Nonlinear Soil-structure Interaction Research Articles

Ductility demand estimation of high-rise steel special moment frames due to structure-pile-soil interaction

ABSTRACT This study is concerned with variation of ductility demands in a range of tall buildings comprising 15, 20, 25, and 30-story steel special moment frames resting on pile groups in a flexible soil medium. Nonlinear soil–structure interaction analysis is performed using the direct method by considering an adequate extent of soil around the structures terminating at appropriate boundaries. Eleven consistent ground motions are used for nonlinear dynamic analysis of the systems and the ductility demands are evaluated by tracing the rotation history of the plastic hinges. It is concluded that simultaneous contribution of soil–structure interaction and p-∆ effect results in more than 40% increase of the ductility demand and 20% increase of the story drifts in the worst case that includes the lower stories of the tallest building.

Numerical investigation of nonlinear soil-structure interaction effects on response of irregular RC buildings

Kathmandu, located in a high seismic zone, predominantly features irregular structures among its building stock. These structures are particularly susceptible to severe damage during seismic events, primarily due to torsional effects. Traditional seismic designs rely particularly on fixed-base conditions that underestimate forces and displacement primarily on soft soil conditions leading to irrational design practices. This study aims to quantify the seismic performance of buildings on various base conditions through fully nonlinear Soil-structure Interaction (SSI). The soil nonlinear behaviour was modelled using the Pressure-Independ-Multi-Yield (PIMY) material with an octahedral shear stress-strain backbone curve. Three distinct soil types were considered, and structures with irregular plan configurations were modelled using finite elements in both Opensees and STKO platforms. Structural performance was analyzed through nonlinear dynamic analysis, and outputs were evaluated based on seismic parameters. Comparing nonlinear SSI with linear SSI and fixed-base conditions revealed a significant increase in structural response, expressed in terms of displacement, drift ratio, and base shear. The magnitude of diaphragm rotation was found to be influenced by a combination of building torsional irregularity and SSI effects. It is suggested that the conventional practice of using the torsional irregularity ratio as a measure of torsional irregularity be revised and enhanced to better account for these influences. It has been quantified that torsional irregularity has a relatively lesser impact on displacements, drifts, and base shear compared to SSI. In all cases, fixed-base conditions consistently exhibited the minimum response. The study explored that linear SSI and fixed-base conditions tend to underestimate structural responses, while nonlinear SSI coupled with dynamic analysis provides a more accurate representation of realistic structural behaviour for seismic design particularly in soft soil cases.

Multi-hazard stochastic response analysis and reliability evaluation of a 5 MW monopile offshore wind turbine based on extended platform FAST-S

This study investigates the random dynamic response of a 5 MW monopile offshore wind turbine (MOWT) subjected to wind, wave and earthquake loads. Based on the aero-hydro-servo-elastic code FAST, a multi-field coupled simulation module considering earthquake, FAST-S, is developed for the fully coupled multi-hazard analysis of OWTs. Compared to the original FAST code, a seismic analysis module (SeismoDyn) and a soil-structure interaction (SSI) module (SoilDyn) have been supplemented in FAST-S. SeismoDyn is developed by modifying the Kane’s kinetic equation in the FAST, and the SoilDyn is developed through Winkler foundation model in order to consider the nonlinear SSI. Moreover, FAST-S has been validated by other recognized codes. Based on FAST-S, a fully coupled numerical analysis model of the NREL 5 MW MOWT is established, the random responses and reliability evaluation of the offshore wind turbine under wind, wave and earthquake loads are analyzed by probability density evolution method. The results show that the aerodynamic and hydrodynamic actions increase the damping of the wind turbine system, which has a certain effect on inhibiting the tower’s vibration caused by the earthquake. Therefore, compared with the coupled wind-wave-earthquake case, the sole earthquake case may be more unfavorable, and should be paid more attention to in high risk earthquake regions. The results show that the probability density functions of offshore wind turbine response under strong earthquakes obviously deviates from the typical regular distribution models. Based on the theory of equivalent extreme value event, the dynamic reliability of the offshore wind turbine is calculated. Seismic actions maybe the major factor in the design of the support structure. Nevertheless, owing to the aerodynamic and hydrodynamic damping effects of wind and wave loadings, the structural responses under wind-wave-earthquake are more moderate than ones subjected to solely earthquake. The strong seismic loads would cause significant complex variations of time-dependent probability density function of the OWT response.

