Dynamic Seismic Analysis Research Articles

A novel hybrid framework based on modified continued-fraction for pile-soil dynamic interaction of large-scale nuclear power structures

Accurate unbounded domain radiation damping and ground motion input in the near field are important for analyzing the dynamic safety of large-scale nuclear power structures (NPSs). The scaled boundary finite element method (SBFEM) can automatically satisfy the abovementioned radiation condition. However, owing to the coupling of time and space, conventional SBFEM is not competent to the analysis of large-scale structures. In this investigation, a novel coupled method is developed to improve the computational efficiency of unbounded domain dynamic stiffness using a modified continued-fraction technique. Furthermore, a set of systematic and efficient computational procedures for soil-structure interaction (SSI) are implemented based on parallel programming using a special preprocess. The proposed method is verified using three numerical examples, and another numerical application is analyzed for large-scale NPSs with a pile-raft foundation (PRF). The results show that the innovative method has wide engineering applicability with high numerical accuracy and stability, indicating that this method can be applied to the SSI dynamic seismic analysis of large-scale NPSs.

A comprehensive study on seismic dynamic responses of stochastic structures using sparse grid-based polynomial chaos expansion

The seismic response is a critical aspect of structural engineering, as it directly influences the design and safety evaluation of such systems. Structural seismic response becomes more complicated when unavoidable uncertainties in the structure are considered. Therefore, solving and analyzing the stochastic dynamic response of structures efficiently and accurately is of great significance. Various uncertainty quantification methods such as the stochastic finite element method, Monte Carlo method, and polynomial chaos expansion method have made significant progress in this field. However, these methods do not provide a comprehensive study of the seismic response of stochastic structures and efficiency problems rapidly emerge as the number of random variables increases. This paper delivers a comprehensive study of the seismic dynamic response of space truss and reticulated shell structure considering uncertainties in material properties, geometry, and loading. To this end, the finite element model of the structure was first modeled and the deterministic solutions were obtained. Then, polynomial surrogates are modeled for the natural frequency, mode participation factor, mode superposition response, and transient response of the structure under stochastic uncertainties. The sparse grid technique is used to select sparse quadrature points, which overcomes the curse of dimensionality caused by full grid integration. The results demonstrate that the sparse grid-based polynomial chaos expansion is more efficient. Uncertainty quantification reveals the uncertainty of modal analysis, response spectrum analysis, and transient response analysis of space truss and reticulated shell under seismic excitation. In summary, this study provides valuable insights and an efficient and accurate uncertainty quantification tool for the seismic dynamic analysis of stochastic structures, ultimately contributing to safer and more robust structural designs.

The Effect of Edge Beams in The Static and Dynamic Seismic Analysis of High-Rise Building Structures

The Effect of Edge Beams in The Static and Dynamic Seismic Analysis of High-Rise Building Structures

A Fracture Model for Dynamic Sliding Safety Evaluation of a Concrete Dam Subjected to Seismic Excitation

The Sliding Safety Factor (SSF) is a crucial criterion for the sliding stability evaluation of concrete dam structures. A concrete gravity dam subjected to strong earthquakes undergoes progressive fractures, in addition to pre-existing fractures, at the dam–foundation interface, which causes a reduction in the shear strength against sliding. In this study, a new SSF is suggested to take account of the progressive fractured area at the dam–foundation interface. A contact and sliding model for the dam–foundation system is also suggested to compute the dynamically varying normal forces and sliding motions for the suggested SSF. To investigate the effect of the progressively fractured area on the sliding safety evaluation, the conventional, improved, and newly suggested SSFs are compared using the dynamic seismic analysis results of a concrete gravity dam. The conventional formulation of the SSF, in which the fractured area is not represented, yields extremely overestimated sliding safety judgements when a dam is subjected to strong earthquakes. On the other hand, the newly suggested SSF with the proposed contact–sliding model provides more realistic and conservative sliding safety evaluation results than the others.

