Earthquake Input Motions Research Articles

Soil-structure interaction analysis of nuclear power plant structure using multi-step method in time-domain

Recently, several countries have experienced strong earthquakes, and there has been growing interest in the seismic design of structures. Particularly, consideration of soil-structure interaction (SSI) has become important when performing seismic response analysis for nuclear power plant (NPP) structures. A seismic analysis method that considers SSI in the time domain has been proposed in previous studies. This method is applicable to the seismic response of structures, because it can consider the influence of the SSI effect with the impedance function in the frequency domain and simultaneously considers the structural nonlinearity. However, it has only been applied to the structure comprising a single beam-stick. In this study, a modified method for applying it to more general structures is proposed, and its applicability is validated with an actual reactor containment building (RCB) structure comprising a three beam-sticks. Validation was performed by comparing the seismic responses with those of ACS SASSI. Using the proposed method, SSI analysis was performed with three soil profiles and the results were compared to investigate the effect of SSI on seismic responses, including the in-structure response spectrum (ISRS) and time history acceleration. For more realistic analysis, soil profile and earthquake input motion occurred in South Korea are adopted. Further, a multi-step method considering nonlinear behavior was also performed and compared with the linear case.

Site effect on seismic response of buried nuclear power plant structure

The development of multifunctional, multipurpose small modular next generation nuclear reactors has become a trend in designing small-scale nuclear power stations. In this study, taking a new next-generation buried nuclear power structure as the target structure, a 3D finite element model of the site-nuclear power plant structure system was established, and its response at different sites was studied. Using the internal substructure method, this study initially explored the impact of earthquake input and artificial boundary locations on the structural response. The results indicate that the internal substructure method enhances computational efficiency without compromising accuracy. For this model, it is recommended to input earthquake motion close to the structure, set the lateral boundary location to three times the width of the structure, and set the bottom boundary location to two times the depth of the structure. Subsequently, an investigation into the response of the structure at varying site wave velocities is conducted. The results show that as the wave velocity increases, the acceleration response intensifies, while the displacement response diminishes. However, the relationship is nonlinear; the response exhibits less variation with increasing site wave velocity. The seismic response of a structure is profoundly influenced by site conditions, emphasizing the imperative need for careful consideration of specific site characteristics in seismic analyses. In addition, the response pattern of the overall structure is significantly different from that of conventional large surface-sited nuclear power plants, and further research should be conducted on the seismic response characteristics of buried nuclear power plants.

Ataköy Gözlem Kuyusunda Saha Tepki Tahminleri

Site response analyses are seen to be the reliable way of reproducing and predicting earthquake input motions. The analyses are generally performed by adopting equivalent linear or nonlinear approaches solving the problem in time or frequency domains. Instrumented geotechnical downhole arrays, in this regard, are very important as to obtaining earthquake data through the soil deposits. This data can eventually be used to verify the approaches developed for site response analyses. In this study, the input motions of the 24.05.2014 (Aegean) earthquake event recorded at relatively recently installed Atakoy geotechnical downhole array are assessed. Moreover, the recorded input motions at the bottom bedrock level of the downhole array are simulated in the East-West and North-South directions. The site response analyses are conducted based on frequency domain equivalent linear approach. The peak ground acceleration and the spectral accelerations of the predicted input motions are compared with the recorded ones at 70 m, 50 m, 25 m and at the ground surface. The results indicate that the spectral acceleration predictions can be simulated well until the depth of 50 m. At 25 m and at ground surface, the predictions are always greater than the recorded one. However, the predictions still exhibits good indication of actual values in the North-South direction. In terms of peak ground acceleration and shear strain profiles, the predictions display the soil layers featured with different soil properties. The equivalent linear approach appears to be suited reasonably well in site response analysis.

