the saturation level of soils causes an increase on the lateral roof displacement of the saturated elasto-plastic soil. This situation was interpreted as the increase in the saturation levels of the soils caused a decrease in the rigidity. Furthermore, neglecting the effect of SSI leads to underestimated results of the structural behavior.

Comparing the performance of substructure and direct methods to estimate the effect of SSI on seismic response of mid-rise structures

ABSTRACT The effects of soil–structure interaction on seismic responses of structures have always been a challenging topic for earthquake and structural engineers. Over the years, different ways have been introduced by researchers to consider the effect of this phenomenon during design procedure of structures. In this study, the performance of three different modelling methods including one direct and two substructure approaches has been compared to reveal the ability of each method to estimate the seismic responses of mid-rise structures. For this purpose, the seismic behaviour of two steel moment-resisting frames under different modelling conditions has been investigated and the results have been reported in terms of interstorey drift ratio.

Evaluation Method of Story Stiffness and Damping Coefficients Through Structural Response Influenced by SSI Effects

Evaluation Method of Story Stiffness and Damping Coefficients Through Structural Response Influenced by SSI Effects

The seismic isolated Stavros Niarchos Foundation Cultural Center in Athens (SNFCC)

The recently constructed Stavros Niarchos Foundation Cultural Center (SNFCC), houses the National Opera and the National Library of Greece. In order for the structural design to meet the demanding architectural requirements as well as the high-performance seismic specifications that were set, a seismic isolation system was incorporated. SSI effects due to poor silty sands were an additional challenge. After presenting the design parameters and the choice of seismic isolation type, the paper focuses on the methodology for the seismic design. This, performed in three consecutive stages, includes simple analyses using single-degree of freedom model for initial scheming, dynamic response spectrum analyses for detailed design and non-linear time history analyses using two sets of selected earthquake records, semi-artificial and real ones, for verification of the response. The results demonstrate a good correlation between different analysis techniques and provide a valuable insight into the behaviour of two complex, seismically isolated structures under seismic loads. The problems and solutions resulting from the implementation of the seismic isolation are also briefly presented.

Soil Structure Interaction Effects on Hysteretic Energy Demand for Stiffness Degrading Systems Built on Flexible Soil Sites

This paper aims to investigate the effect of soil-structure interaction on plastic energy demand spectra directly derived from the energy-balance equations of soil-shallow-foundation structure with respect to an ensemble of far-field strong ground motions recorded on alluvium soil. The superstructure is modeled as a single-degree-of-freedom (SDOF) oscillator with Modified Clough stiffness degrading modelresting on flexible soil. The soil below the superstructure is modeled as a homogeneous elastic half space and is considered through the concept of Cone shallow foundation Models. A parametric study is carried out for 2400 soil-structure systems with various aspect ratios of the building as well as dimensionless frequency with wide range of fundamental fixed-base period and target ductility demand values subject to an ensemble of 19 earthquakes. Results show that generally for the structure located on softer soils severe dissipated energy drop will be observed with respect to the corresponding fixed-base system. The only exception is for the case of short period slender buildings in which the hysteretic energy demand of soil-structure systems could be up to 70% larger than that of their fixed-base counterparts. Moreover, dissipated energy spectra are much more sensitive to the variation of target ductility especially for the case of drastic SSI effect.

SSI effects on seismic demand of reinforced concrete moment resisting frames

We present the results of nonlinear dynamic analyses performed on reinforced concrete (RC) moment resisting frames (MRFs). The analyses were performed considering SSI by means of both a plane-strain soil-structure finite element model approach and a structure-on-springs approach. The results show that the complete FE model approach may produce significant differences in the evaluation of the seismic demand, in terms of maximum inter-storey drift, with respect to the fixed-base structure and to the structure-on-springs approach, mainly because of the different incorporation of the damping in the two modeling approaches.Differences in the soil properties, the seismic design level of the structures and the modeling technique of SSI effects are reflected as reduction in the seismic demand with respect to a fixed-base model, up to 50% in maximum inter-story drift ratio and up to 20% in maximum base shear for the complete FE model and up to 20% in both maximum base shear and maximum inter-story drift ratio for the simplified BNWF model.

