• 한국전산구조공학회논문집
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• 제23권4호
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• pp.435-443
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• 2010

본 연구에서는 MR(Magneto-Reological)제어기가 설치된 단자유도 구조물의 응답을 예측하기 위하여 구조물의 운동방정식을 해석적으로 분석하고 주요변수를 파악하였다. MR제어기의 수치 모델로는 마찰 및 점성감쇠로 단순모델한 Bingham모델을 사용하였다. 자유진동과 조화진동일때의 응답감쇠를 결정짓는 주요변수가 각각 마찰력과 최대정적복원력의 비 $R_f$, 마찰력과 최대조화가진력의 비 $R_h$ 임을 파악하였다. 비선형 미분방정식을 등가의 선형 미분방정식으로 변환하기 위하여 마찰력에 의한 에너지 소산을 등가의 점성에너지로 치환하여 등가점성감쇠와 등가점성감쇠비를 유도하였다. 마지막으로 등가선형화과정을 검증하기 위하여 실제 지진에 대한 구조물의 응답을 비선형 미분방정식의 해와 비교하였다.

• Earthquakes and Structures
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• 제7권1호
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• pp.83-99
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• 2014

This study is devoted to estimate higher-mode effects for multi-story structures with considering soil-structure interaction subjected to decomposed parts of near-fault ground motions. The soil beneath the super-structure is simulated based on the Cone model concept. Two-dimensional structural models of 5, 15, and 25-story shear buildings are idealized by using nonlinear stick models. The ratio of base shears for the soil-MDOF structure system to those obtained from the equivalent soil-SDOF structure system is selected as an estimator to quantify the higher-mode effects. The results demonstrate that the trend of higher-mode effects is regular for pulse component and has a descending variation with respect to the pulse period, whereas an erratic pattern is obtained for high-frequency component. Moreover, the effect of pulse component on higher modes is more significant than high-frequency part for very short-period pulses and as the pulse period increases this phenomenon becomes vice-versa. SSI mechanism increases the higher-mode effects for both pulse and high-frequency components and slenderizing the super-structure amplifies such effects. Furthermore, for low story ductility ranges, increasing nonlinearity level leads to intensify the higher-mode effects; however, for high story ductility, such effects mitigates.

• Earthquakes and Structures
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• 제2권2호
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• pp.149-169
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• 2011

Dynamic response of two adjacent single degree-of-freedom (SDOF) structures connected with friction damper under base excitation is investigated. The base excitation is modeled as a stationary white-noise random process. As the force-deformation behavior of friction damper is non linear, the dynamic response of connected structures is obtained using the equivalent linearization technique. It is observed that there exists an optimum value of the limiting frictional force of the damper for which the mean square displacement and the mean square absolute acceleration responses of the connected structures attains the minimum value. The close form expressions for the optimum value of damper frictional force and corresponding mean square responses of the coupled undamped structures are derived. These expressions can be used for initial optimal design of the friction damper for connected structures. A parametric study is also carried out to investigate the influence of system parameters such as frequency ratio and mass ratio on the response of the coupled structures. It has been observed that the frequency ratio has significant effect on the performance of the friction damper, whereas the effects of mass ratio are marginal. Finally, the verification of the derived close from expressions is made by correlating the response of connected structures under real earthquake excitations.

• 대한토목학회논문집
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• 제26권3A호
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• pp.473-484
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• 2006

역량스펙트럼 방법은 비선형 거동을 하는 구조물의 최대 변위응답을 간편하게 산정하는데 사용된다. 역량스펙트럼 방법을 사용하여 다경간 교량의 내진성능을 평가하기 위해서는 구조계를 대표하는 하나의 응답을 등가단자유도계 방법을 이용하여 다자유도 응답들로부터 유도하여야 한다. 등가단자유도 방법은 비탄성 정적해석에 의해 산정된 힘-변위 곡선들로부터 역량곡선을 계산하는데 사용된다. 역량스펙트럼 방법에 사용되는 등가단자유도 방법의 정확성을 평가하기 위하여, 몇 개의 등가단 자유도방법과 결합된 역량스펙트럼 방법에 의해 산정된 최대변위응답을 설계지진스펙트럼에 대응되는 인공지진을 사용한 비탄성 시간이력해석의 변위응답과 비교하였다.

