Soil-structure Interaction Effects Research Articles

Soil-Structure Interaction Effects on Seismic Response of Multi-storey Buildings

The effect of soil-structure interaction (SSI) on the seismic responses of multi-storey buildings is investigated. The execution of SSI effects is conducted in two ways viz. Winkler approach and soil continuum approach. Time-history analysis methods are used for the seismic evaluation of parameters like time period, modal mass participation, base shear, lateral displacement, storey drift and inter-storey drift ratio. The present study consists of two parts; one is fixed base analysis i.e. without SSI, and the other is flexible base analysis i.e. with SSI. The buildings are modelled using finite element-based software SAP2000, where the equilibrium equations are solved by Hilber-Hughes-Taylor (HHT) method. A parametric study is performed with existing ground motion and varying numbers of stories to inherit the above parameters' responses. The results obtained from flexible base conditions are compared to those corresponding to fixed base conditions. The study shows that the behaviour of the structure changes under the SSI conditions and it may become vital in some cases; however, ambiguity also subsists with SSI.

Urban scale risk assessment including SSI and site amplification

Large-scale risk analysis is typically performed considering existing fragility curves, calculated in most cases without adequately accounting for local site amplification (SAmp) and soil-structure interaction (SSI) effects. Nevertheless, foundation flexibility and local site effects may lead to a substantial difference in the fragility or loss estimates. Including these effects on the city-scale vulnerability analysis is challenging due to the complexity of defining the whole interacting urban system. We propose a novel framework for the fragility assessment of structures considering the influence of SSI and local site amplification effects, suitable for large-scale applications. The applicability of the proposed approach is based on globally available data regarding the soil, the foundation, and the building portfolio. Site amplification is considered directly in the resulting fragility curves using site response analyses. An improved taxonomy is adopted to make the approach implementable in the OpenQuake software, introducing VS,30 and H/B within the structural features as proxies for the site and SSI effects. Finally, following the performance-based earthquake engineering framework, the outcomes of the methodological framework are adopted to estimate the nominal probability of failure for selected building classes belonging to the majority of structural types of the city of Thessaloniki, Northern Greece. The main findings demonstrate that the conventional way of calculating fragility curves may lead to a different seismic risk evaluation, especially in soft soil formations.

Seismic response of a nuclear island building with base isolation considering the soil–structure interaction effect

AbstractThis study aims to investigate the influence of soil–structure interaction (SSI) on the seismic response of a nuclear island (NI) building with base isolation. Hence, modal and dynamic time‐history analyses of the NI building with base isolation based on different soil dynamic numerical models that are applicable for homogeneous and layered sites to consider the SSI effect were conducted. After a comparison analysis of natural frequencies, floor response spectra (FRS), and acceleration response of superstructure, the following results are obtained. (i) For homogeneous sites, the degrees of freedom of the horizontal translation and torsion of the NI building with base isolation calculated using different site dynamic numerical models have equivalent natural frequencies. For layered sites, the natural frequencies increase slightly with the improvement of the shear wave velocity of the upper layered soil. (ii) For homogeneous sites, FRS calculated by the massless foundation model is generally larger than those of the dynamic model proposed by the ASCE code and the viscoelastic artificial boundary site model. Both the spectral and peak values of horizontal FRS at a low frequency band calculated by considering the SSI effect are larger than those without the SSI effect. (iii) For layered sites, both the spectral and peak values of horizontal FRS at a low frequency band have an amplification effect compared with that of a homogeneous site. (iv) For layered sites, the calculated horizontal acceleration response does not have evident law that changes with the degree of hardness and softness of the upper soil. Therefore, the SSI effect for particular homogeneous and layered sites should be considered when calculating the seismic response of the NI building with base isolation.

