• 한국지진공학회논문집
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• 제22권3호
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• pp.103-111
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• 2018

This study examines the seismic failure of RC low-rise building structures having irregularities at the ground story during the 15 November 2017 Pohang, Korea, earthquake, $M_w=5.4$, which is the second strongest since the government began monitoring them in 1978 in South Korea. Some 2,000 private houses were damaged or destroyed in this earthquake. Particularly, serious damage to the piloti story of RC low-rise residential building structures of fewer than five stories was observed within 3 km of the epicenter with brittle shear failure of columns and walls due to severe torsional behavior. Buildings below six stories constructed before 2005 did not have to comply with seismic design requirements, so confinement detailing of columns and walls also led to inadequate performance. However, some buildings constructed after 2005 were damaged at the flexible side of the piloti story due to the high torsional irregularity. Based on these results, this study focuses on the problems of the seismic torsion design approach in current building codes.

• Earthquakes and Structures
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• 제18권4호
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• pp.437-449
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• 2020

It is quite apparent that engineering concerns related to the influence of masonry infills on seismic behavior of reinforced concrete (RC) structures is likely to remain relevant in the long term, as infill walls maintain their functionalities in construction practice. Within this framework, the present paper mainly deals with the issue in terms of modal expansion of effective earthquake forces and the resultant modal responses. An adequate determination of spatial distribution of effective earthquake forces over the height of the building is highly essential for both seismic analysis and design. The possible influence of infill walls is investigated by means of modal analyses of two-, three-, and four-bay RC frames with a number of stories ranging from 3 to 8. Both uniformly and non-uniformly infilled frames are considered in numerical analyses, where infill walls are simulated by adopting the model of equivalent compression strut. Consequently, spatial distribution of effective earthquake forces, modal static base shear force response of frames, modal responses of story shears from external excitation vector and lateral floor displacements are obtained. It is found that, infill walls and their arrangement over the height of the frame structure affect the spatial distribution of modal inertia forces, as well as the considered response quantities. Moreover, the amount of influence varies in stories, but is not very dependent to bay number of frames.

• 복합신소재구조학회 논문집
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• 제4권1호
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• pp.40-46
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• 2013

This paper presents the design, fabrication and performance of a reinforced concrete beam strengthened by GFRP box plate and its possibility for structural rehabilitations. The load capacity, ductility and failure mode of reinforced concrete structures strengthened by FRP box plate were investigated and compared with traditional FRP plate strengthening method. This is intended to assess the feasibility of using FRP box plate for repair and strengthening of damaged RC beams. A series of four-point bending tests were conducted on RC beams with or without strengthening FRP systems the influence of concrete cover thickness on the performance of overall stiffness of the structure. The parameters obtained by the experimental studies were the stiffness, strength, crack width and pattern, failure mode, respectively. The test yielded complete load-deflection curves from which the increase in load capacity and the failure mode was evaluated.

• Earthquakes and Structures
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• 제7권5호
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• pp.691-704
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• 2014

Reinforced concrete (RC) shear walls are commonly used for building structures to resist seismic loading. While the RC shear walls can have a high load-carrying capacity, they tend to fail in a brittle mode under shear, accompanied by forming large diagonal cracks and bond splitting between concrete and steel reinforcement. Improving seismic performance of shear walls has remained a challenge for researchers all over the world. Engineered Cementitious Composite (ECC), featuring incredible ductility under tension, can be a promising material to replace concrete in shear walls with improved performance. Currently, the application of ECC to large structures is limited due to the lack of the proper constitutive models especially under shear. In this paper, a new Cyclic Softening Membrane Model for reinforced ECC is proposed. The model was built upon the Cyclic Softening Membrane Model for reinforced concrete by (Hsu and Mo 2010). The model was then implemented in the OpenSees program to perform analysis on several cases of shear walls under seismic loading. The seismic response of reinforced ECC compared with RC shear walls under monotonic and cyclic loading, their difference in pinching effect and energy dissipation capacity were studied. The modeling results revealed that reinforced ECC shear walls can have superior seismic performance to traditional RC shear walls.

• Advances in concrete construction
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• 제1권3호
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• pp.253-272
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• 2013

The use of steel bracing systems is a popular method for the strengthening of existing reinforced concrete (RC) frames and may lead to a substantial increase of both strength and stiffness. However, in most retrofitting cases, the main target is the increase of the energy dissipation capacity. This paper studies numerically the efficiency of a specific strengthening methodology which utilizes a steel link element having a cross-section of various shapes, connected to the RC frame through bracing elements. The energy is dissipated through the yielding of the steel link element. The case studied is a typical one bay, single-storey RC frame, constructed according to older code provisions, which is strengthened through two different types of link elements. The presented numerical models are based on tests which are simulated in order to gain a better insight of the behaviour of the strengthened structures, but also in order to study the effects of different configurations for the link element. The behaviour of the strengthened frames is studied with respect to the one of the original bare frame. Moreover, the numerically obtained results are compared to the experimentally obtained ones, in order to verify the effectiveness of the applied simulation methodology.