• Earthquakes and Structures
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• 제12권3호
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• pp.271-284
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• 2017

This paper presents a multimodal adaptive nonlinear static method of analysis that, differently from the nonlinear static methods suggested in seismic codes, does not require the definition of the equivalent Single-Degree-Of-Freedom (SDOF) system to evaluate the seismic response of structures. First, the proposed method is formulated for the assessment of r.c. plane frames and then it is extended to 3D framed structures. Furthermore, the proposed nonlinear static approach is re-elaborated as a displacement-based design method that does not require the use of the behaviour factor and takes into account explicitly the plastic deformation capacity of the structure. Numerical applications to r.c. plane frames and to a 3D framed structure with inplan irregularity are carried out to illustrate the attractive features as well as the limitations of the proposed method. Furthermore, the numerical applications evidence the uncertainty about the suitability of the displacement demand prediction obtained by the nonlinear static methods commonly adopted.

• Smart Structures and Systems
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• 제2권1호
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• pp.1-24
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• 2006

The optimal design of multiple tuned mass dampers (multiple TMD's) to suppress multi-mode structural response of beams and floor structures was investigated. A new method using a numerical optimizer, which can effectively handle a large number of design variables, was employed to search for both optimal placement and tuning of TMD's for these structures under wide-band loading. The first design problem considered was vibration control of a simple beam using 10 TMD's. The results confirmed that for structures with widelyspaced natural frequencies, multiple TMD's can be adequately designed by treating each structural vibration mode as an equivalent SDOF system. Next, the control of a beam structure with two closely-spaced natural frequencies was investigated. The results showed that the most effective multiple TMD's have their natural frequencies distributed over a range covering the two controlled structural frequencies and have low damping ratios. Moreover, a single TMD can also be made effective in controlling two modes with closely spaced frequencies by a newly identified control mechanism, but the effectiveness can be greatly impaired when the loading position changes. Finally, a realistic problem of a large floor structure with 5 closely spaced frequencies was presented. The acceleration responses at 5 positions on the floor excited by 3 wide-band forces were simultaneously suppressed using 10 TMD's. The obtained multiple TMD's were shown to be very effective and robust.

• Structural Engineering and Mechanics
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• 제45권6호
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• pp.741-758
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• 2013

In this study, inelastic displacement ratios are investigated for existing systems with known lateral strength considering soil structure interaction. For this purpose, SDOF systems for period range of 0.1-3.0 s with different hysteretic behaviors are considered for a number of 18 earthquake motions recorded on soft soil. The effect of stiffness degradation on inelastic displacement ratios is investigated. The Modified Clough model is used to represent structures that exhibit significant stiffness degradation when subjected to reverse cyclic loading and the elastoplastic model is used to represent non-degrading structures. Soil structure interaction analyses are conducted by means of equivalent fixed base model effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. A new equation is proposed for inelastic displacement ratio of system with SSI with elastoplastic or degrading behavior as a function of structural period ($\tilde{T}$), strength reduction factor (R) and period lengthening ratio ($\tilde{T}$/T). The proposed equation for $\tilde{C}_R$ which takes the soil-structure interaction into account should be useful in estimating the inelastic deformation of existing structures with known lateral strength.

