Seismic Response Of Structures Research Articles

Seismic experiments on short coaxial multi-layered cylindrical shells with fluid–structure interaction in fast reactors

As the most important component of pool-type fast reactors, the main vessel contains most of the equipment for the primary circuit and thousands of tons of liquid sodium. The fluid–structure interaction effects of the coaxial multi-layer thin-walled cylindrical shells formed by the main vessel and its thermal shield cannot be neglected. Though the research on the fluid–structure interaction of the liquid in the pool is sufficient, the research on the short coaxial multi-layer cylindrical shells is not enough, especially the axial and circumferential mode shapes and the ratio of each mode under seismic conditions. So, it is necessary to study the fluid–structure interaction of short coaxial multilayer shells. This paper presents shaking table tests performed on double- and triple-layered cylindrical shells to investigate fluid–structure interaction and seismic response, respectively. The experiments reveal that when the aspect ratio is less than 2, Mode (1,6) exhibits the most significant response under sine wave excitation conditions, while Mode (1,1) demonstrates the highest response under seismic conditions. The first three modes are characterized as out-of-phase modes. Additionally, the pressure component of the first circumferential mode contributes 20% to the overall response of the first 12 modes under seismic conditions.

Seismic response and theoretical analysis of grain bulk material-steel silo structure under earthquake action

In order to study the earthquake action of the grain bulk material-steel silo structure, a numerical model of flat-bottom steel silo with the same size as the shaking table test conducted by our research group was established and compared with the experimental results, verifying the rationality and reliability of the numerical simulation method. Subsequently, a refined finite element model (FEM) was established based on an actual flat-bottom steel silo project, analyzing the seismic response of silo models with different grain loading heights, as well as a summary was developed to investigate their dynamic characteristics and seismic responses law. Finally, the calculation formulas for the dynamic response under different loading states of the silo are fitted based on MATLAB software. The results indicate that as the storage material increases, the silo natural frequency demonstrates a decrease in trend and the acceleration response is increased with the increasing of storage load. In addition, the effects of different peak ground accelerations and measurement point heights on the acceleration magnification factor, peak relative displacement, and dynamic lateral pressure all exhibit a linear relationship.

Seismic response analysis of pile-supported wharf under three types of near-fault ground motion

Near-fault pulse-like ground motions exhibit distinct properties, such as forward-directivity and fling-step effects. It is necessary to study the seismic response characteristics of the pile-supported wharf (PSW) under different near-fault ground motions. In this study, thirty near-fault ground motions were utilized as input motions, including forward-directivity, fling-step and non-pulse ground motions. A three-dimensional (3D) nonlinear finite element (FE) model was created to simulate the PSW structure. The seismic response (displacement, bending moment, and acceleration) of the PSW structure under 30 ground motions with peak ground acceleration (PGA), effective peak acceleration (EPA), improved effective peak acceleration (IEPA), peak ground velocity (PGV) and effective peak velocity (EPV) scaling were calculated and compared. The simulation results demonstrate that the PSW structure responds more significantly under two types of near-fault pulse-like ground motion. For near-fault pulse-like ground motions, PGV scaling is better for studying displacement/bending moment response of PSW structure than others. EPA scaling is suitable for studying the acceleration response of PSW structure.

Effect of Frozen Ground on Seismic Response of Pile-Supported Bridge

With the rapid development of China’s economy, the linear traffic infrastructure in the permafrost region has also developed rapidly. Many engineering problems in pile-supported bridges are caused by the freeze–thaw cycles and seismic activity on the roadbed when linear traffic passes over the frozen ground. Therefore, this study focused on the seismic response of a pile-supported bridge in frozen ground. A three-dimensional (3D) nonlinear finite-element (FE) model was established based on a pile-supported bridge, and various modeling techniques and methods were presented in detail. Specifically, the p−y curves in the frozen or unfrozen soil were calculated based on the experimental results from modeling the soil–pile interactions. Based on the computed results, the seismic response of a pile-supported bridge structure in the frozen ground was comprehensively investigated and compared with that in the unfrozen ground. The effect of the frozen ground on the seismic response of a bridge structure was systematically explored. The modeling technique and the derived insights could be significant for pile-supported bridges in frozen ground.

