• Steel and Composite Structures
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• 제32권1호
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• pp.67-77
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• 2019

Pushover analysis captures the behavior of a structure from fully elastic to collapse. In this analysis, the structure is subjected to increasing lateral load with constant gravity one. Neglecting the effects of the higher modes and the changes in the vibration characteristics during the nonlinear analysis are the main obstacles of the proposed lateral load patterns. To overcome these drawbacks, whereas some methods have been presented to achieve updated lateral load distribution, these methods are not precisely capable to predict the response of structures, precisely. In this study, a new method based on optimization procedure is developed to obtain a lateral load pattern for which the difference between the floor displacements of pushover and Nonlinear Dynamic Analyses (NDA) is minimal. For this purpose, an optimization problem is considered and the genetic algorithm is applied to calculate optimal lateral load pattern. Three special moment resisting steel frames with different dynamic characteristics are simulated and their optimal load patterns are derived. The floor displacements of these frames subjected to the proposed and conventional load patterns are acquired and the accuracy of them is evaluated via comparing with NDA responses. The outcomes reveal that the proposed lateral load distribution is more accurate than the previous ones.

• 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.

• 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.

• 전산구조공학
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• 제8권3호
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• pp.103-111
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• 1995

지진하중과 같은 동적인 하중에 대한 다자유도 구조물의 비선형 해석은 많은 양의 계산을 요구한다. 이런 계산상의 어려움을 감소시키기 위하여 다자유도를 가진 복잡한 구조물의 비선형해석을 간략화된 동위 구조물 (Equivalent Nonlinear System(ENS))을 이용해 구할 수 있는 약산법을 제시한다. 간단한 동위 구조물은 원구조물의 가장 중요한 구조물의 성질을 가지고 있는데 구조물의 처음 두 개의 주기(natural periods)의 동적 특성 및 전체 항복변위(global yield displacement)를 가진다. 구조체 반응으로 이 논문에서는 구조체의 전체변위 및 층간변위가 고려된다. 구조체의 전체 변위 및 층간변위를 얻기 위하여 전체 반응수정계수(global response scaling factor) R/sub G/와 국부반응수정계수(local response scaling factor)R/sub L/을 동위 구조물로부터 얻어진 변위에 적용한다. 이 반응수정계수는 다자유도 구조물의 비선형 해석을 통하여 얻어진 변위들과 동위 구조물을 이용해 얻어진 변위들을 이용해 광범위한 회기분석을 통하여 구조물의 연성과 첫번째 두 모드의 질량참여계수의 함수형태로 얻는다. 반응수정계수를 가진 동위 구조물을 만들기 위하여 철골 모멘트 연성 골조 방식의 구조물(Special Moment Resisting Steel Frames (SMRSF))을 이 논문에서는 고려한다. 함수형태로 표현된 반응수정계수는 동위 구조물의 반응에 적용되어 복잡한 구조물의 비선형 반응을 얻을 수 있다.

• 한국지진공학회논문집
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• 제12권5호
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• pp.47-56
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• 2008

본 연구는 높은 지진의 위험이 내재된 지역에 위치한 3층, 9층 그리고 20층 철골 모멘트저항골조에 대한 반응수정계수와 주기의 영향을 평가하기 위한 것이다. 각 구조물들은 IBC 2000과 KBC 2005에서 제시하고 있는 8의 반응수정계수로 설계되었고 건물에 기대되는 최소의 성능과 최대의 성능을 평가하기 위해서 상한범위와 하한범위의 설계가 고려되었다. 또한 반응수정계수에 대한 영향을 조사하기 위하여 4개의 다른 반응수정계수들이(9, 10, 11, 12) 각 구조물에 대하여 적용되었고 각 구조물의 고유주기 값 외의 4개의 다른 주기를 추가로 적용하여 구조물의 동적거동시 주기에 대한 영향을 조사하였다. 총 150개의 해석모델들은 50년 동안 2%의 초과확률(재현 주기 2500년)을 가진 20개의 지반운동에 대하여 평가되었다. 구조물의 성능평가를 위하여 정적 Pushover와 비선형 시간이력해석이 수행되었으며 구조물의 연성능력을 평가하기 위해서 변위연성요구가 고려되었다. 3층과 9층 구조물은 변위연성요구 값이 비교적 안정적인 거동을 보인 반면 20층 구조물은 동적 불안정성을 야기하는 요소에 의해 민감하게 나타나는 것으로 조사되었다.

