탄소섬유보강근을 철근 대체재로 사용하기 위해서 단기 역학적 특성뿐 아니라 장기간 역학적특성에 대한 연구가 필히 수행 되어야 하고 현재도 진행 중이다. 이에 따라 본 연구에서는 CFRP bar의 지속하중에 대한 저항성을 평가하기 위해 ASTM 기준에 따라 약 1,000시간 동안 탄소섬유보강근 인장강도의 40%를 재하하는 크리프 시험을 진행 후 잔류 인장강도 확인을 위한 추가 인장시험을 진행하였다. 크리프 시험 결과, 탄소섬유보강근의 변형률은 지속하중 하에서 1,000시간 경과 후 하중재하 초기 변형률보다 약 4.9% 상 승하였고 크리프 파괴는 발생하지 않았다. 잔류 인장강도는 일반 인장강도의 95% 수준으로 측정되었고 잔류 탄성계수는 일반 탄성계 수의 85 % 수준이었다. 따라서 본 연구에서 진행한 인장강도의 40 %가 1,000시간 동안 재하되었을 때 탄소섬유보강근은 안전한 것으 로 확인되었다.

외부하중을 받는 구조물로부터 계측된 신호의 파워 스펙트럴 밀도함수는 모달 파라미터(고유진동수, 감쇠비)에 대한 상당량 의 정보를 함축하고 있다. 시스템 식별기술은 이러한 신호나 해당 스펙트럼으로부터 모달 파라미터를 추출하는 기법이라고 볼 수 있 다. 파라미터를 추출하는 또 다른 기법으로는 샘플링(신호)을 이용하여한 확률분포의 모수(평균, 분산)를 추정하는 기법이다. 본 연구 에서는 파워 스펙트럼 밀도함수를 확률분포로 치환함으로써 기존 확률통계분야에서 모수를 추출하는 기법(최대우도법)에 의해 모달 파라미터를 추정하는 기법을 제안한다. 모드형상을 추정하는 기법을 개발하고 모드형상에 의해 분해된 모드응답으로부터 고유진동수, 고유감쇠비를 순차적으로 산정하는 기법을 제시한다. 더 나아가, 외부하중이 스펙트럼 해석모델로 치환 가능한 경우에는 이 하중모델 은 통합하여 모델 파라미터까지 산정하는 기법으로 확대한다. 본 연구에서 제시된 기법을 검증하기 위한 수치해석과 실구조물의 응답 에 대한 적용이 이루어졌으며, 검증결과 제안된 모드식별체계가 안정적이며, 신뢰도가 높은 모달파라미터 추정이 가능함을 알 수 있었다.

A timber lattice roof, which has around 30m span, was constructed. In order to figure out the realistic buckling load level, the structural analysis of this roof structure was performed especially by stiffness of connection with various asymmetric snow load. Due to the characteristics of application of snow load, the load combinations of snow should be considered not only global area but also local part so that the critical buckling load could be observed as easy as possible. Geometrical imperfection was simulated to consider inaccurate shape of structure. And then nonlinear analysis were performed. Finally, this paper could investigate that the asymmetric snow load with the lower level stiffness of connection decreased the level of buckling load significantly.

In this paper, the instability of the domed spatial truss structure using wood and the characteristics of the buckling critical load were studied. Hexagonal space truss was adopted as the model to be analyzed, and two boundary conditions were considered. In the first case, the deformation of the inclined member is only considered, and in the second case, the deformation of the horizontal member is also considered. The materials of the model adopted in this paper are steel and timbers, and the considered timbers are spruce, pine, and larch. Here, the inelastic properties of the material are not considered. The instability of the target structure was observed through non-linear incremental analysis, and the buckling critical load was calculated through the singularities and eigenvalues of the tangential stiffness matrix at each incremental step. From the analysis results, in the example of the boundary condition considering only the inclined member, the critical buckling load was lower when using timber than when using steel, and the critical buckling load was determined according to the modulus of elasticity of timber. In the case of boundary conditions considering the effect of the horizontal member, using a mixture of steel and timber case had a lower buckling critical load than the steel case. But, the result showed that it was more effective in structural stability than only timber was used.

The governing equation for a dome-type shallow spatial truss subjected to a transverse load is expressed in the form of the Duffing equation, and it can be derived by considering geometrical non-linearity. When this model under constant load exceeds the critical level, unstable behavior is appeared. This phenomenon changes sensitively as the number of free-nodes increases or depends on the imperfection of the system. When the load is a periodic function, more complex behavior and low critical levels can be expected. Thus, the dynamic unstable behavior and the change in the critical point of the 3-free-nodes space truss system were analyzed in this work. The 4-th order Runge-Kutta method was used in the system analysis, while the change in the frequency domain was analyzed through FFT. The sinusoidal wave and the beating wave were utilized as the periodic load function. This unstable situation was observed by the case when all nodes had same load vector as well as by the case that the load vector had slight difference. The results showed the critical buckling level of the periodic load was lower than that of the constant load. The value is greatly influenced by the period of the load, while a lower critical point was observed when it was closer to the natural frequency in the case of a linear system. The beating wave, which is attributed to the interference of the two frequencies, exhibits slightly more behavior than the sinusoidal wave. And the changing of critical level could be observed even with slight changes in the load vector.

