Real Seismic Events Research Articles

A stochastic approach for the generation and combination of vertical and horizontal strong ground motion

Damage to structures during near-fault earthquakes often indicates that the vertical component was larger than what is usually considered in seismic design. Commonly, the vertical component of seismic ground motions is associated with the P-wave. In contrast, the horizontal seismic ground motions’ component is usually related to the arrival of the S-wave. However, findings of recent near-fault events indicate that both the horizontal and the vertical motions are a mixture of S and P-waves. Therefore, the need to generate three-component artificial accelerograms for structural design arises. This paper proposes a double aim: starting from the well-noted Snell’s law, a physical explanation of the mixture of S and P-waves is outlined. Then, a novel integrodifferential filter system for the stochastic simulation of the three components of strong motion is presented. The proposed study is applied to some theoretical applications as well as to two real Italian seismic events.

Direct Estimation of the Source Corner Frequency of Minor to Moderate Earthquakes from Fourier Phase Spectra Fitting

ABSTRACT Estimating the corner frequency (fc) of an earthquake is of fundamental importance to improving our knowledge of the physics of the rupture that gives rise to a seismic event, while also having important implications by providing information on the high-frequency radiation for seismic hazard studies. However, the estimation of fc through spectral-fitting methods suffers from trade-offs with the estimation of seismic wave attenuation, making the obtained values precise but not necessarily accurate. For this reason, after a review of the source model proposed by Brune (1970), a new method of estimating fc, based on the phase fitting of Fourier spectra of the Brune’s seismic pulse related to S-waves, called Fourier phase spectra fitting (FPS), is proposed and evaluated in this study. The method can be applied in cases in which Brune’s model may be appropriate, while also considering the effects of propagation on impulse deformation, for which the synthetic tests have been conducted. The results, obtained first using synthetic seismograms generated under controlled conditions and then on a data set of recordings of real seismic events collected at the Groningen gas field in the Netherlands, showed the method to be promising (being accurate and precise) and at the same time pointed out its limitations, with its applicability being restricted to short hypocentral distances of <20 km.

Analysis of Vibration Characteristics of Bridge Structures under Seismic Excitation.

Bridges may undergo structural vibration responses when exposed to seismic waves. An analysis of structural vibration characteristics is essential for evaluating the safety and stability of a bridge. In this paper, a signal time-frequency feature extraction method (NTFT-ESVD) integrating standard time-frequency transformation, singular value decomposition, and information entropy is proposed to analyze the vibration characteristics of structures under seismic excitation. First, the experiment simulates the response signal of the structure when exposed to seismic waves. The results of the time-frequency analysis indicate a maximum relative error of only 1% in frequency detection, and the maximum relative errors in amplitude and time parameters are 5.9% and 6%, respectively. These simulation results demonstrate the reliability of the NTFT-ESVD method in extracting the time-frequency characteristics of the signal and its suitability for analyzing the seismic response of the structure. Then, a real seismic wave event of the Su-Tong Yangtze River Bridge during the Hengchun earthquake in Taiwan (2006) is analyzed. The results show that the seismic waves only have a short-term impact on the bridge, with the maximum amplitude of the vibration response no greater than 1 cm, and the maximum vibration frequency no greater than 0.2 Hz in the three-dimensional direction, indicating that the earthquake in Hengchun will not have any serious impact on the stability and security of the Su-Tong Yangtze River Bridge. Additionally, the reliability of determining the arrival time of seismic waves by extracting the time-frequency information from structural vibration response signals is validated by comparing it with results from seismic stations (SSE/WHN/QZN) at similar epicenter distances published by the USGS. The results of the case study show that the combination of dynamic GNSS monitoring technology and time-frequency analysis can be used to analyze the impact of seismic waves on the bridge, which is of great help to the manager in assessing structural seismic damage.

