Variation Of Seismic Response Research Articles

Seismic response of deep soft soil sites with varying shear wave velocities

The variations in seismic response between deep soft soil sites with different shear wave velocities were not fully understood. This study focuses on the seismic response of deep soft soil sites in the lower reaches of the Yangtze River, China. A nonlinear dynamic finite element model was developed for two representative deep soft soil sites with borehole profiles and the shear wave velocity tested by the single borehole method. Two nonlinear cyclic constitutive models are used and thus compared through the site seismic response. To accurately calibrate the nonlinear cyclic model parameters, resonant column tests were conducted on 21 soil samples collected from the two boreholes. The results show that the peak ground acceleration (PGA) under low-frequency (Liuan) input motion was higher for soft soil sites compared to that under medium- and high-frequency (Kobe and Nahanni) input motions. The PGA amplification factor for deep soft soil sites under different input motions can be approximated by an exponential function. The peak ground acceleration tends to be lower as the equivalent shear wave velocity (Vse) decreases. The shapes of the spectral acceleration were similar for the two sites, despite a substantial difference in the Vse between them. Additionally, a crossover point was observed in the spectral acceleration for the two sites. The period corresponding to this crossover point increased with increasing intensity of input motions, indicating that the sites became softer with higher intensity and thus generally exhibited a longer characteristic period of the spectral acceleration. This paper also highlights the significance of selecting nonlinear constitutive models and the precise calibration of model parameters in the seismic response analysis of deep soft soil sites, providing a scientific basis for future similar site analyses.

Microzonation Approach for Analyzing Regional Seismic Response: A Case Study of the Dune Deposit in Concón, Chile

Urban areas located on complex geological formations, such as dune deposits, require detailed seismic risk assessments that extend beyond standard seismic codes. This study focuses on the city of Concón, Chile, where a significant portion of the urban area is situated on a coastal dune deposit. The research integrates seismic microzonation with a three-dimensional finite element model (3D FEM) to comprehensively evaluate the regional seismic response. Field data from 208 strategically distributed points were collected and combined with geotechnical and geomorphological information to construct a detailed 3D model of the region. This model allowed for the simulation of seismic behavior under various conditions, highlighting the limitations of general seismic codes in capturing local variations in seismic response. The results underscore the importance of considering local geological conditions in structural design, particularly in areas with irregular topography and complex subsurface conditions. This study concludes that incorporating microzonation into urban planning and seismic analysis can significantly enhance infrastructure resilience and disaster preparedness, providing a replicable approach for other cities facing similar geological challenges.

Numerical study on seismic performance of a prefabricated subway station considering the influence of construction process

In previous seismic analyses of cast-in-place stations, the importance of the construction process was typically not emphasized. Unlike cast-in-place stations, prefabricated subway stations feature innovative construction methods. The effect of ignoring the complete construction process on the seismic performance of prefabricated subway stations remains unclear, and this study aims to address this issue. In this research, a three-dimensional nonlinear numerical model considering soil-structure interaction (SSI) was established. First, the complete construction process of the station, including excavation of the foundation pit and structural assembly, was replicated. The initial state before dynamic loading was clearly defined. Subsequently, the seismic response mechanisms of the station, including deformation, SSI, acceleration, and internal forces, were thoroughly investigated, revealing the impact of structural type and construction method on seismic performance. The results indicate that neglecting the complete construction process leads to differences in the initial state before dynamic loading, resulting in variations in seismic response. Specifically, ignoring the assembly process causes an average bending moment error of 59 % and an axial force error of 35 % for each component. By comprehensively analyzing these findings, a deeper understanding of the intricate interplay between assembly techniques, structural behavior, and construction processes in seismic contexts can be attained, thereby informing more robust engineering practices.

Spherical-wave elastic inversion in transversely isotropic media with a vertical symmetry axis