Seismic Behavior and Dissipated Plastic Energy of Performance-Based-Designed High-Rise Concrete Structures with Considering Soil–Structure Interaction Effect

Since the structure and foundation are built on soil, the soil is the major platform by which seismic vibrations are transmitted to the structure, and has noticeable effects on the response and behavior of structure during earthquakes. In this research, the recently introduced Performance-based plastic design (PBPD) and its modified Performance-based plastic design (MPBPD) method in which soil and structure interaction effect has been considered underwent the seismic evaluation. In order to do evaluation, a twenty-floor concrete structure with MPBPD method and conventional PBPD was designed and analyzed in accordance with the time history of the 22 far-field quake records. In this study, cone model is employed for modeling the soil and foundation. With a detailed three-dimensional finite element model of a twenty-story high-rise structure constructed and exploited in the OpenSees software, it is attempted to consider a more realistic behavior of the structure. The results of six related parameters with the maximum response of the structure demonstrate the efficiency and performance of the MPBPD method for the purpose of considering the SSI effect, compared with the conventional method of PBPD. The Results show that, in the MPBPD design method, maximum displacement, acceleration, inter-story drift and shear force dropped leading to a better distribution of energy in the structure compared to the PBPD method.

Incorporation of Dynamic SSI Effects in the Design Response Spectra

Many studies in the past on dynamic soil–structure interactions have revealed the detrimental and advantageous effects of soil flexibility. Based on such studies, the design response spectra of international seismic codes are being improved worldwide. The improvements required for the short period range of the design response spectra in the Indian seismic code (IS 1893:2002) are presented in this paper. As the recent code revisions has not incorporated the short period amplifications, proposals given in this paper are equally applicable for the latest code also (IS 1893:2016). Analyses of single degree of freedom systems are performed to predict the required improvements. The proposed modifications to the constant acceleration portion of the spectra are evaluated with respect to the current design spectra in Eurocode 8.

Damage Index Distributions in RC Dual Lateral Load-Resistant Multi-Story Buildings Considering SSI Effects Under Bidirectional Earthquakes

Inelastic seismic responses of flexibly supported reinforced concrete (RC) moment-resisting frames representing short-to-tall structures stiffened with ductile RC structural walls were evaluated considering both far-field and near-field ground motions. A dual shear wall-frame resisting system with symmetric reference plan was created by adding shear walls into excitation direction of the three-dimensional frames developed by generic structure algorithm. The current study also aims to take into account soil–structure interaction effects in to damage assessment of multi-story RC buildings in terms of ductility demand, damage index, story shear force and overturning moment, as well as kinetic energy profile over the structure height. In doing so, the developed set of generic frames was considered accounting for different values of story strength, stiffness distribution and number of stories. A realistic modeling of nonlinear ductile behavior of RC elements was developed in combination with the sub-structuring method to consider the foundation flexibility in nonlinear seismic responses. Conducting a parametric study through nonlinear static analyses (pushover) as well as nonlinear response history analyses, the results indicated that the near-field ground motion presents much more damage than the far-field one. Inelastic dynamic responses to near-field records demonstrated that structures with a fundamental period greater than the pulse period respond differently from those that have shorter periods. The results were also presented as charts and tables that provide helpful information for engineering design purposes such as damage assessment of multi-story RC buildings with specific fundamental natural period and base shear strength.

Seismic Response of Multistoried Building with Different Foundations Considering Interaction Effects

Current seismic design practice assumes the base of the building to be fixed and does not consider the flexibility of foundation and soil. This assumption is realistic only when the structure is founded on solid rock or when the relative stiffness of the foundation soil compared to the superstructure is high. Whereas, in reality due to natural ability of soil to deform, supporting soil medium modifies the response of the structure during earthquake to some extent. In this work the effect of soil structure interaction on seismic response of building resting on different types of foundation was studied. Present work aims to study the effect of soil structure interaction on seismic response of building resting on fixed base, pile foundation, raft foundation and combined pile-raft foundation. G+9 RCC building is analyzed for earthquake loads considered in zone III by response spectrum method and storey displacement and base shear force of building by considering and without considering SSI effect is found out by using MIDAS GEN software.