Nonlinear dynamic seismic analysis of a modern concrete core wall building in Los Angeles using the BTM‐shell methodology

AbstractThis paper discusses the nonlinear dynamic seismic response of a 14‐story reinforced concrete core wall building designed with the prescriptive requirements of the 2019 California Building Code for a near‐fault site in Los Angeles, California, simulated with a detailed nonlinear analysis of the complete structure and subjected to an ensemble of three‐component ground motion input. The study follows up on a recently published work by the authors, which examined the response of the specific building to static lateral loads. The nonlinear model of the building was developed in the software FE‐Multiphys using a shell‐element implementation of the beam–truss model (BTM). The BTM has been extensively validated through prior studies for planar, flanged, and coupled walls under static and dynamic loading. The building model was subjected to an ensemble of ground motions scaled at the design and risk‐targeted maximum considered earthquake levels. The vertical ground motion component and the out‐of‐plane shear degradation of wall piers were included in the simulations. The analyses elucidate the profound effect of nonlinear flexure–shear interaction and of the multidirectional behavior of the flanged coupled core wall on the evolution and localization of damage and on residual deformations. The coupling behavior between the core wall, the slabs, and the columns is also analyzed, and the importance of modeling the nonlinear behavior of all slabs for the residual damage evaluation is demonstrated. The aim of this study is to improve the understanding of issues arising from prescriptive design requirements as well as of issues associated with limitations of standard nonlinear seismic analysis.

Influence of spatially heterogeneous deterioration patterns on strength and ductility of corroded reinforced concrete bridge piers

This work reports on some preliminary results obtained within the framework of a wide research project aimed to study the influence of the corrosion of in Reinforced Concrete (RC) piers on the overall seismic performances of bridges. In this context, after the statistical evaluation of a large database of real structures, a consistent set of bridges and piers has been selected as a sample representative of typical bridge profiles, pier heights and cross-sections as well as of material properties. In the first part of the project, pushover analyses of isolated piers with different corrosion patterns and intensity are carried out to evaluate the residual strength and ductility of corroded piers. In the second part, nonlinear static and dynamic seismic analyses of bridges with corroded piers are carried out to evaluate the influence of the deterioration on the overall seismic performance. Due to specific environmental conditions exposure or to water percolation from the superstructures, it is often the case that corrosion is non-uniformly distributed over piers producing non-homogeneous spatial deterioration patterns. The nonlinear modeling of this type of situations represents specific challenges related to the description of the deterioration patterns and the calibration of material properties. To this end, a multi-level modeling approach based on fiber-based finite elements has been developed and implemented in a specific OpenSeesPy software that allows users to accurately model RC piers subject to arbitrary corrosion patterns, up to their ultimate limit states. In this work, a specific case study of a typical RC rectangular hollow bridge extracted from the mentioned above database subject to different corrosion intensity and patterns is studied. In particular, the influence of the corrosion-induced deterioration on residual strength and ductility are studied. Results show that depending on the intensity and on the patterns significant variations of both strength and ductility can be observed with respect to the undamaged conditions.

Nonlinear time history seismic analysis of inelastic 3D frame buildings in a reduced modal space

This research investigates the formulation of a reduced modal space for the nonlinear dynamic seismic analysis of elasto-plastic 3D frame buildings. Starting from a full finite element model, the modal shapes of the reduced model for the kinematics are selected as the relevant linear elastic modes of the generalized stiffness/mass linear eigenvalue problem in terms of participation factor plus collapse mechanisms associated to appropriate static lateral loads. The internal forces are evaluated on the full model to guaranty an accurate description of the constitutive laws. The equations of motion are then projected in the modal space for the step-by-step solution by a Newmark average acceleration scheme. The advantage is that the Newton iteration of the implicit method are carried out by inverting only the reduced tangent matrix. The proposed reduction method is tested for a reinforced concrete building varying frequency content, direction and amplitude of the ground motion. Accuracy and robustness are demonstrated employing a few tens of modes, including elastic modes and plastic collapse mechanisms. The need for plastic modes for describing the structural dynamics in case of seismic actions leading to significant plastic excursions is highlighted, together with the limits of simplified approaches, as the pushover analysis, based on the hypothesis of shape conservation in the inelastic range regardless of the building regularity.

Seismic safety evaluation method based on fiber-element strain for square-section steel piers

Inconsistency and incompatibility exist between the seismic capacity values obtained from shell-element models and the seismic demand results obtained from beam-based models in engineering. In this paper, the improved fiber model which can consider local instability of steel plates is used uniformly to conduct seismic capacity and seismic demand analyses under bidirectional earthquake actions. First, the restoring-force interaction curves of square-section steel piers are obtained under horizontal unidirectional and oblique loading; however, the evaluation method based on the restoring-force interaction curves may produce incorrect evaluation results according to the elastoplastic stability theory. Therefore, a new seismic safety evaluation method, based on the fiber-element strain within the effective damaged length (Led), is further proposed through the quasistatic analysis under the square spiral loading path. Dynamic seismic response analysis is conducted to verify the effectiveness of the proposed strain-based evaluation method. The results show that the ultimate state according to the compressive strain limit obtained via the square spiral loading is consistent with that based on the elastoplastic stability theory under bidirectional earthquake actions. The proposed method can not only coordinate the demand and capacity results, but also avoid misjudgment cases and facilitate engineering application.