Seismic isolated bridge performance evaluation and design proposal using artificial neural network

AbstractSeismic isolators such as rubber bearings and other dampers are critical components of seismic design. The hysteresis behavior of such bearings is complicated, and engineers are using a bilinear model or equivalent linearization method in design practice. The response evaluation and initial design parameter assumptions are highly dependent on engineers' expertise and need repeated analysis. Therefore, this study proposed a machine learning‐based approach to conduct bridge seismic isolation performance evaluation and design parameters proposal without repeating the nonlinear simulations. The training data were generated by conducting a nonlinear time history analysis of the bridge structure model with input design earthquakes. Four trained three‐layer neural network models could perform bridge seismic response evaluation, predict the structure's seismic response, and suggest design proposal using some input parameters.

Seismic assessment of the steel Moment Resisting Frame equipped with friction beam‐to‐column joints

AbstractSupplementary dissipative devices are viable solutions to enhance the seismic response of building structures. In particular, friction devices are low‐cost and easy‐to‐maintain systems that can be easily inserted into moment‐resisting beam‐to‐column joints of steel Moment Resisting Frames. The effectiveness of dissipative friction joints has been widely demonstrated in many research project. In Europe, the first building equipped with such devices will be fabricated in Italy within the framework of the ongoing RFCS DREAMERS project. The preliminary seismic assessment of this prototype building using the framework of performance‐based earthquake engineering method at different performance levels is summarized in the present paper. To this end, nonlinear dynamic analyses are carried out on three‐dimensional (3‐D) models of the prototype developed in “OpenSees”. The results show that this type of structure can be free of damage under earthquakes corresponding to significant damage and near collapse limit states.

Simplified Nonlinear Dynamic Analysis by Hexagonal Collapse Surface Model of Steel Frame Structure

AbstractBased on the need for effective evaluation of multistorey structures response to seismic loading, this research includes the study of simplified nonlinear dynamic analysis (SNDA) by hexagonal collapse surface model. Existing conventional analysis methods such as FEMA440, restrict the extended use of Nonlinear Static Procedure (NSP) and Nonlinear Dynamic Procedure (NDP) by using the equivalent one‐degree‐of‐freedom (SDOF) model on multi‐degree‐of‐freedom (MDOF) structure. A large error known as Multiple‐Degree‐of Freedom Effects occurs in the elastoplastic behavior. To overcome the limitations of this analysis technique, the understanding of it in the entire structural system due to the influence of the higher‐order vibration modes are investigated, in addition to distinguish the elastoplastic behavior of a structure more precisely. Based on the important collapse mechanisms that are probable to occur during earthquake response, the development of a simplified dynamic analysis technique in which higher‐order vibration mode components were extracted to construct the plastic collapse safety region of a structure. Simplified nonlinear dynamic analysis (SNDA) aims to develop such method whereby multiple vibration mode components are properly considered. Primary and secondary mode of vibrations are generally examined with multiple load patterns corresponding to the condition whereby several independent variables reach maximum concurrently. The formation of hexagonal plastic collapse surface from the probability limit analysis based on proportional load results was discussed. The target for this study is to investigate the competency of this simplified analysis approach in seismic response of structure evaluating techniques.

