• Steel and Composite Structures
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• 제34권6호
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• pp.863-875
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• 2020

After medium or strong earthquakes, damage in the reduced portion of RBS connections occurs due to plastic deformations. The purpose of this paper is to numerically and experimentally investigate the reduced depth section connection as a replaceable fuse. In this regard, three commonly used rigid connections with RBS, a replaceable fuse with RBS, and a replaceable fuse with Reduced Depth Section (RDS-F) were evaluated. All specimens were subjected to quasi-static cyclic load until failure. Although the final strength of the RDS-F is lower than that of the other two, laboratory results showed that it had the maximum ductility among the three samples. The numerical models of all three laboratory samples were constructed in ABAQUS, and the results were verified with great accuracy. The results of more than 28 numerical analyses showed that the RDS-F sample is more ductile than the other specimens. Moreover, the thickness of the web and the plastic section modulus increasing, the final strength would be equal to the other specimens. Therefore, the modified RDS-F with replaceability after an earthquake can be a better alternative for RBS connections.

• 한국지진공학회논문집
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• 제20권7_spc호
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• pp.553-560
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• 2016

After an earthquake occurred in the Gyeongju, 2016, many low-story buildings have been questioned in terms of the seismic performance since mostly they have been exempted from the seismic design requirement since 1988. In this study, a 3-story moment resisting frame (MRF) building was analyzed and evaluated the seismic performance. Due to the insufficient seismic performance required for the seismic performance levels, three different seismic retrofit schemes were proposed and their seismic performances were re-evaluated. While steel brace and open shear wall retrofit systems mainly focused on the strength retrofit, the VES damper retrofit system is mainly to enhance the energy dissipation capacity of the system and resultes in the increased ductility. The original building and 3 retrofitted buildings were evaluated using the nonlinear static and nonlinear dynamic analyses and suggestions were proposed. Through the analysis of nonlinear time history and push-over using MIDAS/Gen program, damages of the building in terms of top story and average story drift and effect of reinforcement were analyzed.

• Structural Engineering and Mechanics
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• 제14권1호
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• pp.21-38
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• 2002

A control algorithm combining viscous and non-linear Reid damping mechanisms has been recently proposed by the authors to command active friction dampers. In this paper, friction dampers and the proposed algorithm are applied to control the seismic responses of a nonlinear 20-story building. Piezoelectric stack actuators are used to implement the control algorithm. The capacity of each damper is determined by the practical size of piezoelectric actuators and the availability of power supply. The saturation effect of the actuators on the building responses is investigated. To minimize the peak story drift ratio or floor acceleration of the building structure, a practical sequential procedure is developed to sub-optimally place the dampers on various floors. The effectiveness of active friction dampers and the efficiency of the proposed sequential procedure are verified by subjecting the building structure to four earthquakes of various intensities. The performance of 80 dampers and 137 dampers installed on the structure is evaluated according to 5 criteria. Numerical simulations indicated that the proposed control algorithm effectively reduces the seismic responses of the uncontrolled 20-story building, such as inelastic deformation. The sub-optimal placement of dampers based on peak acceleration outperforms that based on peak drift ratio for structures subjected to near-fault ground motions. Saturation of piezoelectric actuators has adverse effect on floor acceleration.

• Earthquakes and Structures
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• 제9권5호
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• pp.957-981
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• 2015

Earthquakes occur as a cluster in many regions around the world where complex fault systems exist. The repeated shaking usually induces accumulative damage to affected structures. Damage accumulation in structural systems increases their level of degradation in stiffness and also reduces their strength. Many existing analytical tools of modeling RC structures lack the salient damage features that account for stiffness and strength degradation resulting from repeated earthquake loading. Therefore, these tools are inadequate to study the response of structures in regions prone to multiple earthquakes hazard. The objective of this paper is twofold: (a) develop a tool that contains appropriate damage features for the numerical analysis of RC structures subjected to more than one earthquake; and (b) conduct a parametric study that investigates the effects of multiple earthquakes on the response of RC moment resisting frame systems. For this purpose, macroscopic constitutive models of concrete and steel materials that contain the aforementioned damage features and are capable of accurately capturing materials degrading behavior, are selected and implemented into fiber-based finite element software. Furthermore, finite element models that utilize the implemented concrete and steel stress-strain hysteresis are developed. The models are then subjected to selected sets of earthquake sequences. The results presented in this study clearly indicate that the response of degrading structural systems is appreciably influenced by strong-motion sequences in a manner that cannot be predicted from simple analysis. It also confirms that the effects of multiple earthquakes on earthquake safety can be very considerable.