Experimental and numerical studies on shield building on non-rock site

Fluid-structure interaction (FSI) and soil-structure interaction (SSI) affect the seismic response of third-generation pressurized water reactor (PWR) nuclear power plants on non-rock site. In this paper, two 1/50 scaled simplified models were designed and a series of shaking table tests were carried to study the seismic responses of models considering FSI and SSI effect. Dynamic characteristics, acceleration, strain, hydrodynamic pressure and experimental phenomenon of the two models were analyzed. Moreover, the numerical analysis was performed and numerical results were compared with test data. The results show that the presence of model soil reduces the system’s frequency, and the presence and sloshing of water reduce the seismic response of model structure. The reasonableness and feasibility of the method used for the numerical simulation is verified. This study could provide a reference for analyzing the seismic response of prototype structure of nuclear power plant.

Nonlinear Static Seismic Analysis and Its Application to Shallow Founded Buildings with Soil-Structure Interaction

This paper presents new research in the field of nonlinear static seismic analysis and the N2 method for soil-structure systems. The rationale for this study stems from the inclusion of soil-structure systems in simplified displacement-based design methods. The conducted research comprises three parts, including original experimental investigations, the development of numerical models and the validation of results. A new methodology is presented that provides a step-by-step procedure for the implementation of the N2 method on soil-structure systems. Results of a dynamic shake-table test on a simplified scaled structural model founded on compacted dry sand are presented, and a numerical model of the experiment is developed and calibrated with the inclusion of soil-structure interaction effects. This indicates one main significance of this paper, which is the variation between the experimental and the analytical model and how they can be compared. Lastly, a case study was conducted on a numerical model of a 3D steel building. The building was analysed using pushover analysis for a fixed base-case and by considering soil-structure interaction effects. The results of both observed cases were mutually compared and further examined by validating them with nonlinear dynamic analyses. A comparison was conducted considering the inter-story drifts, calculated according to the N2 method and time-history analyses. The results show good agreement when the N2 method is used for buildings on compliant soils. Overall, it was observed that a decrease in the inter-story drifts appears at ground level of the building. This research also provides a framework for future research in the examined field, for instance, on different types of buildings, building typologies and irregularities of the structural system.

Estimation of response reduction factor for Indian standard code designed reinforced concrete frames considering nonlinear soil-structure interaction effects

To incorporate the advantages of inelastic behaviour in design of civil engineering structures under seismic excitations, contemporary seismic design codes adopt a factor, termed as response reduction (or modification) factor ( R ). This factor is considered to calculate the seismic demand of a structure by estimating the inelastic base shear from its linear counterpart. This study first evaluates the adequacy of R values provided in Indian seismic codes by performing numerical studies on different reinforced concrete (RC) frame buildings, which are designed following the provisions of contemporary Indian seismic codes. In particular, to assess the values of R for multi-storey RC frames, the present work utilises rigorous incremental dynamic analysis (IDA). Next, in order to understand the influence of flexible base conditions on R values, elastic and inelastic soil-structure interactions (SSI) are incorporated in the analysis. In flexible base condition, Type II (medium) and Type III (soft) soil conditions (as per Indian seismic code) are considered to characterise the base soil and for designing the isolated footings of the frame structures considered in this study. It has been observed from this study that for both fixed and flexible base conditions, the code specified R value may not be conservative in some cases.

Effect of soil structure interaction on the dynamic response of reinforced concrete structures

During severe seismic events, the dynamic response of the structure is affected not only by the behavior of the superstructure but also by the nature and behavior of the soil present in and around the substructure. The conventional structural design process usually assumes the base of the foundation to be completely restrained, i.e., in a fixed condition. However, this assumption is inaccurate as it neglects the effect of flexibility offered by the interaction of the soil with the structure. There is no clear consensus on either the beneficial or detrimental effects of soil-structure interaction (SSI) on the seismic response of structures. The main objective of this paper is to study the effect of SSI on a multi-story (G + 10) building resting on a mat foundation. The building is modeled using Finite Element Method (FEM) software and SSI is incorporated using Winkler's (un-coupled) and pseudo-coupled approaches. A case study is done to understand the non-linear dynamic response of building with different soil bearing capacities. The results are represented in terms of fundamental period, base shear, and story drift.

