Seismic Analysis Method Research Articles

Simple method for probabilistic seismic landslide hazard analysis based on seismic hazard curve and incorporating uncertainty of strength parameters

Seismic landslide hazard assessment is typically based on deterministic analysis to calculate slope displacements during an earthquake. However, deterministic analysis is unable to account for various uncertainties in the analysis process. This study focuses on utilizing the established results from probabilistic seismic hazard analysis (PSHA) and extending probabilistic seismic landslide hazard analysis (PSLHA) to account for the uncertainties of ground motions and soil strengths. Two simplified methods, being flexible and fast, are proposed and evaluated by comparing with the fully but complex probabilistic method. One of the methods that yields a better performance is applied to evaluate the probabilistic seismic landslide hazard in the Tsao-Ling area of Taiwan using information regarding the seismic hazard curve and it's deaggregation results. Lastly, seismic landslide hazard maps are constructed for different return periods and compared with the deterministic map for the 1999 Chi-Chi earthquake.

Seismic Facies Visualization Analysis Method of SOM Corrected by Uniform Manifold Approximation and Projection

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">As a common seismic facies visualization analysis method, SOM projects the waveform or seismic attribute vectors into a two-dimensional topological plane in a nonlinear way, which can effectively and efficiently discover the topological structure of a dataset. SOM does not need to set the number of classes in prior, and has friendly visualization characteristics and excellent generalization, which are conducive to seismic facies interpretation using unlabeled data. However, due to the competitive learning used in SOM and the imbalance of data distribution in real world, the samples from majority classes are expanded on the topological plane and the minority classes are compressed. As a result, the plane cannot accurately describe the global structure of data distribution. To improve the visualization precision by modifying the topological relationship of the prototype vectors of SOM, we utilize UMAP (Uniform Manifold Approximation and Projection), a novel manifold learning technique for dimension reduction, to correct the prototype vectors generated by SOM. By combing the advantages of SOM and UMAP in the representation of data topological structure, the global relationship between seismic data samples can be properly established, and the internal relative spatial structure of majority class samples can be retained as much as possible, resulting in a more reliable classification. Meanwhile, the framework maintains the advantages of SOM in visualization. In the modeling tests and real data experiments, we have demonstrated the effectiveness and rationality of UMAP-SOM on the spatial structure representation of three-dimensional seismic data</i> .

On the seismic response of rack structures affected by pinching

The nonlinear static and dynamic behavior of rack structures affected by joint pinching are studied using a simplified single-degree-of-freedom system. Since the joints of steel rack structures play a crucial role in the capacity design methodology, as they are the main source of energy dissipation, their behavior is widely studied in the literature, highlighting their reduced hysteresis loop. However, no systematic study investigates and associates these characteristics with a possible increase in displacement demand. Using a single-degree-of-freedom system focuses attention on the type of cyclic behavior and allows a comparison of linear and nonlinear responses, the latter evaluated using both elastic-plastic and pinching laws. At prescribed ductility, the elastic-plastic and pinching responses can be compared with the prescriptions of Italian and European building codes. This simplified method was also applied to case studies of experimental pushover tests on racks found in the literature. Results showed that neglecting the joint pinching behavior for a rack structure can lead to an underestimation of the displacement demand in the case of the application of the nonlinear static seismic analysis method and hence to the overestimation of the q-factor for the application of linear seismic analysis methods.

Seismic microzonation based on HVSR inversion results for shear wave (Vs30) mapping and soil vulnerability in West Sulawesi and South Sulawesi Regions

The Horizontal to Vertical Spectral Ratio (HVSR) is a seismic analysis method used to obtain information about subsurface geological characteristics. This method is based on the spectral ratio analysis between the horizontal and vertical components of earthquakes or other vibration sources. HVSR has proven to be an effective tool in evaluating rock layers, layer thickness, rock hardness, and geological hazard potential. In the HVSR method, seismic data are measured using three-component seismometers, the N-S (North-South), E-W (East-West), and vertical components. In this study, the HVSR method is used for Vs30 inversion to estimate shear wave velocity at a depth of 30m. The southern and western regions of Sulawesi have various geological conditions and high seismicity levels. The results of this inversion can be used for mapping soil vulnerability indices. The obtained soil vulnerability index values indicate high vulnerability near the Palu-Koro fault, with A0 9.27 at F0 3.2 Hz. This method can also estimate shear wave velocity values at a depth of 30 m. Vs30 values range from 200 m/s to 500 m/s at various measurement points, indicating variability. According to the SNI 1726:2012 and NEHRP classifications, the research area has soil conditions ranging from medium to soft.