SUMMARY Although subsurface media are usually assumed to be isotropic, anisotropy is ubiquitous in crustal rocks and leads to the variation of seismic response with direction. Transversely isotropic media with a vertical symmetry axis (VTI media) are widely found in the real world, such as in textured shale reservoirs. Plane-wave reflection coefficients (PRCs) in VTI media have been widely exploited in amplitude variation with offset (AVO) inversion to estimate the elastic and anisotropy parameters of subsurface media. However, the PRCs in VTI media meet some fundamental problems, especially at near-critical or post-critical incidence angles where the spherical-wave effect is significant. To consider the wave front curvature, a complex spherical-wave reflection coefficient (SRC) in VTI media is derived. To better understand the spherical-wave seismic response in VTI media, we investigate the dependence of the complex SRC on frequency, reflector depth and Thomsen anisotropy parameters ($\varepsilon $ and $\delta $). Based on a complex convolution model, a spherical-wave AVO inversion approach in VTI media is proposed to estimate the vertical (symmetry-axis) compressional and shear wave velocities (P and S waves), density and Thomsen anisotropy parameters from observed seismic data with different incidence angle and frequency components. Synthetic data with Gaussian random noise are used to verify the robustness of the spherical-wave AVO inversion approach in VTI media. Field data examples show that the proposed approach can produce reasonable inversion results that match well with the well-logging data.

Effect of slab stiffness on floor response spectrum and fragility of equipment in nuclear power plant building

The floor response spectrum (FRS) is used to evaluate the seismic demand of equipment installed in nuclear power plants. In the conventional design practice of NPP structure, the FRS is simplified using the lumped-mass stick model (LMSM), assuming the floor slab as a rigid diaphragm. In the present study, to study the variation of seismic response in a floor, the FRSs at different locations were generated by 3-D finite element model, and the response was compared to that of the rigid diaphragm model. The result showed that the FRS significantly varied due to the large opening in a floor, which was not captured by the rigid diaphragm model. Based on the result, seismic fragility analysis was performed for the anchorage of a heat exchanger, to investigate the effect of location-dependent FRS disparity on the high confidence low probability of failure (HCLPF).

Effect Of Setback Irregularity On Elastic Seismic Demand Of Reinforced Concrete Building

Now a day, many building have not regular configuration both in plan and in elevation due to different functional and aesthetic requirements. Hence, the evaluation of the seismic behavior of reinforced concrete building with plan and elevation irregularity is required. In this study the evaluation of elastic seismic demand of reinforced concrete building with setback irregularity was carried out. The standards used for analysis of base case building and vertical irregular building using response spectrum analysis (RSA) method are adopted according to the provision of ES EN 1998-1:2015. The evaluation of elastic demand of building (story displacement, story drift, story shear and base shear) were assessed in detail using seven different building. Story eight and Story twelve reinforced concrete building with different stiffness and setback irregularity were selected and their responses were compared with the ones of a corresponding base case was done using ETABS 2016.1.0 software. The setback of building is formed by the abrupt reduction in different floor area along the height of the building.The seismic response of setback buildings was found to be significantly different from the base case building, according to the findings of this study.The findings reveal that the seismic response variation of setback building from the base case is dependent not only on the size of the irregularity, but also on the placement of the irregularity. This research compares the seismic response of reinforced concrete buildings with setbackirregularity to that of conventional buildings.

Effect Of Vertical Irregularity On Fundamental Period And Stability Of Reinforced Concrete Building

Now a day, many building have not regular configuration both in plan and in elevation due to different functional and aesthetic requirements. Hence, the evaluation of the seismic behavior of reinforced concrete building with plan and elevation irregularity is required. In this study the evaluation of the effect setback irregularity on fundamental and stability of reinforced concrete. The standards used for analysis of base case building and vertical irregular building using response spectrum analysis (RSA) method are adopted according to the provision of ES EN 1998-1:2015. The evaluation of fundamental period and stability based on the value of sensitive inter-story drift were assessed in detail using seven different building. Story eight and Story twelve reinforced concrete building with different setback irregularity were selected and their responses were compared with the ones of a corresponding base case was done using ETABS 2016.1.0 software. The setback of building is formed by the abrupt reduction in different floor area along the height of the building. The fundamental period and stability of setback buildings was found to be significantly different from the base case building, according to the findings of this study. It was discovered that the fundamental period of rigidity irregular buildings is longer than that of equivalent regular buildings. The fundamental period of a setback structure is shorter than that of a comparable regular structure. The findings reveal that the seismic response variation of setback building from the base case is dependent not only on the size of the irregularity, but also on the placement of the irregularity.

