• 한국강구조학회 논문집
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• 제13권4호
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• pp.363-372
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• 2001

본 연구의 목적은 보항복형 비가새 골조의 $P-{\Delta}$영향을 실험적 방법을 통하여 조사하는데 있다. 이를 위하여 4개의 1층 1스팬의 보항복형 비가새 골조에 대한 가력실험을 실시하였다. 실험의 변수로는 기둥의 강성과 축력비를 적용하였다. 실험결과 저축력 상태의 보항복형 비가새 골조에서는 축력의 정량적인 크기가 $P-{\Delta}$효과로서 골조의 안정성에 영향을 미치는 것으로 나타났다. 그리고 최대수평하중은 기둥의 강성과 지점 회전강성에 비례하여 증가하며 저축력상태의 보항복형 비가새 골조는 붕괴가구 형성이 비교적 안정적인 상태에서 이루어짐을 알 수 있었다. 그리고 한계상태설계기준의 $B_2$ 계수는 골조의 비탄성거동시 $P-\Delta$효과를 적절히 고려하지 못하는 것으로 판단된다.

• 한국강구조학회 논문집
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• 제22권1호
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• pp.87-97
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• 2010

본 연구는 비대칭 비가새 골조를 대상으로 강구조 설계기준에서 제시하고 있는 하중증폭계수를 적용한 2차 해석법의 타당성을 해석적 방법을 통해 평가하는데 그 목적이 있다. 이를 위해 KBC 2005에서 제안하고 있는 B1 및 B2 계수를 적용한 2차 해석과 KBC 2009에서 제안하고 있는 하중증폭계수를 적용한 직접해석을 5층 2스팬 및 5층 4스팬 비대칭 비가새 강구조 골조에 대해 실시하고, 그 해석 결과를 2차 비탄성 해석 결과와 비교하여 기준에서 제안된 2차 해석법들을 평가하였다. 해석의 주요 변수로는 골조 형상, 기둥 축력비, 해석방법, 기둥수평위치 등이 적용되었다. 연구 결과 구조물의 비대칭성은 B2 계수 및 제안된 해석법의 유효성에 영향을 미치는 것으로 나타났으며, 특히 기둥삭제 및 경사 기둥의 경우 오차의 범위가 증가하는 것으로 나타났다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.1740-1743
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• 2007

In this study, two types of fatigue tests were conducted. First, cyclic bending tests were performed using the micro-bending tester. A four-point bending test method was adopted, because it induces uniform stress fields within a loading span. Second, thermal fatigue tests were conducted using a pseudo power cycling machine which was newly developed for a realistic testing condition. The pseudo-power cycling method makes up for the weak points in a power cycling and a chamber cycling method. Two compositions of solder are tested in all test condition, one is lead-free solder (95.5Sn4.0Ag0.5Cu) and the other is eutectic lead-contained solder (63Sn37Pb). In the cyclic bending test, the solder that exhibits a good reliability can be reversed depending on the load conditions. The lead-contained solders have a longer fatigue life in the region where the applied load is high. On the contrary, the lead-free solder sustained more cyclic loads in the small load region. A similar trend was detected at the thermal cycling test. A three-dimensional finite element analysis model was constructed. A finite element analysis using ABAQUS was performed to extract the applied stress and strain in the solder joints. A constitutive model which includes both creep and plasticity was employed. Thermal fatigue was occurred due to the creep. And plastic deformation is main damage for bending failure. From the inelastic energy dissipation per cycle versus fatigue life curve, it can be found that the bending fatigue life is longer than the thermal fatigue life.

• Earthquakes and Structures
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• 제9권1호
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• pp.127-143
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• 2015

In conventional seismic design, structures are assumed to be fixed at the base. To reduce the impact of earthquake loading, while at the same time providing an economically feasible structure, minor damage is tolerated in the form of controlled plastic hinging at predefined locations in the structure. Uplift is traditionally not permitted because of concerns that it would lead to collapse. However, observations of damage to structures that have been through major earthquakes reveal that partial and temporary uplift of structures can be beneficial in many cases. Allowing a structure to move as a rigid body is in fact one way to limit activated seismic forces that could lead to severe inelastic deformations. To further reduce the induced seismic energy, slip-friction connectors could be installed to act both as hold-downs resisting overturning and as contributors to structural damping. This paper reviews recent research on the concept, with a focus on timber shear walls. A novel approach used to achieve the desired sliding threshold in the slip-friction connectors is described. The wall uplifts when this threshold is reached, thereby imparting ductility to the structure. To resist base shear an innovative shear key was developed. Recent research confirms that the proposed system of timber wall, shear key, and slip-friction connectors, are feasible as a ductile and low-damage structural solution. Additional numerical studies explore the interaction between vertical load and slip-friction connector strength, and how this influences both the energy dissipation and self-centring capabilities of the rocking structure.

