• 한국지반공학회논문집
• /
• 제19권2호
• /
• pp.57-64
• /
• 2003

지진하중조건에서 포화된 모래의 액상화 가능성은 심도 있는 연구가 진행되어 왔다. 이러한 연구에서 대표적인것은 실험실에서 반복삼축압축시험에 의하여 모래의 반복강도를 결정하는 것이다. 본 연구는 재성형된 포화 균등모래의 액상화 특성에 있어서 시편의 성형방법에 따른 영향을 검증하기 위하여 수행되었다. 건조시료의 공기중낙하다짐, 습윤층다짐, 습윤진동층다짐 등 3가지 방법에 의하여 동일한 밀도로 다짐된 포화된 균등한 모래에 대하여 삼축압축시험이 수행되었다. 같은 밀도에서 다른 방법에 의하여 성형된 포화된 균등한 모래의 액상화 저항특성인 반복응력비는 크게 다른 것으로 확인되었다.

• Geomechanics and Engineering
• /
• 제7권5호
• /
• pp.569-587
• /
• 2014

Triaxial compression creep tests were performed on salt rock samples using cyclic confining pressure with a static axial pressure. The test results show that, up to a certain time, changes in the confining pressure have little influence on creep properties of salt rock, and the axial creep curve is smooth. After this point, the axial creep curve clearly fluctuates with the confining pressure, and is approximately a straight line both when the confining pressure decreases and when it increases within one cycle period. The slope of these lines differs: it is greater when the confining pressure decreases than when it increases. In accordance with rheology model theory, axial creep equations were deduced for Maxwell and Kelvin models under cyclic loading. These were combined to establish an axial creep equation for the Burgers model. We supposed that damage evolution follows an exponential law during creep process and replaced the apparent stress in creep equation for the Burgers model with the effective stress, the axial creep damage equation for the Burgers model was obtained. The model suitability was verified using creep test results for salt rock. The fitting curves are in excellent agreement with the test curves, so the proposed model can well reflect the creep behavior of salt rock under low-frequency cyclic loading. In particular, it reflects the fluctuations in creep deformation and creep rate as the confining pressure increasing and decreasing under different cycle periods.

• 한국지진공학회논문집
• /
• 제27권1호
• /
• pp.37-47
• /
• 2023

A new clamped mechanical splice system was proposed to develop structural performance and constructability for precast concrete connections. The proposed mechanical splice resists external loading immediately after the engagement. The mechanical splices applicable for both large-scale rebars for plants and small-scale rebars for buildings were developed with the same design concept. Quasi-static lateral cyclic loading tests were conducted with reinforced and precast concrete members to verify the seismic performance. Also, shaking table tests with three types of seismic wave excitation, 1) random wave with white noise, 2) the 2016 Gyeongju earthquake, and 3) the 1999 Chi-Chi earthquake, were conducted to confirm the dynamic performance. All tests were performed with real-scale concrete specimens. Sensors measured the lateral load, acceleration, displacement, crack pattern, and secant system stiffness, and energy dissipation was determined by lateral load-displacement relation. As a result, the precast specimen provided the emulative performance with RC. In the shaking table tests, PC frames' maximum acceleration and displacement response were amplified 1.57 - 2.85 and 2.20 - 2.92 times compared to the ground motions. The precast specimens utilizing clamped mechanical splice showed ductile behavior with energy dissipation capacity against strong motion earthquakes.

• 복합신소재구조학회 논문집
• /
• 제4권1호
• /
• pp.33-39
• /
• 2013

Structural insulated panels, structurally performed panels consisting of a plastic insulation bonded between two structural panel facings, are one of emerging products with a viewpoint of its energy and construction efficiencies. These components are applicable to fabricated wood structures. In Korea, there are few technical documents regulated structural performance and engineering criteria in domestic market. This study was conducted to identify fundamental performance of both monotonic load and quasi static cyclic load for SIPs in shear wall application. Static test results showed that maximum load was 44.3kN, allowable shear load was 6.1kN/m, shear stiffness was 1.23 M N/m, and ductility ratio was 3.6. Cyclic test was conducted by two kinds of specimens : single panel and double panels. Cyclic test results, which were equivalent to static test results, showed that maximum load was 45.42kN, allowable shear load was 6.3kN/m. Furthermore the accumulated energy dissipation capability for double panels was as 2.3 times as that for single panel. From performance of structural tests, it was recommended that the allowable shear load for panels was at least 6.1kN/m.