Seismic Ground Response Analysis of Input Earthquake Motion and Site Amplification Factor at KUET

Ground motion is the movement of the earth's surface due to explosions or the propagation of seismic waves. In the seismic design process, ground response analysis evaluates the impact of local soil conditions during earthquake shaking. However, it is difficult to determine the dynamic site response of soil deposits in earthquake hazard-prone areas. Structural damage has a great influence on the selection of input ground motion, and in this study, the importance of bedrock motion upon the response of soil is highlighted. The specific site response analysis is assessed through “DEEPSOIl" software with an equivalent linear analysis method. Furthermore, four input motions including Kobe, LomaGilroy, Northridge, and Chi-Chi were selected to obtain normalized response spectra. This study aims to obtain the site amplification of ground motion, peak spectral acceleration (PSA), and maximum peak ground acceleration (PGA) based on shear wave velocity from the detailed site-specific analysis of Bangabandhu Sheikh Mujibor Rahman hall at Khulna University of Engineering & Technology. The maximum shear wave velocity obtained was 205 m/s while the amplification factor varied from 4.01 (Kobe) to 1.8 (Northridge) for rigid bedrock properties. Furthermore, the Kobe earthquake produced the highest (4.3g) PSA and the Northridge earthquake produced the lowest (1.08g) PSA for bedrock, with Vs=205 m/s. The surface PGA values were acquired in the range of 0.254g (Northridge) to 0.722g (Kobe), and the maximum strain values for Kobe earthquakes were in the range of 0.016 to .303. Therefore, the surface acceleration values were very high (>0.12g) for the Kobe earthquake motion.

Ground vibration analysis under combined seismic and high-speed train loads

The rise of high-speed railway induces an increased probability of serious derailment accidents of operating high-speed trains during earthquakes. A two-and-half-dimensional finite element model (2.5D FEM) was developed to investigate the ground vibration under combined seismic and high-speed train loads. Numerical examples were demonstrated and the proposed method was turned out to provide an effective means for estimating ground vibration caused by high-speed train load during earthquakes. The dynamic ground displacement caused by combined seismic and high-speed train loads increases with the increase of the train speed, and decreases with the increase of the stiffness of ground soil. Compared with the seismic load alone, the coupling effect of the seismic and high-speed train loads results in the low-frequency amplification of ground vibration. The moving train load dominants the medium–high frequency contents of the ground vibration induced by combined loads. It is observed that the coupling effects are significant as the train speed is higher than a critical speed. The critical train speed increases with the increase of the ground stiffness and the intensity of the input earthquake motion.

Effect of soil-rock interface position on seismic response of subway station structure

For subway stations in a site with thin soil layers on the engineering rock, the lower part of the subway station is embedded in the hard rock mass and the upper part is buried in the soil layers. The presence of the soil-rock interface may lead to significant increase to the seismic responses of the adjacent soil masses and underground structures. In this paper, the effect of the soil-rock interface position on the seismic response of a two-story and three-span subway station structure is investigated by numerical analyses. It is found from the numerical analyses that a most detrimental soil-rock interface position exists and makes the underground structure have maximum responses under a given artificial earthquake motion. For the upper floor, the most detrimental soil-rock interface position is near the middle slab. For the lower floor, the most unfavorable soil-rock interface position is near the bottom slab. Softer site generally leads to greater structural responses under the same intensity of ground motion excitation. On the basis of the above findings, three earthquake motions included above an artificial earthquake motion and other two real earthquake motions and three burial depths of structure are further studied. Same conclusions can be obtained for the structure with different burial depths or subjected to different input earthquake motions. The conclusions drawn from the numerical examples of this paper may be useful for seismic design of subway station structure buried in shallow soil layers on rock.

