• 한국지진공학회:학술대회논문집
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• 한국지진공학회 1998년도 추계 학술발표회 논문집 Proceedings of EESK Conference-Spring 1998
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• pp.57-64
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• 1998

This paper presents the cyclic seismic performance of slip-critically designed, high-strength bolted-beam splice in steel moment frame. Before the moment connection reaching its plastic strength, unexpected premature slippage occurred at the slip-critically designed beam splice during the test. The experimentally observed frictional coefficients were as low as about 50% to 60% of nominal (code) value. Nevertheless, the bearing type behavior mobilized after the slippage transferred the increasing cyclic loads successfully, i.e., the consequence of slippage into bearing was not catastrophic to the connection behavior. The test result seems to indicate that the traditional beam splice design basing upon (bolt-hole deducted) effective flange area criterion may not be sufficient in developing the plastic strength of moment connections under severe earthquake loading. New procedure for achieving slip-critical beam splice design is proposed based on capacity design concept.

• Steel and Composite Structures
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• 제7권5호
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• pp.391-404
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• 2007

This paper presents push-out tests of stud shear connectors to examine their fatigue behavior for developing a new composite bridge deck system. The fifteen push-out specimens of D16 mm stud welded on 9 mm steel plate were fabricated according to Eurocode-4, and a series of fatigue endurance test and residual strength test were performed. Additionally, the stiffness and strength variations by cyclic loading were compared. The push-out test, when the stiffness reduction ratio of the specimens was 0.95 under cyclic load, resulted in the failure of the studs. The stiffness variation of the push-out specimens additionally showed that the application of cyclic loads reduced the residual strength. The fatigue strength of the shear connectors were compared with the design values specified in the Eurocode-4, ASSHTO LRFD and JSSC codes. The comparison result showed that the fatigue endurance of the specimens satisfies the design values of these codes.

• 대한치과보철학회지
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• 제47권2호
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• pp.156-163
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• 2009

연구목적: 4종 구치용도재관(Full-porcelain-occlusal-surfaced PFG, Half-porcelain-occlusal-surfaced PFG, Empress 2, Ice Zirkon)과 선별된 한국음식의 fracture load와 dynamic cyclic load를 측정하여 구치용 도재관에 파절을 일으킬 가능성이 있는 한국음식을 선별하는데 있다. 연구재료 및 방법: 4종의 각 porcelain 보철물 system 당 15개의 축대칭을 이루는 crown을 제작했다. 이때 occlusal reduction은 1.5-2.0 mm로 했다(중심부 1.5 mm, 교두부 2.0 mm). 각 15개의 시편의 교합면 중앙부에 직경 5 mm의 stainless steel ball을 위치시킨 후 Instron 4465 universal testing machine(Instron, Norwood, MA USA)을 이용하여 5 mm/min의 crosshead speed로 수직 부하를 주어 파절을 일으키는 최대 부하(N)를 기록했다. 이후, 한국음식 중 삶은 게, 닭(뼈포함), 소갈비(뼈포함), 마른 오징어, 건멸치, 사탕, 호두껍질을 표본으로 설정하고 이들을 파절시키는 최대 부하(N)를 universal testing machine(Instron 4465) 에서 측정하여 기록했다. 각 항목당 15번을 측정했다. 음식물을 파절시킬 때 필요한 최대부하와 각 보철물의 파절저항을 비교하여 한국의 식습관과 도재를 이용한 보철물 파절의 상관관계를 조사하였다. fracture loads는 analysis of variance 와 Post Hoc tests를 이용해서 분석하였다($\alpha$=0.05). 차후에 위에서 얻은 결과를 바탕으로 Hydraulic Dynamic Fatigue Testing Machine(858 Bionix II, MTS systems, Eden Prairie, MN USA)를 이용하여 4종의 각 porcelain 보철물 system당 5개의 crown에 14Hz Cyclic Load를 가하여 crown에 파절을 일으키는 masticatory cycle수를 알아 보았다. Load 수치는 41.0 N(건멸치 파절강도), 169.0 N(마른오징어 파절강도), 382.9 N(닭뼈 파절강도), 2224.8 N(사탕 파절강도)로 설정하였다. 결과: 95% confidence intervals for mean fracture load는 2599.3-2809.1 N(완전도재교합면 PFG), 3689.4-3819.9 N(반도재교합면 PFG), 1501.2-1867.9 N(Ice Zirkon), 803.2-1188.5 N(Empress 2)로 나왔고 95% confidence intervals for dynamic cyclic load on fracture는 instron 상에서 도재보철물에 파절을 일으키지 않은 load인 2224.8 N(사탕 파절강도)와 382.9 N(닭뼈 파절강도)로 실험했을 때, 2224.8 N에서 4796.8-9321.2 cycles(완전도재교합면 PFG), 2224.8 N에서 881705.1-1143565.7 cycles(반도재교합면 PFG), 382.9 N에서 979993.0-1145773.4 cycles(Ice Zirkon), 382.9 N에서 564.1-954.7 cycles(Empress 2)로 나왔다. 결론: 통계학적으로 유의할 만한 차이가 그룹들 간 fracture load에서 나타났다. 한국음식물 중 소갈비(뼈포함)와 사탕(자두맛캔디)은 구치용 도재보철물을 파절시킬 가능성이 있는 음식물로 밝혀졌다. 단일수직부하에서는 파절이 생기지 않는 경우라 할지라도 dynamic cyclic load를 줄 경우 일정 주기 후에 파절이 생기는 결과를 얻을 수 있었다.

