• Earthquakes and Structures
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• 제9권4호
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• pp.789-830
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• 2015

The recent re-assessment of the seismic hazard in Europe led for many regions of low to moderate seismicity to an increase in the seismic demand. As a consequence, several modern unreinforced masonry (URM) buildings, constructed with reinforced concrete (RC) slabs that provide an efficient rigid diaphragm action, no longer satisfy the seismic design check and have been retrofitted by adding or replacing URM walls with RC walls. Of late, also several new construction projects have been conceived directly as buildings with both RC and URM walls. Despite the widespread use of such construction technique, very little is known about the seismic behaviour of mixed RC-URM wall structures and codes do not provide adequate support to designers. The aim of the paper is therefore to propose a displacement-based design methodology for the design of mixed RC-URM edifices and the retrofit of URM buildings by replacing or adding selected URM walls with RC ones. The article describes also two tools developed for estimating important quantities relevant for the displacement-based design of structures with both RC and URM walls. The tools are (i) a mechanical model based on the shear-flexure interaction between URM and RC walls and (ii) an elastic model for estimating the contribution of the RC slabs to the overturning moment capacity of the system. In the last part of the article the proposed design method is verified through nonlinear dynamic analyses of several case studies. These results show that the proposed design approach has the ability of controlling the displacement profile of the designed structures, avoiding concentration of deformations in one single storey, a typical feature of URM wall structures.

• 한국전산구조공학회논문집
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• 제24권5호
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• pp.473-480
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• 2011

반복적인 구조해석의 실행없이 부재 변위 기여도를 이용하여 부재 사이즈를 조절함으로써 건물의 변위를 만족시키는 재분배 기법은 실용적인 변위 설계법으로 인식되고 있다. 기존 연구에서 재분배 기법은 풍하중, 지진하중과 같은 횡하중을 받는 건물의 횡변위를 탄성범위 내에서는 효과적으로 제어할 수 있었으나, 재분배 기법에 따른 비탄성 성능 변화에 대한 연구는 미흡하였다. 본 연구에서는 재분배 기법에 의해 재설계된 구조물의 비탄성 성능변화를 확인하기 위해 7층 철근 콘크리트 전단벽-골조 시스템 예제에 재분배 기법을 적용하였다. 재분배 적용결과, 전단벽-골조 시스템의 상호작용 특성때문에 하층부에서는 전단벽의 물량이 증가하고 상층부에서는 골조의 물량이 증가하였다. 이러한 물량 재분배를 통해 초기 강성은 증가하였으며 연성 성능은 비슷한 수준으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제15권3호
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• pp.106-115
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• 2011

본 연구에서는 비선형 지진응답해석을 이용하여 유도된 전단 및 휨파괴형 부재가 혼합된 저층 철근콘크리트(RC) 건물의 비선형 요구내력스펙트럼을 수식화하여, 특정 연성률 별로 지진입력수준과 내진성능잔존률을 산정하여, 건물의 지진손상정도를 정량적으로 평가 가능한 새로운 내진성능 평가법을 제안하였다. 또한 저층 RC 건물을 대상으로 본 연구의 내진성능 평가법을 적용하여 평가한 결과와 보다 정밀한 부재수준의 비선형 동적해석을 실시하여 그 결과를 각각 비교 검토함과 동시에, 내진진단기준에서 입력지진동 0.2g 수준에 대해서 구조체에 대규모이상의 지진피해를 막기 위한 임계값으로 설정한 내진성능판정지표값 (Es=0.6)과의 상관관계를 분석하여 본 연구에서 제안한 내진성능 평가법의 타당성 및 그 적용가능성을 검증하였다. 본 평가법은 비선형해석 또는 능력스펙트럼법 등의 상세 내진성능 평가법을 수행하지 않고도 대상건물에 대한 연성률 단계별의 입력지진 수준, 지진손상도를 정량적으로 평가할 수 있다. 향후 전단 및 휨파괴형 부재가 혼합된 저층 RC 건물의 내진성능을 효과적으로 평가하기 위한 자료로서 활용이 가능하다고 판단된다.

