• Computers and Concrete
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• 제21권3호
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• pp.269-278
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• 2018

In this paper, two methods M1 and M2 to determine long-term deflection through finite element analyses including the effect of creep and relaxation are proposed and demonstrated for a PSC box-girder. In both the methods, the effect of creep is accounted by different models from international standards viz., ACI-209R-92, CEB MC 90-99, B3 and GL2000. In M1, prestress losses due to creep and relaxation and age adjusted effective modulus are estimated through different models and have been used in finite element (FE) analyses for individual time steps. In M2, effects of creep and relaxation are implemented through the features of FE program and the time dependent analyses are carried out in single step. Variations in time-dependent strains, prestress losses, stresses and deflections of the PSC box-girder bridge through M1 and M2 are studied. For the PSC girder camber obtained from both M1 and M2 are lesser than simple bending theory based calculations, this shows that the camber is overestimated by simple bending theory which may lead to non-conservative design. It is also observed that stresses obtained from FEM for bottom fibre are lesser than the stresses obtained from bending theory at transfer for the PSC girder which may lead to non-conservative estimates.

• Smart Structures and Systems
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• 제16권4호
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• pp.725-742
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• 2015

Tuned mass dampers (TMD) are devices employed in vibration control since the beginning of the twentieth century. However, their implementation for controlling the seismic response in civil structures is more recent. While the efficiency of TMD on structures under far-field earthquakes has been demonstrated, the convenience of its employment against near-fault earthquakes is still under discussion. In this context, the study of this type of device is raised, not as an alternative to the seismic isolation, which is clearly a better choice for new buildings, but rather as an improvement in the structural safety of existing buildings. Seismic records with an impulsive character have been registered in the vicinity of faults that cause seismic events. In this paper, the ability of TMD to control the response of structures that experience inelastic deformations and eventually reach collapse subject to the action of such earthquakes is studied. The results of a series of nonlinear dynamic analyses are presented. These analyses are performed on a numerical model of a structure under the action of near-fault earthquakes. The structure analyzed in this study is a steel frame which behaves as a single degree of freedom (SDOF) system. TMD with different mass values are added on the numerical model of the structure, and the TMD performance is evaluated by comparing the response of the structure with and without the control device.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.813-820
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• 2005

In this study, finite element modeling and structural vibration analyses of a gyrocopter have been conducted considering dynamic hub-loads due to rotating blades. For this research, 3D CATIA models for most mechanical parts are exactly prepared and assembled into the final aircraft configuration. Then the dynamic finite element model including several non-structural parts are constructed based on the exact 3D CAD data. Computational structural dynamics technique based on finite element method is applied using both MSC/NASTRAN and developed in-house code which can largely reduce the pre and postprocessing time of general transient dynamic analyses. Modal based transient and frequency response analyses are used to efficiently investigate vibration characteristics. The results include natural frequency comparison for different fuel and pilot conditions, fundamental natural mode shapes, frequency responses and transient acceleration responses of the present gyrocopter model.

• Earthquakes and Structures
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• 제6권4호
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• pp.335-350
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• 2014

Historical masonry mosques are the most important structures of Islamic societies. To estimate the static and dynamic behavior of these historical structures, an examination of their restoration studies is very important. In this study, Kara Mustafa Pasha Mosque, which was built as a domed mosque by Kara Mustafa Pasha between 1666-1667 in Amasya, Turkey, has been analyzed. This study investigates the structural behavior and architectural features of the mosque. In order to determine specific mechanical properties, compression and three-point bending tests were conducted on materials, which have similar age and show similar properties as the examined mosque. Additionally, a three-dimensional finite element model of the mosque was developed and the structural responses were investigated through static and dynamic analyses. The results of the analyses were focused on the stresses and displacements. The experimental test results indicate that the construction materials have greatly retained their mechanical properties over the centuries. The obtained maximum compression and tensile stresses from the analyses have been determined as smaller than the materials' strengths. However, the stresses calculated from dynamic analysis might cause structural problems in terms of tensile stresses.

• 항공우주기술
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• 제9권1호
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• pp.9-16
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• 2010

본 연구에서는 이전에 구조시험[3]을 실시하였던 압축하중을 받는 샌드위치 패널 시편에 대한 구조 해석을 수행하였다. 구조 해석을 위해 세 가지 방식의 유한요소 모델링을 고려하였으며, 각각의 유한요소 모델을 이용해 선형좌굴해석과 비선형해석을 수행하였다. 이를 통해, 복합재 샌드위치 패널의 압축 좌굴 하중의 정확한 예측을 위해서는 면재는 쉘요소로 심재는 솔리드 요소로 모델링하는 것이 적절함을 확인하였다. 이것은 전체 샌드위치를 쉘요소로 하는 경우, 심재의 국부적인 crushing 효과와 심재의 전단 강성의 영향을 고려할 수 없기 때문이다. 만일 샌드위치 패널이 좌굴 하중 보다 면재의 재료 파손이 더 취약한 경우, 면재의 재료 파손 하중 및 파손 위치의 정확한 예측을 위해서는 샌드위치를 두께 방향으로 한 개의 쉘 요소로 모델링 하는 것이 적절하였다.