• 대한기계학회논문집A
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• 제31권12호
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• pp.1165-1172
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• 2007

The spacer grid set is a part of a nuclear fuel assembly. The set has a spring and the spring supports the fuel rods safely. Although material nonlinearity is involved in the deformation of the spring, nonlinearity has not been considered in design of the spring. Recently a nonlinear response structural optimization method has been developed using equivalent loads. It is called nonlinear response optimization equivalent loads (NROEL). In NROEL, the external loads are transformed to the equivalent loads (EL) for linear static analysis and linear response optimization is carried out based on the EL in a cyclic manner until the convergence criteria are satisfied. EL is the load set which generates the same response field of linear analysis as that of nonlinear analysis. Shape optimization of the spring is carried out based on EL. The objective function is defined by minimizing the maximum stress in the spring while mass is limited and the support force of the spring is larger than a certain value. The results are verified by nonlinear response analysis. ABAQUS is used for nonlinear response analysis and GENESIS is employed for linear response optimization.

• Nuclear Engineering and Technology
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• 제52권12호
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• pp.2918-2927
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• 2020

This paper proposes a simplified elastic-plastic analysis procedure using the penalty factors presented in the Code Case N-779 for strain-based fatigue assessment of nuclear safety class 1 components under severe seismic loads such as safety shutdown earthquake and beyond design-basis earthquake. First, a simplified elastic-plastic analysis procedure for strain-based fatigue assessment of nuclear safety class 1 components under the severe seismic loads was proposed based on the analysis result for the simplified elastic-plastic analysis procedure in the Code Case N-779 and the stress categories corresponding to normal operation and seismic loads. Second, total strain amplitude was calculated directly by performing finite element cyclic elastic-plastic seismic analysis for a hot leg nozzle in pressurizer surge line subject to combined loading including deadweight, pressure, seismic inertia load, and seismic anchor motion, as well as was derived indirectly by applying the proposed analysis procedure to the finite element elastic stress analysis result for each load. Third, strain-based fatigue assessment was implemented by applying the strain-based fatigue acceptance criteria in the ASME B&PV Code, Sec. III, Subsec. NB, Article NB-3200 and by using the total strain amplitude values calculated. Last, the total strain amplitude and the fatigue assessment result corresponding to the simplified elastic-plastic analysis were compared with those using the finite element elastic-plastic seismic analysis results. As a result of the comparison, it was identified that the proposed analysis procedure can derive reasonable and conservative results.

• 콘크리트학회논문집
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• 제12권2호
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• pp.53-62
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• 2000

Under severe lateral loads, ductile moments-resisting reinforced concrete frames will be subjected to large loads and displacements. Thus, large deformation and shear stree are occurred at the beam-column joints which are the most critical region in ductile moments-resisting system. The purpose of this study was to investigate the shear strength of beam-column connection using high strength concrete. Four subassemblies were designed 2/3 scale of read structures and tested. The obtained results are as follows. 1) The transverse beams increase the shear resistance and ductility of joint, 2) The slab was contributed to increase of the flexural capacity of the beam, but was not contributed to increase the joint ductility under cyclic loads. 3) The shear stress factors. given by the ACI code would be modified in evaluating the shear strength of beam-column joints of frame which were constructed with high-strength concrete.