Variation of reliability-based seismic analysis of an electrical cabinet in different NPP location for Korean Peninsula

The area of this study will cover the location-wise seismic response variation of an electrical cabinet in nuclear power point (NPP) based on classical reliability analysis. The location-based seismic ground motion (GM) selection is carried out with the help of probabilistic seismic hazard analysis using PSHRisk-tool, where the variation of reliability analysis can be understood from the relation between the reliability index and intensity measure. Two different approaches such as the first-order second moment method (FOSM) and Monte Carlo Simulation (MCS) are helped to evaluate and compare the reliability assessment of the cabinet. The cabinet is modeled with material uncertainty utilizing Steel01 as the material model and the fiber section modeling approach is considered to characterize the section's nonlinear reaction behavior. To verify the modal frequency, this study compares the FEM result with recorded data using Least-Squares Complex Exponential (LSCE) method from the impact hammer test. In spite of a few investigations, the main novelty of this study is to introduce the reader to check and compare the seismic reliability assessment variation in different seismic locations and for different earthquake levels. Alongside, the betterment can be found by comparing the result between two considered reliability estimation methods.

Application of Petrophysical Evaluation and Seismic Interpretation to Generate New Prospects Map of N-Field Rio Del Rey Basin, Cameroon

The N-Field area of the Rio Del Rey Basin was interpreted on 3D seismic data, in order to provide an updated new prospects map of the area. The objective of creating the maps is to evaluate infill opportunities in N-Field. Three main horizons were picked in detail for this seismic interpretation, one in each target reservoir group (S6.1, S6.2 and S6.3) as well as two deeper horizons to ascertain the sedimentary architecture of the basin. The reservoirs and deeper sands show lateral variations in seismic response which are related to changes in reservoir properties but also to possible presence of hydrocarbons. Sedimentary features such as channels and pinch-outs can be seen on seismic, which likely act as stratigraphic traps to the east. All major faults were picked, as well as approximately five smaller, less well-defined faults and interpreted as straight normal faults, along many faults; the throw is variable, often decreasing to no visible throw at one or both ends The evaluation of the petrophysical characteristics revealed that the reservoirs are of good quality with average net to gross, porosities, water saturation and hydrocarbon saturation ranging from 0.774 to 0.980, 0.220-0.339, 0.133-0.367 and 0.633-0.867, respectively. Variation in the petrophysical parameters and the uncertainty in the reservoir structure of the three reservoirs were considered in calculating range of values of gross rock volume from generated prospects map.

Numerical investigation on seismic behaviour of aged concrete gravity dams to near source and far source ground motions

This study presents a numerical investigation on the seismic behaviour of aged concrete gravity dams under near source and far source ground motions. Two-dimensional formulation of a concrete gravity dam is carried out implementing the finite element technique, considering full reservoir and rigid base condition. Degradation of concrete properties due to hydro-chemo-mechanical effects and the influence of sediment layers are taken into account to calculate the response of the dam-reservoir coupled system at different ages. Two near source and far source ground motions from real earthquake events are selected for time-history analysis. Seismic performance evaluation is also carried out to assess the probable damage level of the dam. The outcomes of this study show the variation of seismic response of the dam over the ages and the necessity of considering the aging effect, e.g. degradation of concrete and influence of sediment layers, in the inspection of seismic safety issues of concrete gravity dam. This study also reveals the critical effect of near source ground motions on concrete gravity dams at later ages.

Scenario-based seismic hazard analysis using spectral element method in northeastern Pakistan

Seismic hazard analysis is carried out in this study by estimating ground motion for hypothetical earthquakes in the area of Muzaffarabad, Pakistan, with the MT solution of the 2005 Kashmir earthquake. The earth’s topography influences seismic waves by scattering and reflecting it, thereby causing spatial variation in seismic response. Using the moment tensor solution of the 2005 Kashmir earthquake, we perform 25 spectral element method (SEM)-based 3D simulations along major faults in the study area. The SEM model incorporates the topography and homogeneous half-space characteristics. Our results show that, beside topography, the relative location of the source with respect to slopes also has an influence on the observed variation in ground shaking amplitudes. By integrating the mean and standard deviation of estimated ground shaking from 25 simulations, we present a seismic hazard map for the study area. The map summarizes the topographic and potential source location effect on seismic-induced ground shaking in the study area. It provides a classification from hazardous to safe in relative terms and can be used as a guide in earthquake preparedness.

The impact of topography on seismic amplification during the 2005 Kashmir earthquake

Abstract. Ground surface topography influences the spatial distribution of earthquake-induced ground shaking. This study shows the influence of topography on seismic amplification during the 2005 Kashmir earthquake. Earth surface topography scatters and reflects seismic waves, which causes spatial variation in seismic response. We performed a 3-D simulation of the 2005 Kashmir earthquake in Muzaffarabad with the spectral finite-element method. The moment tensor solution of the 2005 Kashmir earthquake was used as the seismic source. Our results showed amplification of seismic response on ridges and de-amplification in valleys. It was found that slopes facing away from the source received an amplified seismic response, and that 98 % of the highly damaged areas were located in the topographically amplified seismic response zone.