• Computers and Concrete
• /
• 제29권1호
• /
• pp.47-57
• /
• 2022

The increase in waste tires has brought serious environmental problems. Using waste tires rubber particles as aggregate in concrete can reduce pollution and decrease the usage of natural aggregate. The paper describes an investigation on flexural bearing capacity of self-compacting concrete (SCC) pavement slabs containing crumb rubber. Cyclic loading tests with different stress ratios and loading frequencies are carried out on SCC pavement slabs containing crumb rubber. Based on Paris Law and test data, the fatigue life of SCC pavement slab containing crumb rubber is discussed, and a revised mathematical model is established to predict the fatigue life of SCC pavement slab containing crumb rubber. The model applies to different stress ratios and loading frequencies. The fatigue life of SCC pavement slab containing crumb rubber is affected by the stress ratio and loading frequency. The fatigue life increases with the increase of stress ratio and loading frequency. Real-time acoustic emission (AE) signals in the SCC pavement slab containing crumb rubber under cyclic loading are measured, and the characteristics of crack propagation in the SCC pavement slab containing crumb rubber under different stress ratios and loading frequencies are compared. The AE signals provide abundant information of fracture process zone and crack propagation. The variation of AE ringing count, energy and b-value show that the fracture process of SCC pavement slab containing crumb rubber is divided into three stages.

• 한국방재학회 논문집
• /
• 제6권1호
• /
• pp.39-48
• /
• 2006

본 시험은 다양한 sine파형을 가진 인장 및 압축 하중 하에서 아스팔트 혼합물의 모듀율값 을 비교평가하기 위하여 수행되었다. 즉, 휴식시간을 가진 반복 인장 haversine 하중, 휴식시간을 가진 반복 압축 haversine 하중, 주기적 인장하중, 주기적 압축하중, 그리고 주기적 인장-압축 반복하중이라는 총 5개의 하중형태가 32, 50, 68, 86, $104^{\circ}F$ (0, 10, 20, 30, $40^{\circ}C$) 라는 5개의 온도하에서 평가되었다. 시험결과, 휴식시간을 가진 반복 haversine 하중으로 인한 아스팔트 콘크리트의 인장 및 압축 모듀율 값은 저온에서 유사한 값을 나타내었지만, 고온에서는 상이한 값을 보였다. 특히, 고온에서 압축 모듀율 값은 인장 모듀율 값보다 높은 수치를 보였다. 또한, 저온에서 일축 직접인장 시험으로부터 구한 모듀율 값은 간접 인장시험으로부터 구한 모듀율 값보다 높은 값을 나타내었다. 그러나, 고온에서는 서로 유사한 값을 보였다. 일반적으로, 휴식시간을 갖는 반복 haversine 하중을 이용하여 얻은 모듀율 값은 주기적 sine파형을 가진 하중으로부터 구한 모듀율 값보다 항상 낮은 값을 나타내었으며 그 두 가지 하중으로부터 구한 모듀율 값의 차이는 온도가 감소함에 따라 더욱 증가되었다.

