• Structural Engineering and Mechanics
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• 제27권6호
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• pp.713-739
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• 2007

Nowadays computers can perform symbolic computations in addition to mere number crunching operations for which they were originally designed. Symbolic computation opens up exciting possibilities in Structural Mechanics and engineering. Classical areas have been increasingly neglected due to the advent of computers as well as general purpose finite element software. But now, classical analysis has reemerged as an attractive computer option due to the capabilities of symbolic computation. The repetitive cycles of simultaneous - equation sets required by the finite element technique can be eliminated by solving a single set in symbolic form, thus generating a truly closed-form solution. This consequently saves in data preparation, storage and execution time. The power of Symbolic computation is demonstrated by six examples by applying symbolic computation 1) to solve coupled shear wall 2) to generate beam element matrices 3) to find the natural frequency of a shear frame using transfer matrix method 4) to find the stresses of a plate subjected to in-plane loading using Levy's approach 5) to draw the influence surface for deflection of an isotropic plate simply supported on all sides 6) to get dynamic equilibrium equations from Lagrange equation. This paper also presents yet another computationally efficient and accurate numerical method which is based on the concept of derivative of a function expressed as a weighted linear sum of the function values at all the mesh points. Again this method is applied to solve the problems of 1) coupled shear wall 2) lateral buckling of thin-walled beams due to moment gradient 3) buckling of a column and 4) static and buckling analysis of circular plates of uniform or non-uniform thickness. The numerical results obtained are compared with those available in existing literature in order to verify their accuracy.

• 한국전산구조공학회논문집
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• 제18권2호
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• pp.181-190
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• 2005

파사드리거는 아웃리거 구조시스템에 rms거하는 것으로 구조물의 외곽에 설치되는 파사드리거는 구조물의 내부에 수직으로 설치된 가새골조로부터 분리되어 구조물의 외곽에 설치된다. 따라서 이 시스템은 중앙의 코아에 부착되는 아웃리거와는 달리 사재로 인한 내부 동선의 장애가 발생하지 않는 장점이 있다. 리거의 현재에 인접한 슬래브가 파사드리거와 가새골조 사이의 전단력을 전달하며 가새골조와 파사드리거를 지지하는 기둥 사이의 상호작용을 일으킨다. 이 논문에서는 등분포하중과 삼각분포하중, 그리고 구조물 상단에 집중하중이 작용하고 구조물의 외곽에 여러개의 파사드리거가 설치된 가새골조에 대한 근사해석방법을 제시하였으며, 구조모델들을 이용하여 MIDAS프로그램에 의한 결과와 비교하였고 만족할만한 결과를 얻었다. 본 연구에서 제시된 매트릭스 해석방법은 구조물 상단의 수평변위나 가새골조 하단의 전도모멘트와 같은 구조물의 거동에 대한 파사드리거의 영향을 신속하게 평가할 수 있으며 구조물 상단의 변위를 최소화할 수 있는 파사드리거의 최적위치 결정을 위해 유용하게 사용될 수 있을 것이다.

• 한국지진공학회논문집
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• 제6권6호
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• pp.25-32
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• 2002

실무에서 교량 교각의 내진해석을 수행할 때 계산의 편의와 보수적인 설계를 위하여 기초의 연성을 고려하지 않고 지반면을 고정단으로 가정하여 해석하는 경우가 많다. 이러한 고정단 모델은 대부분의 경우 설계력 측면에서 매우 보수적인 결과를 주므로, 최근 기초의 연성을 고려하여 현실적으로 교각 기초를 모델링하려는 연구가 수행되고 있다. 본 연구에서는 기초연성의 모델링 방법, 입력응답스펙트럼의 종류 그리고 지반조건을 달리하여 응답스펙트럼 해석을 수행하였다. 수치해석을 통하여 교각에 발생하는 전단력, 모멘트 그리고 변위를 비교하여 기초의 연성을 고려하는 기법과 지반 및 지진파 특성들이 해석결과에 미치는 영향을 분석하였다. 대부분의 경우 고정단 모델에서 큰 전단력과 모멘트가 발생하였지만, 연약 점성토층에 장주기 지진파가 작용하는 특수한 경우에는 기초의 연성을 고려한 모델에서 고정단 모델보다 큰 전단력과 모멘트가 발생하였다. 또한 기초의 연성을 고려하는 여러 모델들의 해석결과를 지반-구조물 동적 상호작용을 고려한 정밀 동해석 결과와 비교하여 그들의 적용성을 평가하였다.