PURPOSES : Concrete pavement is excellent in structural performance and durability. However, its functionality – such as noise and skid resistance – is a shortcoming. Functionality such as noise reduction and skid resistance of concrete pavement is affected by the texture surface, and the texture surface is classified according to the length of the wavelength. In recent years, Fine-size exposed aggregate concrete pavement has been applied, which has excellent structural performance and durability, and secures functionalities such as noise reduction and long-term skid resistance by randomly forming texture surface. Fine-size exposed aggregate concrete pavements are constructed by removing the surface cement binder to randomly expose coarse aggregate and their functionality is mainly governed by the surface texture. However, deteriorated concrete by tire-pavement friction and deicing agent may cause abrasion and aggregate loss on the surface texture; thus reducing their functional performances. Abrasion is created by the thin cutoff of aggregate texture under repeated tire-pavement friction. In addition, aggregate loss is defined by the detachment of aggregates from cement binder. This study aims to evaluate the abrasion and aggregate loss of Fine-size exposed aggregate concrete pavement surface texture under tire-pavement friction and scaling tests. METHODS : In the study, abrasion and aggregate loss of tining and exposed aggregate concrete surface treatments were evaluated. Deterioration of each surface treatment was replicated by scaling test under ASTM C 672 test method. Afterward, abrasion test was conducted by ASTM C779 to simulate the tire-pavement friction under traffic. Consequently, abrasion and aggregate loss were measured. RESULTS : Abrasion depth of non-scaling tining, 10-mm EACP, and 8-mm EACP was 1.76, 1.12, and 1.01mm, respectively. Compared to scaling surface treatments, the difference of abrasion depth in tining texture was the largest with value of 0.4mm. For both textures of finesize exposed aggregate concrete, abrasion depth difference was about 0.1mm. Moreover, The 10-mm EACP exhibited a 2.6% of aggregate loss rate caused by tire-pavement friction before conducting concrete deterioration test. After 40-cycle scaling test, aggregate loss increased up to 12.2%. For 8-mm EACP, aggregate loss rate was 1.7% on non-scaling concrete. Further, this rate was magnified up to 7.3% for the 40-cycle scaling concrete. CONCLUSIONS : Under non-scaling or scaling tests, fine-size exposed aggregate concrete pavement showed better abrasion resistance than tining texture since tining was formed by aggregates and cement binder. Additionally, rate of aggregate loss was significant when EACP experienced the deicing agent under numerous cycles of freeze-thaw action.

In this paper, the dynamic snapping of the 3-free-nodes spatial truss model was studied. A governing equation was derived considering geometric nonlinearity, and a model with various conditions was analyzed using the fourth order Runge-Kutta method. The dynamic buckling phenomenon was observed in consideration of sensitive changes to the force mode and the initial condition. In addition, the critical load level was analyzed. According to the results of the study, the level of critical buckling load elevated when the shape parameter was high. Parallelly, the same result was caused by the damping term. The sensitive asymmetrical changes showed complex orbits in the phase space, and the critical load level was also becoming lowly. In addition, as the value of damping constant was high, the level of critical load also increases. In particular, the larger the damping constant, the faster it converges to the equilibrium point, and the occurrence of snapping was suppressed.

The purpose of this study is to investigate the distribution patterns of displacement and acceleration fields in a nonlinear soil ground based on the interaction of high-speed train, wheel, rail, and ground. For this purpose, a high-speed train in motion was modeled as the actual wheel, and the vertical contact of wheel and rail and the lateral contact, caused by meandering motion, were simulated; this simulation was based on the moving mass analysis. The soil ground part was given the nonlinear behavior of the upper ground part by using the modified the Drucker– Prager model, and the changes in displacement and acceleration were compared with the behavior of the elastic and inelastic grounds. Using this analysis, the displacement and acceleration ranges close to the actual ground behavior were addressed. Additionally, the von-Mises stress and equivalent plastic strain at the ground were examined. Further, the equivalent plastic and total volumetric strains at each failure surface were examined. The variation in stresses, such as vertical stress, transverse pressure, and longitudinal restraint pressure of wheel-rail contact, with the time history was investigated using moving mass. In the case of nonlinear ground model, the displacement difference obtained based on the train travel is not large when compared to that of the elastic ground model, while the acceleration is caused to generate a large decrease.

