• Geomechanics and Engineering
• /
• 제14권2호
• /
• pp.161-174
• /
• 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
• /
• 제16권1호
• /
• pp.163-181
• /
• 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.

• 토지주택연구
• /
• 제12권3호
• /
• pp.97-108
• /
• 2021

교대구조물에서는 교대 배면의 성토체 축조로 인한 수평방향응력의 증가로 인한 측방유동문제 및 구조물에 작용하는 온도하중 등의 영향으로 인해 접속슬래브, 거더, 베어링등의 파손이 빈번히 발생되고 있는 실정이다. 이에 대한 대책공법으로 보강토 일체형 교대(GRS (Geosynthetic-Reinforced Soil) integral bridge)가 제안되었다. 보강토 일체형 교대는 GRS 보강토 옹벽과 일체형 교대의 구조형식을 혼합한 형태의 구조물이다. 본 연구에서는 기존 PSC 거더교, 기존 보강토 일체형 교대 및 브라켓형 보강토 일체형 교대(새롭게 개발된 LH형 GRS 보강토 교대)의 시공순서와 지진하중조건을 고려하여 수치해석을 실시하였다. 그 결과 브라켓형 보강토 일체형 교대가 다른 구조물에 비해 응력집중과 교대·뒷채움간 부등침하 영향에 의한 기초지반의 변형에 대해 가장 유리한 것으로 파악되었다. 더 나아가 GRS 보강토 일체형 교대(브라켓형 포함) 구조물은 내진안정성에서도 가장 안정한 것으로 파악되었다.

• Computers and Concrete
• /
• 제23권1호
• /
• pp.1-10
• /
• 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.

• 국제강구조저널
• /
• 제18권4호
• /
• pp.1210-1218
• /
• 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.

• 한국전산구조공학회논문집
• /
• 제33권6호
• /
• pp.427-435
• /
• 2020

모듈러 건축물은 철근콘크리트 및 철골 구조물에 비하여 상대적으로 경량이고, 단위 모듈간 기둥의 일체성을 기대하기 어려운 구조적 특성을 가진다. 이와 같은 구조적 특성은 모듈러 건축물의 높이가 높아짐에 따라 바람 및 지진과 같은 횡력저항성능에 직접적인 영향을 미친다. 본 연구에서는 횡력저항성능을 향상시키기 위해 긴장재를 활용한 모듈러 구조시스템을 제안하였다. 모듈러 구조시스템을 구성하는 주요 요소인 포스트텐션 기둥-바닥 접합부는 셀프 센터링 거동을 유도하기 위한 형상 및 상세를 가진다. 포스트텐션 기둥-바닥 접합부의 이력 거동을 상세히 파악하기 위해 유한요소해석을 수행하였으며, 그 결과 초기 긴장력 및 보-기둥 접합부의 접합 조건에 따라 이력 거동은 확연한 차이를 보이는 것으로 나타났다.

• Structural Engineering and Mechanics
• /
• 제77권1호
• /
• pp.115-135
• /
• 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.

• 한국지반공학회논문집
• /
• 제38권1호
• /
• pp.17-33
• /
• 2022

본 연구는 지하수 유무에 따른 지진시 풍화지반에 근입된 단말뚝의 동적 거동을 분석하기 위해 수치해석을 수행하였다. 3차원 유한차분해석 프로그램을 사용하여 지하수 및 지반 조건에 따라 동적 수치해석을 수행하였으며, 풍화지반의 물성은 현장에서 채취한 흙의 물성시험을 통해 해석에 적용하였다. 건조한 지반 및 포화된 지반은 Mohr-Coulomb, Finn model을 각각 적용하여 모델링하였고, 각각의 모델링은 원심모형실험 결과와 검증을 수행하였다. 해석결과, 전반적으로 지하수위가 존재하는 경우가 건조한 경우보다 더 큰 말뚝의 수평변형을 나타냈으며, 깊은 심도에서부터 그 차이가 크게 발생하는 것으로 확인되었다. 이는 포화지반에 지진이 발생하게 되면 과잉간극수압의 발생으로 인해 지반 구속압이 감소하게 되는 현상에 지배되는 것으로 확인되었다. 또한, 지반에 근입된 말뚝의 영향으로 인근 지반에서의 전단변형률이 작게 발생하고, 과잉간극수압은 말뚝과 멀리 떨어진 지반에 비해 작게 증가하는 경향을 보였다.

• 한국전산구조공학회논문집
• /
• 제34권6호
• /
• pp.385-392
• /
• 2021

강진 시 원자력발전시설의 비선형 응답이 중요하기 때문에 이 시설의 내진성능에 대한 관심이 증가하였다. 이 연구에서는 원자력 발전소 철근콘크리트 전단벽의 유한요소해석을 위한 재료모델의 적절한 변수를 제시하였다: 최대인장강도, 팽창각, 손상계수. 이를 위해 상용 유한요소 해석프로그램인 ABAQUS를 사용하여 낮은 형상비를 가진 철근콘크리트 전단벽의 비선형 거동과 전단 파괴모드에 대한 이 주요 변수의 효과에 대한 연구를 수행하였다. 연구결과에 기반하여 비선형 시간이력해석을 통해 강진 하의 원자로건물의 비선형 응답을 평가하였다.

• Earthquakes and Structures
• /
• 제23권1호
• /
• pp.35-57
• /
• 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.