• Earthquakes and Structures
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• 제18권6호
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• pp.709-718
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• 2020

Fragility curves are useful tools to estimate the damage probability of buildings owing to seismic actions. The purpose of this study is to investigate seismic vulnerability of reinforced concrete (RC) buildings, according to the 2007 and 2018 Turkish Seismic Codes, using fragility curves. For the numerical analyses, typical five- and seven-storey RC buildings were selected and incremental dynamic analyses (IDA) were performed. To complete the IDAs, eleven earthquake acceleration records multiplied by various scaling factors from 0.2g to 0.8g were used. To predict nonlinearity, a distributed hinge model that involves material and geometric nonlinearity of the structural members was used. Damages to confined concrete and reinforcement bar of structural members were obtained by considering the unit deformation demands of the 2007 Turkish Seismic Code (TSC-2007) and the 2018 Turkey Building Earthquake Code (TBEC-2018). Vulnerability evaluation of these buildings was performed using fragility curves based on the results of incremental dynamic analyses. Fragility curves were generated in terms of damage levels occurring in confined concrete and reinforcement bar of structural members with a lognormal distribution assumption. The fragility curves show that the probability of damage occurring is more according to TBEC-2018 than according to TSC-2007 for selected buildings.

• Structural Engineering and Mechanics
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• 제85권4호
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• pp.511-529
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• 2023

This paper aims to better understand the bonding behavior in Reinforced Concrete beams strengthened with an Ultra-High Performance Fiber Reinforced Concrete (RCUHPFRC) layer on the compression side using experimental tests and numerical analyses. The UHPFRC mix design was obtained through an optimization procedure, and the characterization of the materials included compression and slant shear tests. Flexural tests were carried out in RC beams and RC-UHPFRC beams. The tests demonstrated a debonding of the UHPFRC layer. In addition, 3D finite element analyses were carried out in the Abaqus CAE program, in which the interface is modeled considering a zero-thickness cohesive-contact approach. The cohesive parameters are investigated, aiming to calibrate the numerical models, and a sensitivity analysis is performed to check the reliability of the assumed cohesive parameters and the mesh size. Finally, the experimental and numerical values are compared, showing a good approximation for both the RC beams and the RC strengthened beams.

• Structural Engineering and Mechanics
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• 제45권6호
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• pp.803-819
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• 2013

This paper addresses two main issues relevant to the structural assessment of buildings subjected to explosions. The first issue regards the robustness evaluation of steel frame structures: a procedure is provided for computing "robustness curves" and it is applied to a 20-storey steel frame building, describing the residual strength of the (blast) damaged structure under different local damage levels. The second issue regards the precise evaluation of blast pressures acting on structural elements using Computational Fluid Dynamic (CFD) techniques. This last aspect is treated with particular reference to gas explosions, focusing on some critical parameters (room congestion, failure of non-structural walls and ignition point location) which influence the development of the explosion. From the analyses, it can be deduced that, at least for the examined cases, the obtained robustness curves provide a suitable tool that can be used for risk management and assessment purposes. Moreover, the variation of relevant CFD analysis outcomes (e.g., pressure) due to the variation of the analysis parameters is found to be significant.

• Structural Engineering and Mechanics
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• 제77권2호
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• pp.197-215
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• 2021

Under a severe environment of multiple hazards such as earthquakes and winds, the life-cycle performance of engineering structures may inevitably be deteriorated due to the fatigue effect caused by long-term exposure to wind loads, which would further increase the structural vulnerability to earthquakes. This paper presents a framework for evaluating the lifetime structural seismic performance under the effect of wind-induced fatigue considering different sources of uncertainties. The seismic behavior of a high-rise steel-concrete composite frame with buckling-restrained braces (FBRB) during its service life is systematically investigated using the proposed approach. Recorded field data for the wind hazard of Fuzhou, Fujian Province of China from Jan. 1, 1980 to Mar. 31, 2019 is collected, based on which the distribution of wind velocity is constructed by the Gumbel model after comparisons. The OpenSees platform is employed to establish the numerical model of the FBRB and conduct subsequent numerical computations. Allowed for the uncertainties caused by the wind generation and structural modeling, the final annual fatigue damage takes the average of 50 groups of simulations. The lifetime structural performance assessments, including static pushover analyses, nonlinear dynamic time history analyses and fragility analyses, are conducted on the time-dependent finite element (FE) models which are modified in lines with the material deterioration models. The results indicate that the structural performance tends to degrade over time under the effect of fatigue, while the influencing degree of fatigue varies with the duration time of fatigue process and seismic intensity. The impact of wind-induced fatigue on structural responses and fragilities are explicitly quantified and discussed in details.

• Steel and Composite Structures
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• 제2권2호
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• pp.113-128
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• 2002

The performance of steel MRF with rigid connections, proportioned by adopting different capacity design criteria, is evaluated in order to highlight the effectiveness of static non-linear procedure in predicting the structural seismic behavior. In the framework of the performance-based design, some considerations are made on the basis of the results obtained by both dynamic time histories and push-over analyses, particularly with reference to the damage level and the structure ability to withstand a strong earthquake.