Three-dimensional probabilistic assessment of tunneling induced structural damage using Monte-Carlo method and hybrid finite element model

Probabilistic assessment methods can be used to estimate engineering demand parameters under significant uncertainty, such as in the assessment of building damage due to tunneling. This paper develops a new empirical, theoretical and finite element hybrid three-dimensional model, in which the soil–structure interaction is considered and window and door openings are modeled explicitly, to achieve a reasonably fast and accurate damage prediction. The proposed model is embedded in a Monte-Carlo based probabilistic assessment approach, so that the building damage probabilities under different input uncertainty can be computed. Typical methods to quantify the input uncertainty in tunnel-soil–structure interaction practice are suggested. The probabilistic assessment method and a variance-based (Sobol’s) sensitivity analysis are implemented with a computer program that runs in higher-performance computing clusters, and demonstrated with two case studies. The significance of the soil–structure interaction effect and three-dimensional building effect are studied.

Tunnel-soil-bridge seismic interaction on soft clay

Seismic tunnel-soil-bridge interaction in high plasticity soft clays can lead to significant ground motion variability, affecting on-ground structures located next to or above underground facilities. This technical note presents a numerical study aiming at establishing tunnel-bridge seismic interaction effects on soft clays. Initially, we revised this interaction considering the impact that frequency content, intensity, and strong ground motion duration have on the interplay between incoming seismic waves reflected in the tunnel and the energy feeding back from the bridge swinging back and forth during a large earthquake. Series of three-dimensional finite difference models were developed. Seismic analyses considered both normal and subduction events with a return period of 250 years. From the results gathered in these analyses, the ground motion modification in the surrounding soil occurs in both the transverse and longitudinal components due to tunnel-bridge interaction. The tunnel underneath the bridge establishes detrimental soil-structure interaction effects for normal and subduction events.

Probabilistic assessment of SMRFs with infill masonry walls incorporating nonlinear soil-structure interaction

Infill Masonry Walls (IMWs) are used in the perimeter of a building to separate the inner and outer space. IMWs may affect the lateral behavior of buildings, while they are different from those partition walls that separate two inner spaces. This study focused on the seismic vulnerability assessment of Steel Moment-Resisting Frames (SMRFs) assuming different placement of IMWs incorporating nonlinear Soil-Structure Interaction (SSI). The aim is to explore the damage states of IMWs and use their ability for improving the vulnerability of SMRFs. For this purpose, the three, five, seven, and nine story levels (3-Story, 5-Story, 7-Story, and 9-Story) SMRFs were modeled considering four soil types. Incremental Dynamic Analyses (IDAs) were performed to determine the seismic performance limit-state capacities of SMRFs considering the Far-Fault (FF) record subset suggested by FEMA P695. To accurately model the influence of IMWs on the seismic response of SMRFs, a Tcl programming algorithm was developed to intelligently monitor the damage states of IMWs in each floor level. Results of the analysis show that assuming different placement of IMWs can significantly increase the seismic limit-state capacities of SMRFs with and without considering SSI effects. In addition, IMWs can play a crucial role to improve the seismic performances as well as the seismic collapse probability, which may be suggested for retrofitting purposes.