Earthquake or blast? Classification of local-distance seismic events in Sweden using fully connected neural networks

SUMMARY Distinguishing between different types of seismic events is a task typically performed manually by expert analysts and can thus be both time and resource expensive. Analysts at the Swedish National Seismic Network (SNSN) use four different event types in the routine analysis: natural (tectonic) earthquakes, blasts (e.g. from mines, quarries and construction) and two different types of mining-induced events associated with large, underground mines. In order to aid manual event classification and to classify automatic event definitions, we have used fully connected neural networks to implement classification models which distinguish between the four event types. For each event, we bandpass filter the waveform data in 20 narrow-frequency bands before dividing each component into four non-overlapping time windows, corresponding to the P phase, P coda, S phase and S coda. In each window, we compute the root-mean-square amplitude and the resulting array of amplitudes is then used as the neural network inputs. We compare results achieved using a station-specific approach, where individual models are trained for each seismic station, to a regional approach where a single model is trained for the whole study area. An extension of the models, which distinguishes spurious phase associations from real seismic events in automatic event definitions, has also been implemented. When applying our models to evaluation data distinguishing between earthquakes and blasts, we achieve an accuracy of about 98 per cent for automatic events and 99 per cent for manually analysed events. In areas located close to large underground mines, where all four event types are observed, the corresponding accuracy is about 90 and 96 per cent, respectively. The accuracy when distinguishing spurious events from real seismic events is about 95 per cent. We find that the majority of erroneous classifications can be traced back to uncertainties in automatic phase picks and location estimates. The models are already in use at the SNSN, both for preliminary type predictions of automatic events and for reviewing manually analysed events.

Incorporating Traffic Models into Seismic Damage Analysis of Bridge Road Networks: A Case Study in Central Italy

Transportation networks are one of the most vulnerable civil infrastructures during an earthquake and an estimation of traffic impacts in the post-earthquake scenario is a crucial aspect in the context of risk assessment and evaluation of remedial measures. In this paper, a methodology is presented, combining GIS tools, probabilistic seismic risk analysis and traffic simulation models, which is able to assess the direct and indirect (social) costs: bridge repairs, increase in travel time and a lack of accessibility. Operating issues related to the development and calibration of traffic models applicable to a damaged road network are carefully analysed and reviewed and an innovative approach to evaluate the social cost due to the lack of accessibility is also proposed. The developed modelling framework has been applied on a realistic bridge stock within a road transportation network in central Italy where local land-use data have been collected, extensive traffic surveys have been performed and a traffic model has been calibrated. A probabilistic risk analysis employing a ShakeMap derived from a historical real seismic event has been carried out.

MALMI: An Automated Earthquake Detection and Location Workflow Based on Machine Learning and Waveform Migration

Abstract Robust automatic event detection and location is central to real-time earthquake monitoring. With the increase of computing power and data availability, automated workflows that utilize machine learning (ML) techniques have become increasingly popular; however, ML-based classical workflows still face challenges when applied to the analysis of microseismic data. These seismic sequences are often characterized by short interevent times and/or low signal-to-noise ratio (SNR). Full waveform methods that do not rely on phase picking and association are suitable for processing such datasets, but are computationally costly and lack clear event identification criteria, which is not ideal for real-time processing. To leverage the advantages of both the methods, we propose a new workflow—MAchine Learning aided earthquake MIgration location (MALMI), which integrates ML and waveform migration to perform automated event detection and location. The new workflow uses a pretrained ML model to generate continuous phase probabilities that are then backprojected and stacked to locate seismic sources using migration. We applied the workflow to one month of continuous data collected in the Hengill geothermal area of Iceland to monitor induced earthquakes around two geothermal production sites. With a ML model (EQ-Transformer) pretrained using a global distribution of earthquakes, the proposed workflow automatically detects and locates 250 additional seismic events (accounting for 36% events in the obtained catalog) compared to a reference catalog generated using the SeisComP software. Most of the new events are microseismic events with a magnitude less than 0. Visual inspection of the waveforms of the newly detected events indicates that they are real seismic events of low SNR and are only reliably recorded by very few stations in the array. Further comparison with the conventional migration method based on short-term average over long-term average confirms that MALMI can produce much clearer stacked images with higher resolution and reliability, especially for events with low SNR. The workflow is freely available on GitHub, providing an automated tool for simultaneous event detection and location from continuous seismic data.

