• Geomechanics and Engineering
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• v.14 no.2
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• pp.161-174
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• 2018

The present study investigates the soil-structure interaction (SSI) effects on the seismic performance of smart base-isolated structures. The adopted control algorithm for tuning the control force plays a key role in successful implementation of such structures; however, in most studied carried out in the literature, these algorithms are designed without considering the SSI effect. Considering the SSI effects, a linear quadratic regulator (LQR) controller is employed to seismic control of a smart base-isolated structure. A particle swarm optimization (PSO) algorithm is used to tune the gain matrix of the controller in both cases without and with SSI effects. In order to conduct a parametric study, three types of soil, three well-known earthquakes and a vast range of period of the superstructure are considered for assessment the SSI effects on seismic control process of the smart-base isolated structure. The adopted controller is able to make a significant reduction in base displacement. However, any attempt to decrease the maximum base displacement results in slight increasing in superstructure accelerations. The maximum and RMS base displacements of the smart base-isolated structures in the case of considering SSI effects are more than the corresponding responses in the case of ignoring SSI effects. Overall, it is also observed that the maximum and RMS base displacements of the structure are increased by increasing the natural period of the superstructure. Furthermore, it can be concluded that the maximum and RMS superstructure accelerations are significant influenced by the frequency content of earthquake excitations and the natural frequency of the superstructure. The results show that the design of the controller is very influenced by the SSI effects. In addition, the simulation results demonstrate that the ignoring the SSI effect provides an unfavorable control system, which may lead to decline in the seismic performance of the smart-base isolated structure including the SSI effects.

• Smart Structures and Systems
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• v.16 no.1
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• pp.163-181
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• 2015

This research investigates the structural health monitoring of nonlinear structures after a major seismic event. It considers the identification of flag-shaped or pinched hysteresis behavior in response to structures as a more general case of a normal hysteresis curve without pinching. The method is based on the overall least squares methods and the log likelihood ratio test. In particular, the structural response is divided into different loading and unloading sub-half cycles. The overall least squares analysis is first implemented to obtain the minimum residual mean square estimates of structural parameters for each sub-half cycle with the number of segments assumed. The log likelihood ratio test is used to assess the likelihood of these nonlinear segments being true representations in the presence of noise and model error. The resulting regression coefficients for identified segmented regression models are finally used to obtain stiffness, yielding deformation and energy dissipation parameters. The performance of the method is illustrated using a single degree of freedom system and a suite of 20 earthquake records. RMS noise of 5%, 10%, 15% and 20% is added to the response data to assess the robustness of the identification routine. The proposed method is computationally efficient and accurate in identifying the damage parameters within 10% average of the known values even with 20% added noise. The method requires no user input and could thus be automated and performed in real-time for each sub-half cycle, with results available effectively immediately after an event as well as during an event, if required.

• Land and Housing Review
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• v.12 no.3
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• pp.97-108
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• 2021

In bridge abutment structures, lateral squeeze due to lateral stress of embankment placement and thermal movement of the bridge structure leads to failure of approach slabs, girders, and bridge bearings. Recently, GRS (Geosynthetic-Reinforced Soil) integral bridge has been proposed as a new countermeasure. The GRS integral bridge is a combining structure of a GRS retaining wall and an integral abutment bridge. In this study, numerical analyses which considered construction sequences and earthquake loading conditions are performed to compare the behaviors of conventional PSC (Pre-Stressed Concrete) girder bridge, traditional GRS integral bridge structure and GRS integral bridge with bracket structures (newly developed LH-type GRS integral bridge). The analysis results show that the GRS integral bridge with bracket structures is most stable compared with the others in an aspect of stress concentration and deformation on foundation ground including differential settlements between abutment and backfill. Furthermore, the GRS integral bridge with/without bracket structures was found to show the best performance in terms of seismic stability.

• Computers and Concrete
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• v.23 no.1
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• pp.1-10
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• 2019

The use of non-linear analysis of structures in a functional way for evaluating the structural seismic behavior has attracted the attention of the engineering community in recent years. The most commonly used functional method for analysis is a non-linear static method known as the "pushover method". In this study, for the first time, a cyclic pushover analysis with different loading protocols was used for seismic investigation of curved bridges. The finite element model of 8-span curved bridges in plan created by the ZEUS-NL software was used for evaluating different pushover methods. In order to identify the optimal loading protocol for use in astatic non-linear cyclic analysis of curved bridges, four loading protocols (suggested by valid references) were used. Along with cyclic analysis, conventional analysis as well as adaptive pushover analysis, with proven capabilities in seismic evaluation of buildings and bridges, have been studied. The non-linear incremental dynamic analysis (IDA) method has been used to examine and compare the results of pushover analyses. To conduct IDA, the time history of 20 far-field earthquake records was used and the 50% fractile values of the demand given the ground motion intensity were computed. After analysis, the base shear vs displacement at the top of the piers were drawn. Obtained graphs represented the ability of a cyclic pushover analysis to estimate seismic capacity of the concrete piers of curved bridges. Based on results, the cyclic pushover method with ISO loading protocol provided better results for evaluating the seismic investigation of concrete piers of curved bridges in plan.

