• Structural Engineering and Mechanics
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• 제58권2호
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• pp.259-276
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• 2016

Lead-rubber bearings (LRBs) have been used worldwide in seismic design of buildings and bridges owing to their stable mechanical properties and good isolation effect. We have investigated the effectiveness of LRBs in framed underground structures on controlling structural seismic responses. Nonlinear dynamic time history analyses were carried out on the well-documented Daikai Station, which collapsed during the 1995 Hyogoken-Nanbu earthquake. Influences of strength ratio (ratio of yield strength of LRBs to yield strength of central column) and shear modulus of rubber on structural seismic responses were studied. As a displacement-based passive energy dissipation device, LRBs reduce dynamic internal forces of framed underground structures and improve their seismic performance. An optimal range of strength ratios was proposed for the case presented. Within this range, LRBs can dissipate maximum input earthquake energy. The maximum shear and moment of the central column can achieve more than 50% reduction, whereas the maximum shear displacement of LRBs is acceptable.

• Smart Structures and Systems
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• 제33권3호
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• pp.227-241
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• 2024

Safety and structural integrity of civil structures, like bridges and buildings, can be substantially enhanced by employing appropriate structural health monitoring (SHM) techniques for timely diagnosis of incipient damages. The information gathered from health monitoring of important infrastructure helps in making informed decisions on their maintenance. This ensures smooth, uninterrupted operation of the civil infrastructure and also cuts down the overall maintenance cost. With an early warning system, SHM can protect human life during major structural failures. A real-time online damage localization technique is proposed using only the vibration measurements in this paper. The concept of the 'Degree of Scatter' (DoS) of the vibration measurements is used to generate a spatial profile, and fractal dimension theory is used for damage detection and localization in the proposed two-phase algorithm. Further, it ensures robustness against environmental and operational variability (EoV). The proposed method works only with output-only responses and does not require correlated finite element models. Investigations are carried out to test the presented algorithm, using the synthetic data generated from a simply supported beam, a 25-storey shear building model, and also experimental data obtained from the lab-level experiments on a steel I-beam and a ten-storey framed structure. The investigations suggest that the proposed damage localization algorithm is capable of isolating the influence of the confounding factors associated with EoV while detecting and localizing damage even with noisy measurements.

• Interaction and multiscale mechanics
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• 제3권2호
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• pp.192-211
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• 2010

In most framed structures the nonlinearities and the damages are localized, extending over a limited length of the structural member. In order to capture the details of the local damage, the segments of a member that have entered the nonlinear range may need to be analyzed using the three-dimensional element (3D) model whereas the rest of the member can be analyzed using the simpler one-dimensional (1D) element model with fewer degrees of freedom. An Element-Coupling model was proposed to couple the small scale solid 3D elements with the large scale 1D beam elements. The mixed dimensional coupling is performed imposing the kinematic coupling hypothesis of the 1D model on the interfaces of the 3D model. The analysis results are compared with test results of a reinforced concrete pipe column and a structure consisting of reinforced concrete columns and a steel space truss subjected to static and dynamic loading. This structure is a reduced scale model of a direct air-cooled condenser support platform built in a thermal power plant. The reduction scale for the column as well as for the structure was 1:8. The same structures are also analyzed using 3D solid elements for the entire structure to demonstrate the validity of the Element-Coupling model. A comparison of the accuracy and the computational effort indicates that by the proposed Element-Coupling method the accuracy is almost the same but the computational effort is significantly reduced.

• Steel and Composite Structures
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• 제23권1호
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• pp.53-66
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• 2017

Structures submitted to Fire-After-Earthquake loading situations, are first experiencing inelastic deformations due to the seismic action and are then submitted to the thermal loading. This means that in the case of steel framed structures, at the starting point of the fire, plastic hinges have already been formed at the ends of the beams. The basic objective of this paper is the evaluation of the rotational capacity of steel I-section beams damaged due to prior earthquake loading, at increased temperatures. The study is conducted numerically and three-dimensional models are used in order to capture accurately the nonlinear behaviour of the steel beams. Different levels of earthquake-induced damage are examined in order to study the effect of the initial state of damage to the temperature-evolution of the rotational capacity. The study starts with the reference case where the beam is undamaged and in the sequel cyclic loading patterns are taken into account, which represent earthquakes loads of increasing magnitude. Additionally, the study extends to the evaluation of the ultimate plastic rotation of the steel beams which corresponds to the point where the rotational capacity of the beam is exhausted. The aforementioned value of rotation can be used as a criterion for the determination of the fire-resistance time of the structure in case of Fire-After-Earthquake situations.