Resilient seismic design of reinforced concrete framed buildings with metallic fuses including soil-structure interaction effects

In this paper, the authors propose and validate a code-oriented, resilient design methodology for reinforced concrete buildings with intermediate moment frames (RC-IMFs) and hysteretic energy dissipation devices (HEDDs) mounted in chevron steel bracing design as structural fuses, considering soil-structure effects. The design methodology is based on global lateral stiffness balances among different structural components (frames, bracings and HEDDs). Global seismic design parameters were specifically assessed for such stiffness ratios through extensive parametric studies for the subject structural system under study. In order to achieve an immediate occupancy seismic performance, the design sequence using capacity-design principles is clearly established and emphasized for the design of main structural elements. Soil-structure interaction (SSI) effects are included in the formal design process following the recommendations available in the seismic code for Mexico City. In order to fully test the efficacy of the proposed design methodology under a demanding seismic scenario, three buildings of 8, 15 and 24 stories were designed in soft soil sites of Mexico City close to resonant responses. Different types or HEDDs were considered and evaluated. Pushover analyses were performed in order to verify that subject buildings may achieve the objective resilient deformation mechanism (immediate occupancy) at the maximum useful ductility capacity assumed for the HEDDs. Nonlinear dynamic analyses were performed for the complete 3D designs according to the code under the action of eight pairs of acceleration records, representative of the site where the buildings were located. This was done in order to assess maximum inelastic demands, residual drifts, and fully verify and validate the proposed resilient, structural fuse code-oriented design. From the obtained results, it is confirmed that a resilient structural performance is feasible for RC-IMFs with HEDDs under the proposed code-oriented design methodology.

Impact of local site effects on seismic risk assessment of reinforced concrete bridges

In most practical applications of performance-based earthquake engineering, the local site characteristics are considered simplistically, and soil-structure interaction effects are ignored. Within such a conventional approach, the ground motion record selection uses the time-averaged shear-wave velocity in the top 30 m of the soil profile (VS30) as the main proxy to represent the site where the structure is located. This study aims to assess the impact of local site effects on the risk assessment of reinforced concrete (RC) bridges by incorporating the local-site response and soil-structure interaction effects more realistically within a more detailed approach. For this purpose, seismic risk assessment of RC bridge structures with various configurations located on varying site characteristics was carried out using different levels of refinement in the numerical modelling. Local site amplification was incorporated using site response analysis, and p-y models were used to consider foundation flexibility. Cloud analyses were then carried out on both modelling approaches to obtain and compare the corresponding scenario-based seismic loss estimates for the structures. Moreover, the results of numerical analyses were scrutinized in terms of peak demand to capacity ratio values, and statistical hypothesis testing was used to quantify the similarity between the two approaches further. In some cases of site response modeling, especially when the fundamental periods of the bridge structure and site are sufficiently close, higher displacement demands on bridge piers were obtained, likely leading to higher direct seismic losses.

Seismic Behaviour of Framed Structure Considering Soil Structure Interaction

:Inelastic response of the buildings are often developed without considering soil structure interaction where the base is assumed to be fixed. The present study presents the soil structure interaction and ambiguity effects in soil properties such as Poisson’s ratio of the multy storied framed structure in three different types of soil, namely soft, medium and hard soil with fixed and flexible base considering soil structure interaction. In this paper, a model of G+10 storey building with fixed and flexible base considering raft foundation was analysed using SAP2000. From the analysis, it was observed that the results of lateral displacement, storey displacement, base shear, moment values and the time period were on higher side in the flexible base considering soil structure interaction. The requirements of considering soil structure interaction during design of structure can be understood.

Study Behaviour of PEB Structure with Isolated Foundation Considering Soil Structure Interaction

Abstract: In this study behaviour and concept of Pre- Engineered structure & SSI is included. Behavioural study of preengineered building is observed in this paper. Soil structure interaction (SSI) taken into consideration to study the interface between Soil and the structure rested on that soil. Many resources can be used to gather information on the present theories and practices, including IEEE explorer, technical papers, journal, conferences, patent information research thesis, international and national workshop proceedings. The following case studies the influence of soil structure interaction on pre-engineered building (PEB). By considering the fixed support conditions at the base of structure, the structural behaviour is analysed. The structural response of building seems to be affected because in conventional method the foundation flexibility of soil mass has been ignored. Winkler’s spring model approach is used for the analysis of soil flexibility by integrating. The effect of SSI on various parameters like base shear, lateral displacement, etc. are studied and discussed. The subgrade must be modelled adequately well to get real behaviour of superstructure. The analysis is administered in STAAD Pro. connect edition software using response spectra of IS 1893-2016