Dynamic Soil-Structure Interaction Through 2-D Site-Specific Response Analysis

Seismic response of structures involved soil-structure-interaction (SSI) that need to consider both inertial and kinematic interaction. Many underground SSI has been developed such as modelling the structures and soils as continuum with seismic load simplified as pseudo-static or static equivalent. More recent and more realistic SSI model consider non-linear time-history analysis in the form of 2-D site-specific response analysis (SSRA), in which both inertial and kinematic interaction in combination with non-linear soil model, as well as time-history ground-motions are simulated. This paper presents simplified pseudo-static soil-structure interaction finite-element (FE) response of underground box-station structure under prescribed maximum strain displacement as resulted from 1-D site-specific response analysis under various ground-motions characteristics of subduction and shallow crustal earthquakes. More complex model of SSI system of basement is also presented. This basement SSI model incorporates non-linear time-history analysis with dynamic soil properties considered through 2-D SSRA simulating seismic wave propagation from reference base-rock to ground surface. Various base-rock seismic ground-motions are simulated from results of de-aggregation analysis from probabilistic seismic hazard analysis considering both subduction and shallow crustal earthquakes scaled at various ground-motion periods. The analysis adopts dynamic soil model with non-linear modulus and damping using FLAC computer program.

Seismic performance investigation of building structures equipped with MTMDs considering soil-structure interaction

The traditional tuned mass damper (TMD) design criterion is obtained with the fixed base model, which is suitable for the case without significant soil-structure interaction (SSI) effects. However, when the SSI effects are notable, the TMD designed based on the fixed base model will degrade its performance and even magnify the seismic response of the main structure. Since accurately evaluating the effects of SSI on the natural frequencies of the main structure is difficult due to soil nonlinearity, single tuned mass dampers (STMDs) may easily undergo tuning failure due to frequency-limited control bandwidths. Applying multiple tuned mass dampers (MTMDs) to attenuate the vibration of the main structure may be a promising solution. In this paper, the seismic performance of a 10-story steel structure equipped with MTMDs considering SSI is investigated. A three-dimensional refined finite element model is first built. Then, a comprehensive analysis is presented by considering the different MTMDs design parameters and earthquakes. The research results show that when the SSI effect is significant, the MTMDs in reducing the seismic response of the structure have better effectiveness than the STMDs. With other MTMDs design parameters determined, the MTMDs performance is strengthened by increasing the mass ratio and the number of TMDs. The central frequency ratio is taken as the optimum frequency ratio. The bandwidth is limited to the region formed by 0.9–1.1 times the TMD optimal design frequency. The performance of the MTMDs is less influenced by the different TMD installation positions. Moreover, the MTMDs still have good robustness when considering the SSI effect.

Pendulum tuned mass damper (PTMD) with geometric nonlinear dampers for seismic response control

In engineering applications, the geometric nonlinear (GN) arrangement of pendulum-tuned mass dampers (PTMDs) may induce the damping force to deviate from its intended state. Therefore, this study extends the scope of the structural control strategy by introducing a pendulum-tuned mass damper considering geometric nonlinear dampers (GND). Specifically, the damper developed in this study, termed PTMD with GND, is an inconspicuous pendulum-type tuned mass damper with different GN settings in the initial state. A nonlinear mathematical model of the PTMD with GND is developed, identifying its significant nonlinear characteristics, particularly the "unavailable" locations. The stochastic linearization method (SLM) is adopted to simplify the nonlinear model using the Kanai-Tajimi modified spectrum. The SLM agrees well with the numerical results obtained using the Monte Carlo simulation method. Furthermore, the control strategy of PTMD with GND is proposed with the consideration of filtered random excitation. Several numerical cases have been conducted to investigate the availability of PTMD with GND and the proposed optimal design strategy under 178 real seismic excitations. The results show that the PTMD with GND is nearly as effective as the ideal transitional TMD in mitigating the seismic response of the primary structure and more effective than the inverted rough linear adjustment. It can be concluded that the proposed optimal design strategy for the PTMDs with GND efficiently suppressed the structural vibration through multiple performance indices and used the nonlinearity of the damping mechanism of the GND to provide a sufficient damping energy dissipation effect adaptively.