• Earthquakes and Structures
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• 제14권1호
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• pp.1-10
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• 2018

Seismic retrofitting of existing buildings and design of earth-quake resistant buildings are important issues associated with earthquake-prone zones. Use of metallic-yielding dampers as an energy dissipation system is an acceptable method for controlling damages in structures and improving their seismic performance. In this study, the optimal distribution of dampers for reducing the seismic response of steel frames with multi-degrees freedom is presented utilizing the uniform distribution of deformations. This has been done in a way that, the final configuration of dampers in the frames lead to minimum weight while satisfying the performance criteria. It is shown that such a structure has an optimum seismic performance, in which the maximum structure capacity is used. Then the genetic algorithm which is an evolutionary optimization method is used for optimal arrangement of the steel dampers in the structure. In continuation for specifying the optimal accurate response, the local search algorithm based on the gradient concept has been selected. In this research the introduced optimization methods are used for optimal retrofitting in the moment-resisting frame with inelastic behavior and initial weakness in design. Ultimately the optimal configuration of dampers over the height of building specified and by comparing the results of the uniform deformation method with those of the genetic algorithm, the validity of the uniform deformation method in terms of accuracy, Time Speed Optimization and the simplicity of the theory have been proven.

• 국제초고층학회논문집
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• 제1권4호
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• pp.311-332
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• 2012

Earthquake response of mid-rise to high-rise buildings provided with friction dampers is investigated. The steel buildings are modelled as shear-type structures and the investigation involved modelling of the structures of varying heights ranging from five storeys to twenty storeys, in steps of five storeys, subjected to real earthquake ground motions. Three basic types of structures considered in the study are: moment resisting frame (MRF), braced frame (BF), and friction damper frame (FDF). Mathematical modelling of the friction dampers involved simulation of the two distinct phases namely, the stick phase and the slip phase. Dynamic time history analyses are carried out to study the variation of the top floor acceleration, top floor displacement, storey shear, and base-shear. Further, energy plots are obtained to investigate the energy dissipation by the friction dampers. It is seen that substantial earthquake response reduction is achieved with the provision of the friction dampers in the mid-rise and high-rise buildings. The provision of the friction dampers always reduces the base-shear. It is also seen from the fast Fourier transform (FFT) of the top floor acceleration that there is substantial reduction in the peak response; however, the higher frequency content in the response has increased. For the structures considered, the top floor displacements are lesser in the FDF than in the MRF; however, the top floor displacements are marginally larger in the FDF than in the BF.

• Structural Engineering and Mechanics
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• 제78권3호
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• pp.351-368
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• 2021

This paper, by applying a reliability-based framework, develops seismic vulnerability macrozonation maps for Tehran, the capital and one of the most earthquake-vulnerable city of Iran. Seismic performance assessment of 3-, 4- and 5-story steel moment resisting frames (SMRFs), designed according to ASCE/SEI 41-17 and Iranian Code of Practice for Seismic Resistant Design of Buildings (2800 Standard), is investigated in terms of overall maximum inter-story drift ratio (MIDR) and unit repair cost ratio which is hereafter known as "damage ratio". To this end, Tehran city is first meshed into a network of 66 points to numerically locate low- to mid-rise SMRFs. Active faults around Tehran are next modeled explicitly. Two different combination of faults, based on available seismological data, are then developed to explore the impact of choosing a proper seismic scenario. In addition, soil effect is exclusively addressed. After building analytical models, reliability methods in combination with structure-specific probabilistic models are applied to predict demand and damage ratio of structures in a cost-effective paradigm. Due to capability of proposed methodology incorporating both aleatory and epistemic uncertainties explicitly, this framework which is centered on the regional demand and damage ratio estimation via structure-specific characteristics can efficiently pave the way for decision makers to find the most vulnerable area in a regional scale. This technical basis can also be adapted to any other structures which the demand and/or damage ratio prediction models are developed.

• 한국산학기술학회논문지
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• 제18권12호
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• pp.50-56
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• 2017

고층건물에서 횡력 저항의 주된 역할을 하는 외주골조는 기둥과 보를 직교시켜 구성하는 것이 일반적이었으나 최근 다양한 그리드형태의 부재배치가 이루어지고 있다. 선행연구에서는 아이소트러스 그리드를 고층건물의 외주골조로 적용한 구조적 적합성이 검토되었다. 본 연구에서는 $IsoTruss^{(R)}$ 그리드(ITG) 구조의 예비단계 설계시 외주골조 부재의 소요단면적 산정방법을 제안하였다. 모듈의 변형과 하중과의 평형조건, 허용 횡변위, 그리고 건물의 휨변형 대 전단변형의 비를 변수로 하여 소요단면적을 유도하였다. ITG 구조에서 외주골조의 부재는 횡하중에 직각인 평면(PPR), 평행한 평면(PPL), 경사진 평면(POQ)에 배치되는데 POQ에 배치된 부재는 PPR 또는 PPL에 투영시켜 부재의 강성을 반영하였다. 소요단면적은 모듈에 작용하는 전단력과 모멘트에 의해 영향을 받는데 부재사이즈 조닝을 달리하여 3가지 모델을 비교하였다. 본 연구의 효용성을 검증하기 위해 64층 건물을 설계하여 해석하였다. 최대 횡변위, 철골량, 기둥의 축력강도비를 비교분석하여 부재사이즈 조닝의 효과를 알아보았다. 제안식을 이용한 횡변위가 제한치의 약 97.3%로 나와 제안식을 설계 초기단계에서 부재사이즈의 선정에 유용하게 적용할 수 있다.