Shaking table tests on a stone masonry building: modeling and identification of dynamic properties including soil-foundation-structure interaction

ABSTRACTThis article presents the identification of dynamic properties of a stone masonry building, followed by numerical simulation of its dynamic response accounting for soil-foundation-structure interaction. The first part regards numerical simulations of the earthquake response of a two-story building prototype with timber floors, made of three-leaf stone masonry without laces. This 1:2 scale prototype was tested on a shaking table in its as-built state and after strengthening, at the National Technical University of Athens. Afterward, the building prototype was modeled with flat shell elements and equivalent frames (common frames and macro-elements), for an investigation of its linear and nonlinear seismic response, assuming base fixity. Numerical results were compared to the experimental ones, which yielded conclusions on the considerations of each employed modeling strategy, as well as its efficiency and applicability. The second part considers the effect of soil-structure interaction using appropriately modified foundation stiffness values to account for the foundation soil flexibility. Comparison of the numerical results with and without SSI effects showed how the flexibility of the soil-foundation system and the soil-structure interaction modified the system’s modal characteristics and response within the elastic range, in terms of both seismic loads and deformations, and produced conclusions about its consequences on the overall structural stability.

SSI effects on seismic behavior of smart base-isolated structures

The present study investigates the soil-structure interaction (SSI) effects on the seismic performance of smart base-isolated structures. The adopted control algorithm for tuning the control force plays a key role in successful implementation of such structures; however, in most studied carried out in the literature, these algorithms are designed without considering the SSI effect. Considering the SSI effects, a linear quadratic regulator (LQR) controller is employed to seismic control of a smart base-isolated structure. A particle swarm optimization (PSO) algorithm is used to tune the gain matrix of the controller in both cases without and with SSI effects. In order to conduct a parametric study, three types of soil, three well-known earthquakes and a vast range of period of the superstructure are considered for assessment the SSI effects on seismic control process of the smart-base isolated structure. The adopted controller is able to make a significant reduction in base displacement. However, any attempt to decrease the maximum base displacement results in slight increasing in superstructure accelerations. The maximum and RMS base displacements of the smart base-isolated structures in the case of considering SSI effects are more than the corresponding responses in the case of ignoring SSI effects. Overall, it is also observed that the maximum and RMS base displacements of the structure are increased by increasing the natural period of the superstructure. Furthermore, it can be concluded that the maximum and RMS superstructure accelerations are significant influenced by the frequency content of earthquake excitations and the natural frequency of the superstructure. The results show that the design of the controller is very influenced by the SSI effects. In addition, the simulation results demonstrate that the ignoring the SSI effect provides an unfavorable control system, which may lead to decline in the seismic performance of the smart-base isolated structure including the SSI effects.

Incremental dynamic analysis of nonlinear rocking soil-structure systems

Rocking isolation effect on seismic demands of shear-building structures rested on shallow foundation is investigated in this paper. Building structures with surface raft foundations of various geometrical and structural properties located on soft-to-very dense sites are studied. Two types of near-fault pulses, i.e. fling step and forward directivity, are considered as input excitation. Results show that nonlinear SSI effect is governed by static vertical safety factor of foundation (FS) that is varied in this study. Evidently, it is not necessary to excessively decrease the FS factor. So that rocking isolation is achieved as FS factor is around 2.0. On the other hand, nonlinear SSI effect is strongly correlated with normalized period of the incident near-fault pulse (Tp/T). The most significant effects of nonlinear SSI on mitigating structural demands occur at Tp/T near to unity. It is observed that rocking isolation has the same drawbacks of conventional synthetic translational isolators that work in sway directions. The first drawback is deficiency of rocking isolation subjected to long-period near-fault pulses and the latter is in case of high-rise superstructures.

Investigation the accuracy of FEMA-440 procedure to analyze soil-structure systems

A common analysis method of soil-structure systems in seismic design procedures such as FEMA-440 is to replace the entire soil-structure system by a fixed-base oscillator with an equivalent fundamental period and damping ratio to consider inertial effect of soil-structure interaction. It is generally believed by researchers that ignoring kinematic effect of soil-structure interaction is conservative to determine response of structures and FEMA-440 supports this idea by defining a reduction factor applying to elastic response spectra. Also, the improvements of nonlinear static procedures in FEMA-440 are achieved for fixed-base structures and the soil effects are not perfectly obtained in coefficients and relations of these procedures. Thus, it seems necessary to assess the accuracy of proposed procedures of FEMA-440 to include soil-structure interaction. In this paper, the accuracy of equivalent replacement oscillator and nonlinear static Procedures of Equivalent Linearization and Coefficient methods, defined in FEMA-440, to analyze soil-structure systems with surface and embedded foundations are evaluated. Both kinematic and inertial effects of soil-structure interaction are investigated by conducting a parametric study using 20 ground motions recorded on soft soil site E, on which the more SSI effects are probable.