Feasibility Assessment of Stiff Seismic Base Absorbers

In this paper, a radically new concept of a Stiff Seismic Base Absorber (SBA) is proposed for seismic protection of multistory building structures. An inerter is first implemented, connecting directly the structure to the ground. This results in the decrease of the natural frequency of the structure, without decreasing its structural stiffness. Parallel, a negative stiffness-based absorber is used to increase the apparent damping behavior of the inerter. The additional mass of the SBA is connected to the structure with a negative stiffness (NS) element and to the base with a positive one. Also, an artificial damper is placed in parallel with each stiffness element. The design of the SBA includes the following novel features: (1) the SBA foresees variation in all stiffness elements, (2) the optimal system parameters are selected based on engineering criteria with proper constraints and limitations to the system dynamic responses, (3) the earthquake input motion is selected according to the seismic design codes, (4) a displacement-dependent non-linear configuration is proposed for the realization of the NS element, and (5) the detuning phenomena are observed via sensitivity analysis. Compared to other vibration absorbers, the SBA presents several advantages. An improved superstructure dynamic behavior is observed combined with small base displacements, in the order of a few centimeters. The drastically reduced base displacements render the implementation of the SBA feasible using conventional structural elements. As a result, the SBA is a realistic retrofitting option for seismic protection.

Seismic response analysis and modal identification of a full-scale five-story base-isolated building tested on the NEES@UCSD shake table

This paper presents the analysis of the seismic response and the identification of the dynamic properties of an equivalent linear time-invariant model of a full-scale five-story base-isolated reinforced concrete building tested on the unidirectional NEES@UCSD shake table. A sequence of seven scaled historic earthquake records was applied by the shake table to the building, progressively increasing the seismic demand on the structure and its nonstructural components and systems. The effects of the isolation system on elongating the predominant period of the building, concentrating the displacement in the isolation layer, and augmenting the energy dissipation capacity of the building system are investigated. Low-amplitude white noise (WN) base excitation tests were conducted before and after each seismic test and ambient vibration (AV) data were recorded continuously for a period of approximately sixteen days containing the sequence of seven seismic tests performed. Because of the low intensity of the white noise base and ambient excitations, a quasi-linear response of the base-isolated building is assumed, allowing the modal parameters of an equivalent linear viscously damped time-invariant model to be estimated from vibration data recorded during the WN and AV tests. Different state-of-the-art system identification methods, including output-only and input-output methods, are used to estimate the modal properties of the base-isolated building. Results show that the identified modal parameters obtained from different methods are in good agreement and that the assumption of quasi-linear response for each low-amplitude test is appropriate. The effects of the amplitude of the excitation, earthquake input motions, and environmental conditions are clearly evidenced by the changes induced in the estimated modal parameters of the building.

Study Concept on the Development of an Urban Cyber Physical System for Enhancing the Capability to Respond to Large-Scale Earthquakes

Various technologies for improving earthquake-disaster-mitigation capability in urban communities are being developed and proposed. However, these technologies are sometimes difficult to use in actual applications due to the lack of incentives for owners of buildings or infrastructures, because the owners cannot calculate their cost-effectiveness and thus consider the installation payment for these technologies as a cost to be reduced. To address this problem, we propose the construction of an “Urban cyber physical system (CPS).” This urban CPS evaluates the earthquake-resistant capability of buildings and/or social infrastructures to help owners easily understand the cost-effectiveness of adopting these technologies. The CPS also calculates the effects of newly-developed technologies, thereby allowing owners to accept new technologies based on their effectiveness. The study concept of the urban CPS is as follows: (1) Construction of an “Information platform” by using data aggregation and analysis of existing vibration data of structures, datasets of building (or construction) information modeling and various other available databases; (2) Development of a “Simulation platform” that has a prediction function to calculate the behaviors of urban communities during earthquakes by using data in the Information platform and an identification function to identify structural systems from input earthquake motions and responses of structures; and (3) Establishment of an “Eco-system” to operate the urban CPS in urban community design, based on the perspective of earthquake resilience.

