• Structural Engineering and Mechanics
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• 제17권3_4호
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• pp.357-378
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• 2004

Nonlinear dynamic analysis of a reinforced concrete (RC) frame under earthquake loading is performed in this paper on the basis of a hysteretic moment-curvature relation. Unlike previous analytical moment-curvature relations which take into account the flexural deformation only with the perfect-bond assumption, by introducing an equivalent flexural stiffness, the proposed relation considers the rigid-body-motion due to anchorage slip at the fixed end, which accounts for more than 50% of the total deformation. The advantage of the proposed relation, compared with both the layered section approach and the multi-component model, may be the ease of its application to a complex structure composed of many elements and on the reduction in calculation time and memory space. Describing the structural response more exactly becomes possible through the use of curved unloading and reloading branches inferred from the stress-strain relation of steel and consideration of the pinching effect caused by axial force. Finally, the applicability of the proposed model to the nonlinear dynamic analysis of RC structures is established through correlation studies between analytical and experimental results.

• Earthquakes and Structures
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• 제25권1호
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• pp.1-13
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• 2023

Reinforced concrete (RC) moment frames are used as lateral seismic load resisting systems in mid- and high-rise buildings in different regions of the world. Based on the seismic design provisions and construction details presented in design codes, RC frames with different levels of ductility (ordinary, intermediate, and special) can be designed and constructed. In Iran, there are RC buildings with various uses which have been constructed based on different editions of design codes. The seismic performance of RC structures (particularly moment frames) in real seismic events is of great importance. In this paper, the observations made on damaged RC moment frames after the destructive Sarpol-e Zahab earthquake with a moment magnitude of 7.3 are reported. Different levels of damage from the development of cracks in the structural and non-structural elements to the total collapse of buildings were observed. Furthermore, undesirable failure modes which are not expected in ductile seismic-resistant buildings were frequently observed in the damaged buildings. The RC moment frames built based on the previous editions of the design codes showed partial or total collapse in this seismic event. The extensive destruction of RC moment frames compared with the other structural systems (such as braced steel frames and confined masonry buildings) was attributed not only to the deficiencies in the construction practice of these buildings but also to the design procedure. In addition, the failure and collapse of masonry infills in RC moment frames were frequent modes of failure in this seismic event. In this paper, the main reasons related to design practice which led to extensive damage in the RC moment frames and their collapse are addressed.

• Structural Engineering and Mechanics
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• 제66권5호
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• pp.609-619
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• 2018

When the irregularities occurred in buildings, affect their seismic performance. This paper has focused on one of the types of irregularities at the height that named setback in elevation. For this purpose, several multistorey Reinforced Concrete Moment Resisting Frames (RCMRFs) with different types of setbacks were designed according to new edition of Iranian seismic code. The nonlinear time history analysis was performed to predict the seismic performance of frames subjected to seven input ground motions. The assessment of the seismic performance was done considering both global and local criteria. Results showed that the current edition of Iranian seismic code needs to be modified in order to improve the seismic behaviour of reinforced concrete moment resisting setback buildings. It was also shown that the maximum damages happen at the elements located in the vicinity of the setbacks. Therefore, it is necessary to strengthen these elements by appropriate modification of Iranian seismic code.

• Earthquakes and Structures
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• 제10권2호
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• pp.261-291
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• 2016

This paper deals with the seismic assessment of a real RC frame building located in Italy, designed according to the current Italian seismic code. The first part of the paper deals with the calibration of the structural model of the investigated building. The results of an in-situ dynamic identification test are employed in a sensitivity and parametric study in order to find the best fit model in terms of frequencies and modal shapes. In the second part, the safety of the structure is evaluated by means of nonlinear static analyses, taking into account the results of the previous dynamic study. In order to investigate the influence of the infills on the seismic response of the structure, the nonlinear static analyses are performed both neglecting and taking into account the infill panels. The infill panels differently change the behavior of the structure in terms of strength and stiffness at different seismic intensity levels. The assessment study also verifies the absence of brittle failures in structural elements, which could be caused by either the local interaction with infills or the failure of the strength hierarchy.

• Structural Engineering and Mechanics
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• 제72권4호
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• pp.443-454
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• 2019

In order to reduce the residual drift of a structure in structural engineering field, a combined structural system (dual) consisting of steel buckling-restrained braced frame (BRBF) along with shear wall is proposed. In this paper, BRBFs are used with special reinforced concrete shear walls as combined systems. Some prototype models of the proposed combined systems as well as steel BRBF-only systems (without walls) are designed according to the code recommendations. Then, the nonlinear model of the systems is prepared using fiber elements for the reinforced concrete wall and appropriate elements for the BRBs. Seismic responses of the combined systems subjected to ground motions at maximum considered earthquake level are investigated and compared to those obtained from BRBFs. Results showed that the maximum residual inter-story drift from the combined systems is, on average, less than half of the corresponding value of the BRBFs. In this research, mean of absolute values of the maximum inter-story drift ratio demand obtained from combined systems is less than the 3% limitation, while this criterion has not been fulfilled by BRBF systems.