Evaluation of the reduction of seismic loads effect in tall buildings through their geometric configuration in plan

The research aimed to evaluate the effect of seismic loads on tall buildings through four geometric shapes: square, circle, equilateral triangle, and regular hexagon, around X and Y axis, in three evaluation stages of structural regularity condition and system adopted and three verification phases regarding the story drift limit according to E.030 Peruvian standard. Modelling was conducted in ETABS® v.16.2.1, with reinforced concrete of f’c = 280 kg/cm2 and fy = 4200 kg/cm2, in a minimum area of 400 m2 for ten levels plus a roof terrace with 3.20 m typical story height and with a box for two elevators and integrated stairs located in the centroid of each figure. The spectral modal dynamic seismic analysis was applied with parameters of zone 3, intermediate soil, common use, C value according to pseudo accelerations spectrum and rigid frames/structural walls. Among the figures studied, square one allowed the greatest reduction of seismic loads effect (Wseismic = 4296.8270 ton, Tfundamental = 1.077 s, most decoupled main modal matrix, Ia = Ip = 1 in X and Y, DIX ≈ DIY and SFX ≈ SFY), equilateral triangular one originated the most critical structural irregularity (Ip = 0.75), circular one provided the greatest lateral stiffness (DIX = 0.00512 - DIY = 0.00508) and regular hexagonal one presented the highest and most effective structural stability (SFX = 5.318 - SFY = 4.749) when using structural walls (Ro = 6).

A reduced order model for nonlinear time history seismic analyzes of elasto‐plastic 3D frame structures

AbstractA reduced order model for the nonlinear dynamic seismic analysis of elasto‐plastic 3D frame structures is presented. It is based on an approximated solution space for the displacement field that is assumed as the sum of two subspaces. The first subspace is generated by the relevant linear elastic modes of the generalized stiffness/mass linear eigenvalue problem in terms of participation factor. The second one is defined by collapse mechanisms associated to appropriate static load distributions. The time history analyzes are carried out within the reduced solution space, while the internal forces are evaluated on the full model to guarantee an accurate description of the constitutive laws. The proposed reduction method was tested for different structural geometries varying frequency content, direction and amplitude of the ground motion. Numerical results show accuracy and robustness also employing a few tens of modes, including elastic modes and plastic collapse mechanisms. In particular, the need for plastic modes in capturing the structural dynamics in case of seismic actions leading to significant plastic excursions is emphasized. This highlights the limits of simplified approaches based on the hypothesis of shape conservation in nonlinear problems, regardless of the building regularity.

Simplified procedure for simulating artificial non-stationary multi-point earthquake accelerograms

A simplified procedure is proposed to generate artificial non-stationary multi-point ground motion inputs for the dynamic seismic analysis of long span or large scale structures. The probability distribution parameters for the phase difference were fitted using 438 recordings selected from Center for Engineering Strong Motion Data. Then the time curve of the number of zero crossings were fitted using the same dataset. By implementation of the empirical coherency function, we simulated the non-stationary multi-point artificial ground motions given design earthquake scenario (i.e. magnitude and epicentral distance) of the target site. The generated artificial recordings successfully account for non-stationarity in both the time domain and frequency domain, and the trend of spatial correlation is consistent with the utilized coherency function. The generated artificial ground motions were then applied as multi-support excitations for dynamic time-history analysis of the 190 m continuous rigid-frame box girder bridge. Approximately 15%–30% structural response difference was observed between using multi-support excitations and uniform excitations. The vertical displacement amplitude regarding mid-span of the bridge using multi-support excitations is significantly larger than the results using the uniform excitations. For both uniform input and non-uniform input cases, it is also found that the structural response of studied bridge using fitted mean ± standard deviation time curves of number of zero crossings are smaller than the results using fitted mean time curve. The difference is largely caused by the various energy content of generated recordings that are indicated by Arias intensity. This study provides an efficient procedure to generate artificial non-stationary multi-point earthquake accelerograms without cumbersome computation cost, and could be easily implemented in engineering applications.

