Earticle

본 연구의 목적은 기존연구의 실험에 사용된 2층 철골구조물을 대상으로 감쇠정수비와 지진파 스케일을 변수로 갖는 비선형 동적응답해석을 수행하여 감쇠비가 동적응답에 어떠한 영향을 미치는지 파악하여 해석의 신뢰성을 확보하는데 있다. 첫 번째로, 기초 고정 모델의 해석을 수행하여 선행연구의 실험결과와 비교하여 해석의 신뢰성을 확보한 다음, 기초 면진 모델의 해석을 수행하였다. 기초 고정 구조물의 실험결과로, 실험결과와 해석결과가 유사한 경향을 보이고 있으며, 입력 스케일과 감쇠비를 변수로 가지는 해석의 결과를 가속도·변위의 시간이력, 면진장치의 거동, 에너지의 측면 등에서 분석하였다. 그 결과 동일 입력 스케일에서 감쇠비가 커질수록 가속도 및 변위응답이 감소하였으며, 댐퍼가 흡수하는 에너지가 증가하는 경향을 보였다.

The purpose of this study is to evaluate the dynamic response behaviors of 2-story steel structure by the non-linear dynamic analysis. The variables of non-linear dynamic response analysis are with/without base-isolation system, earthquake wave scale and damping ratio. The results of the analysis compared with the experiment results of shaking table test from the previous study with respect to frequency, acceleration·displacement response, energy, moment-story drift angle of column, shear force-shear drift ratio of isolation device. The conclusions of this study are as follows ; (1) The Frequency is constant value regardless of increasing damping ratio and earthquake wave scale, and correspond with result of experiment. (2) The tendences of acceleration and displacement response are similar to experimental response. (3) As the increase of damping ratio, the acceleration and displacement response are decreased. (4) The proper damping ratio is found by analysis about earthquake wave scale, with/without isolation system. (5) As the increase of earthquake wave scale, the first floor column of base-fixed model yield, and second floor column yield. The upper structure bevavior of isolated model is elastic by the behavior of isolation system.

In this study, non-linear dynamic response analysis were performed with 2-story steel structure. The purpose is to confirm the dynamic response characteristics of the base-isolated structure. The seismic isolation device was modeled as a shear element and the hysteresis model for isolation device was based on material test. The damping ratio of the seismic isolation device couldn't be finded from the shaking table test. Damping ratio applied the whole base-isolated structure. There were two variables, one of them is scale of input seismic wave, another one is damping ratio. As the result of dynamic response analysis of the non-isolated structure, there were similar to compare with results of test and results of non-linear analysis. And the result of the analysis as the variable to scale of the input earthquake wave and damping ratio, the scale of the input earthquake wave was bigger, damping ratio of the whole structure by the base-isolated structure was increase.

The dynamic analysis of a plate with non-linearity due to large deformation was investigated in this study. There have been many theoretical and numerical analyses of the non-linear dynamic behavior of plates examining theoretically or numerically. The problem is how correctly an analytical model can represent the dynamic characteristics of the actual system. To address the issue, the continuous-time system identification technique was used to generate non-linear models, for stiffness and damping terms, and to explain the observed behaviors with single mode assumption after comparing experimental results with the numerical results of a linear plate model.

An analytical method is presented for evaluation of the steady state periodic behavior of nonlinear systems. This method is based on the substructure synthesis formulation and a MS (multiple scales) procedure, which is applied to the analysis of nonlinear responses. The proposed procedure reduces the size of large degrees-of-freedom problem in solving nonlinear equations. Feasibility and advantages of the proposed method are illustrated with the nonlinear rotating machine system as an example of large mechanical structure systems. In addition, its efficiency for nonlinear response prediction will be shown by comparison of other conventional methods.