Large‐scale seismic soil–structure interaction analysis via efficient finite element modeling and multi‐GPU parallel explicit algorithm

AbstractAs urban population increases, integrated underground–aboveground complexes are being constructed at growing paces in major cities. The seismic analysis of such complexes is crucial for the safety and functionality in the threat of potential earthquake disasters. However, fine‐grained numerical modeling and analysis of such large and complex structures are still inefficient due to the consideration of the soil–structure interaction (SSI). To address this challenge, an efficient approach for numerical modeling of large‐scale seismic SSI analysis is presented in this paper to overcome the limitations of existing finite element analysis (FEA) software. Moreover, a multi‐graphic processing unit (GPU) parallel explicit algorithm is implemented for the nonlinear dynamic SSI problems to further increase the computational efficiency. A large underground–aboveground complex project in China is used as an example to demonstrate the capability of the integrated method. The accuracy and reliability of the multi‐GPU parallel explicit finite element algorithm for SSI analysis (GFEA‐SSIA) are verified through a comparative analysis of the linear‐elastic and nonlinear dynamic response of the building calculated by GFEA‐SSIA and common FEA software. Finally, the structural response and structural damage of the underground–aboveground complex are analyzed under multidirectional seismic motions, and the damage distributions of the structures are provided.

Site Specific Non-Linear Ground Response Analysis and Soil Structure Interaction Study of Newly Constructed Dharahara Tower

This study investigates the seismic performance of the recently reconstructed Dharahara tower, a historically significant monument in Nepal that has experienced damage in past earthquakes and was completely destroyed in the recent Gorkha earthquake. Ground Response Analysis (GRA) and Soil-Structure Interaction (SSI) investigations are conducted to assess its structural behavior. GRA includes free field and structure-influenced analyses, with subsequent comparative assessment. Additionally, 3D non-linear finite element analysis is employed to derive equivalent spring constants representing soil and foundation characteristics, which are incorporated into the SSI analysis. These computed spring constants are used to model support conditions, allowing for an evaluation of the super-structural response. The study also employs non-linear dynamic analysis to compare structural responses between fix-based and spring-based models. The results indicate that the presence of the structure significantly influences surface wave motion amplification in GRA, resulting in peak ground accelerations (PGAs) that exhibit de-amplification in the free field and amplification in the presence of the structure. Furthermore, the introduction of an equivalent spring system in the soil-structure model changes the system's vibration period and damping characteristics, leading to enhanced dynamic response compared to the fixed-base model.

Two-way coupling fluid–structure interaction analysis on dynamic response of offshore wind turbine

The monopile-supported offshore wind turbines (OWTs) are subjected to the wave and current loadings. Affected by currents and waves, monopile-supported OWTs are also vulnerable to scour. However, the effect of scour and currents on the dynamic behavior of the monopile are not fully appreciated. This study conducted the model tests to evaluate the effect of scour depth and flow velocity on the lateral responses of support structure. Furthermore, the two-way (T-W) coupling fluid–structure interaction (FSI) method was proposed to evaluate the dynamic responses of piles in sand. The support structure is modeled using ABAQUS, a finite-element models software package, by considering the nonlinear soil–structure interaction effects, STAR-CCM + tools has been employed to model the FSI which are fed into ABAQUS to predict the structure’s dynamic response. Using the proposed method, a parametric study has been conducted to evaluate the effects of scour depths, flow velocities on the dynamic responses of OWTs. The results indicate that scour altered the fundamental frequency of OWT, causing resonance. An increase in scour depth and flow velocity increased the dynamic responses of support structure, which are detrimental for the safety and stability of the OWT system.