Proterozoic tectonothermal processes imaged with magnetotellurics and seismic reflection in southern Australia

Over the last two decades, co-located seismic and magnetotelluric (MT) profiles provided fundamental geophysical data sets to image the Australian crust. Despite their complimentary nature, the data are processed and often interpreted separately without common processes in mind. We here qualitatively compare 2D resistivity inversion models derived from MT and seismic reflection profiles across a region of Archean–Proterozoic Australia to address the causes of variations in seismic response and anomalous conductivity in the crust. We find that there exists a spatial association between regions of low reflectivity in seismic sections and low resistivity in co-located 2D MT modelled sections. These relationships elucidate possible signatures of past magmatic and fluid-related events. Depending on their diffuse or discrete character, we hypothesize these signatures signify fossil melting of the crust due to mafic underplating, magma movement or hydrothermal fluid flow through the crust. The approach discussed herein is a process-oriented approach to interpretation of geophysical images and a significant extension to traditional geophysical methods which are primarily sensitive to a singular bulk rock property or state.

Numerical calculation of bridge seismic response considering beam-block collision effect

During earthquake, collision between the beam and the block is the direct factor causing damage to the block. To better study the problem and the variation of seismic response in transverse direction of bridge arising from collision, it is necessary to perform quantitative analysis. The Kelvin contact unit model and the single-step Houbolt (SSH) numerical calculation method are adopted for the problem in order to deduce the numerical calculation method and procedures of the bridge seismic response considering beam-block collision effect. MATLAB is used to prepare corresponding program. Through comparison of the calculation result with the test data in related references, it is seen that the calculation method put forward in the paper is of high calculation efficiency and accurate result. In addition, a specific example is made to validate the practicability of this method.

Seismic response variation of multistory base-isolated buildings applying lead rubber bearings

The possibility of earthquakes in vulnerable regions indicates that efficient technique is required for seismic protection of buildings. During the recent decades, the concept is moving towards the insertion of base isolation on seismic prone buildings. So, investigation of structural behavior is a burning topic for buildings to be isolated in base level by bearing device. This study deals with the incorporation of base isolation system and focuses the changes of structural responses for different types of Lead Rubber Bearing (LRB) isolators. A number of sixteen model buildings have been simulated selecting twelve types of bearing systems as well as conventional fixed-base (FB) scheme. The superstructures of the high-rise buildings are represented by finite element assemblage adopting multi-degree of freedoms. Static and dynamic analyses are carried out for FB and base isolated (BI) buildings. The dynamic analysis in finite element package has been performed by the nonlinear time history analysis (THA) based on the site-specific seismic excitation and compared employing eminent earthquakes. The influence of the model type and the alteration in superstructure behavior of the isolated buildings have been duly assessed. The results of the 3D multistory structures show that the lateral forces, displacement, inertia and story accelerations of the superstructure of the seismic prone buildings are significantly reduced due to bearing insertion. The nonlinear dynamic analysis shows 12 to 40% lessening in base shear when LRB is incorporated leading to substantial allowance of horizontal displacement. It is revealed that the LRB isolators might be potential options to diminish the respective floor accelerations, inertia, displacements and base shear whatever the condition coincides. The isolators with lower force intercept but higher isolation period is found to be better for decreasing base shear, floor acceleration and inertia force leading to reduction of structural and non-structural damage. However, LRB with lower isolator period seems to be more effective in dropping displacement at bearing interface aimed at reducing horizontal shift of building structure.