Shaking table tests on the seismic response of truss structure with air spring‐FPS three‐dimensional isolation bearing

AbstractTo investigate the isolation effect of the friction pendulum system (FPS) horizontal isolation bearing and the air spring‐FPS three‐dimensional (3D) isolation bearing in truss structure and the influences of long‐period ground motions on the isolated structure, the shaking table test of a truss structure is designed and conducted. The ordinary ground motions, near‐fault pulse‐like ground motions, and far‐field long‐period ground motions with different spectral characteristics are chosen to input into the structure, and the dynamic characteristics such as the acceleration, displacement, and stress of the truss are compared and analyzed. The horizontal frequency of the horizontal isolated structure is reduced after the horizontal isolation, while the vertical frequency is further reduced after 3D isolation. The isolation effect of nodal acceleration, nodal displacement, and member stress under 3D isolation is better than that of horizontal isolation, especially the vertical seismic response is significantly improved. When the ground motion intensity is small, the FPS horizontal isolation bearing slides little, and reducing the seismic response of the structure is limited. There is a better isolation effect of 3D isolated structure. The vertical frequency ratio Rf under ordinary ground motions is far away from 1 and close to 3, basically avoiding the main energy segment of the ground motions. The advantage of 3D isolated structure is relatively reduced under long‐period ground motions, which lies in the rich low‐frequency components of long‐period ground motions which are difficult to isolate effectively.

Bi-directional semi-active tuned mass damper for torsional asymmetric structural seismic response control

Tuned mass damper (TMD) is a popular vibration absorber. To improve the seismic protection performance of a bi-directional passive TMD, a bi-directional semi-active TMD (BSTMD) with adaptive stiffness, variable mass and semi-active damping is proposed in this study. The BSTMD can adapt to structural X- and Y-directional instantaneous frequencies at the same time under bi-directional ground motions, which are identified through wavelet transform (WT), and the instantaneous angle of a diamond spring device is adjusted according to the instantaneous frequency ratio of two directions, which means that the stiffness ratio of two directions is retuned first. Then, the mass is retuned to match the exact instantaneous frequency. At last, the semi-active damping is realized according to an extended output signals-based control algorithm. A two-directional asymmetric torsional benchmark model is proposed as a case study. For comparison, two optimal passive TMDs implemented in X and Y directions separately and two unidirectional STMDs with variable stiffness and damping implemented in X and Y directions separately are investigated as well. Numerical results show that under bi-directional earthquake excitations in the benchmark problem, the two optimal passive TMDs have a good control effect. Two unidirectional STMDs have the best aseismic mitigation effect generally, in both lateral and torsional dynamic responses; while the BSTMD has a comparable control effect with less electromechanical devices, and can reduce the stroke of unidirectional STMD to a great degree. Though the BSTMD is aimed at X- and Y- directional dynamic responses, it can control torsional responses effectively as well, and when the eccentricity is enlarged to double, it remains effective for seismic mitigation.

Influence Analysis of Liquefiable Interlayer on Seismic Response of Underground Station Structure

To study the influence law of the seismic response of underground station structures at liquifiable interlayer sites, a two-dimensional numerical model of the interaction between the soil and station structure was established based on the finite difference software FLAC3D. The nonlinear dynamic response of the station structure located at the liquifiable interlayer site was analyzed considering the location distribution, relative density, and thickness of the liquifiable interlayer. The results show that the deformation of the structure is greatest when the liquifiable interlayer is distributed on both sides of the station side walls, while the interlayer has an energy-dissipating and damping effect on the upper station structure when it is located at the bottom of the structure. The lower the relative density of the liquifiable interlayer is, the stronger the internal dynamic response of the structure will be, and the more unfavorable it will be to the seismic resistance of the structure. When the liquefiable interlayer is only present in the lateral foundation of the station, an increase in its thickness results in a stronger shear effect on the structure and a higher probability of damage. However, when the thickness of the liquifiable interlayer reaches a point where the entire station is placed within it, the lateral force and deformation of the structure are significantly reduced.