• Structural Engineering and Mechanics
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• 제52권6호
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• pp.1135-1156
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• 2014

The ratcheting effect greatly challenges the design of piping components. With the assistance of the quasi-three point bending apparatus, ratcheting and the ratcheting boundary of pressurized straight Z2CND18.12N stainless steel pipe under bending loading and vertical displacement control were studied experimentally. The characteristics of progressive inelastic deformation in axial and hoop directions of the Z2CND18.12N stainless steel pipes were investigated. The experiment results show that the ratcheting strain occurs mainly in the hoop direction while there is less ratcheting strain in the axial direction. The characteristics of the bending ratcheting behavior of the pressure pipes were derived and compared under load control and displacement control, respectively. The results show that the cyclic bending loading and the internal pressure affect the ratcheting behavior of the pressurized straight pipe significantly under load control. In the meantime, the ratcheting characteristics are also highly associated with the cyclic displacement and the internal pressure under displacement control. All these factors affect not only the saturation of the ratcheting strain but the ratcheting strain rate. A series of multi-step bending ratcheting experiments were conducted under both control modes. It was found that the hardening effect of Z2CND18.12N stainless steel pipe under previous cyclic loadings no matter with high or low displacement amplitudes is significant, and the prior loading histories greatly retard the ratcheting strain and its rate under subsequent loadings. Finally, the ratcheting boundaries of the pressurized straight Z2CND18.12N stainless steel pipe were determined and compared based on KTA/ASME, RCC-MR and the experimental results.

• Earthquakes and Structures
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• 제8권5호
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• pp.1039-1054
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• 2015

The purpose of this study was to evaluate the seismic performance of weak-axis column-tree type connections used in steel moment frames. These connections are composed of a shop-welded and fieldbolted steel structure and can improve welding quality. On this basis, column-tree type connections are widely used in steel moment resisting frames in Korea and Japan. In this study, splices designed with a semirigid concept regarding the seismic performance of column-tree connections were experimentally evaluated. The structures can absorb energy in an inelastic state rather than the elastic state of the structures by the capacity design method. For this reason, the plastic hinge might be located at the splice connection at the weak-axis column-tree connection by reducing the splice plate thickness. The main variable was the distance from the edge of the column flange to the beam splice. CTY series specimens having column-tree connections with splice length of 600 mm and 900 mm were designed, respectively. For comparison with two specimens with the main variable, a base specimen with a weak-axis column-tree connection was fabricated and tested. The test results of three full-scale test specimens showed that the CTY series specimens successfully developed ductile behavior without brittle fracture until 5% story drift ratio. Although the base specimen reached a 5% story drift ratio, brittle fracture was detected at the backing bar near the beam-to-column connection. Comparing the energy dissipation capacity for each specimen, the CTY series specimens dissipated more energy than the base specimen.

• Earthquakes and Structures
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• 제11권3호
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• pp.483-503
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• 2016

This study aims to evaluate seismic performance of existing low and mid-rise reinforced concrete buildings by comparing their displacement capacities and displacement demands under selected ground motions experienced in Turkey as well as demand spectrum provided in 2007 Turkish Earthquake Code for design earthquake with 10% probability of exceedance in 50 years for soil class Z3. It should be noted that typical residential buildings are designed according to demand spectrum of 10% probability of exceedance in 50 years. Three RC building sets as 2-, 4- and 7-story, are selected to represent reference low-and mid-rise buildings located in the high seismicity region of Turkey. The selected buildings are typical beam-column RC frame buildings with no shear walls. The outcomes of detailed field and archive investigation including approximately 500 real residential RC buildings established building models to reflect existing building stock. Total of 72 3-D building models are constructed from the reference buildings to include the effects of some properties such as structural irregularities, concrete strength, seismic codes, structural deficiencies, transverse reinforcement detailing, and number of story on seismic performance of low and mid-rise RC buildings. Capacity curves of building sets are obtained by nonlinear static analyses conducted in two principal directions, resulting in 144 models. The inelastic dynamic characteristics are represented by "equivalent" Single-Degree-of- Freedom (ESDOF) systems using obtained capacity curves of buildings. Nonlinear time history analysis is used to estimate displacement demands of representative building models idealized with (ESDOF) systems subjected to the selected ground motion records from past earthquakes in Turkey. The results show that the significant number of pre-modern code 4- and 7-story buildings exceeds LS performance level while the modern code 4- and 7-story buildings have better performances. The findings obviously indicate the existence of destructive earthquakes especially for 4- and 7-story buildings. Significant improvements in the performance of the buildings per modern code are also obvious in the study. Almost one third of pre-modern code buildings is exceeding LS level during records in the past earthquakes. This observation also supports the building damages experienced in the past earthquake events in Turkey.