Response of low-rise building with geotechnical seismic isolation system

The Geotechnical Seismic Isolation (GSI) is recently recommended as an innovative base isolation system placed below the foundation of the superstructure for protection from earthquake damages. Low-shear modulus and high damping material such as Sand-Rubber Mixture (SRM) is used for the GSI layer. However, the compressible nature of SRM in the GSI layer leads to low bearing capacity and high settlement of foundations. In view of this, a GSI system consisting of SRM and geogrid reinforcement is proposed for low-rise buildings in the present study. Finite element based two-dimensional numerical investigation on the seismic performance of a two-storied building supported on raft footing resting on the proposed GSI system was carried out considering the soil–structure interaction. The nonlinearities of the subsurface materials were duly considered using hypoelastic formulations to account for the strain-dependent response. The effectiveness of geogrid reinforcement for the GSI system is demonstrated through seismic settlement analysis based on which optimum geogrid layers were chosen. Effect of various factors such as the thickness of GSI layer, frequency content of earthquake input motions on the seismic demand of the framed structure resting on the proposed GSI system was investigated. While the contribution of SRM was predominant in reducing the peak ground acceleration experienced by the building, the contribution of geogrids was evident in reducing the seismic settlement and lateral deformations on the structure. The results demonstrate the suitability of using the proposed GSI system with a thickness of 0.1B–0.2B (B is the footing width) with double layered geogrid reinforcement in significantly reducing the seismic demands of low-rise building.

In-Cabinet Response Spectrum Generation Using Frequency Domain Analysis Method

Seismic qualification of instruments and devices mounted on electrical cabinets in a nuclear power plant is performed in this study by means of the in-cabinet response spectrum (ICRS). A simple method and two rigorous methods are proposed in the EPRI NP-7146-SL guidelines for generating the ICRS. The simple method of EPRI can give unrealistic spectra that are excessively conservative in many cases. In the past, the time domain analysis (TDA) methods have been mostly used to analyze a structure. However, the TDA requires the generation of an artificial earthquake input motion compatible to the target response spectrum. The process of generating an artificial earthquake may involve a great deal of uncertainty. In addition, many time history analyses should be performed to increase the accuracy of the results. This study developed a numerical analysis program for generating the ICRS by frequency domain analysis (FDA) method. The developed program was validated by the numerical study. The ICRS calculated by FDA thoroughly matched with those obtained from TDA. This study then confirms that the method it proposes can simply and efficiently generate the ICRS compared to the time domain method.

APPLICABILITY OF THE JAPANESE RECIPE FOR PREDICTING STRONG GROUND MOTIONS BY HERP TO EUROPE AND MIDDLE EAST CRUSTAL EARTHQUAKES

The procedure of evaluating fault parameters, so called Recipe, for predicting strong ground motions by the HERP [Headquarters for Earthquake Research Promotion, 2005], Japan, is often applied to assessment of design input earthquake motions for nuclear power plants in Japan. Due to this situation, the International Atomic Energy Agency [2015] adopted this Recipe in Safety Report Series No. 85. However, this Recipe was validated only for Japanese earthquakes. Hence, we examined the validation of the Recipe by comparing the estimated strong ground motions based on the Recipe with those by the GMPE (Ground Motion Prediction Equation) obtained by Akkar et al. [2014] from the Europe and Middle East crustal earthquakes. We concluded that the short-period level in the Recipe should be reduced to 50% for the second-stage earthquakes and that the stress drop equation of a circular crack should be altered. We also concluded that the short-period level should be reduced to 55% for the first-stage earthquakes under the condition that the stress drop equation of a circular crack should be maintained.

Peak ground acceleration prediction by fuzzy logic modeling for Iranian plateau

In this study, fuzzy logic modeling is applied to a complex and nonlinear set of data to predict both horizontal and vertical peak ground accelerations in Iranian plateau. The data used for the model include an up-to-date seismic catalogue from earthquakes in Iran for prediction of both horizontal and vertical acceleration of a probable earthquake. Fuzzy logic toolbox on MATLAB program was used for modeling. Earthquake magnitude ranging from 4 to 7.4, source-to-site distance from 7 to 80 km and three different site conditions were considered: rock, stiff soil and soft soil. Results are compared with those from worldwide and regional attenuation relationships, which show the higher capability of the model in comparison with the other models. After training the model, testing of the fuzzy model with the remaining data set was performed to confirm the accuracy of the model. Changes in the peak ground accelerations in connection with changes in input parameters are studied which are in agreement with basic characteristics of earthquake input motions.