Inelastic lateral and seismic behaviour of concrete-filled steel tubular pile foundations

Undertaken with industry, this paper analyses concrete-filled steel tube (CFTs) pile members in deep foundation systems under cyclic and seismic loads considering inelasticity for both pile and soil. Real seismic events have pointed out that piles may fail by forming multiple plastic hinges at various location or global buckling instability. This study confirms that CFT piles efficiently reduce damage in pile-heads and over the pile length, in depths that is difficult to access and repair the damage. The paper performs a set of analyses that enables understanding of the nonlinear mechanical behaviour of CFT piles and soil-structure interaction effects. The capacity margins of the novel foundation system are firstly assessed through controlled loading analyses (i.e., monotonic and cyclic loading histories), and then investigated further by a two-level seismic-intensity analysis. CFT pile damage patterns, displacement profiles and residual displacement are discussed and compared with those of corresponding concrete piles. Moreover, comparisons with four test campaigns taken from the literature confirm the correctness of the adopted nonlinear models for soil-pile interaction and soil inelasticity. Although its simplicity, the developed p-y modeling can successfully account for soil degradation effects making possible the simulation of the rather demanding, but advanced “s” shape of soil's cyclic behaviour, allowing for a reasonable comparison between composite and concrete piles. While the damage areas of both CFT and RC piles are mainly developed in pile heads and stiffness-discontinuous soil layers, CFT piles exhibit a lower damage than that of the RC piles nearly by 40% on average.

Inelastic seismic behavior of asymmetric structures under bidirectional ground motion: An effort to incorporate the effect of bidirectional interaction in load resisting elements

Seismically driven asymmetric structures are more vulnerable than their symmetric counterparts because of the coupling of lateral and torsional vibration. Though the research effort has been made to study the behavior of asymmetric structures, however, studies under the bidirectional ground motion of such structures are extremely terse. Further, in the inelastic range, the interaction between seismic forces under bidirectional ground motion may influence the yield criteria, inelastic excursion, and displacement demand considerably. In this context, the present paper is an effort to study the influence of bidirectional interaction, which occurs in reality under two orthogonal components of ground motion in real seismic events for asymmetric structures. A recently developed, adequate bidirectional hysteresis model that is capable of capturing the effects of bidirectional interaction is used. The governing equation of motion is solved by step by step integration following Newmark’s β-γ method. For improving the accuracy, iterations are carried out in each time step applying the Newton-Raphson technique. The spring force updates at the end of each time step to account for material nonlinearity with reasonable accuracy. Further, the present study not only helps to develop physical insights into the behavior of asymmetric systems but also shows that inelastic response may be grossly underestimated if the interaction between seismic forces along two principal directions is not incorporated. The broad conclusions developed in the study may be a help to fine-tune the provision for asymmetric structures in seismic code.

An updated parametric catalog of historical earthquakes around the Dead Sea Transform Fault Zone