• Earthquakes and Structures
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• 제5권5호
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• pp.499-526
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• 2013

Seismic isolation is an effective method for the protection of buildings and their contents during strong earthquakes. This research work aims to assess the appropriateness of the linear and nonlinear models that can be used in the analysis of typical low-rise base isolated steel buildings, taking into account the inherent nonlinearities of the isolation system as well as the potential nonlinearities of the superstructure in case of strong ground motions. The accuracy of the linearization of the isolator properties according to Eurocode 8 is evaluated comparatively with the corresponding response that can be obtained through the nonlinear hysteretic Bouc-Wen constitutive model. The suitability of the linearized model in the determination of the size of the required seismic gap is assessed, under various earthquake intensities, considering relevant methods that are provided by building codes. Furthermore, the validity of the common assumption of elastic behavior for the superstructure is explored and the alteration of the structural response due to the inelastic deformations of the superstructure as a consequence of potential collision to the restraining moat wall is studied. The usage of a nonlinear model for the isolation system is found to be necessary in order to achieve a sufficiently accurate assessment of the structural response and a reliable estimation of the required width of the provided seismic gap. Moreover, the simulations reveal that the superstructure's inelasticity should be taken into account, especially if the response of the structure under high magnitude earthquakes is investigated. The consideration of the inelasticity of the superstructure is also recommended in studies of structural collision of seismically isolated structures to the surrounding moat wall, since it affects the response.

• 한국철도학회논문집
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• 제17권1호
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• pp.52-58
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• 2014

노반 성토체에서 발생하는 소성 변형은 콘크리트 궤도의 안정성과 유지보수에 영향을 미친다. 철도 노반에서의 장기적인 소성 변형은 주로 반복적인 열차 통과로 발생하는 누적된 비탄성적 변형률에 의해 발생한다. 누적 소성 변형의 예측은 궤도의 유지보수와 열차의 안전한 운영을 위해서 중요하다. 본 연구에서는 서로 다른 강화노반 두께를 가진 철도노반에서 발생하는 연직 변위를 계산하였다. 누적 소성 변형률을 계산하기 위한 멱함수의 상수는 삼축 실험과 실대형 재하 실험의 결과로부터 구하였다. 표준 노반 단면에 대한 3차원 유한요소해석 결과로부터 강화노반의 두께를 선정하는 가이드라인을 제시하였다.

• 한국지진공학회논문집
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• 제10권2호
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• pp.11-19
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• 2006

본 연구에서는 4층, 10층, 30층 스태거드 트러스 시스템 (STS)의 비탄성 정적해석에 의한 하중-변위 관계와 비탄성거동을 분석하고, 그 결과를 바탕으로 STS의 내진성능을 평가하였다. 또한 동일한 규모의 모멘트골조 및 가새골조의 거동과 비교함으로써 STS의 횡력 저항 능력을 파악하였다. 해석결과에 따르면, STS는 일반적으로 적용되는 구조시스템에 비하여 비교적 만족할 만한 내진성능을 보유하는 것으로 나타났다. 그러나 중층 이상의 STS에 있어서는 상대적으로 강성이 작은 비렌딜 패널 상.하현재에 소성변형이 발생한 후 인접한 수직 가새가 항복함으로써, 다른 층으로 소성변형이 전이되지 못하여 약층의 형성에 의한 취성적인 거동을 보인다. 그러므로 스태거드 트러스 시스템의 연성능력을 확보하기 위해서는 비렌딜 패널의 수직 가새를 보강하여 비렌딜 패널 상하현재에 발생한 소성변형을 다른 층의 비렌틸 패널로 유도하는 것이 필요하다.