Robust output feedback-based neuro-fuzzy controller for seismically excited tall buildings with ATMD accounting for variations in the type of supporting soil

Recently, developing the control algorithms for tuning the voltage/force command of smart control devices for application in seismic-excited buildings and bridges has been well addressed considering soil-structure interaction (SSI) effects. A controller is often designed for a soil pre-set condition. Moreover, considering an exact model of soil in the controller design process is a tedious task due to high computational costs. Consequently, the seismic performance and robustness of the adopted controller are questionable against the variations in soil conditions. The motivation of the present paper is to propose a robust controller for seismic-excited tall buildings against the variations of soil conditions than the pre-set condition. Taking advantage of the optimal output feedback controller (OOFC), a simple and practical controller based on OOFC is proposed for application in tall buildings equipped with an active tuned mass damper (ATMD) accounting for SSI effects. Considering different soil types, a dataset is generated from the proposed OOFC and an adaptive neuro-fuzzy inference system (ANFIS) is trained to fit them in a robust dataset. Then, a robust output feedback-based ANFIS controller, namely ROFBANFISC, is proposed. The robustness of the OOFC and ROFBANFISC are validated for different soil types. Considering six performance criteria, the numerical studies are conducted on a 40-story structure subjected to five real ground motions. The simulation results carried out for different soil conditions show that the proposed ROFBANFISC is more robust than the OOFC. Also, it can maintain its appropriate seismic performance in different soil types.

Seismic response analysis of slope reinforced by pile-anchor structures under near-fault pulse-like ground motions

Many post-earthquake investigations have found that natural slopes and geotechnical structures near the faults can be seriously damaged by earthquakes. Pile-anchor structure is one of slope reinforcement measure that widely used in earthquake-prone areas due to its flexible characteristic. To explore the seismic responses and behavior of slopes reinforced by this kind of retaining structure near faults, a series of shaking table model tests were performed. The effect of pule-like ground motions on the seismic responses of system are systematically analyzed by the results from the excitation of pulse-like and no-pulse ground motions in terms of acceleration responses, amplification effect, wave reflection effect and the soil-structure interaction effect. The results demonstrate that the pulse-like ground motions can seriously aggravate the seismic responses and reduce the stability of the system. To better reveal the effect from the pulse-like ground motions, a special shaking scenario, based on the semi-artificial ground motions generated by the wavelet analysis approach, was also conducted to study the effect from different components in the pulse-like ground motions on the seismic responses of system. The results obtained in present study can promote the understanding of the seismic behavior of slopes and slope retaining structures under the pulse-like ground motions, and provide a basis for the seismic design of pile-anchor structures near the faults in earthquake-prone regions.

Numerical investigation of the contribution of the soil-structure interaction effects to the seismic performance and the losses of RC buildings

Seismic vulnerability and loss analyses of buildings are usually estimated under the fixed-based condition, omitting the soil-structure interaction (SSI) effects. However, according to the literature and the seismic damage due to past events, mid-to high-rise buildings located on soft soils can present a worse seismic performance. This manuscript aims to investigate whether the SSI effects affect the seismic performance and the losses of reinforced concrete (RC) buildings. To do so, a real 5-storey RC building has been selected as the case study. It was built prior to restrictive Spanish seismic codes. The building was constructed over soft alluvial strata and it has a shallow foundation. The area is characterised by a moderate seismic hazard. Nonlinear static analysis (NLSA) and incremental dynamic analysis (IDA) have been performed to assess the seismic behaviour and the losses expected of the case study building. The calculations have been done in the OpenSees finite-element framework. The direct method has been used to model the SSI. The results have been obtained for the fixed-base and for the SSI models. The numerical outcomes have shown the remarkable effect of the SSI on the fragility and on the performance of these structures. It has been observed that the severe damage expected can be worsened by up to 38% if SSI is taken into account. Additionally, the soft-storey mechanism at the ground floor concentrates all the damage expected, showing that this is the most seismic vulnerable part of the building (owing to higher interstorey-drift ratios and peak floor acceleration values). The losses expected derived for structural and non-structural components have been 140% higher if the SSI is considered.