In this study, we present the work done to review the existing historical earthquake information of the Dead Sea Transform Fault Zone (DSTFZ). Several studies from various sources have been collected and reassessed, with the ultimate goal of creating of new homogenized parametric earthquake catalog for the region. We analyze 244 earthquakes between 31 BC and 1900, which are associated with the geographical buffer extending from 27 N to 36 N and from 31 E to 39 E. Of these, 93 were considered real seismic events with moment magnitude (Mw) greater than 5 that indeed occurred within this zone. While we relied on past parametric data and did not assign new macroseismic intensities, magnitude values, or epicenters for several controversial events, we did however resort to the primary sources to obtain a more critical perspective for the various assigned macroseismic intensities. In order to validate the derived parametric information, we tried to associate the events present in the historical records, with any evidence coming from past field investigations, i.e., geological or archaeological studies. Acknowledging the uneven quality and quantity of data reporting each event, we provided each entry with an uncertainty range estimate. Our catalog lists 33 events of Mw ≥ 6 absent from the latest published compilation with compatible time span and areal coverage. The whole catalog is considered complete down to Mw 7 and in certain areas down to Mw 6 after the year 1000, with majority of the larger earthquakes located in the part of DSTFZ, which extends from the southeast part of Dead Sea lake till Antioch.

Damage assessment of autoclaved aerated concrete buildings: some Italian case studies

The present work deals with the damage assessment of some Italian case studies of structures/walls realised in autoclaved aerated concrete (AAC) blocks. Initially, examples of static damage of walls caused by excessive deformability of the slabs, differential loads on walls, and foundation settlements, are shown. Then, the seismic behaviour of AAC masonry buildings is analysed. In particular, the behaviour of two pre-seismic code buildings damaged by the Emilia 2012 earthquake is described and compared with modern engineered buildings. Then, the behaviour of non-structural walls damaged by the Central Italy 2016 earthquake is reported. Very few case studies focusing on the damage assessment of AAC masonry buildings during real seismic events can be found in the literature. This work provides an opportunity to advance our knowledge on the behaviour of this material.

Evolution in seismic monitoring system and updating seismic zones of Egypt

ABSTRACT On 3 September 2015, an unexpected earthquake with magnitude MB = 4.5 occurred in a completely silent area, located at 40 km south El Alamein city north western desert, where there are ~ 20 million pieces of unexploded ordnance. This study aims to: i) review and interpret the widespread seismic activity in Egypt during the last three decades, and ii) delineate the active seismic source zones map of Egypt based on realistic assumptions. These assumptions include only the real and accurate seismic events from the whole earthquake catalogue of Egypt. The idea based on the accuracy of the monitoring system, magnitude size of earthquakes, and detailed structure elements map of Egypt. The seismic catalogue of Egypt was updating to the end of 2019 including the historical and instrumental earthquakes since −2200 BC. The seismicity map of Egypt was outlined along five interval periods based on the significant evolution in the seismic monitoring system. The advanced monitoring period in the detection and location of seismic events in entire Egypt was supposed to begin in 2003 where the ENSN almost accomplished. Seismicity of advanced monitoring period 2003–2019 can be used as a tracer of real seismicity boundaries entire Egypt. Active seismic source zones map was delineated based on the advanced monitoring period and the unified Mw ≥ 4.5 instrumental catalogue from 1900 to 2019. To validate the seismic zones model, it compared with the structural elements map and given a rational matching. The new local seismic spots entire Egypt was discussed because of the invention in the seismic monitoring system entire Egypt and attributed to the misdetection and/or dislocation events due to the lack of monitoring system before the accomplished of ENSN. In conclusion, a validated active seismic zones map of Egypt was delineated using real and accurate seismic and geologic data based on powerful assumptions.

Displacement-based seismic design with damage control of asymmetric buildings

Abstract This paper presents a procedure for the displacement-based seismic design of in-plan asymmetric buildings with earthquake-induced damage control. Damage is defined on the structural elements in the in-plan and elevation layout of the structure. The proposed method is based on the concepts of the performance-based seismic design philosophy and the application of basic equations of structural dynamics that are regularly used for the current design of buildings. In its application, the simultaneous bidirectional seismic demand is characterized by smooth design spectrum as proposed by most current regulations. To illustrate the steps required in the application of the design method proposed, the paper presents the design process of a 15- and 12-story buildings with in-plan asymmetric distribution of stiffnesses and subjected to a design demand given by the spectrum a real seismic event representative of soft soil sites such as those of the bed-lake of Mexico City. The results obtained are compared with the corresponding results of the nonlinear dynamic step-by-step analyses under the same seismic demand. Based on the results obtained, the relevance of this procedure in the displacement-based seismic design of asymmetric buildings and the implications for its consideration in future regulations are discussed. Graphical Abstract