Comparison of seismic fragility analysis methods for arch dams

Comparison of seismic fragility analysis methods for arch dams

Effect of Seismic Analysis Approach and Provision of Shear Walls on Parameters for Raft Foundation Design

The present work attempts to understand the effect of different methods of seismic analysis on the design of building raft foundation. The study also evaluates the role of shear wall on the foundation response. A ten storey building with raft foundation has been analyzed in STAAD Pro using three different seismic analysis methods, viz., Linear static analysis, Linear dynamic analysis and Non-linear dynamic analysis. Furthermore, building with two different arrangements of shear walls (peripheral and core region) are studied by Non-linear dynamic analysis and compared with the model without shear wall. The raft is modeled with plate elements supported by soil springs using Winkler's approach. To consider the effect of different soil and raft stiffness, three different soil spring values and two raft thickness values have been considered. It has been concluded from the study that linear static analysis yields lower values of all foundation design parameters (viz., base pressure, settlement, foundation bending moment and shear stress) as compared to dynamic analysis. Dynamic analysis yields higher variation in base pressure and settlement distribution, which suggests adopting dynamic analysis approach for obtaining more realistic response, especially for settlement sensitive structures. Further the provision of shear wall has negligible influence on base pressure and settlement of foundation, while maximum bending moment and shear stress in foundation increases. Hence, provision of shear wall may increase cost of foundation, however, considering its role in improving structural integrity, shear walls are deemed important. Further, the increase in soil stiffness and reduction in raft thickness yields higher maximum base pressure and variation in base pressure, which confirms the importance of considering the effect of soil-foundation interaction for design of foundation. It is opined that the findings of the study would help in more realistic foundation design to achieve better performance during its life cycle.

Pushover Analaysis of Irregular Tall RCC Structures

The paper is based on the study of the Response of Irregular Plan Tall RCC structures by Pushover Analysis in order to find the Base Shear, Pushover Curve, Performance limit, Shear force Diagrams, Bending Moment of the structure. Nonlinear Static Analysis, is also called as “pushover analysis”, and is also regarded as the most widely used analysis method for estimation of performance of Irregular tall RCC structures. Most of the significant Seismic Codes which proposes methods for seismic analysis of new or existing tall RCC Structures have been originally defined for simple regular structures. Therefore the analysis of the seismic response of irregular Tall RCC Structures is difficult due to nonlinear and inelastic response of the structures and more difficult than that of regular structures. Most of the codes (IS 1893 (Part 1) 2016[1], ATC-40 1996[2], EC8-1 2004[3]) uses the concept of “regularity”, taking into account distribution of mass, stiffness and strength in the structures, both in plan and in elevation. But real structures seldom act in accordance with these regularity requirements, resulting in a narrowly dependable application of the basic non-linear static analysis. For the study we are considering two G+19 storey T shaped and U shaped irregular tall framed RCC structures having height of 68 meters each and storey height of 3.3 meters. Pushover Analysis is carried out using shear walls at different locations in the structure. The objective of this study is to finds out which irregular plan tall structure is the most efficacious in resisting lateral loads. The software used for modelling and analysis is ETABS 2017.

Shaking table tests and numerical study of a sliding isolation bearing for the seismic protection of museum artifacts

Isolation bearings are a seismic strengthening technique widely applied in building structures. However, sliding isolation bearings are seldom used for the seismic protection of artifacts housed in museums. The purpose of this study is to investigate the ability of the designed sliding isolation bearing to protect museum artifacts during earthquakes considering floor acceleration amplification. To better explore the effect of the magnification of the floor acceleration response on the seismic performance of the sliding isolation bearing, a three-story reinforced concrete frame structure was constructed, and a sliding isolation bearing-showcase-artifact system was placed on the floor of the structure. The seismic effectiveness of the proposed system was then evidenced by carrying out shaking table tests. It was observed from the tests that the sliding isolation bearing can effectively reduce the peak input acceleration, thus ensuring the safety of the artifact. Moreover, a seismic fragility analysis method is developed to evaluate the seismic performance of the sliding isolation bearing in the museum-showcase-artifact system subjected to unidirectional ground motions. Furthermore, the influences of the horizontal stiffness and the sliding displacement limitation of the bearing on the protective effect of artifacts are discussed based on the seismic performance assessment of the sliding isolation bearing.