• Earthquakes and Structures
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• 제7권2호
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• pp.141-157
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• 2014

The Conditional Mean Spectrum represents a powerful link between the seismic hazard information and the selection of strong ground motion records at a particular site. The scope of the paper is to apply for the city of Bucharest for the first time the method to obtain the Conditional Mean Spectrum (CMS) presented by Baker (2011) and to select, on the basis of the CMS, a suite of strong ground motions for performing elastic and inelastic dynamic analyses of buildings and structures with fundamental periods of vibration in the vicinity of 1.0 s. The major seismic hazard for Bucharest and for most of Southern and Eastern Romania is dominated by the Vrancea subcrustal seismic source. The ground motion prediction equation developed for subduction-type earthquakes and soil conditions by Youngs et al. (1997) is used for the computation of the Uniform Hazard Spectrum (UHS) and the CMS. The disaggregation of seismic hazard is then performed in order to determine the mean causal values of magnitude and source-to-site distance for a particular spectral ordinate (for a spectral period T = 1.0 s in this study). The spectral period of 1.0 s is considered to be representative for the new stock of residential and office reinforced concrete (RC) buildings in Bucharest. The differences between the Uniform Hazard Spectrum (UHS) and the Conditional Mean Spectrum (CMS) are discussed taking into account the scarcity of ground motions recorded in the region of Bucharest and the frequency content characteristics of the recorded data. Moreover, a record selection based on the criteria proposed by Baker and Cornell (2006) and Baker (2011) is performed using a dataset consisting of strong ground motions recorded during seven Vrancea seismic events.

• Structural Engineering and Mechanics
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• 제63권4호
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• pp.429-438
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• 2017

Structural design has an imperative role in deciding the failure possibility of a Reinforced Concrete (RC) structure. Recent research works achieved the goal of predicting the structural failure of the RC structure with the assistance of machine learning techniques. Previously, the Artificial Neural Network (ANN) has been trained supported by Particle Swarm Optimization (PSO) to classify RC structures with reasonable accuracy. Though, keeping in mind the sensitivity in predicting the structural failure, more accurate models are still absent in the context of Machine Learning. Since the efficiency of multi-objective optimization over single objective optimization techniques is well established. Thus, the motivation of the current work is to employ a Multi-objective Genetic Algorithm (MOGA) to train the Neural Network (NN) based model. In the present work, the NN has been trained with MOGA to minimize the Root Mean Squared Error (RMSE) and Maximum Error (ME) toward optimizing the weight vector of the NN. The model has been tested by using a dataset consisting of 150 RC structure buildings. The proposed NN-MOGA based model has been compared with Multi-layer perceptron-feed-forward network (MLP-FFN) and NN-PSO based models in terms of several performance metrics. Experimental results suggested that the NN-MOGA has outperformed other existing well known classifiers with a reasonable improvement over them. Meanwhile, the proposed NN-MOGA achieved the superior accuracy of 93.33% and F-measure of 94.44%, which is superior to the other classifiers in the present study.

• Structural Engineering and Mechanics
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• 제20권5호
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• pp.505-526
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• 2005

The influence of the inter-story structural pounding on the seismic behaviour of adjacent multistory reinforced concrete structures with unequal total heights and different story heights is investigated. Although inter-story pounding is a common case in practice, it has not been studied before in the literature as far as the authors are aware. Fifty two pounding cases, each one for two different seismic excitations, are examined. From the results it can be deduced that: (i) The most important issue in the inter-story pounding is the local effect on the external column of the tall building that suffers the impact from the upper floor slab of the adjacent shorter structure. (ii) The ductility demands for this column are increased comparing with the ones without the pounding effect. In the cases that the two buildings are in contact these demands appear to be critical since they are higher than the available ductility values. In the cases that there is a small distance between the interacting buildings the ductility demands of this column are also higher than the ones of the same column without the pounding effect but they appear to be lower than the available ductility values. (iii) It has to be stressed that in all the examined cases the developed shear forces of this column exceeded the shear strength. Thus, it can be concluded that in inter-story pounding cases the column that suffers the impact is always in a critical condition due to shear action and, furthermore, in the cases that the two structures are in contact from the beginning this column appears to be critical due to high ductility demands as well. The consequences of the impact can be very severe for the integrity of the column and may be a primary cause for the initiation of the collapse of the structure. This means that special measures have to be taken in the design process first for the critically increased shear demands and secondly for the high ductility demands.