• Steel and Composite Structures
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• 제34권6호
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• pp.891-907
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• 2020

Many studies reveal that during destructive earthquakes, most of the structures enter the inelastic phase. The amount of hysteretic energy in a structure is considered as an important criterion in structure design and an important indicator for the degree of its damage or vulnerability. The hysteretic energy value wasted after the structure yields is the most important component of the energy equation that affects the structures system damage thereof. Controlling this value of energy leads to controlling the structure behavior. Here, for the first time, the hysteretic behavior and energy dissipation capacity are assessed at presence of elliptical braced resisting frames (ELBRFs), through an experimental study and numerical analysis of FEM. The ELBRFs are of lateral load systems, when located in the middle bay of the frame and connected properly to the beams and columns, in addition to improving the structural behavior, do not have the problem of architectural space in the bracing systems. The energy dissipation capacity is assessed in four frames of small single-story single-bay ELBRFs at ½ scale with different accessories, and compared with SMRF and X-bracing systems. The frames are analyzed through a nonlinear FEM and a quasi-static cyclic loading. The performance features here consist of hysteresis behavior, plasticity factor, energy dissipation, resistance and stiffness variation, shear strength and Von-Mises stress distribution. The test results indicate that the good behavior of the elliptical bracing resisting frame improves strength, stiffness, ductility and dissipated energy capacity in a significant manner.

• Steel and Composite Structures
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• 제37권1호
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• pp.15-26
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• 2020

The top-and-seat angles with double web angles are commonly used in the design of beam-to-column joints in Asian and North American countries. The seismic behavior analysis of these joints with large cross-section size of beam and column (often connected by four or more bolts) is a challenge due to the effects from the relatively larger size of stiffened angles and the composite action from the adjacent concrete slab. This paper presents an experimental investigation on the seismic performance of exterior composite beam-to-column joints with stiffened angles under cyclic loading. Four full-scale composite joints with different configuration (only one specimen contain top angle in concrete slab) were designed and tested. The joint specimens were designed by considering the effects of top angles, longitudinal reinforcement bars and arrangement of bolts. The behavior of the joints was carefully investigated, in terms of the failure modes, slippage, backbone curves, strength degradation, and energy dissipation abilities. It was found that the slippage between top-and-seat angles and beam flange, web angle and beam web led to a notable pinching effect, in addition, the ability of the energy dissipation was significantly reduced. The effect of anchored beams on the behavior of the joints was limited due to premature failure in concrete, the concrete slab that closes to the column flange and upper flange of beam plays an significant role when the joint subjected to the sagging moment. It is demonstrated that the ductility of the joints was significantly improved by the staggered bolts and welded longitudinal reinforcement bars.

• 대한토목학회논문집
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• 제32권5C호
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• pp.221-229
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• 2012

NATM터널의 안정성 확보를 위해 지반조건이 불량한 경우 숏크리트에 격자지보나 H형강 등의 강지보를 보강하는 경우가 많다. 그러나 설계 시 강지보를 숏크리트가 경화되기 전 임시지보재로 간주하여 수치해석 시 고려하지 않는 것이 일반적이며, 수치해석에 고려하더라도 모델링 방법이 다양하다. 본 연구에서는 휨강도실험, 압축강도실험, 그리고 실대형실험을 통하여 강지보와 숏크리트 합성부재의 거동과 하중 부담률을 분석하였다. 또한 실험과 같은 조건에서 숏크리트와 강지보의 고려방법을 달리하여 수치해석을 실시하여 실험결과와 비교분석하였다. 연구결과 숏크리트와 강지보는 경계면에서의 미끄러짐(slip)으로 인하여 일체로 거동하지 않으며, 수치해석 시 휨모멘트는 강지보가 모두 부담하고 축력은 숏크리트와 강지보가 압축강성비에 따라 분담하는 것으로 고려하는 것이 적절한 것으로 평가되었다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1998년도 추계학술대회
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• pp.155-156
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• 1998

Screw loosening and subsequent pullout can be attributed to the reduction in bone mineral density in the vertebrae manifested by osteoporosis in which the decrease in fixation strength between the cancellous bone and screw threads are accelerated by repeated loads exerted by patients own weight and activities following the surgery. In this study, the change in pullout strength of the pedicle screws was investigated before and after repeated loads were imparted. For this purpose. Diapason pedicle screws $(6.7\times40mm)$ were inserted onto fresh porcine spine specimens (T1-L5) after bone mineral density was measured using a DEXA. With an MTS, an axial load was applied at a loading rate of 0.33mm/sec until failure to measure the maximum pullout strength. Flexion moment of 7.5N-m was then imparted at 0.5Hz for 2000 cycles. It was found that the maximum pullout strength was exponentially related to BMD regardless of load types ($107.71\;\times\;\exp^{(1.43{\times}BMD)}r^2=0.93$, P<0.0001 without repeated load; ($107.71\;\times\;\exp^{(2.19{\times}BMD)}r^2=0.78$, P<0.0001 with repeated load). The results suggest that the reduction in pullout strength for pedicle screws is far more prominent in osteoporotic spine than in normal spine especially as number of repeated load was increased. More importantly, it was demonstrated that the level of bone mineral density and the activity level of the patient should be evaluated in more detail for successful implementation of pedicle screw systems in spinal surgery.

