Improved equivalent mass-spring model for seismic response analysis of two-dimensional soil strata

The fluid–structure interaction (FSI) effect should be carefully considered in a seismic analysis of nuclear reactor internals to obtain the appropriate seismic responses because the dynamic characteristics of reactor internals change when they are submerged in the reactor coolant. This study suggests that a seismic analysis methodology considered the FSI effect in an integral reactor, and applies the methodology to the System-Integrated Modular Advanced Reactor (SMART) developed in Korea. In this methodology, we especially focus on constructing a numerical analysis model that can represent the dynamic behaviors considered in the FSI effect. The effect is included in the simplified seismic analysis model by adopting the fluid elements at the gap between the structures. The overall procedures of the seismic analysis model construction are verified by using dynamic characteristics extracted from a scaled-down model, and then the time history analysis is carried out using the constructed seismic analysis model, applying the El Centro earthquake input in order to obtain the major seismic responses. The results show that the seismic analysis model can clearly provide the seismic responses of the reactor internals. Moreover, the results emphasize the importance of the consideration of the FSI effect in the seismic analysis of the integral reactor.

The Campi Flegrei area, located in southern Italy, is characterized by complex geological stratigraphy and elevate seismic and volcanic risks, exacerbated by ongoing bradyseismic phenomena.This region, located in a densely populated context, poses significant challenges for seismic hazard assessment due to its geological complexity, frequent seismic activity and the vulnerability of infrastructuresThe recently recorded seismic swarms, including those of 2023, further highlight the need for accurate subsurface characterization to assess and mitigate seismic risks.In this context, a geophysical campaign is being conducted as part of a larger project aimed at advancing seismic microzonation and providing detailed data for risk mitigation strategies. This contribution focuses on the application of an integrated geophysical methodology for reconstructing a detailed subsurface model for local seismic response analysis at several sites of particular interest for civil protection purposes in the Campi Flegrei area.In this study, new geophysical data were acquired and then processed through integration with geological data. Geophysical surveys include both passive seismic measurements, carried out with single-station and array configurations, and active seismic testing using the Multichannel Analysis of Surface Waves (MASW) method. These passive and active seismic techniques yield information on shear-waves velocity profiles and subsurface heterogeneities.The ongoing analyses aim to explore the characteristics of the volcanic subsurface, contributing to a better understanding of its structural complexity. A strong emphasis is placed on integrating geophysical and geological data to improve the resolution and accuracy of the subsurface model.This work highlights the critical role of non-invasive geophysical methodologies, such as passive and active seismic methods, in urban and volcanic areas. These efforts support the strategic objectives of urban geophysics by promoting urban resilience and sustainability, while also providing actionable insights for prevention and urban planning in the Campi Flegrei area.By integrating advanced geophysical techniques, this research enhances the understanding of subsurface properties and their interaction with seismic phenomena, laying the foundation for effective risk mitigation and resilience-building measures in this highly complex and dynamic region.

Offshore platforms in seismically active areas should be designed to survive severe earthquake excitations with no global structural failure. In seismic design of offshore platforms, it is often necessary to perform a dynamic analysis that accounts for nonlinear pile soil structures interaction effects. This paper summarizes an inexpensive and practical procedure compatible with readily available structural analysis software (ANSYS) for estimating the nonlinear lateral response of fixed offshore platforms resting on flexible piles subjected to seismic loading. In the proposed model, piles and jacket members are modeled using BNWF (Beam on Nonlinear Winkler Foundation) and FE (Finite Element) approaches respectively in an integrated model. In this paper, nonlinear seismic response analysis of an existing sample offshore platform has been performed and sensitivity of the results to the model main parameters is investigated.

Machine learning and finite element integration-driven surrogate model for fluid-structure interaction seismic response analysis of aqueduct structures

Using a quasi‐static method based on an axisymmetric finite element model for seismic response analysis of seismically isolated tunnels, the seismic isolation effect of the isolation layer is studied, and the seismic isolation mechanism of the isolation layer is clarified. The results show that, along the longitudinal direction of the tunnel, the seismic isolation effect is mainly affected by the shear modulus of the isolation material. The smaller the shear modulus is, the more evident the seismic isolation effect is. This is due to the tunnel being isolated from deformation of its peripheral ground through shear deformation of the isolation layer. However, along the transverse direction of the tunnel, the seismic isolation effect is mainly affected by the shear modulus and Poisson’s ratio of the isolation material. When Poisson’s ratio is close to 0.5, a seismic isolation effect is not evident because the tunnel cannot be isolated from deformation of its peripheral ground through compression deformation of the isolation layer. Finally, a seismic isolation system comprising a shield tunnel in which flexible segments are arranged at both ends of an isolation layer is proposed, and it is proved that the seismic isolation system has significant seismic isolation effects both on the longitudinal direction and on the transverse direction.