Shaking Table Test of a Split-Foundation RC Frame Structure with One Lower Story Compared with a Conventional RC Frame Structure

Split-foundation (SF) building structures, as a kind of hill-side buildings, are widely used in mountainous regions due to the scarcity of plain areas. In order to experimentally investigate the seismic responses of the SF structure, shaking table test was carried out on two 1/8-scale models: a split-foundation RC frame structure supported by foundations at two different levels and a conventional RC frame structure supported by foundations at one single level. The failure patterns, dynamic characteristics, acceleration responses, displacement responses, and torsion responses of the two models were assessed and compared under seismic ground motions. The test results indicate that the two models were severely damaged after the last intensity level excitation and showed an intermediate failure mechanism. The damage to the SF model was uneven and special with relatively severe damage of the upper grounded columns. The difference in natural frequencies between the two models resulted from the effect of the lower story on lateral stiffness, and the effect was relatively dramatic in the transverse direction. The difference in structural stiffness led to larger acceleration amplification factors of the SF model and smaller acceleration amplification factors in the longitudinal direction. Although the restriction at upper ground level created a certain effect on displacement responses of the SF model especially in the first story, the curve shapes of displacement responses of the two models were similar from the first floor to fourth floor. In addition, the torsion responses of the SF model, especially in the first story (upper ground story), were obviously much larger than those of the conventional model. The torsional effect cannot be ignored in the SF structure which is a torsionally sensitive structure.

Shaking table test and numerical analysis of an innovative precast reinforced concrete building structure

This paper presents an innovative precast concrete (PC) building structure consisted of discretely connected PC floors (DCPCF) and PC frames with dry beam-column connections. A 1/4-scale model of a 4-story 2-bay single-span frame structure was designed and tested on the shaking table under the designed seismic excitation to evaluate the dynamic characteristics and seismic responses of the innovative building structure. In the whole process of loading, beam-plate joints and slab joints can reliably transfer loads without obvious damage, making the innovative PC building structure has good seismic performance, and all indicators meet the requirements of GB 50011-2010. In addition, a finite element model (FEM) was established using nonlinear dynamic modeling program and was calibrated by test results. Here we compare the innovative PC building structure seismic response with the cast-in-situ structure by numerical simulation method, and the diaphragm performance and rigidity characteristics of the DCPCF in orthogonal slab laying (OSL) direction were analyzed, Additionally, design suggestions of the innovative PC building structure were proposed.

Effects of constitutive soil models on the seismic response of an offshore jacket platform in clay by considering pile-soil-structure interaction

Offshore jacket platforms are widely used for wind energy generation and gas and oil field development. The South Pars gas field, located in the Persian Gulf, stands as one of the largest gas fields in the world. This gas field is situated in a seismically active region predominantly characterized by clay soil. Considering the significant impact of clay soil on the seismic response of offshore structures and their vulnerability to damage, it is essential to conduct comprehensive studies on the seismic behavior of offshore structures in this particular area while considering the nonlinear behavior of soil and pile-soil-structure interaction (PSSI). However, due to the laboratory limitations, it is difficult to experimentally investigate the seismic behavior of these structures on a real scale by considering the actual soil environment. This paper aims to adopt a nonlinear kinematic hardening model for clay in Abaqus software and calibrate this model parameters for the South Pars gas field region to carefully investigate the effects of nonlinear behavior of soil and PSSI on the seismic response of an offshore jacket platform. In addition, the perfectly elasto-plastic Mohr-Coulomb model is employed as a simple and common constitutive soil model to compare the results. To achieve the study goals, firstly, the numerical modeling techniques are validated. Subsequently, the main parameters of the nonlinear kinematic hardening model are calibrated for the South Pars gas field region, which has not been done for this region in previous works. Detailed numerical models, including the fixed-base model and the pile-soil-structure (PSS) model, are then developed and analyzed using different selected ground motion records. The results indicate that considering the effect of PSSI has a significant effect on the seismic responses of the structure. Moreover, PSSI effect has a great dependence on the constitutive soil model. The results of this study are expected to provide useful insights into the seismic design of offshore structures in similar geological conditions.