• 한국강구조학회 논문집
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• 제9권4호통권33호
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• pp.557-578
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• 1997

이 연구의 목적은 매우 큰 지진하에 휨 모멘트에 의해서만 항복하는 부재와 휨 모멘트와 축 방향력에 의하여 항복하는 부재를 모델 할 수 있는 보-기둥 요소를 개발하는데 있다. 이 요소는 직렬 힌지 모델 (one-component series hinge model)로 간주 될 수 있으며, 축 방향 강성도 변화와 축 방향 소성 변형을 고려 할 수 있고 또한 단조, 주기, 임의 하중 등을 적절히 모델 할 수 있는 경화 법칙 (hardening rules)을 고려한다. 일반적으로 이 요소는 실험 결과 및 화이버 모델 (fiber model)에 비교하여 볼 때 기존의 이직선 힌지 모델 (bilinear hinge model)보다 우수한 거동을 보였고 모멘트 저항 뼈대 구조물의 강 부재의 보-기둥 거동을 적절하게 모델 할 수 있었다. 개발된 보-기둥 요소는 지진 하중하에서 구조물의 전체적인 거동과 설계에 필요한 국부 변형량을 기존의 이직선 힌지 모델 보다 매우 정확하게 예측 할 수 있다.

• 한국강구조학회 논문집
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• 제9권4호통권33호
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• pp.479-487
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• 1997

강구조 건축물의 접합에서 강접합, 단순접합 이외에 반강접합의 이용이 고려될 수 있다. 반강접합의 장점으로서는 시공의 용이성과 부재의 효율적인 모멘트 분배가 가능하다는 점이다. 본 연구는 기존의 T-stub를 더 많은 회전능력이 생기도록 한 개량 T-stub를 접합요소로 선정하여 중층정도의 건축물에의 적용 가능성을 확인하기 위한 연구의 기초적 단계이다. 연구방법으로서는 개량 T-stub의 역학적 거동을 조사하기 위한 개량 T-stub요소의 인장 및 압축 실험과 개량 T-stub를 이용한 기둥-보 접합부의 단순재하실험이 실시되었다. 실험결과로부터 개량 T-stub의 정성적인 거동을 파악하였고, 개량 T-stub를 이용하면 반강접합으로서의 가능성도 확인하였다.

• 한국농공학회지
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• 제40권3호
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• pp.83-92
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• 1998

Field experiment was performed from August 1996 to January 1998 to examine the applicability of constructed wetland system for wastewater treatment in rural area. The pilot plant was installed in Kon-Kuk University and the school building septic tank effluent was used as an influent to the treatment basin. Hydraulic loading rate was about 0.1 6$0.16^3/m^2$ day and theoretical detention time in the system was 1.38 days. The treatment basin was composed of sand and reed. The influent DO concentration was low and many cases close to zero, but effluent concentration was higher than the influent which implies that oxygen was supplied naturally. The average concentration of influent BOD was 126mg/L, and with average removal rate of 69 % the average effluent concentration was 4Omg/L which satisfied the effluent water quality standard for the system of interest. The average influent concentration of COD was 2Olmg/L and average effluent concentration was 75mg/L with average removal rate of 60%. The performance of BOD and COD tends to deteriorate in the low temperature, and appropriate action needs to be taken during the cold winter time for stable operation. The average influent concentration of SS was 5Omg/L, and effluent was 1 1mg/L with average removal rate of 76% which satisfied the effluent water quality standard for the system of interest. The results for the regulated components, SOD and SS, from the experiment showed that constructed wetland system can meet the effluent water quality standards. The average influent concentration of total phosphorus was 25.6mg/L and average effluent concentration was 7.8mg/L with average removal rate of 63%. Not like the performance of the above components, average nitrogen removal rate was only 11.2% which is not satisfactory. Although, nitrogen is not regulated at this moment, it can cause many environmental problems including eutrophication. Therefore, nitrogen removal efficiency should be improved for actual application. From the result of the field experiment, constructed wetland system was thought to be an appropriate alternative for wastewater treatment in rural area.