Dynamic behavior of form-found shell structures according to Modal and Dynamic Funicularity

Civil thin shell structures are generally designed with the objective to achieve an ideal membrane behavior and pursuing criteria of structural efficiency and minimization of the material used. During the shell form finding process, gravity loads are considered, while the role of horizontal loading is ignored. Today shells with complex geometries are being designed and built, and are used to shelter people during extreme events such as earthquakes, but the dynamic behavior of civil thin shells has always been subjected to limited research. This paper investigates the effects of dynamic loading on the behavior of civil thin shells form-found under gravity loads. A two-phased methodology is presented. In the first phase a modal analysis of the shell is performed and the R-Funicularity Ellipse Method is applied to the modal stress distribution obtained to observe which modes show a more funicular behavior. In the second phase, the structure is analyzed performing a time-history analysis under single and multi frequencies spectra defined using ad hoc functions based on the outputs of phase one. The results of such a phased approach applied to benchmark studies, show that the frequency content of the different areas of the shell can give insights onto its membrane behavior. Finally the form-found shell is analyzed under the action of the L’Aquila Earthquakes (Italy, 2009) to prove how the methodology proposed can help to identify the vulnerable area of a shell under a real seismic event.

Frictional Heating in Double Curved Surface Sliders and Its Effects on the Hysteretic Behavior: An Experimental Study

The hysteretic behavior of friction isolators is affected by the variability of the friction coefficient caused by heating phenomena at the sliding interface. The aim of this paper is to investigate such heating phenomena through a series of full-scale experimental tests on a double curved surface slider. The prototype isolator is equipped with eight thermocouples placed in different points of the isolator, which are embedded in the sliding plate. The probes of the thermocouples are in contact with the stainless steel sheet covering the sliding plate, in such a manner that their measurements are representative of the temperature rise occurring at the sliding interface. By investigating different axial loads and sliding velocities, we discuss the measured temperature rise and its implications on the hysteretic behavior of the prototype isolator. Friction variation is observed in the cyclic response of the isolator, which reduces the energy dissipated per cycle and, consequently, may lead to some underestimations of the displacements occurring during real seismic events if a constant friction coefficient is assumed. The proposed data can be helpful to calibrate sophisticated thermo-mechanical finite element models, which is the object of ongoing research.

Mobile Application and a Web-Based Geographic Information System for Sharing Geological Hazards Information in East and Southeast Asia

This paper presents a mobile application and a web-based geographic information system for an efficient and cost-effective sharing of geological hazards information in East and Southeast Asia. The information system uses the Open Geospatial Consortium (OGC), Web Map Service (WMS) and Web Processing Service (WPS) for spatial data rendition and processing online. Free and Open Source Software (FOSS) is also used for other important spatial data processing and sharing operations. WMS and WPS are formulated to access and view the geological hazard data in the system’s database. The mobile application is developed to access and share the system’s geospatial contents by sending requests to these web services. The application also makes geological hazard mitigation measures more effective by incorporating the mobile device’s GPS location information with geological hazard data. Information like the distance from the nearest active fault, active volcano and earthquake hypocenter can be easily determined using the application. The mobile application provides an interface for the users to easily access geological hazard information such as active fault, active volcanoes, shorelines inundated by tsunamis, and historical and real time seismic events. The widespread use of mobile devices with Internet connection makes geological hazard information dissemination very efficient using the application. The mobile application is called G-EVER Mobile. G-EVER stands for Asia Pacific Region Global Earthquake and Volcanic Eruption Risk Management consortium. The application can be accessed at https://ccop-geoinfo.org/gever-mo/index.php.