• 한국전산구조공학회논문집
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• 제22권4호
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• pp.355-362
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• 2009

국내에 많이 건설되고 있는 빌라형 주택은 건축적인 요구를 위하여 저층부에 필로티를 두고 있는 경우가 많다. 구조물 상층부의 비내력벽에 의하여 저층에 연약층을 유발하고 따라서 지진에 매우 취약하다. 그러나 설계시 일반적인 설계방법과 동일하게 상부층의 칸막이벽은 비구조체로 간주되어 무시된다. 그러므로 설계단계에서 무시되는 비내력벽의 유무에 따라서 건축물이 어떠한 지진거동의 차이점을 보이는지 살펴볼 필요가 있다. 본 연구에서는 대상 건축물의 지진취약도 해석을 통하여 비내력벽의 유무에 따른 건축물의 지진거동을 평가하였다. 비내력벽의 유무에 따른 동일한 골조를 가지는 저층 철근콘크리트 건축물을 적용하여 지진거동에서 비내력벽의 영향을 평가하였다. 비내력벽은 보편화된 모형화 방법인 등가의 대각 압축 스트럿으로 고려하였다. 골조만 있는 모델과 연약층이 있는 모델의 취약도곡선을 비교하였다. 해석 결과로 연약층이 있는 RC 건물의 내진성능은 설계기준에서 제시하고 있는 성능수준을 만족하지 못하며 지진에 취약함을 보여준다.

• Earthquakes and Structures
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• 제11권2호
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• pp.281-295
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• 2016

This paper presents a study on a non-seismically designed reinforced concrete (RC) frame structure. The structure was a existing three-story office building constructed according to the 1990s practice in Vietnam. The 1/3 scaled down versions of structure was tested on a shake table to investigate the seismic performance of this type of construction. It was found that the inter-story drift and the overall behavior of structure meet the requirements of the actual seismic design codes. Then, nonlinear time history analyses are carried out using the fiber beam- column elements. The comparison between the experimental and simulation results shows the performance of the time history analysis models.

• 한국지진공학회논문집
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• 제14권5호
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• pp.13-22
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• 2010

철근콘크리트 건축물에서 비내력벽(Masonry Infill Walls)은 내부 칸막이벽이나 중저층 규모의 건물 외벽에 흔히 사용된다. 그렇지만 대부분의 경우에 비내력벽은 비구조체이므로 구조설계시 건물의 모형화에서 무시된다. 따라서 본 연구에서는 비내력벽을 보편화된 모형화 방법인 등가의 대각 압축 스트럿(Equivalent Diagonal Strut)으로 고려하여 비내력벽의 유무에 따른 저층 철근콘크리트 건축물의 전체적인 지진거동의 양상을 평가하고자 하였다. 해석결과로 비내력벽을 고려하면 시스템의 추가적인 강도 및 강성을 확보하여 층간변위비를 줄일 수 있으나 진동주기가 짧아져서 설계단계에서 고려한 지진하중보다 큰 하중을 받게 된다. 연약층이 있는 모델의 경우에는 기둥에 소성거동이 집중됨을 알 수 있으며 부분적인 붕괴가 전체 시스템의 붕괴 원인의 가능성을 가진다.

• Structural Engineering and Mechanics
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• 제41권5호
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• pp.645-662
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• 2012

Deteriorative effects of steel corrosion on the structural response of reinforced concrete are simulated for varying degrees of corrosion. The simulation approach is based on a three-dimensional irregular lattice model of the bulk concrete, in which fracture is modeled using a crack band approach that conserves fracture energy. Frame elements and bond link elements represent the reinforcing steel and its interface with the concrete, respectively. Polylinear stress-slip properties of the link elements are determined, for several degrees of corrosion, through comparisons with direct pullout tests reported in the literature. The link properties are then used for the lattice modeling of reinforced concrete beams with similar degrees of corrosion of the main reinforcing steel. The model is successful in simulating several important effects of steel corrosion, including increased deflections, changes in flexural cracking behavior, and reduced yield load of the beam specimens.

• Earthquakes and Structures
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• 제6권4호
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• pp.409-436
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• 2014

Although it is widely accepted that the interaction -between masonry infill and structural members significantly affects the seismic response of reinforced concrete (RC) frames, this interaction is generally neglected in current design-oriented seismic analyses of structures. Moreover, the role of masonry infill is expected to be even more relevant in the case of existing frames designed only for gravitational loads, as infill walls can significantly modify both lateral strength and stiffness. However, the additional contribution to both strength and stiffness is often coupled to a modification of the global collapse mechanisms possibly resulting in brittle failure modes, generally related to irregular distributions of masonry walls throughout the frame. As a matter of principle, accurate modelling of masonry infill should be at least carried out by adopting nonlinear 2D elements. However, several practice-oriented proposals are currently available for modelling masonry infill through equivalent (nonlinear) strut elements. The present paper firstly outlines some of the well-established models currently available in the scientific literature for modelling infill panels in seismic analyses of RC frames. Then, a parametric analysis is carried out in order to demonstrate the consequences of considering such models in nonlinear static and dynamic analyses of existing RC structures. Two bay-frames with two-, three- and four-storeys are considered for performing nonlinear analyses aimed at investigating some critical aspects of modelling masonry infill and their effects on the structural response. Particularly, sensitivity analyses about specific parameters involved in the definition of the equivalent strut models, such as the constitutive force-displacement law of the panel, are proposed.