Effective-mode superposition response spectrum method for three dimensional seismic response analysis of underground structures

Response spectrum method (RSM) has been applied in seismic analysis of underground structures. However, the RSM is computationally low efficient for processing large soil domains. In this paper, the dynamic characteristics of underground structures are first investigated through three rectangular subway station structures. The results show that only a small number of effective frequencies and modes of soil-structure interaction (SSI) system significantly affect the seismic response of underground structure. These effective frequencies and modes are related to the natural vibration characteristics of site. An effective method is then developed to obtain the effective natural frequencies and modes of the SSI system. Subsequently, the effective modal superposition response spectrum method (ERSM) for seismic analysis of underground structure is developed by only combining the effective natural frequencies and modes of the SSI system to improve efficiency. Finally, the accuracy of ERSM is investigated through seismic response analysis of subway station structures. Numerical examples show that the ERSM can be used for seismic analysis of underground structures considering 3D SSI.

Improved intensity measures considering soil inelastic properties via multi-regression analysis

At certain depths, the elastic properties of the ground are not affected by seismic waves. However, as they reach the surface, the soil density decreases and so does its elastic limit. This means that the expected ground motion acting at the foundation of a structure cannot be adequately described without considering the inelastic response of the soil near the surface. Therefore, one of the key elements in characterizing the seismic response of civil structures is the site effect. These depend mainly on the parameters of the soil beneath the structure and the features of the ground motion acting at the depth, where non-linear effects are negligible. Therefore, the main objective of this paper is to find an intensity measure that incorporates the information provided by the soil profile under the structure and the ground motion acting at the bedrock level. Due to the random nature of both elements, a probabilistic framework using Monte Carlo simulation has been developed to analyze this problem. For this purpose, random soil profiles have been generated to obtain a representative sample of likely scenarios of the study area. A large database of Colombian ground motion records has been used to model the seismic hazard. Finally, power functions capable of relating the input variables to the dynamic response of a large set of reinforced concrete structures have been derived by considering multi-regression analysis. It has been observed that, in several cases, intensity measures extracted from the displacement spectrum appear in the mathematical arrangements. These functions could be used to improve the efficiency of seismic risk prediction at the urban level.

Effects of green roof damping and configuration on structural seismic response

Effects of green roof damping and configuration on structural seismic response

Research on irregular plane mid story isolation structures in castor earthquake prone areas considering SSI effect

The rock composition of karst area is mainly limestone, which is easy to be eroded and dissolved by water, forming a complex and fragile tectonics. Under the action of earthquake, the instability of stratum is aggravated. The mid story isolation structure is a new type of isolation structure developed from the basic isolation structure, and irregular mid story isolation buildings are highly susceptible to adverse seismic conditions. Previous studies have mostly adopted the assumption of rigid foundations, neglecting the influence of soil on irregular structures. In order to study the seismic response of isolated structures in irregular planes in karst earthquake prone areas considering soil structure interaction, a finite element model of isolated structures in irregular planes considering soil component interaction was established, and the seismic response of the structure under rigid foundation was calculated. Soft and hard soil foundations were studied, and compared with structures without considering SSI effect. Research shows that when considering the SSI effect, the seismic response of the structure increases and the damage to the structure intensifies; When considering SSI, the seismic response of soft soil is greater than that of hard soil, and the softer the soil, the more obvious it becomes; After considering the SSI effect, the torsional effect caused by the irregularity of the plane increases; The design of building structures should fully consider the adverse effects of soil layers on the seismic response of structures under plane interlayer seismic irregularities. In the design of building structures, it is necessary to fully consider the adverse effects of irregular planes on the seismic response of the structure. This consideration is particularly important in the design of soft soil high-rise buildings in karst earthquake areas to prevent unsafe designs and consider the SSI effect in actual seismic resistance.