• 콘크리트학회논문집
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• 제22권1호
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• pp.3-10
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• 2010

이 연구에서는 중력 전단비에 따른 철근콘크리트 플랫 플레이트 골조의 내진성능을 평가하였다. 이를 위하여, 이 연구에서는 3층, 7층 골조를 중력하중만 고려하여 설계하고, 대상 건물에 대한 비선형 정적 푸쉬 오버 해석과 비선형 동적 해석을 수행하였다. 그리고 이 연구는 그 비선형 해석에서 중력 전단비의 차이에 따른 뚫림 전단과 파괴 메커니즘을 예측할 수 있도록 제안한 슬래브-기둥 접합부 모델을 사용하였다. 이 연구 결과에 따르면 중력 전단비가 골조의 내진성능에 큰 영향을 미치는 것으로 나타났다. 특히 중력 전단비가 커짐에 따라 골조 접합부의 파괴가 취성적인 파괴를 나타내어 내진 성능이 떨어지는 것으로 나타났다.

• 국제초고층학회논문집
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• 제5권1호
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• pp.43-50
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• 2016

The reinforced-concrete multi-story shear-wall structure, which can free a building from beams and columns to allow the planning of a vast room, has increasingly been used in Japan as a high-rise reinforced-concrete structure. Since this structural system concentrates the seismic force onto multi-story shear walls inside, the bending deformation of the walls may cause excessive deformation on the upper floors during an earthquake. However, it is possible to control the bending deformation to within a certain level by setting high-strength and rigid beams (outriggers) at the top of the multi-story shear walls; these outriggers restrain the bending behavior of the walls. Moreover, it is possible to achieve high energy dissipation by placing vibration control devices on the outriggers and thus restrain the bending behavior. This paper outlines the earthquake response analysis of a high-rise residential tower to demonstrate the effectiveness of the outrigger frame incorporating vibration control devices.

• 한국지진공학회논문집
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• 제20권4호
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• pp.211-222
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• 2016

Reinforced concrete shear walls with deficient reinforcement details are tested under cyclic loading. The deficiency of reinforcement details includes insufficient splice length in U-stirrups at the ends of horizontal reinforcement and boundary column dowel bars found in existing low- to mid-rise Korean buildings designed non-seismically. Three test specimens have rectangular, babel and flanged sections, respectively. Flexure- and shear-controlled models for reinforced concrete shear walls specified in ASCE/SEI 41-13 are compared with the flexural and shear components of force-displacement relation extracted separately from the top displacement of the specimen based on the displacement data measured at diverse locations. Modification of the shear wall models in ASCE/SEI 41-13 is proposed in order to account for the effect of bar slip, cracking loads in flexure and shear. The proposed modification shows better approximation of the test results compared to the original models.

• Earthquakes and Structures
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• 제11권4호
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• pp.723-740
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• 2016

Reinforced concrete corbels are generally used to transfer loads within a structural system, such as buildings, bridges, and facilities in general. They commonly present low aspect ratio, requiring an accurate model for shear strength prediction in order to promote flexural behavior. The model described here, originally developed for walls, was adapted for corbels. The model is based on a reinforced concrete panel, described by constitutive laws for concrete and steel and applied in a fixed direction. Equilibrium in the orthogonal direction to the shearing force allows for the estimation of the shear stress versus strain response. The original model yielded conservative results with important scatter, thus various modifications were implemented in order to improve strength predictions: 1) recalibration of the strut (crack) direction, capturing the absence of transverse reinforcement and axial load in most corbels, 2) inclusion of main (boundary) reinforcement in the equilibrium equation, capturing its participation in the mechanism, and 3) decrease in aspect ratio by considering the width of the loading plate in the formulation. To analyze the behavior of the theoretical model, a database of 109 specimens available in the literature was collected. The model yielded an average model-to-test shear strength ratio of 0.98 and a coefficient of variation of 0.16, showing also that most test variables are well captured with the model, and providing better results than the original model. The model strength prediction is compared with other models in the literature, resulting in one of the most accurate estimates.