Method for the seismic performance evaluation of fasteners used for securing cultural artifacts

Earthquakes may damage not only the museum structures but also the cultural artifacts collected in museums, but little seismic risk assessment has been carried out toward museum collections. While museum staff usually rely on their own experience to secure cultural artifacts with fasteners to prevent them from being damaged during an earthquake. To reasonably evaluate the seismic performance of fasteners, this study first puts forward an analysis method for use in the museum-showcase-artifact system, and then puts forward a seismic fragility analysis method for cultural artifacts based on logistic regression. Finally, a method is proposed for the evaluation of the seismic performance of fasteners by comparing the seismic risk of cultural artifacts when freestanding and secured with fasteners. Via finite element analysis, the proposed evaluation method is further explained and verified, and the impacts of the height, type and number of the fastener on its seismic performance are analyzed. Based on the proposed evaluation method, the seismic performance of the fasteners used for securing a precious cultural pot exhibited in a museum in northern China is evaluated. The results show that the evaluation method proposed in this study can quantify the seismic performance of fasteners, and provides a scientific basis for the selection of fasteners for cultural artifacts.

Comparisons Between Array Derived Dynamic Strain Rate (ADDS) and Fiber‐Optic Distributed Acoustic Sensing (DAS) Strain Rate

AbstractDistributed acoustic sensing (DAS) strain rate and particle velocity can be compared through approximate scaling with medium velocity. We instead performed a direct comparison between array derived dynamic strain (ADDS) rate and DAS strain rate for six frequency bands. The PoroTomo project at Brady's Hot Springs, Nevada, deployed a 240‐geophone 3C array co‐located with fiber‐optic DAS system and 8.7 km of buried cable. We selected subsets of the geophone array to create four smaller arrays and computed ADDS. The horizontal components of the ADDS were rotated into the direction of the fiber‐optic cable and then compared with the observed DAS strain rates. From three example regional earthquakes of local magnitudes 2.9, 4.1, and 4.3, the ADDS are found to be coherent with DAS for frequencies ≤1 Hz. For frequencies &gt;1‐Hz, this correlation decays quickly. Small differences between linear and areal dynamic strains at 1‐Hz suggest poor signal‐to‐noise or localized strain that is perturbed by shallow heterogeneities compare to the average strain propagating across the geophone array. The implication is that around 1‐Hz, straight fiber DAS is measuring axial strain along the fiber and can provide good approximations to translational particle motions. However, above 1‐Hz, DAS becomes more sensitive to shallow velocity gradients that can be beneficial for geophysical imaging yet becomes a limitation for traditional seismic analysis methods depending on absolute amplitude and phase from translational particle motions.

Nonlinear Seismic Analysis of Ground Structure to Evaluate the Capacity of a Permanent Tunnel Lining

ABSTRACT In this paper, in addition to the linear analysis used for typical tunnels, nonlinear seismic analysis of a tunnel has been investigated using pseudo-static method and a damaged concrete behavior model introduced in ABAQUS® software. The simulations were carried out under three conditions, free field, ovaling and racking, at two hazardous earthquake levels according to an Operation Design Earthquake (ODE) and a Maximum Design Earthquake (MDE). Then, the structural capacity curve and the behavior factor for the final tunnel lining were obtained. In order to extend the studies as well as to verify the pseudo-static analyses, seven nonlinear dynamic analyses compatible with the site under MDE conditions have been performed. The results showed that the tunnel lining procedure created limited tensile cracks under compression. At the bottom corners of the tunnel structure, the resultant stresses in the tunnel lining under two earthquakes caused failure and created tensile cracks. Therefore, it was necessary to reinforce the lining at corners. Comparison between different nonlinear time history seismic analysis and pseudo-static methods indicated that the pseudo-static methods resulted in 10–30% less acceleration than the average results obtained from time history analysis.