Simplified Estimation Method for Collective Uncertainty-Propagations of Hysteretic Energy Dissipating Device’s Properties

Hysteretic energy dissipating devices (HEDDs) have been increasingly applied to building construction to improve the seismic performance. The seismic responses of such damped structures are significantly affected by HEDD’s structural properties. An accurate investigation on the propagation of HEDD’s structural properties is required for reasonable evaluation of the seismic performance of a structure. This study aims to develop simplified methods that can estimate the collective uncertainty-propagation to the seismic response of damped structures employing HEDDs. To achieve this, three- and six-story steel moment-resisting frames were selected and the propagations of the individual HEDD’s property-uncertainties were evaluated when they are subjected to various levels of seismic demand. Based on the result of individual uncertainty-propagations, a simplified method is proposed to evaluate the variation of seismic response collectively propagated by HEDD’s property-uncertainties and is verified by comparing with the exact collective uncertainty-propagation calculated using the Monte Carlo simulation method. The proposed method, called as a modified SRSS method in this study, is established from a conventional square root of the sum of the squares (SRSS) method with the relative contributions of the individual HEDD’s property-uncertainty propagations. This study shows that the modified SRSS method provides a better estimation than the conventional SRSS method and can significantly reduce computational time with reasonable accuracy compared with the Monte Carlo simulation method.

Impact of Mesh and DEM Resolutions in SEM Simulation of 3D Seismic Response

This study shows that the resolution of a digital elevation model (DEM) and model mesh strongly influences 3D simulations of seismic response. Topographic heterogeneity scatters seismic waves and causes variation in seismic response (am-plification and deamplification of seismic amplitudes) at the Earth’s surface. DEM resolution influences the accuracy and detail with which the Earth’s surface can be represented and hence affects seismic simulation studies. Apart from the spatial resolution of a DEM, the mesh resolution, adopted in the creation of a 3D spectral element meshing, also changes the detailedness of surface topography. Working with high-resolution data is in most cases not possible on a regional scale because of its costliness in terms of time, money, and computation. In this study, we evaluate how low the resolution of DEM and mesh can become before the results are significantly affected. We simulated models with different combinations of DEM and mesh resolutions. The peak ground displacement (PGD) obtained from these simulations was compared with the PGD of the model with the finest mesh and DEM resolution. Our results show that any mesh or DEM resolution of 540 m or coarser will give unrealistic results. These results are valid for similar terrains as studied here and might not be directly applicable to regions with significantly different topography.

Seismic analysis of shear wall buildings incorporating site specific ground response

During earthquake, the motion of ground is affected significantly by source characteristics, source-to-site path properties and local site conditions. Due to the influence of local soil conditions different places experience distinctive amplitude of surface ground motion. Ground response analysis of a specific site utilizing the borehole information at different locations is done in present study. The ground motion with the highest peak ground acceleration for this site obtained from the ground response analysis is used in finite element soil-structure interaction analysis of multi-storey shear wall buildings with various positions of shear walls. The variation in seismic response of buildings and advantageous position of shear wall are determined. The study reveals that providing shear wall at the core of buildings at the specific site is advantageous among all shear wall configurations considered.

Effect of soil stiffness on seismic response of reinforced concrete buildings with shear walls

Buildings are subjected to lateral loads caused by wind, blasting and earthquakes. The high stresses developed by these loads literally tear the building components apart, which are in general designed for gravity loads. To resist these lateral forces, shear walls can be introduced in buildings. Present study aims to determine the apt shear wall position which attracts the least earthquake forces in symmetric plan multi-storey buildings. Dynamic response of a structure is significantly influenced by the underlying soil due to its natural ability to deform. Three dimensional finite element soil–structure interaction analyses of reinforced concrete shear wall buildings with shear walls placed at various locations is carried out in time domain using scaled down Elcentro ground motion to determine the seismic response variation in the structure due to the effect of stiffness of soil. Four different soil types based on shear wave velocity and six varying shear wall positions in multi-storey buildings up to 16 storeys are considered to determine the effect of soil–structure interaction. From the study, it is found that structural response as per conventional fixed base condition is very conservative. For buildings founded on soil with Vs ≤ 300 m/s, providing the shear walls at the core is advantageous whereas for soil with Vs > 300 m/s, the shear walls placed at exterior corners of the building attracts the least earthquake force.

Seismic response variation of tight gas sand for uniform and patchy saturation patterns

When tight sand reservoir is gas–water saturated the distribution pattern of mixed fluid will lead to different velocity–saturation relationships, which will eventually cause the variation of seismic response. Assuming the gas–water mixed fluid in tight sand is uniform saturation or patchy saturation, theoretical velocity–saturation relationships are calculated by using the Gassmann equation and patchy equation respectively. Based on the two trends of velocity, we built a numerical model and analyzed the variations of AVO response, AVO attribute and prestack inversion by using numerical simulation results. The AVO analysis and prestack inversion results all show that when tight sand reservoir is gas–water saturated patchy saturation is more conducive to the prediction of gas content.