• Structural Engineering and Mechanics
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• 제90권1호
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• pp.51-70
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• 2024

Poorly designed reinforced concrete (RC) columns of actual moment-resisting frame (MRF) buildings can undergo Axial Compression Ratios (ACR) so high as their demand exceeds their capacity, even for serviceability gravity load combinations, this lack commonly leads to insufficient seismic strength. Nonetheless, many seismic design codes do not specify limits for ACR. The main contribution of this research is to investigate the need to limit the ACR in seismic design. For this purpose, three prototype 6 and 11-story RC MRF buildings are analyzed in this paper, these buildings have columns undergoing excessive ACR, according to the limits prescribed by standards. To better that situation, three types of alterations are performed: retrofitting the abovementioned overloaded columns by steel jacketing, increasing the concrete strength, and reducing the number of stories. Several finite element analyses are conducted using the well-known software SAP2000 and the results are used for further calculations. Code-type and pushover analyses are performed on the original and retrofitted buildings, the suitability of the other modified buildings is checked by code-type analyses only. The obtained results suggest that ACR is a rather reliable indicator of the final building strength, hence, apparently, limiting the ACR in the standards (for early stages of design) might avoid unnecessary verifications.

• 한국구조물진단유지관리공학회 논문집
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• 제18권2호
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• pp.9-20
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• 2014

철골 중간모멘트골조는 강한 지반운동에 대하여 적합한 저항능력을 확보하기 위한 지진력저항시스템으로서 일반적으로 사용되고 있다. 하지만 국내의 대다수 중 저층 철골건축물은 내진설계가 도입되기 이전에 건설되었거나 현재의 내진설계기준의 요구조건을 준수하지 않은 것들로, 이러한 건물들이 가지는 내진성능에는 의문점이 존재한다. 이와 같은 문제점의 인식에 기반하여 본 연구에서는 국내 철골 중간 모멘트골조의 내진성능에 대한 정량적 제시를 목표로 우선 층수 종류, 지진에 대한 보유내력, 부재 연성도, 제진장치의 유무를 변수로 하여 표본 건물을 설계하였다. 표본 건물의 내진 성능과 붕괴 매커니즘은 비선형 정적해석과 증분동적해석으로부터 획득한 붕괴여유비와 붕괴확률을 이용하여 분석하였다. 해석결과를 통하여 현행 국내기준에 따라 내진설계된 신축건물은 설계지진에 대해 충분한 내진성능을 가졌으며, 이에 반해 구조부재의 연성저감이 발생하거나 낮은 설계 밑면전단력에 대한 저항력을 가진 기존건물의 경우에는 높은 붕괴확률을 가지며 목표로 한 내진성능을 만족시키지 못하는 것으로 나타났다. 이와 같은 내진성능을 충족시키지 못하는 내진설계 도입 이전의 건물에 대해서 에너지 소산장치를 통해 보강하게 되면 장치의 에너지 소산능력뿐만 아니라 소성힌지의 재분배를 통해 붕괴확률 및 내진성능이 신축건물 수준으로 향상되었다.

• 한국구조물진단유지관리공학회 논문집
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• 제26권2호
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• pp.84-91
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• 2022

본 연구에서는 국내 내진설계기준에 의해 중간모멘트골조로 설계된 철골 모멘트접합부에서 면외방향 어긋남을 갖는 보가 접합부의 거동에 미치는 영향을 평가하였다. 기둥을 중심으로 보가 접합되는 형식에 따라 2가지 경우(단면접합 및 양면접합)와 각각의 경우에 대하여 4개 수준의 어긋남 각도(0°, 10°, 20°, 30°)를 조합하여 총 14개의 유한요소해석 모델을 구성하였다. 해석결과, 면외 어긋남을 갖는 대상 모멘트접합부는 국내 구조기준에 따른 중간모멘트골조의 성능수준을 만족하는 것으로 나타났다. 그러나, 면외 어긋남 각도가 커질수록 접합부 시스템의 하중저항능력이 감소하였다. 면외 어긋남 각도가 30°인 접합부에서 보-기둥이 직교된 접합부에 비하여 최대 하중은 약 13% 감소하였고, 층간 변위각 0.02 rad까지의 에너지 소산능력은 최대 26% 감소하였다. 또한, 어긋남 형상에 기인하여 접합부와 인접한 보 플랜지에서 응력이 비대칭으로 분포되며, 보 플랜지와 기둥 플랜지가 예각을 이루는 내측 플랜지(Inner Flange)에 응력이 집중되었다. 본 연구에서 고려한 보-기둥 접합에서는 어긋난 보에 의해 기둥의 축방향 회전에 미치는 영향은 미미하여 무시할 만 하였다.