Numerical Simulation of Reinforced Concrete Piers after Seawater Freeze–Thaw Cycles

The reinforced concrete (RC) piers of offshore bridges inevitably experience seawater freeze–thaw cycles due to the periodic movement of tides in cold climates. The damage caused by seawater freeze–thaw cycles will reduce the durability and mechanical properties of concrete, and then affect the seismic performance of RC piers. The method of seismic performance analysis on RC piers by numerical simulation is gradually emerging because the process of the conventional experiment is relatively complicated, and the heterogeneity and degradation of concrete after seawater freeze–thaw cycles should be considered. In this study, the method of meso-element equivalent and layered modeling was used to simulate a low cyclic loading test on an RC pier after seawater freeze–thaw cycles with ABAQUS software. The numerical simulation results were compared with the experimental results; the deviation value of peak load was not more than 6%, and the deviation value of peak displacement was not more than 10%. The result of the numerical simulation matched well with the experimental results, and the influence of different parameters was analyzed through the practical method of numerical simulation. It can be determined that the peak load decreased by 11%, while the peak displacement increased by 40% after 125 seawater freeze–thaw cycles. In the same 125 freeze–thaw cycles, the peak load increased by 15% and 27% while the axial compression ratio and the longitudinal reinforcement diameter increased. As the stirrup spacing of specimens decreased, the peak load remained unchanged, but the ductility coefficient of the specimens increased by 20%.

Algorithms and Measuring Complex for Classification of Seismic Signal Sources, Determination of Distance and Azimuth to the Point of Excitation of Surface Waves

Machine learning and digital signal processing methods are used in various industries, including in the analysis and classification of seismic signals from surface sources. The developed wave type analysis algorithm makes it possible to automatically identify and, accordingly, separate incoming seismic waves based on their characteristics. To distinguish the types of waves, a seismic measuring complex is used that determines the characteristics of the boundary waves of surface sources using special molecular electronic sensors of angular and linear oscillations. The results of the algorithm for processing data obtained by the method of seismic observations using spectral analysis based on the Morlet wavelet are presented. The paper also describes an algorithm for classifying signal sources, determining the distance and azimuth to the point of excitation of surface waves, considers the use of statistical characteristics and MFCC (Mel-frequency cepstral coefficients) parameters, as well as their joint application. At the same time, the following were used as statistical characteristics of the signal: variance, kurtosis coefficient, entropy and average value, and gradient boosting was chosen as a machine learning method; a machine learning method based on gradient boosting using statistical and MFCC parameters was used as a method for determining the distance to the signal source. The training was conducted on test data based on the selected special parameters of signals from sources of seismic excitation of surface waves. From a practical point of view, new methods of seismic observations and analysis of boundary waves make it possible to solve the problem of ensuring a dense arrangement of sensors in hard-to-reach places, eliminate the lack of knowledge in algorithms for processing data from seismic sensors of angular movements, classify and systematize sources, improve prediction accuracy, implement algorithms for locating and tracking sources. The aim of the work was to create algorithms for processing seismic data for classifying signal sources, determining the distance and azimuth to the point of excitation of surface waves.

Analysis of infilled steel frames subjected to lateral loading

In Recent days Earthquake resistant design of structure has earned a lot of scope as Earthquake has become more common. Lateral loading behaviour and energy absorption capacity of monolithic Steel framed structures is significantly affected by Presence of infill which adds to the bracing of the structure, Researchers developed new methods of seismic analysis to analyse the behaviour of structure during occurrence of an Earthquake. Performance based seismic design gives methodology for accessing the performance of structure occupancy, life safety or Collapse prevention level. A non-linear static pushover analysis can be used to analyse the inelastic response of structure to lateral load or displacement. In the present research a 3D model of G + 8 story steel framed building is considered for seismic design and performance evaluation. The model was analysed using ETABS software by response spectrum method for zone V according to IS 1893–2016. The performance is accessed by Capacity Spectrum Method using non-linear pushover analysis. The result of all models are analysed and compared in terms of base shear, story displacement, pushover curve, spectrum curve, performance point of the structure. Overall performance of the structure is found in safer limits.

A novel strong ground motion duration to reduce computation time of structural time history analysis

As a widely used dynamic computation method for seismic response analysis of structures, time history analysis (THA) can be a time-consuming procedure in some situations. In order to reduce the calculation time, this study proposed a novel strong ground motion duration which can truncate the head and tail weak signals of records before THA. The initial point of proposed duration refers to the concept of bracketed duration, while the termination point is determined by the maximum displacement responses of equivalent single-degree-of-freedom (SDOF) systems of the structure. The relationship between the fundamental period and period-lengthening level of structure is counted from previous research and fitted with a formula which is used to compute the period range of equivalent SDOF systems. After comparing the structural responses and time-saved percentage of truncated records by proposed duration with those by other definition of durations, results prove that the proposed duration has significant time-saving procedure and reliable computation results on THA.