Refined three-dimensional pile element formulation for second-order analysis of pile-supported structures accounting for complex loading conditions

The second-order analysis method is a simulation-based design method but less utilized for pile-supported structures due to the current inaccurate and unstable analysis methods for piles, especially for those under complex loading conditions in pile-supported structures. A refined Three-dimensional Pile Element (3DPE) formulation is proposed to promote the application of the second-order analysis method in pile-supported structures. The proposed refined 3DPE formulation can efficiently capture the nonlinear Soil-Structure Interaction (SSI) that is over-simplified in the conventional analysis method. Compared with the existing Pile Element formulation, the proposed refined 3DPE formulation can more accurately capture the structural behaviors of piles under complex loading conditions, including the shear effect and axial-torsional coupled response. Furthermore, three soil stiffness matrices are firstly proposed to improve the numerical stability of the spatial analysis using the existing element formulation. Extensive examples are provided to validate the effectiveness of the refined 3DPE formulation, indicating its applicability in extending the second-order analysis to pile-supported structures.

Optimal intensity measures in probabilistic seismic demand model of subway station

Ground motion intensity measure (IM), which is a key link between the seismic hazard analysis and structural seismic response analysis, plays an important role in the performance-based earthquake engineering framework. The objective of this paper is to evaluate the most commonly used IMs with respect to their capability to predict the seismic response of underground subway station structures. Because the properties of the surrounding soil has significant influence on the seismic response of subway station structure, four typical classes of engineering sites ranging from Class I to IV according to Chinese code for seismic design of urban rail transit structures are selected in this study. Dynamic time history analyses considering nonlinear soil-structure interaction (SSI) are performed on four two-dimensional finite element models consisting of two-storey three-span subway stations embedded in four different engineering sites in this paper. Both the near-fault without velocity pulse and far-fault ground motions are used as the seismic inputs for the nonlinear SSI models in this study. Ground motion excitation is converted into equivalent seismic load at the artificial boundary for the discretized finite element model to realize the seismic load input. The applicability of 20 ground motion IMs commonly used in earthquake engineering research are investigated in this study. Statistical regression analysis is carried out for those IMs and engineering demand parameters (EDPs) of the subway station structure measured by maximum inter-storey displacement ratio obtained from nonlinear time history analyses. Based on the criteria of efficiency, practicality, proficiency and sufficiency, the optimal IMs in probabilistic seismic demand model that can best estimate the seismic response of the subway station structure are identified among those commonly used IMs. It is found that for sites of Class I and Class II, the Arias intensity followed by the velocity spectrum intensity are the optimal candidates, and for sites of Class III and Class IV, the Arias intensity is the optimal IM.

Nonlinear time-domain soil-structure interaction analysis of a mid-rise building benchmarked against earthquake recordings: A case study of the BRI's annex building

Performing soil-structure interaction (SSI) analysis under strong shaking scenarios using the direct method is becoming more prevalent in engineering practice. However, given the pronounced nonlinearity in soil, structure, and foundation response, the robustness of current methodologies is open to question, and benchmarking these methodologies against instrumented case histories is needed to identify the strengths and weaknesses in the approach. In this study, a three-dimensional (3D) Nonlinear (NL) Soil-Structure Interaction (SSI) analysis methodology in the time-domain code LS-DYNA is benchmarked against the actual recordings for a mid-rise building. The well-instrumented Building Research Institute (BRI) Annex Building (ANX) in Tsukuba City northeast of Tokyo, Japan, which features an adjacent free-field geotechnical downhole array, is used for this case study. A Finite Element (FE) three-dimensional 3D SSI model of the site, including the BRI ANX building, that considers both material and geometric nonlinearities is first developed. Two events are applied to the model: the 2011 Tohoku-Oki earthquake main shock (Mw9.1), referred to as the Great East Japan Earthquake (GEJE), and the 2002 Southern Ibaraki Prefecture earthquake (Mw4.9), selected from the BRI strong motion network due to the relatively wide amplitudes recorded at the site. The former event induced maximum shear strains in the soil of 1.6%, while the latter event induced maximum shear strains of 0.08%. For both horizontal and vertical components of shakings, the predicted response of the structure and adjacent free-field downhole array are compared with the corresponding recordings. The results show that the structural response is significantly affected by the accuracy of the predicted free-field ground surface response, especially at the structural fundamental period as opposed to the site period. In addition, results indicate that the fixed-base and flexible-base structural models’ responses are substantially different, mainly attributed to the SSI effects that cannot be captured in the fixed-base model. Finally, a comprehensive discussion on the minimum amount of data required to adequately capture nonlinear structural response using the proposed SSI methodology is provided in this case study.