Dynamic Seismic Analysis of Multi Storey Buildings in Seismic Zone V

Abstract: In India, multi-storied buildings area unit sometimes created because of high value and deficiency of land. Earthquake could be a phenomenon which might generate the foremost harmful forces on structures. Buildings ought to be created safe for lives by correct style and particularisation of structural members so as to possess a ductile sort of failure. To protect such civil structures from significant structural damage, the seismic response of these structures is analyzed along with wind force calculation and forces such as support reactions and joint displacement are calculated and included in the structural design for a vibration resistant structure. The primary objective is to make associate earthquake resistant structure by enterprise seismal study of the structure by static equivalent methodology of study and do the analysis and design of the building by using STAAD PRO software in both static and dynamic analysis Keywords: Dynamic Seismic Analysis, Staad.Pro.

Seismic dynamic analysis and structural integrity assessment of the PWR spent fuel pool under beyond design basis earthquake

A series of numerical analyses were carried out to assess the safety of spent fuel pool (SFP) of a pressurized water reactor (PWR) power plant in Taiwan. These analyses performed seismic force evaluation and 3D nonlinear finite element analysis (FEA) for the SFP under beyond design basis earthquake (BDBE). In addition, this study considered various in-structural response spectra (ISRS) with various damping ratios and the reduced factors to account for the partial cracking effects from BDBE. In the seismic force evaluation, the results show that the pool base takes the greatest uniform equivalent loading resulted from the cooling water, racks, and spent fuel components. For the walls, the south wall suffers the greatest equivalent force. The results of 3D FEA indicated that the largest values of stress and strain appear at the bottom corner near south wall of the channel between the main pool and cask loading pit for the overall SFP structure. It is also found that the influences of cracking effects on the seismic force calculation and structural analysis are significant. But comparing the results of numerical analysis by 5% damping ratio with 0.7 reduced factor and 10% damping ratio with 0.5 reduced factor, the impacts on the liner of the SFP are insignificant. Because the cooling water leakage depends on the liner failure, the influence on the leakage is small.

Dynamic seismic analysis of nuclear power plant buildings and bearing stratum

Various approaches are used for simulating seismic loading and collaboration of a structure and a bearing stratum when carrying out dynamic seismic analysis in specialized software. In the present work, the kinematic parameters of various structures and bearing stratum were calculated using SCAD and STAR_T software. Seismic performance of a reference tower type supporting frame was calculated for 7 grade earthquake. As a result, the floor accelerograms were calculated, and the floor response spectra were built. The calculation results obtained by various methods and structure models were analyzed and compared.

Endurance Time Analysis of Bridges with Unbonded Prestressed Piers

The endurance time method (ETM) is a novel dynamic seismic analysis, which employs intensified artificial earthquakes as the input. This method can ensure both the structural dynamic effect and the computation efficiency when conducting the seismic evaluation of complex structural systems. Based on these advantages, this study investigated the applicability of ETM in the self-centering bridges incorporating prestressed concrete-filled steel tube (CFST) piers. A 3D finite-element model of a typical four span continuous-beam bridge which adopted prestressed CFST piers was established by OpenSees software. Compared with the incremental dynamic analysis (IDA) results, the feasibility of ETM to predict the seismic response of self-centering bridges was validated. Also, the effect of prestressing force in piers on the seismic performance of self-centering bridge systems was studied by ETM. Numerical results show that ETM can be used in the seismic evaluation of bridges with prestressed self-centering piers. The seismic response, such as PT force and residual displacement, can be predicted using this method. In addition, the influence of prestressing force on the seismic response of bridges is related to the type of bearings and the intensity of earthquakes. For the superstructure, the displacement of the main deck can be reduced by increasing the prestressing force, but the shear force of fixed bearings increases accordingly. For the substructure, the piers with sliding bearings are less influenced by the prestressing force, while the seismic internal force of fixed piers increases with the occurrence of prestressing force. Therefore, it is necessary to comprehensively consider the structural system arrangement and seismic basic intensity of the site during the seismic design of such bridges.

Seismic performance evaluation of different strategies for retrofitting RC frame buildings

Defect RC frames are vulnerable to seismic excitation, which need to be retrofitted to enhance performance during seismic event. An applicable procedure is required to reveal the benefits and potential weakness of different retrofit strategies for RC frame buildings with different structural vibration characteristics, which are lacking in previous studies. This research investigation on evaluating the seismic performance of RC frames retrofitted with common methods, with the consideration of fundamental period varying. The seismic dynamic analysis was conducted in a simplified way for the analysis of Single Degree of Freedom (SDOF) systems with hysteresis behaviour factors calibrated on the response from the fiber finite element model of a real RC frame. The variation on the fundamental period of structures in range from 0.6 s to 2 s was considered to obtain a general result, with the consideration of five reinforcement strategies, three strength reduction factors of structures. To study the effect of peak ground acceleration, 20 real earthquake time histories and five seismic intensities were considered. The analysis results show that increasing the secondary-stiffness of the structure with dampers equipped represent an excellent effect in suppressing seismic demand of the structure. However, the strengthening by directly increasing the strength and stiffness has a potential risk of deteriorating the seismic performance of some structures under high intensity earthquakes.