• Earthquakes and Structures
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• 제7권4호
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• pp.587-607
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• 2014

Progressive collapse, which is referred to as the collapse of the entire building under local damages, is a common failure mode happened by earthquakes. The collapse process highly depends on the whole structural system. Since, asymmetry of the building plan leads to the local damage concentration; it may intensify the progressive collapse mechanism of asymmetric buildings. In this research the progressive collapse of regular and irregular 6-story RC ordinary moment resisting frame buildings are studied in the presence of the earthquake loads. Collapse process and collapse propagation are investigated using nonlinear time history analyses (NLTHA) in buildings with 5%, 15% and 25% mass asymmetry with respect to the number of collapsed hinges and story drifts criteria. Results show that increasing the value of mass eccentricity makes the asymmetric buildings become unstable earlier and in the early stages with lower number of the collapsed hinges. So, with increasing the mass eccentricity in building, instability and collapse of the entire building occurs earlier, with lower potential of the progressive collapse. It is also demonstrated that with increasing the mass asymmetry the decreasing trend of the number of collapsed beam and column hinges is approximately similar to the decreasing trend in the average story drifts of the mass centers and stiff edges. So, as an alternative to a much difficult-to-calculate local response parameter of the number of collapsed hinges, the story drift, as a global response parameter, measures the potential of progressive collapse more easily.

• 한국강구조학회 논문집
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• 제18권3호
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• pp.385-393
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• 2006

목구조의 효율적인 이용은 건설산업에 있어 자재생산에 따른 에너지의 대량소비 및 폐기물유발을 감소할 수 있어 친환경적인대응방안으로 주목받고 있다. 이러한 친환경적인 목재의 수요를 증대시키기 위해서는 중 대형 목구조를 필요로 하는데 기존의 단일부재 및 접합부로써 중 대형 목구조를 실현하는 데는 한계가 있다. 그러므로 중 대형 목구조의 가능성을 높이기 위해서는 구조용집성재의 사용 및 다른 재료를 병합한 효율적인 접합방법이 필요로 하게 된다. 본 연구는 중 대형 목구조용 2방향 라멘접합부 개발을 목표로 하여 H형강과 구조용집성재를 사용한 플랜지의 두께(None, 6mm, 9mm, 12mm)이며, 접합부의 휨 실험을 통해 강성, 강도, 구조용집성재의 응력분포, H형강 플랜지의 변형도 및 파괴형상을 파악하였다. 실험결과, H 형강의 플랜지 두께가 9mm, 12mmm인 실험체는 높은 강도와 우수한 변형능력을 발휘하였다. 또한 H 형강의 플랜지 두께가 9mm, 12mm인 실험체의 이력거동은 매우 크고 매우 높은 에너지 흡수능력을 가지고 있었다.

• Earthquakes and Structures
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• 제18권6호
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• pp.677-689
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• 2020

A building structural system of moment resisting frame (MRF) with concrete filled steel tubular (CFST) columns and wide flange H beams, is one of the most conveniently constructed structural systems. However, there were few studies on evaluating seismic performance of full-scale CFST columns under high axial compression. In addition, some existing famous design codes propose various limits of width-to-thickness ratio (B/t) for steel tubes of the ductile CFST composite members. This study was intended to investigate the seismic behavior of CFST columns under high axial load compression. Four full-scale square CFST column specimens with a B/t of 42 were carried out that were subjected to horizontal cyclic-reversal loads combined with constantly light, medium and high axial loads and with a linearly varied axial load, respectively. Test results revealed that shear strength and deformation capacity of the columns significantly decreased when the axial compression exceeded 0.35 times the nominal compression strength of a CFST column, P₀. It was obvious that the higher the axial compression, the lower both the shear strength and deformation capacities were, and the earlier and faster the shear strength degradation occurred. It was found as well that higher axial compressions resulted in larger initial lateral stiffness and faster degradation of post-yield lateral stiffness. Meanwhile, the lower axial compressions led to better energy dissipation capacities with larger cumulative energy. Moreover, the study implied that under axial compressions greater than 0.35P₀, the CFST column specimens with B/t limits recommended by AISC 360 (2016), ACI 318 (2014), AIJ (2008) and EC4 (2004) codes do not provide ultimate interstory drift ratio of more than 3% radian, and only the limit in ACI 318 (2014) code satisfies this requirement when axial compression does not exceed 0.35P₀.