Non-linear soil-structure interaction effect on the seismic response of a building

Non-linear soil-structure interaction effect on the seismic response of a building

Integration of Building Information Modeling Interoperability into Nonlinear Finite Element Analysis of Bridge Substructures

Acceptance of building information modeling (BIM) throughout the bridge industry is widely recognized as inevitable. However, while adoption of BIM technologies has proliferated throughout the building industry, advances pertaining to BIM for bridges and other structures remain underway. The present study aims to increase the potential for integrating BIM processes into software packages that possess capabilities for nonlinear finite element analysis (FEA) of bridge substructures. Moreover, the present study is intended to galvanize stakeholders within the area of soil–structure interaction (SSI) modeling and analysis to more effectively participate in interoperability workflows as part of bridge design. A proof-of-concept exporter tool was formulated in a modular manner to robustly export finite element model data stored in a selected SSI analysis package into the Industry Foundation Classes (IFC) standard, with the IFC standard chosen as the target schema owing to its widespread usage in the construction industry. The ability of the exporter tool to—with fidelity—convert a model from the selected analysis software to the IFC standard is showcased through an illustrative case study. In carrying out the case study, collections of geotechnical modeling parameters were identified that, while being common to numerous nonlinear SSI analysis packages, are not present in the existing IFC schema. Inclusion of these parameters in the IFC schema is proposed, serving to: 1) lower the barrier for entry of SSI modeling and analysis stakeholders to take part in interoperability processes and 2) encourage adoption of novel BIM processes in the bridge industry.

Offshore wind farms as additional coolant power sources to enhance seismic resilience of nuclear power plants– A case study

Continuous supply of cooling power is a critical aspect in operations of Nuclear Power Plants (NPPs) as evidenced in the major nuclear disasters. Design engineers follow rigorous standard guidelines in planning several levels of safety for power sources in NPPs. However, any unprecedented man-made or natural events may lead to the loss of coolant requirements. This study proposed a seismic resilient strategy using sustainable wind power through which the robustness of cooling power for NPPs during seismic events can be enhanced. Proposed strategy involves various steps starting from estimation of coolant power requirements for nuclear reactors, design of offshore wind turbine (OWT) and supporting system, and seismic safety assessment of proposed OWT for scenario levels at the site of interest. An existing NPP in India (Madras Atomic Power Station-MAPS, Chennai) is chosen as the case study for demonstrating the applicability of proposed strategy. Seismic analysis of proposed OWT is performed incorporating the state-of-the-art understanding on existing seismic scenario, geological and loading conditions, nonlinear seismic soil structure interaction (SSSI), and liquefaction susceptibility. Based on the analysis, it is concluded that the proposed offshore wind farm is seismically resilient for the anticipated scenario at the site and could cater the coolant requirements of MAPS. The current study can advance the research on integration of sustainable and resilient energy sources to increase the reliability of NPPs located in seismic prone regions.

Estimation of the inelastic displacement ratio for structures considering nonlinear soil-structure interaction

Estimation of the inelastic displacement ratio for structures considering nonlinear soil-structure interaction

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 (). 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.