SummaryA new finite element model to analyze the seismic response of deformable rocking bodies and rocking structures is presented. The model comprises a set of beam elements to represent the rocking body and zero‐length fiber cross‐section elements at the ends of the rocking body to represent the rocking surfaces. The energy dissipation during rocking motion is modeled using a Hilber–Hughes–Taylor numerically dissipative time step integration scheme. The model is verified through correct prediction of the horizontal and vertical displacements of a rigid rocking block and validated against the analytical Housner model solution for the rocking response of rigid bodies subjected to ground motion excitation. The proposed model is augmented by a dissipative model of the ground under the rocking surface to facilitate modeling of the rocking response of deformable bodies and structures. The augmented model is used to compute the overturning and uplift rocking response spectra for a deformable rocking frame structure to symmetric and anti‐symmetric Ricker pulse ground motion excitation. It is found that the deformability of the columns of a rocking frame does not jeopardize its stability under Ricker pulse ground motion excitation. In fact, there are cases where a deformable rocking frame is more stable than its rigid counterpart. Copyright © 2016 John Wiley & Sons, Ltd.

A 2.5D equivalent linear model for longitudinal seismic analysis of tunnels in water-saturated poroelastic half-space

Seismic facies analysis plays a key role in stratigraphy and has developed rapidly in the context of deep learning methods. However, seismic facies analysis cannot only be regarded as an image segmentation or classification task because this would exclude prior knowledge of geophysicists on seismic interpretation. Seismic parameters summarized by geophysicists were included in the seismic facies analysis model. Seismic parameters were used to calibrate the different seismic facies units, and well logging data and sequence stratigraphy were integrated to perform geological interpretation and to establish a training dataset. A multi-head seismic parameter classification (MSPC) model was then established to divide the seismic facies units. A seismic facies geological interpretation (SFGI) model was constructed for the geological interpretation of seismic facies units, and an end-to-end seismic facies analysis model was designed based on the MSPC model and the SFGI model. The proposed model effectively improves the accuracy of the seismic interpretation, solves the intra-facies noise problem, and is easy to train and use.

Performance-based seismic evaluation is usually done by considering simplified models for the liquid storage tanks therefore, it is important to validate those simplified models before conducting such evaluation. The purpose of this study is to compare the seismic response results of the FSI (fluid-structure interaction) model and the simplified models for the cylindrical liquid storage tanks and to verify the applicability of the simplified models for estimating failure probability. Seismic analyses were carried out for two types of storage tanks with different aspect ratios (H/D) of 0.45 and 0.86. FSI model represents detailed 3D fluid-structure interaction model and simplified models are modeled as cantilever mass-spring model, frame type mass-spring model and shell type mass-spring model, considering impulsive and convective components. Seismic analyses were performed with modal analysis followed by time history analysis. Analysis results from all the models were verified by comparing with the results calculated by the code and literature. The results from simplified models show good agreement with the ones from detailed FSI model and calculated results from code and literature, confirming that all three types of simplified models are very valid for conducting failure probability analysis of the cylindrical liquid storage tanks.

In a previous paper, ambient vibration tests were conducted on a cable stayed bridge with resilient-friction base isolation systems (R-FBI) to extract the dynamic characteristics of the bridge and compare the results with a seismic analysis model. In this paper, a nonlinear seismic analysis model was established for analysis of the bridge to compare the difference in seismic responses between nonlinear time history analysis and multi-mode spectral analysis methods in the seismic design phase of cable supported bridges. Through these studies, it was confirmed that the seismic design procedures of the “Korean Highway Bridge Design Code (Limit State Design) for Cable Supported Bridges” is not suitable for cable supported bridges installed with R-FBI. Therefore, to reflect the actual dynamic characteristics of the R-FBI installed on cable-supported bridges, an improved seismic design procedure is proposed that applies the seismic analysis method differently depending on the seismic isolation effect of the R-FBI for each seismic performance level.