An analytical method is presented for evaluation of the steady state periodic behavior of nonlinear structural systems. This method is based on the substructure synthesis formulation and a harmonic balance procedure, which is applied to the analysis of nonlinear responses. A complex nonlinear system is divided into substructures, of which equations are approximately transformed to modal coordinates including nonlinear term under the reasonable procedure. Then, the equations are synthesized into the overall system and the nonlinear solution for the system is obtained. Based on the harmonic balance method, the proposed procedure reduces the size of large degrees-of-freedom problem in the solving nonlinear equations. Feasibility and advantages of the proposed method are illustrated using the study of the nonlinear rotating machine system as a large mechanical structure system. Results obtained are reported to be an efficient approach with respect to nonlinear response prediction when compared with other conventional methods.

Geometrical non-linearity due to the flexibility of cables must be considered efficiently in the dynamic analysis of cable structures. In this paper, formulation of tangent stiffness matrix of elastic catenary cable is derived by using relative nodal displacements, self-weight and unstressed cable length. Free vibration analysis of simply supported cable using elastic catenary cable elements is conducted and compared with that using truss elements. The result shows that elastic catenary cable elements are more compatible than truss elements in the case of analysis of cable structures. Furthermore, the characteristic of dynamic behaviors of cable structures by temporary unstability phenomenon is confirmed.

In the dynamic analysis of cable structures, geometrical non-linearity due to the flexibility of cables must be considered efficiently. In this paper, formulation of tangent stiffness matrix of elastic catenary cable is derived by using relative nodal displacements, self-weight and unstressed cable length. Free vibration analysis of simply supported cable using elastic catenary cable elements is conducted and compared with that using truss elements. The result shows that elastic catenary cable elements are more compatible than truss elements in the case of analysis of cable structures. Furthermore, the characteristic of dynamic behaviors of cable structures by temporary unstability phenomenon is confirmed.

2016년 경주지진 이후로 국내에서도 본격적으로 건축물의 지진대책 강구가 시급한 시점에서 국내에 널리 보급되어 있는 R/C 건축물의 효율적인 내진성능 평가 및 내진보강을 포함한 내진대책을 위한 기초적인 자료를 얻고자, 2016년 경주지진에서 지진피해를 받은 R/C 저층 학교건축물(M학교)을 대상으로 지진피해도구분판정법을 이용하여 잔존내진성능과 지진피해정도를 평가함과 동시에, 부재수준의 비선형동적해석을 수행하여 지진피해정도와의 상관관계를 검토하였다. 지진피해도구분판정에 의한 손상도-I로 분류된 기둥은 2개, 손상도-II가 1개, 손상도-III으로 분류된 기둥이 3개로 각각 평가되어, 최종적으로 평가한 내진성능잔존율(R)은 88.2%로 피해분류는 소규모 피해로 판정되었으며, 또한 비선형동적해석 결과 1층 X방향의 최대응답을 나타낸 기둥의 휨변위는 0.7 mm, 전단변위는 6 mm로 전단균열은 발생하였지만, 전단파괴는 발생하지 않았다. 경주지진에서 지진피해를 입은 M학교의 지진피해가 1층의 X방향에 집중되어 있다는 사실, 휨균열보다는 전단균열이 발생하였다는 사실을 고려한다면 본 연구에서 수행한 비선형동적해석 결과는 2016년 경주지진에서 지진피해를 받은 M학교의 지진피해상황을 잘 반영하고 있다고 사료되며, 국내 기존 저층 R/C 건축물의 효율적인 내진성능 평가 및 내진보강을 포함한 내진대책을 위한 기초적인 자료로서 활용가능하다고 사료된다.