Recently, the occurrence frequency of earthquake has increased in Korea, and many cultural assets have been damaged. Cheomseongdae is a valuable cultural assets that must be preserved historically and culturally. But, the masonry structure such as Chemseongdae is vulnerable to lateral forces. Therefore, in this study, structural modeling and dynamic analysis are performed to reflect the ground state and structural form of Cheomseongdae. Also, discrete element analysis technique is applied and dynamic behavior characteristics are analyzed according to earthquake load. For this purpose, displacements and stresses according to locations are reviewed and then swelling and distortion are analyzed.

The objective of this numerical study is to investigate the effect of shaft part’s diameter on the load distribution, under-fill, and metal-flow line characteristics in tubular & solid shaft yoke of Al-IMS. The outer diameter of tubular shaft yoke was changed from 30mm to 35mm, and the shaft diameter of solid shaft yoke was varied from 20mm to 25mm. In this results, the required load for production was linearly increased with increasing the tubular shaft yoke outer diameter. In the solid shaft yoke, the loads for the shaft part extending process were almost constant by 10,000kg, however, the loads for generating the yoke process, which were needed a lot of strain, were increased by 4,000kg with increasing the diameter of shaft part. The under-fill regions according to diameter of the shaft part were not observed in both products, and the metal-flow lines were also straight without folding phenomena.

In this study, we analyzed the structural safety and vibration characteristics of rotational drive in 3D CT scan equipment using finite element analysis. The analysis results showed a safety factor of 9.2 and a left and right vertical deflectional deviation of 0.24mm from the maximum equivalent stress. After applying weight compensation of 27.7kgf, the structural analysis reduced the safety factor to 7.6, but the deflectional deviation of the left and right structure was reduced to 0mm. Also, we presented the optimum design of rotational drive through the vibration analysis.

북미와 유럽 등지에서 주거용 주택소재로서 폭넓게 사용되고 있는 구조단열패널(SIP)의 구조적 성능을 평가하기 위해 면내전단하중 시험을 수행하였다. 국외의 경우, 구조단열패널의 기준과 관련된 연구들이 다양하게 진행되었다. 하지만, 국내의 경우, 구조단열패널에 대한 기준은 마련되어 있지 않으며, 성능평가와 관련된 연구는 극소수이다. 본 연구에서는 구조단열패널을 내력벽으로 활용하기 위한 구조성능평가 실험을 수행하였으며, 벽체에 개구부 설치 후 면내전단하중을 가력하였다. 실험체의 크기는 2,400×2,400㎜이며, 변수로는 개구부의 크기와 개구부 보강방법이다. 실험체의 수량은 총 8개이다. 개구부가 있는 구조단열패널의 구조 해석을 수행 하였다. 해석 결과는 구조 실험 시험 결과와 비교하였다. 이를 통해 구조단열패널의 구조 거동을 예측할 수 있는 해석 모델을 완성하였다. 개구 크기를 변수로 하여 면내전단하중을 받는 구조단열패널의 거동을 유한 요소 해석을 통해 분석하였다. 연구를 통해 구조단열패널의 최적 개구부 크기를 제안한다.

니티놀이라고 하는 니켈-티타늄 형태의 형상기억 합금(SMA)은 상당한 양의 변형이 발생한 후에 추가적인 열을 가하지 않더라도 상온에서 원래 모양으로 복원될 수 있는 초탄성 효과를 가진다. 이러한 독특한 재료 특성 때문에, 니티놀은은 의료, 전기, 전자 및 기계 분야뿐만 아니라 토목 공학 분야의 내진 개량을 위한 변위 제어 장치로 널리 사용되어 왔다. 탄소강과 달리 초탄성 형상기억합금은 피로 저항성이 강하며 하중 속도에 따라 강성(하중-변위특성)등의 기계적 물성치가 변화한다. 본 연구에서는 하중 사이클의 반복 횟수와 속도에 따라 초탄성 형상기억합금의 기계적 물성치가 어떻게 변하는가에 대한 실험적 연구를 수행하였다. 본 연구로 인해 표준화된 초탄성 형상기억합금의 기계적 물성치는 이후 초탄성 형상기억합금을 적용한 내진 장치의 설계과정에서 활용함으로써 설계 효율성을 높일 수 있을 것으로 기대된다.

The arched stone bridge has been continuously deteriorated and damaged by the weathering and corrosion over time, and also natural disaster such as earthquake has added the damage. However, masonry stone bridge has the behavior characteristics as discontinuum structure and is very vulnerable to lateral load such as earthquake. So, it is necessary to analyze the dynamic behavior characteristics according to various design variables of arched stone bridge under seismic loads. To this end, the arched stone bridge can be classified according to arch types, and then the discrete element method is applied for the structural modelling and analysis. In addition, seismic loads according to return periods are generated and the dynamic analysis considering the discontinuity characteristics is carried out. Finally, the dynamic behavior characteristics are evaluated through the structural safety estimation for slip condition.