Dynamic Seismic Analysis and Design of R.C.C Multi Purpose Building (G+15) By using E-Tabs

An earthquake is a sudden, rapid shaking of the earth caused by the breaking and shifting of rock beneath the earth’s surface. Earthquakes are among the most powerful events on earth, and their results can be terrifying. In0general for0design of tall0buildings both0wind as well0as earthquake0loads need0to be0considered. Governing0criteria for0carrying out0dynamic analyses0for earthquake0loads are different0from wind0loads. However many tall buildings are not so resistant in lateral loads due to earthquake. Reinforced concrete multi-storied buildings in India were for the first time subjected to a strong ground motion shaking in Bhuj earthquake. It has been concluded that the principal reasons of failure may be attributed to soft stories, floating columns, mass irregularities, poor quality of construction materials faulty construction methods, unstable earthquake response, soil and infrastructure, which were determined to cause damage to the attached structure. High-rise buildings are in high demand due to global urbanization and population growth, and high-rise buildings are likely to suffer the most damage from earthquakes. Since earthquake forces are irregular and unnatural in nature, engineering tools need to be sharpened to analyze the structure in the work of these forces. In this study, to understand the behaviour of structure located in seismic zones III for G+15 Multi-Purpose storey building model is considered for study. Performance of frame is studied through Response Spectrum analysis and comparison is made on shear force, storey drift, storey displacement and storey stiffness.

Comparison of Quasi-Static and Dynamic Stress-Strain Analysis in Earth Dams (Case Study: Azadi Earth Dam)

Seismic analysis of earth and rockfill dams is generally done in two ways: quasi-static and dynamic. However, a quasi-static method with easy application and simple assumptions may lead to unsafe and uneconomical results. In the present study, two static and dynamic analyzes have been used nonlinearly using the Rayleigh Damping rule to calculate the stress and strain of Azadi Dam in the stages of the end of construction and steady-state seepage. Also, in numerical analysis, Abaqus software and a simple elastoplastic behavior model based on the Mohr-Coulomb criterion have been used. The results show that in both quasi-static and dynamic seismic analysis, the highest strain of the Azadi Dam core occurred at the upper levels of the core and the highest stress occurred at the level of the core floor. The stress in the dynamic state is higher than the quasi-static one in the directions σxx 49%, σxy 30%, and σyy 28%, respectively. Also, the maximum shell stress at 1255 m, 1275 m, and 1300 m levels is 29%, 68%, and 72% higher than the core,

Dynamic seismic analysis of bridge using response spectrum and time history methods

Dynamic analysis is very important to better understand the performance of structural elements of a bridge. For this purpose, a seismic analysis of an Algerian highway bridge designed with the new Algerian seismic bridge regulation (RPOA -2008) was carried out using linear and nonlinear analyses. Therefore, response spectrum, time history analyses were performed to evaluate the seismic responses of the designed bridge. The performance of the designed bridge is assessed using 10 ground motion records. The proposed methodology allows an efficient comparison of the seismic response of the bridge in terms of base shear forces, bending moment and displacements. Finally, the paper concludes with a discussion of the specific outcomes.

Assessment of Coupled Effect of Steam Pipes on Seismic Analysis of Reactor Coolant System

Reactor coolant system is connected with auxiliary pipes, surge pipes and steam pipes. In order to facilitate the dynamic analysis of reactor coolant system, it is necessary to decouple the pipes connected with the reactor coolant system. Although some international standards stipulating requirements for the decoupling of subsystems from the main system, in order to further explore the influence of decoupling steam pipes, the seismic response of reactor coolant system with or without steam pipes is simulated by using ANSYS program. Firstly, the modal analysis of reactor coolant system is carried out to analysis the influence of steam pipes on the resonant frequency of reactor system. Then, the standardized seismic dynamic analysis of reactor system with or without steam pipes is carried out. The nozzle load (inlet and outlet nozzle load of main device, such as reactor pressure vessel, steam generator, pump) and support load (of main device such as reactor pressure vessel, steam generator, pump) are output and compared. According to nozzle load and support load, it can be seen that the steam pipes have little influence on the seismic analysis of reactor coolant system, i.e. steam pipes can be decoupled in the seismic analysis of reactor coolant system.