On September 12, 2016, the Gyeongju District was strongly shaken with M=5.8, which was the largest one since measured by the actual seismometer in Korea, and some buildings were damaged. The field survey of reinforced concrete school buildings in the affected area was carried out, and their residual seismic capacities(R) were estimated based on the Japanese Standard for post-earthquake damage evaluation. In this study, the M school, which was greatly damaged by the 2016 Gyeongju Earthquake, was selected, and its damage level was evaluated on the basis of the Japanese Standard. The seismic capacity of the M school was also evaluated using the nonlinear dynamic analysis, and relationships between its damage level and seismic capacity was also conducted to investigate causes of earthquake damage. The damage level of M school was classified into light with R=88.2%. The result of the dynamic analysis agreed reasonably well with the damage of M school sustained by the 2016 Gyeongju earthquake. This will provide fundamental data for earthquake preparedness measures, such as the seismic rehabilitation of low-rise reinforced concrete buildings in Korea.

Dynamic analysis of a plate with non-linearity due to large deformation is performed in the study. There have been many researches about the non-linear dynamic behavior of plates examining by means of theoretical or numerical analyses. But it is important how exactly model the actual system. In this respect, the Continuous-Time system identification technique is used to generate non-linear models, for stiffness and damping terms, to explain the observed behaviors with single mode assumptions for the simplicity after comparing the experimental results with the numerical results of a linear plate model.

본 논문은 경제정의연구소에서 2004년 ~ 2015년간 발표한 경제정의지수(KEJI Index)를 활용하여 국내 상장기업의 사회적 책임(Corporate Social Responsibility, CSR) 활동이 기업가치에 어떠한 영향을 미치고 있는지를 분석하였다. 이에 대한 많은 선행연구가 진행되어왔고, 국내연구에서는 대체로 기업의 CSR이 기업가치를 증가시킬 수 있다고 보고하고 있으나 방법론 및 활용 자료에 따라 상이한 결과가 나타난다. 본 논문에서는 기존 국내연구들과는 다르게 기업가치의 지속성을 반영하기 위하여 동태패널모형(Dynamic Panel Model)으로 분석을 진행하였고, CSR이 기업가치에 미치는 영향이 비선형일 것으로 판단하여 CSR의 제곱항을 추가적인 변수로 고려하였다. 주요 결과는 다음과 같다. 첫째, 기업가치의 지속성을 반영한 동태패널모형에서 CSR은 기업가치에 유의한 음(-)의 영향을 주는 것으로 나타났고, 1시점 전 시차에서도 동일한 결과를 보였다. 이는 정태 모형을 활용하여 CSR이 기업가치를 상승시킬 수 있다고 주장한 기존 국내연구들과 대비되는 결과이다. 둘째, CSR과 기업가치 사이에 비선형관계가 존재하는지를 분석한 결과, 1시점 전 시차에서 CSR이 기업가치에 미치는 영향이 부정적에서 긍정적으로 바뀌는 U자형 비선형관계가 있음을 확인하였다. 즉, 동일시점에서는 CSR이 기업가치에 악영향을 줄 수 있지만, CSR이 임계점 이상인 경우 1시점 시차를 두고 기업가치를 상승시킬 수 있는 것으로 나타났다. 이러한 점에서 국내 경영진의 CSR에 대한 부정적 인식은 재고되어야 할 필요가 있다. 셋째, 이러한 U자형 비선형 관계는 중소기업과 대기업에서 모두 나타으나, CSR이 기업가치에 미치는 영향이 부정적에서 긍정적으로 바뀌는 임계점은 대기업보다 중소기업에서 더 낮게 나타났고, CSR이 기업가치에 미치는 한계효과도 대기업보다 중소기업에서 상대적으로 더 크게 나타났다. 이러한 점에서 대기업과 비교하여 중소기업은 기업가치를 증대시키기 위한 방안으로 CSR을 전략적으로 활용하는 것이 바람직할 수 있다.