Enhancing seismic performance of rigid and semi-rigid connections equipped with SMA bolts incorporating nonlinear soil-structure interaction

Nowadays, using smart connections can improve the performance of buildings with some recentering features that are from the superelastic behavior of Shape Memory Alloys (SMAs). It seems that there is different rigidity between the designed connection and the real one in Steel Moment-Resisting Frames (SMRFs), which can be considered as a problematic issue due to the importance of connections in seismic performance assessment. This paper aims to investigate the seismic limit-state capacities of rigid and semi-rigid connections implemented in the 3-Story, 5-Story, 7-Story, and 9-Story SMRFs considering the nonlinear Soil-Structure Interaction (SSI) effects. A Tcl programming code was developed to model semi-rigid connection and SSI effects using Opensees. Incremental Dynamic Analyses (IDAs) were employed to assess the seismic performance levels of SMRFs considering Near-Fault Pulse-Like (NF-PL) and Near-Fault No-Pulse (NF-NP) records suggested by FEMA-P695. The results showed that assuming semi-rigid connections with rigidity of 80%, 70%, and 60%, significantly decreased the median values of IDA curves compared to rigid connection. Considering the SSI effects can considerably decrease the Sa(T1) values of IDA curves and seismic collapse probability in all soil types; therefore, it is suggested to assume the real condition of the structure by modeling the connection rigidity and the SSI effects. It can be concluded that SMA bolts have the ability to improve the seismic performance of connection to compensate the lack of rigidity in semi-rigid connections of SMRFs; as well as, they can be used as a retrofitting strategy for existing buildings.

Dynamic optimum torsion axis under soil-structure interaction effects

The present paper deals with the dynamic optimum torsion axis of asymmetric buildings under soil-structure interaction effects. The soil-foundation-building system is subject to a torsional base acceleration. Under the aforementioned loading, the optimum torsion axis is defined as the vertical axis where the sum of the squares of the resultant translation displacements receives a minimum value. The equations of motion are written and are transferred to the frequency domain in order to take into account the frequency-dependency of the foundation’s impedance functions. The optimum torsion axis criterion is applied and is further elaborated so as mathematical formulae are provided for the determination of the dynamic optimum torsion axis under soil-structure interaction effects. Numerical examples are provided by the implementation of a programming code written for this purpose. Apart from the structural eccentricity reduction another important finding is that the dynamic optimum torsion axis of a flexibly based building generally coincides with the static optimum torsion axis. A few deviations are observed in the very high frequency range.

지반 임피던스 함수를 고려한 원전 구조물기반 질량집중모델에 대한 시간영역 지진응답해석

In this paper, a seismic analysis method of nuclear reactor containment buildings (RCBs), considering both soil-structure interaction (SSI) and structural nonlinearity, is proposed and verified. To consider the SSI effect, a frequency-dependent soil impedance function is calculated and transformed into an impulse response in the time domain, which is applied to the structure in sway-rocking model form. Seismic analysis of the structure considering structural nonlinearity is then conducted in the time domain. As a structural model, a beam-stick model based on OPR1000, an in-service RCB in Korea, is used. The IMK hysteretic model is adopted for seismic analysis to consider the structural nonlinearity of the RCB, which is mainly composed of concrete shear wall. Three different soil profiles are used for the comparison, and a series of analyses are performed with PGA = 0.3 g and 2 g. The seismic responses of the structure are represented as in-structure response spectra and compared.