A method is proposed to identify within seismic catalogs those earthquakes that are most relevant to the seismic hazard. The approach contrasts with the classical approach to decluster the seismic catalog with the expectation that the remaining main shocks will be the relevant events for the seismic hazard analysis. We apply a time window like in the window declustering approach of Gardner and Knopoff, but the time window is motivated by relevance to engineering. A ground motion criterion replaces the spatial window. An event in the time window is included in the “Maximum Shaking Earthquake Catalog (MSEQ catalog)” if the median ground motion at its epicenter exceeds the predicted median ground motion there from the main shock, using a locally appropriate ground motion prediction equation. Ground motion can be measured by any parameter that is estimated by a ground motion prediction equation. We consider peak acceleration and spectral amplitude (SA) at periods of 0.2, 1.0, and 3.0 s. The longer period parameters systematically remove more small events. The purpose is not to produce a declustered catalog, in which each group of physically related earthquakes is represented by its largest event. Statistical properties of the MSEQ catalog somewhat resemble the corresponding declustered catalog in three tested regions, but the MSEQ catalogs all retain more large-magnitude earthquakes. The MSEQ catalog may better represent the potential hazard in a region, and thus might be considered as an alternative to a declustered catalog in developing the seismicity model for probabilistic seismic hazard analysis.

Machine learning-based automatic seismic facies analysis has increased significantly over the past few decades. The key is to select the most representative features (such as the commonly used poststack amplitude data or the induced seismic attributes) as the input of the different machine learning algorithms. As an advanced branch of machine learning, deep learning can be used to extract the discriminatively deep features from seismic data similar to those used in image classification. In this study, we havedeveloped an unsupervised seismic facies analysis method by using a recurrent autoencoder model. First, we have constructed and trained an autoencoder architecture combined with long short-term memory-based recurrent operation. Its main aim is to learn the deep discriminative features by taking the windowed poststack seismic data as the input time series data. This type of unsupervised learning takes advantage of the no labeling requirement of seismic data. In addition, the recurrent operation is beneficial in delineating the time-sequential characteristics of seismic data. Second, we have taken the learned features as the input of simple K-means clustering and analyzed the corresponding seismic facies. In other words, the clustering is executed in the learned feature space (learned feature-based clustering). Real data results have demonstrated that our method reveals more details than the original amplitude-based K-means clustering, depending on the cluster calibration. In particular, according to the known natural gamma-ray logs and lithological descriptions of five wells, different amounts of sandstone and mudstone deposit are more accurately discriminated, which is substantially informative in reservoir prediction and hydrocarbon exploration. Furthermore, the estimated average silhouette scores have quantitatively shown the effectiveness of our method.

Earthquakes cause severe damages to bridge structures, and rocking isolation of piers has become a superior option for the seismic protection of bridges during earthquakes. A seismic isolation method with free rocking mode is proposed for railway bridge piers with medium height. Experimental and numerical analysis are conducted to evaluate the seismic performance of the rocking-isolated bridge pier. Shaking table test is carried out with a scaled model by using three strong input earthquake records. The measured data includes displacement, acceleration and time history response of the pier-top and the bending moment of the pier-bottom. Test results show that the expected uplift and rocking of the isolated pier occur under strong earthquakes and the rocking-isolated pier has self-centering capacity. Slight damage appears at the collision surface between pier and base due to pier uplift, while there is no damage in the pier body. The bending moment of pier-bottom is less affected by the spectrum of input ground motions. The two-spring model is provided to simulate the isolated pier with free rocking mode under earthquakes. A seismic response analysis model for the rocking-ioslated pier is established with the assistance of OpenSees platform. The simulated results agree well with the measured results by shaking table test. Therefore, the seismic isolation method with a self-centering pier is worthy of promotion for railway bridges in high seismic risk regions.

Steel tubular bridge pier with inner cruciform plates has high seismic performance. In this paper, the applicability of static-dynamic verification method for seismic design of steel tubular bridge piers with inner cruciform plates is studied. The ultimate strength and state of steel tubular stub columns with inner cruciform plate subjected to compression and bending were investigated through finite element analysis. The validity of the proposed design formula of the failure strain which was obtained from the stub column analysis was examined by analysis on tubular steel bridge piers with inner cruciform plates under cyclic loading. The dynamic response analysis of the same steel bridge piers was carried out on the basis of the spring-mass model and the fiber element model. These results indicated the static-dynamic verification method of the seismic response analysis through the spring-mass model are good agreement with dynamic verification method of seismic response analysis by the fiber element model.

Low-frequency absorption band in a thin acoustic metamaterial using acoustic black hole termination