• Steel and Composite Structures
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• 제30권3호
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• pp.217-230
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• 2019

One of the most important design criteria in underground structure is to design lightweight protective layers to resist significant blast loads. Sandwich blast resistant panels are commonly used to protect underground structures. The front face of the sandwich panel is designed to resist the blast load and the core is designed to mitigate the blast energy from reaching the back panel. The design is to allow the sandwich panel to be repaired efficiently. Hence, the underground structure can be used under repeated blast loads. In this study, a novel sandwich panel, named RC panel - Helical springs- RC panel (RHR) sandwich panel, which consists of normal strength reinforced concrete (RC) panels at the front and the back and steel compression helical springs in the middle, is proposed. In this study, a detailed 3D nonlinear numerical analysis is proposed using the nonlinear finite element software, AUTODYN. The accuracy of the blast load and RHR Sandwich panel modelling are validated using available experimental results. The results show that the proposed finite element model can be used efficiently and effectively to simulate the nonlinear dynamic behaviour of the newly proposed RHR sandwich panels under different ranges of free air blast loads. Detailed parameter study is then conducted using the validated finite element model. The results show that the newly proposed RHR sandwich panel can be used as a reliable and effective lightweight protective layer for underground structures.

• Structural Engineering and Mechanics
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• 제85권5호
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• pp.655-664
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• 2023

Reinforced concrete (RC) shear wall structures are one of the most widely used structural systems to resist seismic loading all around the world. Although there have been several efforts to provide conceptually simple procedures to reasonably assess the seismic demands of structures over recent decades, it seems that lesser effort has been put on a number of structural forms such as RC shear wall structures. Therefore, this study aims to represent a simple linear response spectrum-based method which can acceptably predict the nonlinear displacements of a non-ductile RC shear wall structure subjected to an individual ground motion record. An effective period and an equivalent damping ratio are introduced as the dynamic characteristics of an equivalent linear SDOF system relevant to the main structure. By applying the fundamental mode participation factor of the original MDOF structure to the linear spectral response of the equivalent SDOF system, an acceptable estimation of the nonlinear displacement response is obtained. Subsequently, the accuracy of the proposed method is evaluated by comparison with another approximate method which is based on linear response spectrum. Results show that the proposed method has better estimations for maximum nonlinear responses and is more utilizable and applicable than the other one.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.689-692
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• 1999

In recent years, FRP plates have been studied for flexural reinforcement of RC structures due to easy installation and good quality control. This study presents experimental results for the effectiveness of flexural reinforcement of the RC beams using thin CFRP and GFRP stripe made by the pultrusion process. For the selected FRP strips of various thicknesses and widths, it was demonstrated that both flexural strength and ductility were considerably increased with relatively easy installation when compared to the other methods used for the composite reinforcement.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.539-541
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• 2005

The purpose of this study is to accurately understand the flexural behavior in RC beam with strrup on repair thickness of DFRCC. Using a four-point bending test, the shear strengths and shear stress-deflection relations of DFRCC repair RC specimens are obtained. The results show that DFRCC can be effectively used for repairing materials for concrete structures.

• 콘크리트학회논문집
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• 제15권1호
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• pp.25-34
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• 2003

최근 들어 물리 화학적 침해로 인한 RC 구조물의 열화에 대한 관심이 높아지고 있는 실정이다. RC 구조물의 성능을 저하시키는 여러 가지 요인 중에서 특히 염소이온 침투로 인한 콘크리트내의 철근 부식이 가장 심각한 문제로 인식되고 있다. 본 연구에서는 콘크리트내의 염소이온 침투에 대한 수학적 모델을 제안하였다. 기존의 모델을 개선하기 위해 콘크리트 내부로 염소이온 침투에 대한 모델을 염수의 침투와 공극수를 통한 염소이온 확산항으로 구성하였다. 또한, 수화도, 상대습도, 온도, 염소이온 구속도에 따른 확산계수의 변동성을 염소이온 침투 모델에 고려하였다. 제안한 모델의 검증을 위하여 염소이온 침투 현상 해석 프로그램인 Life-365와의 해석 결과와 비교하였으며, 다양한 예제의 해석 결과를 비교 분석함으로써 염소이온 침투현상에 미치는 주요 인자의 영향과 제안된 모델의 적용성을 검토하였다. 향후 제안한 염소이온 침투 모델을 적용하여 RC 구조물의 사용수명 혹은 잔존수명을 예측하여 이를 RC 구조물의 내구성 설계와 유지관리에 활용할 수 있을 것으로 기대된다.