This study focuses how CSR(Corporate Social Responsible) activities effect firm's value for the period 2004-2015 in Korea using Korean Economic Justice Institute(KEJI) Index as a measure of CSR activities. Earlier studies appear to be rather inconclusive with respect to the question of whether CSR activities improve firm's value. This study performs system generalized method of moments(GMM) estimation on a dynamic panel model which allow for the examination of both linear and nonlinear relationships to be considered. The results of the analysis are as follows: First, CSR activities have a significantly negative impact on firm's value in dynamic panel model, which is in contrast to the studies using static model that claims that CSR activities can increase firm's value. Second, the nonlinear models provide the evidence that CSR activities have a lagged U-shaped impact on firm's value. In other words, companies with high CSR activities can improve firm's value by time lag, although CSR activities may be negative for firm's value at the same time. In this regard, Korean CEOs with a negative stance on CSR activities should change their perceptions. Third, the U-shaped non-linear relationship appears in both SMEs and large corporations, and critical point where the influence of CSR activities on firm's value is changed is lower in SMEs than in large corporations. Therefore, SMEs could be encouraged to promote CSR activities as a strategy to increase firm's value.

Dynamic behaviors of the Korean High-speed Train(KHST) have been analyzed to investigate the performance on the stability, the safety and the ride comfort. Multi-body dynamics analysis program using Recursive method, called RecurDyn, have been employed in the numerical simulation. To model the wheel-rail contact, the RecurDyn uses its built-in module which uses the square root creep law. The accuracy of the rail module in RecurDyn. however, decreases in the analysis of flange contact because it linearizes the shape of the wheel and rail. To solve this problem, a nonlinear contact theory have been developed that considers the profiles of the wheel and rail. The results show that the KHST still needs more stability. The problem should be solved by the examinations of module and modeling.

본 논문에서는 자성재료의 비선형성을 고려한 단상 직입 영구자석형(LSPM) 동기전동기의 기동특성해석을 다룬다. 전동기의 운전상태에 따른 자성재료의 비선형특성을 고려하기 위해 정자장 유한요소법을 이용하여 d축과 q축에 대해 전류변화에 따른 인덕턴스를 추출하였다. 계산된 인덕턴스를 LSPM의 등가회로에 적용하였으며 Runge-Kutta 법을 이용하여 시간차분해석을 수행하였다. 제시된 해석방법으로 계산된 기동특성과 유한요소해석결과를 비교함으로써 비선형의 영향을 고찰 하였다.

본 논문에서는 구조물에 작용하는 하중의 크기와 진동수에 따른 거동의 비선형성을 확인하고 정확한 예측을 위한 방법을 모색하기 위하여 외팔보의 정적 및 동적해석의 수행에서 선형, 비선형 해석의 결과를 비교하는 연구를 진행하였다. 우선 보의 자유단에 수직방향의 정적 및 동적 하중을 가한 상황을 예측하였다. 선형 해석방법으로 고전 외팔보 이론을 적용하였고, co-rotational dynamic 유한요소해석 기법을 개발하여 비선형 해석방법으로 사용하였다. 먼저 정적해석에서 외력의 크기가 달라질 때 선형 및 비선형 해석 예측이 어떠한 차이를 보이는지 비교하였다. 그리고 동적해석을 통해 가진 진동수의 변화에 따른 보 끝단의 무차원화된 변위의 양상을 연구하였고, 공진진동수 근방에서의 상당한 변위가 발생함을 보였다. 마지막으로 주파수 지연현상을 조사하기 위해 특정 진동수에서의 시간 경과에 따른 보의 변위를 확인하였다.

In this paper, the behaviour of a cantilevered beam was predicted to examine the difference between linear and non-linear static, dynamic analysis for a structure by using CR nonlinear formulation. Then, external transverse static and dynamic loads were applied at the free tip of the beam. Classical theories were used for the present linear analysis and co-rotational dynamic FEM program was used for the present nonlinear analysis. In the static analysis, effects of the load for the beam deflection were observed in both linear and nonlinear analysis. Then, normalized displacement at the tip of the beam was predicted for different frequency ratio and a significant difference was obtained in the vicinity of the resonant frequency. In addition, effects of frequency and time for the beam deflection were investigated to find the frequency delay.