• Earthquakes and Structures
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• 제17권2호
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• pp.221-232
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• 2019

Material non-linearity of Reinforced Concrete (RC) framed structures is studied by modelling concrete using the Concrete Damage Plasticity (CDP) theory. The stress-strain data of concrete in compression is modelled using the Hsu model. The structures are analyzed using a finite element approach by modelling them in ABAQUS / CAE. Single bay single storey RC frames, designed according to Indian Standard (IS):456:2000 and IS:13920:2016 are considered for assessing their maximum load carrying capacity and failure behavior under the influence of gravity loads and lateral loads. It is found that the CDP model is effective in predicting the failure behaviors of RC frame structures. Under the influence of the lateral load, the structure designed according to IS:13920 had a higher load carrying capacity when compared with the structure designed according to IS:456. Ultra High Performance Fiber Reinforced Concrete (UHPFRC) strip is used for strengthening the columns and beam column joints of the RC frame individually against lateral loads. 10mm and 20mm thick strips are adopted for the numerical simulation of RC column and beam-column joint. Results obtained from the study indicated that UHPFRC with two different thickness strips acts as a very good strengthening material in increasing the load carrying capacity of columns and beam-column joint by more than 5%. UHPFRC also improved the performance of the RC frames against lateral loads with an increase of more than 3.5% with the two different strips adopted. 20 mm thick strip is found to be an ideal size to enhance the load carrying capacity of the columns and beam-column joints. Among the strengthening locations adopted in the study, column strengthening is found to be more efficient when compared with the beam column joint strengthening.

• 헤리티지:역사와 과학
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• 제47권1호
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• pp.134-151
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• 2014

본 논문은 전라남도 나주시 대호동 심향사의 극락전 내에 안치되어 있는 협저아미타불상의 구조 및 제작기법에 관해 고찰한 것이다. 연구방법으로는 X-ray 투과촬영 데이터와 2차례에 걸친 현장조사결과를 종합하여 검토하였으며, 파손된 부분에서 박락된 시료를 분석하여 바탕층의 구조와 재료에 대해 살펴보았다. 조사 결과, 심향사상은 심목을 상 내부에 짜 넣지 않은 완전히 텅 빈 상태의 협저불상이며, 외부 옷주름의 요철(凹凸)과 동일한 옷주름이 내부에도 뚜렷하게 나타나 있기 때문에 원형(原型)이 되는 소조상(塑造像)을 조성하는 단계에서 거의 완전한 형태로 만들어 협저층을 올린 것을 알 수 있었다. 또한 원형의 흙과 심목(心木)을 제거하기 위해 정수리에서 뒷목까지 사선으로 절개하였으며, 다른 부분에서는 절개선이 확인되지 않는다. 머리를 절개한 부분에는 꿰맨 흔적이 없고 접착제(칠(漆) 혹은 호칠(糊漆))를 사용하여 접착한 것이 관찰되었다. 눈의 검은자위 부분에 구슬을 감입하였고, 양쪽 귀와 손, 치마(裙)의 띠와 매듭은 나무로 제작하였다. 이러한 특징은 고려후기 제작으로 알려진 선국사 협저불좌상이나 동경 오쿠라집고관 협저보살좌상, 그리고 조선초기 작품인 죽림사 협저아미타불좌상, 불회사 협저비로자나불좌상, 실상사 협저아미타불좌상 및 협저보살입상 등에서도 동일하게 나타나고 있다. 바탕층 분석결과에 의해 회칠층(灰漆層)과 주칠층(朱漆層)은 제작 당시의 층으로 판단되었다. 특히 회칠층에 사용되어진 골분은 고려시대 나전칠기의 제작뿐만 아니라 불상의 회칠층에도 이용되었음을 밝힐 수 있었으며, 불상에 금박을 붙이기 위한 바탕층에는 주칠을 올렸던 것을 알 수 있었다. 또 근대에 들어서만도 두 차례 이상의 개금불사가 행해졌던 것이 관찰되었으며, 여러 차례의 개금불사가 있었음에도 불구하고 제작 당시의 층은 훼손되지 않고 잘 보존되어 있음이 밝혀졌다.