• Earthquakes and Structures
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• 제16권2호
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• pp.165-175
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• 2019

Incremental dynamic analysis (IDA), as an accurate method to evaluate the parameters of structural performance levels, requires many non-linear time history analyses, using a set of ground motion records which are scaled to different intensity levels. Therefore, this method is very computationally demanding. In this study, a new method is presented to estimate the summarized (16%, 50%, and 84% fractiles) IDA curves of a first-mode dominated structure using discrete wavelet transform and bees optimization algorithm. This method reduces the number of required ground motion records for the prediction of the summarized IDA curves. At first, a subset of first list ground motion records is decomposed by means of discrete wavelet transform which have a low dispersion estimating the summarized IDA curves of equivalent SDOF system of the main structure. Then, the bees algorithm optimizes a series of factors for each level of detail coefficients in discrete wavelet transform. The applied factors change the frequency content of original ground motion records which the generated ground motions records can be utilized to reliably estimate the summarized IDA curves of the main structure. At the end, to evaluate the efficiency of the proposed method, the seismic behavior of a typical 3-story special steel moment frame, subjected to a set of twenty ground motion records is compared with this method.

• 한국지진공학회논문집
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• 제12권2호
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• pp.69-80
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• 2008

본 연구에서는 중고층 건물과 같이 고차모드의 영향이 커지는 구조물의 지진에 대한 성능점을 간략하고 정확하게 구할 수 있는 개선된 능력스펙트럼법을 제안한다. 능력스펙트럼법은 주어진 지진의 응답스펙트럼과 다자유도 구조물을 변환한 등가 단자유도 시스템을 이용하여 지진으로 인하여 발생하는 지붕층의 최대 비탄성변위를 간략하게 구하는 방법이다. 제안된 방법에서는 구조물의 탄성 및 비탄성 동적해석을 수행하지 않고, 기존의 능력스펙트럼법에서 요구되는 정적푸쉬오버해석과 탄성변위를 이용하여 비탄성변위를 예측하는데, 기존 연구에서 개발한 $C_R$을 이용한다. 본 연구는 제안한 방법의 정확도를 평가하기 위해 LA 지역의 3, 9, 20층 철골모멘트저항골조를 선택한다. 이 건물들의 지진에 대한 각 층별 최대 층간변위비를 개발한 CSM으로 구하고, 이를 비선형 응답이력해석(NL-RHA)으로 구한 결과와 비교하였다. 사용한 지진은 재현주기 475년과 2475년의 위험수준에 대한 각각 20개의 지진집단들이다. 또한 본 연구에서는 ATC-40에 제시된 CSM 방법과 N2 방법으로 구한 각 건물의 최대 층간변위비도 비교한다. 개발된 CSM은 기존에 개발된 방법에 비하여 보다 정확한 최대 층간변위비를 예측하는 것으로 나타났다.

• Structural Engineering and Mechanics
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• 제51권3호
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• pp.447-470
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• 2014

Numerical simulation of the non-linear behavior of (RC) structural walls subjected to severe earthquake ground motions requires a reliable modeling approach that includes important material characteristics and behavioral response features. The objective of this paper is to optimize a simplified method for the assessment of the seismic response and damage development analyses of an RC structural wall building using macro-element model. The first stage of this study investigates effectiveness and ability of the macro-element model in predicting the flexural nonlinear response of the specimen based on previous experimental test results conducted in UCLA. The sensitivity of the predicted wall responses to changes in model parameters is also assessed. The macro-element model is next used to examine the dynamic behavior of the structural wall building-all the way from elastic behavior to global instability, by applying an approximate Incremental Dynamic Analysis (IDA), based on Uncoupled Modal Response History Analysis (UMRHA), setting up nonlinear single degree of freedom systems. Finally, the identification of the global stiffness decrease as a function of a damage variable is carried out by means of this simplified methodology. Responses are compared at various locations on the structural wall by conducting static and dynamic pushover analyses for accurate estimation of seismic performance of the structure using macro-element model. Results obtained with the numerical model for rectangular wall cross sections compare favorably with experimental responses for flexural capacity, stiffness, and deformability. Overall, the model is qualified for safety assessment and design of earthquake resistant structures with structural walls.