Exact artificial boundary condition and 1D time-domain method for seismic response analysis of layered saturated poroelastic half-space

This study proposed a one-dimensional (1D) time-domain finite element method (FEM) for seismic response analysis of a layered saturated soil half-space under obliquely incident plane waves, based on Biot's u-w wave equations. The spatially two-dimensional problem was transformed into an equivalent 1D time-domain problem along the depth according to Snell's law. An exact artificial boundary condition for saturated poroelastic media was developed to simulate the wave absorption and input effects of the truncated half-space. Using the displacement and stress continuity conditions between the adjacent saturated poroelastic-medium layers and combining all finite elements and the exact artificial boundary condition, the total dynamic equation for the spatially 1D problem was obtained. The 1D dynamic equation was solved using the FEM with explicit time integration. The proposed method was verified by analyzing two engineering sites in the time domain and a comparison with the frequency-domain transfer matrix method with fast Fourier transform.

Integrating the foundation component into seismic fragility analysis of bridges

A component-based seismic fragility analysis method for bridges recently developed by the authors is extended here to include the foundation component. In line with the treatment of other components like the piers or abutments, the foundation system is analysed separately, and its capacity and limit state thresholds are described in terms of the displacement of a monitoring point, which in the usual case of pile foundations is the pile cap; in this way all sources of strength and stiffness degradation are accounted for. The influence of the way the pile cap is loaded in the foundation component analysis is estimated by exploring various ‘scenarios’ of increasing complexity. Components of two typical overpass bridges are analysed; one with single column piers and one with wall-type piers, to evaluate the effect of foundation on bridge fragility in the case that energy dissipation occurs primarily in the plastic hinges of the piers and the case that part of the dissipation takes place in the foundation system. It is concluded that in the case of hinging piers the pile foundation is not critical for the bridge fragility and may be ignored for simplicity, whereas this is no more the case when piers remain elastic and damage in the piles and/or the soil occurs.

System-Level Analysis on the Effects of Seismic on Reliability of Rectifier Transformer for ITER Poloidal Field Converter Unit

This article proposed a seismic analysis method for rectifier transformer of International Thermonuclear Experimental Reactor (ITER) poloidal field converter based on response spectrum. The seismic response of structure under specific seismic excitation is evaluated by using the earthquake spectrum of seismic level one (SL-1) with damping factor of 2% provided by ITER. The results show the maximum deformation and stress are 31.18 mm (control cubicle) and 181.62 MPa (support of oil tank), respectively, which are less than the allowable stress. In addition, the simulation analysis is introduced in detail and the results as the displacements, stresses, and reactive forces are also presented. The seismic analysis method proposed in this article provided a reference for the seismic design of rectifier transformer of ITER polar field converter, and also provides ideas for the seismic design of similar large electrical equipment.

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.

The Criteria for Assessing the Safety of Buildings with a Reinforced Concrete Frame during an Earthquake after a Fire

In the paper, there was researched sensitivity of the criteria for evaluation of seismic resistance of reinforced structures (modes and frequencies of oscillations, displacements, and strains) in relation to various position of fire impact as exemplified by three-span five-storey reinforced concrete space frame. The relevance of the study is justified, the degree of the problem’s development is grounded. There were analyzed the main lines of the research connected with experimental and numerical testing of both discrete structures and full-sized buildings. Numerical analysis was conducted by means of the software complex Ansys, the linear-spectral method was used. Fire impact is simulated by means of damages to reinforced concrete members in one of the building’s units. 16 variants of points of fire outbreak were considered. According to the calculation results, it was stated that for all the variants of fire outbreak frequencies of self-oscillations for reinforced concrete frames after the fire had been found lower than for the non-damaged frame. The modal analysis has shown that the type of longitudinal and bending oscillations had undergone changes. The maximum amplitude of frames’ oscillations after the fire was found insignificantly lower than for the non-damaged frame. Within the floor of fire outbreak location, the displacement increased immensely so that led to failure to comply with the value of inter-floor shifts and the increase of the 2nd order effects. Redistribution of bending moments in reinforced concrete framings was observed. The loading in damaged members decreased due to the members’ strain capacity whereas the extra loading is added to the adjacent members. If compared with the case of the frame non-damaged by fire, overloading of columns can reach up to 20%. Conceptual description of fracture behavior of the frame is outlined assuming its non-linear behavior. The possible lines of further development are set for the methods of seismic analysis of the buildings with reinforced concrete frame after the event of fire.