Soil-structure interaction effects on the seismic performances of reinforced concrete moment resisting frames

The paper investigates the influence of Soil-Structure-Interaction (SSI) effects on the seismic performances of 2D reinforced concrete (RC) moment resisting frames (MRFs), which were investigated by means of non-linear dynamic analyses. The goal was pursued by means of a parametric study in which (1) the soil properties, (2) the modelling technique of the SSI effects, (3) the seismic design level of the structures were varied. The soil classes suggested by Eurocode 8 were taken as reference to define the mechanical properties of soil. As concerns the SSI modelling, both a sub-structures approach and a direct approach were considered. Finally, structures of 4 and 8 floors designed for vertical loads only or according to the Italian regulations for constructions (NTC-08) were considered. RC-MRFs founded on soft soils were considered, because SSI effects on the seismic response are expected higher. The study shows that SSI affects the seismic demand in terms of maximum base shear and maximum inter-story drift ratio with different significance depending on the modelling approach.

SSI prevention measures and effects at the department of orthopaedic surgery in Municipal Ena Hospital

SSI prevention measures and effects at the department of orthopaedic surgery in Municipal Ena Hospital

Optimum lateral load distribution for seismic design of nonlinear shear-buildings considering soil-structure interaction

The lateral load distributions specified by seismic design provisions are primarily based on elastic behaviour of fixed-base structures without considering the effects of soil-structure-interaction (SSI). Consequently, such load patterns may not be suitable for seismic design of non-linear flexible-base structures. In this paper, a practical optimisation technique is introduced to obtain optimum seismic design loads for non-linear shear-buildings on soft soils based on the concept of uniform damage distribution. SSI effects are taken into account by using the cone model. Over 30,000 optimum load patterns are obtained for 21 earthquake excitations recorded on soft soils to investigate the effects of fundamental period of the structure, number of stories, ductility demand, earthquake excitation, damping ratio, damping model, structural post yield behaviour, soil flexibility and structural aspect ratio on the optimum load patterns. The results indicate that the proposed optimum load patterns can significantly improve the seismic performance of flexible-base buildings on soft soils.

Soil-Structure Interaction on the Dynamic Response of Bridge Piers

The paper analyses the effect of Soil-Structure-Interaction (SSI) on the modal dynamic response of simply-supported span girder bridge with wall piers founded on caissons. A parametric analysis has been carried out in the hypothesis of linear elastic behaviour of all materials (soil and structure) to identify the influence of various design factors, such as the height of the pier, the caisson embedment below the ground level and the soil mechanical properties. The goal of the paper is to highlight SSI effects on the dynamic behaviour of bridges. This is a crucial aspect to be accounted for in order to support monitoring activities on bridges, aimed to structural identification or assessment of structure response under serviceability conditions, or also to have preliminary information for the seismic analysis of the bridge.

An efficient approach for assessing the seismic soil structure interaction effect for the asymmetrical pile group

All of the civil engineering structures involve some type of structural element which is in direct contact with soil. To estimate the accurate response of the superstructure it is necessary to consider the response of the soil supporting structure, and is well explained in the soil structure interaction analysis. Many attempts have been made to model the SSI problem numerically; however the soil nonlinearity, foundation interfaces and boundary conditions make the problem more complex and computationally costlier. To overcome this problem the attempt has been made to optimize the computational efficiency by applying the equivalent pier method for the deep foundation system. In this research paper the L-shape 11 storey building supported by a pile foundation with homogeneous local soil condition is analyzed for dynamic loading including the SSI effect. The significance of the SSI effect has been studied by comparing the responses of the system for fixed base and flexible base condition. A new approach has been proposed to provide simplicity in SSI modeling and reduce the computational cost (both memory and time wise). The approach includes the applicability of the equivalent pier method for the asymmetrical pile groups system, including SSI effect of the pile foundation system. The approach is validated for group effect and found that equivalent pile method can successfully be adopted and helps to reduce the computational cost of SSI problem. To understand the applicability of EPM approach, the parametric study has been carried out for different input of earthquakes and soil types. In accordance with this the three distinct earthquakes, including 1995 Chamba (M = 4.9), 1999 Uttarkashi (M = 6.9) and 2001 Bhuj (M = 7.7) and soil types including cohesive, cohesionless and C-Phi soils have been considered for SSI analysis. The study observed that, earthquake magnitude and soil type shows the major impact on the response of the SSI system.