The improvement in computing systems and sensor technologies devotes to conduct data-driven structural health monitoring algorithms for existing civil infrastructures. Despite of the development of techniques, the uncertainty oriented from the measurement results in the discrepancy to the actual structural parameters and let engineers or decision makers hesitate to adopt such techniques. Many studies have shown that the modal identification results can be affected by the uncertainties due to the applied methods and the types of loading. This paper aims to compare the performance of modal identification methods using Structural Modal Identification Toolsuite (SMIT) which has been developed to facilitate multiple identification methods with a user-friendly designed platform. The data fed into SMIT processes three stages for the comprehensive identification including preprocessing, eigenvalue estimation, and post-processing. The seismic and white noise response for shear frame model was obtained from numerical simulation. The identified modal parameters is compared to the actual modal parameters. In order to improve the quality of coherence in identified modal parameters, several hurdles including modal phase collinearity and extended modal amplitude coherence were introduced. Numerical simulation conducted on the 5 dof shear frame model were used to validate the effectiveness of using these parameters.

구조물의 감쇠비는 내풍성능을 평가하는 가장 중요한 요소 중의 하나이다. 구조물의 실제 감쇠비는 대부분 계측된 응답을 기반으로 시스템 식별기술에 의하여 이루어진다. 그러나 예측된 감쇠비는 계측조건, 계측시간 및 시스템 식별기술에 따라 오차를 보이는 등 불확실성을 가지고 있다. 본 연구에서는 기 개발된 가상 동적진동기(Virtual Dynamic shaker)에 주요 개념으로 사용되었던 외부하중 스펙트럼의 전체 평탄성을 국부 평탄성으로 개념을 확대하여 감쇠비 추정을 보다 정교하게 하는 기법을 개발하였다. 국부 평탄성을 개념을 사용하여 감쇠비를 구하고자 하는 대상 모드의 고유진동수 부근에 적용함으로서 보다 정확하게 감쇠비 추정하는 기법을 다루었다. 본 개발된 기법을 검증하기 위하여 고층건물의 상시진동에 대하여 적용하였으며, 기존 시스템 식별법, 자유진동실험에 의한 결과와 비교 평가하였다. 그 결과 전체 평탄성을 가지는 개념에 비하여 국부평탄성을 가지는 VDS가 보다 정확하게 감쇠비를 추정하는 것을 보였다.

This paper relates to the study of load characteristics applicable to wind turbine generators induced by earthquakes. An artificial design earthquake wave generated through the target spectrum and the envelope function of Richter Magnitude Scale (ML) 7.0 as in ASCE4-98 was created. A simulation of earthquake loads were performed according to the design load cases (DLC) 9.5~9.7 of GL guidelines. Additionally, simulation of seismic loads experienced by Wind Turbines installed in the Gyeongju region were carried out utilizing artificial earthquakes of ML 5.8 simulating the real earthquakes during the Gyeongju Earthquakes of Sept. 2016.

건물외피 발생하는 열교현상은 건물의 단열성능 및 외피의 내구성에 영향을 미치며, 국내의 일반적인 주거형식인 공동주택의 발코니에 있어서 이러한 열교현상은 중요하게 고려되고 있다. 이와 같이 내·외부 발코니 슬래브 사이에서 발생하는 열교현상을 최소화하기 위한 목적으로 열교차단장치가 개발되었으며 다수의 건설현장에서 적용되고 있다. 철근콘크리트 슬래브 벽-슬래브 접합부에 열교차단장치를 적용함으로써 건물의 단열성능을 향상될 수 있으나 풍하중과 같은 양방향의 하중에 의해 열교차단장치 삽입부위가 적합한 구조성능을 확보하고 있는지에 대한 검증이 요구된다. 따라서 본 연구에서는 철근콘크리트 슬래브에 적용된 열교차단장치의 구조성능을 확인하기 위해 변위제어 방식으로 30 싸이클의 반복하중을 가력하였다. 열교차단장치가 삽입된 접합부는 요구되는 구조성능을 확보하며, 최대 모멘트강도, 에너지소산능력, 연성비가 기존의 철근콘크리트 슬래브와 비교하여 향상되는 것으로 나타났다.

A single-layerd steel lattice roof, which has 50m span, was constructed. In order to figure out the realistic buckling load level, the structural analysis of this roof structure was performed especially by local snow load. Due to the characteristics of application of snow load, the load combinations of snow should be considered not only global area but also local part so that the critical buckling load could be observed as easy as possible. Geometrical imperfection was simulated to consider inaccurate shape of structure. And then nonlinear analysis were performed. Finally, this paper could investigate that the local snow load with geometrical imperfection decreased the level of buckling load significantly.