Non-stationary stochastic modulation function definition based on process energy release

Many real physical events are characterized by a random nature, as for earthquakes, sea waves, wind pressure, sea waves and so on. A common way to define these events is to think them as a realization of a stochastic process, and the simplest way to model them is to adopt stationary processes characterized mainly by their frequency contents. However, sometime it is necessary to consider also their evolutionary nature in the time, in order to properly take into account the non-stationary nature, as in case of seismic records. In these circumstances, a common mathematical approach is to assume the process as a non-stationary separable one, and then a key problem is to define appropriately a modulation function able to represent the time variation of the physical event. This paper purposes a method based on the energy release velocity definition of the modulation function with the aim to represent time intensity evolution of real non-stationary phenomena. With this scope, the envelope function is assumed related to the manner in which the input energy is built-up over time. Using the Iwan and Hou mathematical formulation, the procedure defines modulation function parameters in a consistent way with excitation input energy evolution. Finally, a closed formulation is obtained to set up the modulation function coherently with the energy release velocity of a single record, or of the mean value of a class of records. An example based on a real seismic event shows the effectiveness of the proposed method.

Damage classification and derivation of damage probability matrices from L’Aquila (2009) post-earthquake survey data

Post-earthquake damage data represent an invaluable source of information for the seismic vulnerability assessment of the exposed building stock, as they are a direct evidence of the actual buildings’ performance under real seismic events. This paper exploits a robust and homogeneous database of damage data collected after the 2009 L’Aquila (Italy) earthquake, to derive damage probability matrices for several building typologies representative of the Italian building stock. To this aim, the first part of the work investigates several issues related to the definition of damage to be associated with each inspected building. Different approaches and damage conversion rules are applied, pointing out advantages and weaknesses of each one. Considering the widespread seismic damage observed on masonry infill panels and partitions of reinforced concrete constructions, the impact of this type of non-structural damage on empirical damage and functional loss distributions is explored. The second part of the study proposes different possible interpretations of the repartition of the observed damage in the different damage levels, showing in some cases a bimodal trend. Two novel hybrid procedures are outlined and compared with the classical binomial approach for predicting the subdivision of damage in the different levels. The application of the proposed methodologies to the different building typologies allows the selection, for each one, of the method providing the best fit to empirical results. The parameters required for the application of the optimal approach are reported in the paper, so that results can be used for forecasting the expected seismic damage in sites with similar seismic hazard and exposed buildings.