• International journal of steel structures
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• v.18 no.4
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• pp.1210-1218
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• 2018

A new type of earthquake-resisting element that consists of a steel plate shear wall with slits is introduced. The infill steel plate is divided into a series of vertical flexural links with vertical links. The steel plate shear walls absorb energy by means of in-plane bending deformation of the flexural links and the energy dissipation capacity of the plastic hinges formed at both ends of the flexural links when under lateral loads. In this paper, finite element analysis and experimental studies at low cyclic loadings were conducted on specimens with steel plate shear walls with multilayer slits. The effects caused by varied slit pattern in terms of slit design parameters on lateral stiffness, ultimate bearing capacity and hysteretic behavior of the shear walls were analyzed. Results showed that the failure mode of steel plate shear walls with a single-layer slit was more likely to be out-of-plane buckling of the flexural links. As a result, the lateral stiffness and the ultimate bearing capacity were relatively lower when the precondition of the total height of the vertical slits remained the same. Differently, the failure mode of steel plate shear walls with multilayer slits was prone to global buckling of the infill steel plates; more obvious tensile fields provided evidence to the fact of higher lateral stiffness and excellent ultimate bearing capacity. It was also concluded that multilayer specimens exhibited better energy dissipation capacity compared with single-layer plate shear walls.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.33 no.6
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• pp.427-435
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• 2020

Modular structures are relatively lightweight compared to reinforced-concrete or steel structures. However, it is difficult to achieve structural integrity between the columns of unit modules in a modular structure, which causes undesirable effects on the lateral force resistance capacity against wind and earthquake loads. This is more prominent in modular structures whose overall heights are greater. Hence, a post-tensioned modular structural system is proposed herein to improve the lateral force resistance capacity of a typical modular structure. A post-tensioned column-base connection, which is the main component of the proposed modular structural system, is configured with shapes and characteristics that allow inducing self-centering behaviors. Finite element analysis was then performed to investigate the hysteretic behaviors of the post-tensioned column-base connection. The analysis results show that the hysteretic behaviors are significantly affected by the initial tension forces and beam-column connection details at the base.

• Structural Engineering and Mechanics
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• v.77 no.1
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• pp.115-135
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• 2021

This paper focuses on examining the effects of span arrangements on displacement responses of plan-symmetric RC frame buildings designed using the direct displacement-based design (DDBD) method by employing non-linear analyses and the skew seismic attack. In order to show the desired performance of DDBD design approach, the force-based design approach is also used to examine the seismic performance of the selected structures. To realize this objective, 8-story buildings with different plans are selected. In addition, the dynamic behavior of the structures is evaluated by selecting 3, 7, and 12-story buildings. In order to perform non-linear analyses, OpenSees software is used for modeling buildings. Results of an experimental model are used to validate the analytical model implemented in OpenSees. The results of non-linear static and non-linear dynamic analyses indicate that changing span arrangements does not affect estimating the responses of structures designed using the DDBD approach, and the results are more or less the same. Next, in order to apply the earthquake in non-principle directions, DDBD structures, designed for one-way performance, are designed again for two-way performance. Time history analyses are performed under a set of artificial acceleration pairs, applied to structures at different angles. It is found that the mean maximum responses of earthquakes at all angles have very good agreement with the design-acceptable limits, while the response of buildings along the height direction has a relatively acceptable and uniform distribution. Meanwhile, changes in the span arrangements did not have a significant effect on displacement responses.

• Journal of the Korean Geotechnical Society
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• v.38 no.1
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• pp.17-33
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• 2022

This study describes the effect of ground water table on the dynamic analysis of single piles subjected to earthquake loading. The dynamic numerical analysis was performed for different dry and saturated soils with varying the relative densities of surrounding weathered soils (SM). The test soil was a weathered soil encountered in the engineering field and bender element tests were conducted to estimate the dynamic properties of test soil. The Mohr-Coulomb model and Finn model were used for soil, dry and saturated conditions, respectively. These models validated with results of centrifuge tests. When compared with the results from the soil conditions, saturated cases showed more lateral displacement and bending moment of piles than dry cases, and this difference caused from the generation of excess porewater pressure. It means that the kinematic effect of the soil decreased as the excess pore water pressure was generated, and it was changed to the inertial behavior of the pile.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.6
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• pp.385-392
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• 2021

Interest in the seismic performance of nuclear facilities under strong earthquakes has increased because their nonlinear response is important. In this paper, we proposed appropriate parameters for the nonlinear finite element analysis of a concrete material model, for a reinforced concrete (RC) shear wall in nuclear facilities: maximum tensile strength, dilation angle, and damage parameter. The study of the effects of the important parameters, on the nonlinear behavior and shear failure mode of the RC shear wall having low aspect ratio, was conducted using ABAQUS finite element analysis program. Based on the study results the nonlinear response of a nuclear reactor containment building (RCB) subjected to a strong earthquake was evaluated using nonlinear time-history analysis.

• Earthquakes and Structures
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• v.23 no.1
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• pp.35-57
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• 2022

This article presents a computationally efficient framework for multi-objective seismic design optimization of steel moment-resisting frame (MRF) structures based on the nonlinear dynamic analysis procedure. This framework employs the uniform damage distribution philosophy to minimize the weight (initial cost) of the structure at different levels of damage. The preliminary framework was recently proposed by the authors based on the single excitation and the nonlinear static (pushover) analysis procedure, in which the effects of record-to-record variability as well as higher-order vibration modes were neglected. The present study investigates the reliability of the previous framework by extending the proposed algorithm using the nonlinear dynamic design procedure (optimization under multiple ground motions). Three benchmark structures, including 4-, 8-, and 12-story steel MRFs, representing the behavior of low-, mid-, and high-rise buildings, are utilized to evaluate the proposed framework. The total weight of the structure and the maximum inter-story drift ratio (IDRmax) resulting from the average response of the structure to a set of seven ground motion records are considered as two conflicting objectives for the optimization problem and are simultaneously minimized. The results of this study indicate that the optimization under several ground motions leads to almost similar outcomes in terms of optimization objectives to those are obtained from optimization under pushover analysis. However, investigation of optimal designs under a suite of 22 earthquake records reveals that the damage distribution in buildings designed by the nonlinear dynamic-based procedure is closer to the uniform distribution (desired target during the optimization process) compared to those designed according to the pushover procedure.