Numerical modeling of a pile-supported wharf subjected to liquefaction-induced lateral ground deformations

Fully-coupled nonlinear dynamic analysis is increasingly used for assessing the seismic performance of pile-supported wharf structures subjected to liquefaction-induced lateral ground deformations. Several numerical challenges exist for analysis of this highly nonlinear soil-structure interaction, which require robust, yet practical, solutions that are validated with experimental data. This study presents a numerical model of a pile-supported wharf and evaluates the applicability of a soil constitutive model, and modeling assumptions and methods by using recorded data from a well-instrumented, large-scale centrifuge test. The objectives of this study include: (a) evaluating the performance of a recently developed pressure-dependent multi-yield surface constitutive soil model (PDMY03) to simulate the behavior of a liquefiable sand (b) assessing the effectiveness of a soil–pile interaction modeling approach in capturing the kinematic displacement demands on piles from a laterally spreading ground, and (c) evaluating the effectiveness and limitations of the 2D numerical model in approximating the 3D behavior of a wharf structure supported by multiple rows of piles, including the dynamic response of the centrifuge container. The implications of these assumptions and lessons learned from this study provide guidance for researcher modelers and practitioners for numerical modeling of similar soil–structure systems.

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.

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.

Enhancing displacement coefficient method for multi degree of freedom buildings (MDOF) considering nonlinear soil structure interaction

Enhancing displacement coefficient method for multi degree of freedom buildings (MDOF) considering nonlinear soil structure interaction

Effect of nonlinear soil−structure interaction and lateral stiffness on seismic performance of mid−rise RC building

In this study, the nonlinear soil-structure interaction (SSI) is considered to analyse the mid-rise structure's seismic performance with proportional lateral stiffness of columns in the orthogonal direction. The model's geometry is created using a finite element-based software package (ABAQUS). Cap plasticity and hysteretic models are used to mimic the nonlinear behaviour of soil and structural components, respectively. Truncated soil mass is incorporated using the spring and dashpot at the boundaries node with a MATLAB code for the dynamic analysis. The methodology validation is carried out on the shallow foundation under the cyclic loading and found in good agreement. Static pushover analysis of 4-storey, 8-storey mid-rise structures and 12-storey dual RC frame system is carried out to estimate the yielding displacement of the building structure at the roof level, which is further used in the incremental dynamic analysis (IDA) of the SSI and fixed base system. IDA is carried out for earthquake intensities ranging from 0.1g to 0.6g. IDA results are represented in terms of displacement ductility demand, normalised peak settlement, base shear, normalised peak foundation sliding and drift ratio. From the IDA analysis, the fragility assessment of the building is carried out for both the cases (fixed and SSI base). The present study concluded that lateral stiffness and SSI significantly affect the seismic performance of mid-rise buildings.

Analysis of nonlinear soil-structure interaction using partitioned method

For the current state-of-practice in soil-structure interaction (SSI) of nuclear facilities, the strain-dependent characteristics of soil are considered indirectly via equivalent linear methods in the frequency domain, typically represented by the SASSI program. SSI analysis in the time-domain, although directly involving material nonlinearity of the soil, is inefficient in practice up to now. Based on Partitioned Analysis of SSI (PASSI), a method for nonlinear soil-structure interaction analysis is developed in this paper, by applying implicit time-step integration and explicit one with different time steps to nuclear island and to soil, respectively. The incremental equilibrium equation and explicit decoupling method are used to analyze the soil nonlinearity described by the Davidenkov model with simplified loading-reloading rules, which avoids solving algebraic equations and iteration processes. An asynchronous parallel algorithm for nonlinear SSI analysis is given. A simple example is given to verify the partitioned approach with explicit-implicit co-computation against the full-explicit approach. Seismic response characteristics of nuclear power plants are investigated by comparing responses of nonlinear analysis with linear analysis. Different results address the importance of nonlinear SSI analysis for the seismic performance of nuclear structures.