• Structural Engineering and Mechanics
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• 제25권6호
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• pp.675-690
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• 2007

In order to study the ductility and the lateral load carrying capacity of the masonry walls strengthened with CFRPs (Carbon Fiber Reinforced Polymer sheets), three pieces of masonry walls subjected to cyclic loads with low frequency and vertical load of constant amplitude have been tested. Two different strengthening methods have been used. The strengthening efficiency is affected by the strengthening method. A simplified calculation approach has been introduced based on the experimental test results, and the theoretical results agree reasonably well with the experimental results. It is found that the critical loads, the critical displacements, the ultimate loads, the ultimate displacements and the ductile coefficients of the masonry walls strengthened with CFRPs improve remarkably (6%~57%). Therefore, the masonry structures strengthened with CFRPs are of better ductility and of better lateral load carrying capacity than the masonry structures without any strengthening measurements.

• Structural Engineering and Mechanics
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• 제25권1호
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• pp.107-126
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• 2007

The problem related to the computation of bounds on plastic deformations for structures in plastic shakedown condition (alternating plasticity) is studied. In particular, reference is made to structures discretized by finite elements constituted by elastic perfectly plastic material and subjected to a special combination of fixed and cyclic loads. The load history is known during the steady-state phase, but it is unknown during the previous transient phase; so, as a consequence, it is not possible to know the complete elastic plastic structural response. The interest is therefore focused on the computation of bounds on suitable measures of the plastic strain which characterizes just the first transient phase of the structural response, whatever the real load history is applied. A suitable structural model is introduced, useful to describe the elastic plastic behaviour of the structure in the relevant shakedown conditions. A special bounding theorem based on a perturbation method is proposed and proved. Such theorem allows us to compute bounds on any chosen measure of the relevant plastic deformation occurring at the end of the transient phase for the structure in plastic shakedown; it represents a generalization of analogous bounding theorems related to the elastic shakedown. Some numerical applications devoted to a plane steel structure are effected and discussed.

• Steel and Composite Structures
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• 제22권2호
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• pp.235-255
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• 2016

This paper experimentally investigated the behavior of steel frame structures of traditional-style buildings subjected to combined constant axial load and reversed lateral cyclic loading conditions. The low cyclic reversed loading test was carried out on a 1/2 model of a traditional-style steel frame. The failure process and failure mode of the structure were observed. The mechanical behaviors of the steel frame, including hysteretic behaviors, order of plastic hinges, load-displacement curve, characteristic loads and corresponding displacements, ductility, energy dissipation capacity, and stiffness degradation were analyzed. Test results showed that the Dou-Gong component (a special construct in traditional-style buildings) in steel frame structures acted as the first seismic line under the action of horizontal loads, the plastic hinges at the beam end developed sufficiently and satisfied the Chinese Seismic Design Principle of "strong columns-weak beams, strong joints-weak members". The pinching phenomenon of hysteretic loops occurred and it changed into Z-shape, indicating shear-slip property. The stiffness degradation of the structure was significant at the early stage of the loading. When failure, the ultimate elastic-plastic interlayer displacement angle was 1/20, which indicated high collapse resistance capacity of the steel frame. Furthermore, the finite element analysis was conducted to simulate the behavior of traditional-style frame structure. Test results agreed well with the results of the finite element analysis.

• Earthquakes and Structures
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• 제18권5호
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• pp.637-648
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• 2020

In this study, a new steel cylindrical shell configuration of the dissipative energy device is proposed to improve lateral ductility and to reduce the damage of the structures against seismic forces. Four nested-eccentric- cylindrical shells are used to constructing this device; therefore, this proposed device is named nested-eccentric-cylindrical shells damper (NECSD). The particular configuration of the nested-eccentric-cylindrical shells is applied to promote the mechanical characteristics, stability, and overall performance of the damper in cyclic loads. Shell-type components are performed as a combination of series and parallel non-linear springs into the in-plan plastic deformation. Numerical analysis with respect to dimensional variables are used to calculate the mechanical characteristics of the NECSD, and full-scale testing is conducted for verifying the numerical results. The parametric study shows the NECSD with thin shells were more flexible, while devices with thick shells were more capacious. The results from numerical and experimental studies indicate that the NECSD has a stable behavior in hysteretic loops with highly ductile performance, and can provide appropriate dissipated energy under cyclic loads.