The sensitivity of earthquake input motion correlation with arias intensity and amplification, case study: Yogyakarta Special Region

Earthquake problems are a fascinating topic that discussed among the scientific and academic in the world, including of these is the parameter of a sensitivity. In this study, the sensitivity level of earthquake input motion in bedrock correlated with intensity arias and amplification occurring at the surface. The selected location of the study is an earthquake-prone area with the last record of a major earthquake in 2006, i.e., Yogyakarta Special Region. There are 3 (three) study areas with different geological environments. The analysis is determined by these steps: (1) Probabilistic Seismic Hazard Analysis/PSHA (2) disaggregation (3) selection of motion input and (4) wave propagation analysis to obtain a graph of Arias intensity and amplification value. All of those are aided by EzFrisk and DeepSoil software. The results of this study, i.e., the higher natural frequency at the site, then the lesser amplification developed. The highest amplification takes place at BH-04 which has the smallest natural frequency. On the other hand, the lowest value occurred at BH-02 on the highest natural frequency. There is a tendency that the smaller delta on the effective time arias intensity, the more significant amplification be occurred, except for Loma Prieta ground motion.

Three-dimensional finite element modelling for seismic response analysis of pile-supported bridges

Soil-structure interaction (SSI) is involved in the pile-supported structures. Such effect is mainly accounted for soil-pile interaction (SPI) driven by the deformation of pile and surrounding soil, and thus it can become significantly obvious due to large soil deformation during a severe earthquake. To capture this characteristic of simply supported bridge structure with pile foundations, a three-dimensional (3D) finite element (FE) model is developed using the computational platform OpenSees considering SPI. A two-span reinforced concrete bridge with a single pier located in multi-layered clay is employed as a test-bed. A variety of seismic responses of this coupled soil-pile-bridge system are systematically investigated. Furthermore, a parametric study is performed to explore the influences of SPI, multidirectional excitation and earthquake characteristic on the seismic responses of soil and structure. The results show that: (1) the seismic response of the bridge structure is significantly affected by its longitudinal and transversal different configuration; (2) the fixed-base support type noticeably influences the seismic response of bridge structure and (3) the direction and characteristic of base input earthquake motion greatly influence the seismic response of the bridge-soil system.

Numerical modeling of a tunnel in jointed rocks subjected to seismic loading

The studies on the performance of tunnels under static loads are reported extensively in the literature but their performances under dynamic loads are limited. The present study highlights some of the important aspects of jointed rock tunnels during seismic loading. The literature review provides a shake table experimental study of a jointed rock tunnel. A Universal Distinct Element Code (UDEC) model is developed from this shake table experiment. The model tunnel is subjected to a scaled input motion of the 1985 Mexico earthquake. The numerical results are validated systematically with the findings of the shake table experiment. Further, the developed numerical model is used to perform parametric studies to understand the effect of in-situ stress, joint angles, joint stiffness, and joint friction angle on the deformation and stability of the tunnel under the same earthquake input motion. It is observed that some joint angle combinations form a wedge that yields excessive deformation and subsequently a complete failure. An exponential decrease in deformation occurred in the tunnel as the joint stiffness increases. It is found that the shallow tunnels are more susceptible to damage under the action of earthquake loads.