• 한국지반공학회논문집
• /
• 제22권12호
• /
• pp.89-98
• /
• 2006

본 논문에서는 지진이 발생한 지역에서 다시 지진이 발생할 경우에 포화된 사질토 지반의 동적거동에 관한 연구를 수행하였다. 반복 직접단순전단시험을 실시하여 느슨한 모래지반에서 간극수압발생량과 재액상화발생여부의 상관관계를 분석하였다. 최초의 전단하중으로 인하여 지반이 원래 가지고 있던 유효수직응력의 약 90%까지 간극수압이 발생하였을 경우 시간 경과에 따라 과잉간극수압이 전부 소산된 이후 다시 전단하중을 가하였을 때 지반의 액상화에 대한 저항력은 증가하였다. 하지만 최초 진동으로 지반이 완전히 액상화되었을 경우에는 다음에 전달되는 전단하중에는 이전보다도 지반이 더욱 조밀해짐에도 불구하고 액상화 저항력은 증가하지 않았다. 이와 같은 실내시험결과를 진동 중에 발생하는 간극수압 변화와 흙의 강성저하를 고려할 수 있는 유효응력모델인 UBCSAND모델에 적용하였으며, 최초 전단하중에서 발생하는 간극수압비에 따라 구성모델의 액상화 저항력을 결정하였다. 이 구성모델을 이용하여 재액상화현상을 연구한 원심모형실험의 결과를 예측하였으며, 계측치와 서로 비교하였다. 국내에서도 일본과 가까운 남부지역에서는 약한 지진이지만 자주 발생하고 있는 시점에서 이와 같은 유효응력모델을 이용한 재액상화 현상에 관한 연구가 절실히 요구되어진다.

• Structural Engineering and Mechanics
• /
• 제12권6호
• /
• pp.615-632
• /
• 2001

Ductility of open piled wharves under reversed cyclic loads has been investigated. Experimental testing of five wharf models having a scale of about 1:4 was conducted under the application of horizontal reversed cyclic loading. The experiments were designed to focus on the horizontal ultimate load, ductility and failure mode of the considered wharf models. Nonlinear numerical analyses using the finite element method were also performed on numerical models representing the experimentally tested wharves. The results of the experimental tests showed that open piled wharves possessed favourable ductile behaviour and that their load bearing capacity did not depreciate until a ductility factor of 3 to 4 was reached. The numerical analysis showed that the relative rotation that took place at the joints between the steel piles and the R.C. beam was responsible for a considerable portion of the total horizontal deformation of the wharves. Therefore, it was concluded that introducing the joint stiffness in calculating the deformations of open piled wharves was important to achieve reasonable accuracy.

• 국제초고층학회논문집
• /
• 제3권3호
• /
• pp.231-241
• /
• 2014

Ductile fracture is one of the most common failure modes of steel beam-to-column connections in moment resisting frames. Most proposed evaluation methods of the plastic deformation capacity of a beam until ductile fracture are based on steel beam tests, where the material's yield strength/ratio, the beam's moment gradient, and loading history are the most important parameters. It is impossible and unpractical to cover all these parameters in real tests. Therefore, a new attempt to evaluate a beam's plastic deformation capacity through analysis is introduced in this paper. Another important issue is about the loading histories. Recent years, the effect on the structural component under long-duration ground motion has drawn great attentions. Steel beams tends to experience a large number of loading cycles with small amplitudes during long-duration earthquakes. However, current research often focuses on the beam's behavior under standard incremental loading protocols recommended by respective countries. In this paper, the plastic deformation capacity of steel beams subjected to long duration ground motions was evaluated through analytical methodology.

• Earthquakes and Structures
• /
• 제18권5호
• /
• pp.581-598
• /
• 2020

This paper aims to investigate the seismic behavior and influence parameters of the large-scaled thin-walled reinforced concrete (RC) tubular columns in air-cooled supporting structures of thermal power plants (TPPs). Cyclic loading tests and finite element analysis were performed on 1/8-scaled specimens considering the influence of wall diameter ratio, axial compression ratio, longitudinal reinforcement ratio, stirrup reinforcement ratio and adding steel diagonal braces (SDBs). The research results showed that the cracks mainly occurred on the lower half part of RC tubular columns during the cyclic loading test; the specimen with the minimum wall diameter ratio presented the earlier cracking and had the most cracks; the failure mode of RC tubular columns was large bias compression failure; increasing the axial compression ratio could increase the lateral bearing capacity and energy dissipation capacity, but also weaken the ductility and aggravate the lateral stiffness deterioration; increasing the longitudinal reinforcement ratio could efficiently enhance the seismic behavior; increasing the stirrup reinforcement ratio was favorable to the ductility; RC tubular columns with SDBs had a much higher bearing capacity and lateral stiffness than those without SDBs, and with the decrease of the angle between columns and SDBs, both bearing capacity and lateral stiffness increased significantly.