Modelo morfométrico para determinar áreas susceptibles a procesos de ladera

In tropical countries where both internal and external active geodynamic conditions exist and relief modeling is constantly changing, hillside processes are one of the most recurring natural hazards that cause human and economic losses each year. In Costa Rica, for example, these phenomena cause approximately 30% of the disasters that affect the country each year. The study area comprises a section of 52 km2 in the extreme geographical coordinates: 10,23 ° N and 10,18 ° S; -84.23 ° W and -84.14 ° E; which is located on the northeast slope of the Poás volcano in Costa Rica and has the physical characteristics of rainfall above 2000 mm per year, intense tectonic dynamics associated with different tectonic faults and dense tropical vegetation. The objective of this work is to show a morphometric model to determine susceptible areas to hillslope processes, starting from the case study of the most affected region by the landslides triggered during the Cinchona Earthquake in 2009. The morphometry or geomorphometry is the quantitative analysis of the terrestrial surface; among its fundamental variables are altimetry or hypsometry, slope of the terrain and drainage density. The morphometric methods used are based on the approaches of Simonov (1985), Lugo (1988) and Zamorano (1990). Seven morphometric maps were developed that indirectly explain the geomorphological dynamics of this territory. Firstly, the cartography of dissection density, depth of dissection, relief energy and total erosion were performed. The density of the dissection calculates the concentration of river channels in a specific area, aiming to establish zones of greater or lesser concentration of river courses and therefore with greater river erosion. The depth of the dissection aims to measure the erosive capacity or activity of rivers vertically, as it analyzes the areas where river erosion has been more (or less) intense over time and provides an indirect relationship of the parameters that allow the dissection to increase, such as lithology, terrain inclination, precipitation and substrate weakness planes. The relief energy determines the maximum difference of the relative height in meters in a specific area and represents the potential energy that emerges from the relief. The total erosion determines zones with greater or less erosion of the recorded relief by means of the density of the curves of level in a determined area (by minimum spatial unit of analysis). All these parameters were analyzed from the three morphological regions that make up the study area (Poás volcanic complex, pyroclastic ramps and valley slopes), and then integrate these variables into the slope susceptibility map. Subsequently, the results of the map of susceptibility to hillside processes were compared with the coseismic mass movements of 2009, which resulted in that 98% of these phenomena coincided with the areas of frequent occurrence and maximum occurrence. In addition, the rupture surfaces of the gravitational processes of 2009 were used to validate this model with a real seismic event, giving 78% of prediction. It is possible to affirm that the model showed a very good performance to predict coseismic slope movements despite the fact that the model does not use any seismic parameters. It would then be expected that their verification with slope movements induced by extreme weather events would be equally acceptable. In view of the obtained results, it can be affirmed that the greatest virtue of the morphometric model is the use of easily obtained morphometric parameters from two fundamental variables: the hydrographic network and the elevation contours. It is for these reasons that the method can be applied in the territories of poor countries, by virtue of the provision of this base information. However, the limitation of the model is on the scale of the data sources and the size of the analysis cells that compose the grid of the study area. Finally, this model could be replicated in other regions or countries as a basic input for decision making in disaster risk management and land use planning.

Seismically isolated buildings in Italy: State-of-the-art review and applications

This paper presents a state-of-the-art on seismic isolation in Italy and the most important applications. After a brief introduction on the basic concepts of seismic isolation, applications to new strategic and public buildings are shown, as well as to new residential buildings, pointing out the very good behavior shown by the seismically isolated structures during real seismic events. Then, attention is focused on the retrofit of existing buildings, which represents the real challenge for the future. The most interesting applications on existing reinforced concrete, masonry and historic structures are shown, pointing out the specific challenges for each case. Finally, recordings obtained during the seismic sequence that struck Central Italy since August 24th, 2016, are presented and discussed. These are useful in analyzing the behavior of base isolation systems and their effectiveness under low energy earthquakes.

Dynamic soil-structure interaction: A three-dimensional numerical approach and its application to the Lotung case study

This paper presents a three-dimensional non-linear finite element (FE) approach to analyse the dynamic soil-structure interaction (SSI) phenomena observed at the Lotung Large-Scale Seismic Test (LSST) site. The numerical study is carried out in the time domain by a commercial FE code, taking into account the non-linear behaviour of soil and the multi-directional nature of real seismic events. The soil response is simulated by an isotropic hardening elasto-plastic hysteretic model (HSsmall) implemented in the material model library of the code. This model allows to describe the non-linear cyclic response ranging from small to large strain amplitudes and to account for the variation of the initial stiffness with depth.In the paper, the FE numerical approach is first validated through a series of parametric analyses simulating simplified cases (i.e. linear visco-elastic structures founded on a homogeneous linear visco-elastic soil deposit) for which analytical solutions exist. Then, it is adopted to back-analyse the behaviour of the 1/4-scale nuclear power plant containment structure constructed at the Lotung LSST site which was shook by several earthquakes of different intensities and frequency contents. The FE results are thus compared to the recorded in-situ free-field and structural motions, highlighting the satisfactory performance of the numerical model in replicating the observed response. The overall outcome of this research proves that nowadays complex dynamic SSI phenomena can be tackled by direct approach, overpassing the strong simplifications of the well-established substructure approaches.