PSHA of Van province for performance assessment using spectrally matched strong ground motion records

Within the framework of the performance based earthquake engineering, site specific earthquake spectra for Van province has been obtained. It is noteworthy that, in probabilistic seismic hazard assessment, as a first stage data from geological studies and records from the instrumental period were compiled to make a seismic source characterization for the study region. The probabilistic seismic hazard curves were developed based on selected appropriate attenuation relationships, at rock sites, with a probability of exceedance 2, 10 and 50% in 50 yrs period. The obtained results are compared with the spectral responses proposed for seismic evaluation and retrofit of building structure in Turkish Earthquake Code (2007), section 7. The acceleration response spectrums obtained from probabilistic seismic hazard analysis are matched to adjust earthquake accelerograms recorded during the 2011 Van earthquakes by using SeismoMatch v2.0 software. The aim of this procedure is to obtain a set of reasonable earthquake input motions for the seismic evaluation of existing buildings.

LIQUEFACTION SIMULATION AND RELATED BEHAVIOR OF UNDERGROUND STRUCTURE ON OSAKA GULF COAST

The Kansai area has a high possibility of a huge plate-boundary-type earthquake within 30 years.If an earthquake occurs, the Osaka Gulf coast will be struck by severe liquefaction disasters. Therefore, wetried to apply LIQCA, which is often used for liquefaction analysis, to a site on the Osaka Gulf coast. The inputearthquake motion is the seismic standard spectrum I, which is commonly used in Japan. The calculation timecontinued until the excess pore water pressure dissipated. The site has an underground structure, so weinvestigated not only the liquefaction phenomenon of the ground itself but also the behavior of the undergroundstructure. The results of this analysis indicate that these soil layers of the target area become liquefied. Afterthe excess pore water pressure dissipates, the ground surface settles in the vertical direction and moves in thehorizontal direction. In addition, in the vicinity of the underground structure center, it rises in the verticaldirection and moves in the horizontal direction.

LIQUEFACTION SIMULATION FOR THE OSAKA GULF COAST USING THE LIQCA PROGRAM

A Nankai megathrust earthquake is expected to occur in the Kansai area within the next 30–40 years. According to the worst-case estimations by The Headquarters for Earthquake Research Promotion [1], the earthquake will cause economic losses of approximately 220 trillion yen, and 134,000 buildings will be damaged by liquefaction. To estimate future damage to the Osaka gulf coast, we conduct liquefaction simulations based on the LIQCA program developed by the research group at Kyoto University. The liquefiable layers are composed of relatively loose sand and the underground water level is high. The input earthquake motion is the L2 spectrum Ⅰ earthquake-resistant standard spectrum, according to the Design Standards for Railway Structures and Commentary [2]. We consider not only the increase of excess pore water pressure, but also its dissipation. The calculated effective stresses in the sand layers approached 0, after which the sand layers liquefied and unevenness occurred at the ground surface. We evaluated the damage due to liquefaction by calculating vertical displacements and unevenness of the ground surface. Countermeasures are proposed for the shallow sand layers to reduce future liquefaction damage.

A Discussion on the Seismic Coefficient for Gravity Quay Wall Considering Frequency Characteristics of Input Earthquake

Pseudo-static approach has been conventionally applied for the design of gravity type quay walls. In this method, seismic coefficient (kh), expressed in terms of acceleration due to gravity, is used to convert the real dynamic behavior to an equivalent pseudo-static inertial force for seismic analysis and design. Therefore, the calculation of an appropriate kh considering frequency characteristics of input earthquake is critical for representing the real dynamic behavior. However, the definitions of kh, which is used for simplified analysis in Korea, focuses only on convenience that is easy to use, and the frequency characteristics of input earthquake are not reflected in the kh definitions. This paper evaluates the influences of the frequency characteristics of input earthquake on kh by initially reviewing the kh definitions in the existing codes of Japan for port structures and then by performing a series of dynamic centrifuge tests on caisson gravity quay walls of different earthquake input motions (Ofunato, Hachinohe). A review of the existing codes and guidelines has shown that the kh values are differently estimated according to the frequency characteristics of input earthquake. On the other hand, based on the centrifuge tests, it was found that the permanent displacements of wall are more induced when long-period-dominant earthquake is applied.