• Steel and Composite Structures
• /
• 제31권1호
• /
• pp.99-112
• /
• 2019

Semi-rigid joints have been widely studied in literature in recent decades because they affect greatly the structural response of frames. In literature, the behavior of semi-rigid joints is commonly assumed to be identical under positive and negative moments which are obviously incorrect in many cases where joint details such as bolt arrangement or placement of haunch are vertically asymmetrical. This paper evaluates two common types of steel frames with asymmetrical beam-to-column joints by Direct Analysis allowing for plasticity. A refined design method of steel frames using a proposed simple forth order curved-quartic element with an integrated joint model allowing for asymmetrical geometric joint properties is presented. Furthermore, the ultimate behavior of six types of asymmetrical end-plate connections under positive and negative moment is examined by the Finite Element Method (FEM). The FEM results are further applied to the proposed design method with the curved-quartic element for Direct Analysis of two types of steel frames under dominant gravity or wind load. The ultimate frame behavior under the two different scenarios are examined with respect to their failure modes and considerably different structural performances of the frames were observed when compared with the identical frames designed with the traditional method where symmetrical joints characteristics were assumed. The finding of this research contributes to the design of steel frames as their asymmetrical beam-to-column joints lead to different frame behavior when under positive and negative moment and this aspect should be incorporated in the design and analysis of steel frames. This consideration of asymmetrical joint behavior is recommended to be highlighted in future design codes.

• Kyungpook Mathematical Journal
• /
• 제32권3_spc호
• /
• pp.517-522
• /
• 1992

• 한국도로학회논문집
• /
• 제14권5호
• /
• pp.133-143
• /
• 2012

PURPOSES: Using the collected data for crash, traffic volume, and design elements on ramps between 2007 and 2009, this research effort was initiated to develop traffic crash prediction models for expressway ramps. METHODS: Three negative binomial regression models and three zero-inflated negative binomial regression models were developed for individual ramp types, including direct, semi-direct and loop, respectively. For validating the developed models, authors compared the estimated crash frequencies with actual crash frequencies of twelve randomly selected interchanges, the ramps of which have not been used for model developing. RESULTS: The results show that the negative binomial regression models for direct, semi-direct and loop ramps showed 60.3%, 63.8% and 48.7% error rates on average whereas the zero-inflated negative binomial regression models showed 82.1%, 120.4% and 57.3%, respectively. CONCLUSIONS: Conclusively, the negative binomial regression models worked better in traffic crash prediction than the zero-inflated negative binomial regression models for estimating the frequency of traffic accidents on expressway ramps.

• 대한기계학회논문집A
• /
• 제25권10호
• /
• pp.1541-1550
• /
• 2001

This paper describes experimental investigations in the direct extrusion of copper clad aluminum rods through conical dies. Composite materials consist of two or more different material layers. Copper clad aluminum composite materials are being used fur economic and structural purposes and the development of an efficient production method of copper clad aluminum composite material rods by extrusion is very important, It is necessary to know the conditions in which successful uniform extrusion ,and sound cladding may be carried out without any defects in the direct extrusion. There are several variables that have an influence on determining a sound clad extrusion. In order to investigate the influence of these parameters on the hot direct extrudability of the copper clad aluminum composite material rods, the experimental study have been performed with various extrusion temperatures, extrusion ratios and semi-cone angles of die. Subsequently, the microscopic inspection of interface bonding is carried out for extruded products. By measuring hardness, along extrusion way of products, a variation of hardness has been discussed. Proportional flow state has been considered by measuring radius ratio of Cu sleeve and Al core before and after extrusion.

• 디지털융복합연구
• /
• 제14권4호
• /
• pp.419-424
• /
• 2016

본 논문에서는 광학설계 프로그램을 이용하여 LED 광원의 위치 변화에 따른 배광분포에 대하여 연구하였다. 사용한 LED 조명기구는 엣지형의 LED 배열을 이용하였으며 반사판을 중심으로 도광판 및 확산판을 위와 아래에 배치한 구조이다. LED 칩을 반사판 에지 중심에서 위로 1mm, 2mm 및 3mm로 위치를 바꾸어 시뮬레이션 하였다. LED 칩이 중심에 위치한 경우는 전반확산 배광분포를 보였으며 2mm 이상에서는 효율 0.56의 반직접 배광 분포를 보였다. 3mm 위에 LED 칩을 위치시키면 0.31 효율을 갖는 직접 배광분포를 갖는 배광특성을 나타내었다. 도광판은 평면형 보다 칩 위치에서 밖으로 작아지는 쐐기형의 구조에서 더 좋은 효율을 나타내었다. 그리고 반사면에 반구형의 형상을 0.015mm 씩 증가시키며 방사 형태로 배치한 경우는 파워 1.02W, 효율 0.25, 최대광도 0.104W/sr로서 패턴을 형성하지 않은 경우보다 더 우수한 광 특성을 얻을 수 있었다.

• Smart Structures and Systems
• /
• 제4권4호
• /
• pp.493-515
• /
• 2008

Semi-active control systems have attracted a great deal of attention in recent years because these systems can operate on battery power alone, proving advantageous during seismic events when the main power source of the structure may likely fail. The behavior of semi-active devices is often highly non-linear and requires suitable and efficient control algorithm. This paper presents the comparative study and performance of variable semi-active friction dampers by using recently proposed predictive control law with direct output feedback. In this control law, the variable slip force of semi-active variable friction damper is kept slightly lower than the critical friction force, which allows the damper to remain in the slip state during an earthquake, resulting in improved energy dissipation capability. This control algorithm is able to produce a continuous and smooth slip forces for a variable friction damper. The numerical examples include a structure controlled with multiple variable semi-active friction dampers and with multiple passive friction dampers. A parameter, gain multiplier defined as the ratio of damper force to critical damper control force, is investigated under four different real earthquake ground motions, which plays an important role in the present control algorithm of the damper. The numerically evaluated optimum parametric value is considered for the analysis of the structure with dampers. The numerical results of the variable friction dampers show better performance over the passive dampers in reducing the seismic response of structures.

• 대한기계학회논문집
• /
• 제14권3호
• /
• pp.581-593
• /
• 1990

본 연구에서는 교반기술에 의하여 얻어진 반응고상태의 금속에 단섬유를 첨가 하여 복합재료를 제조하였다. 그리고 제조되어진 복합재료에 있어서 섬유의 분산상 태및 기지재와의 접합관계를 조사하여 압연가공에 필요한 반응고상태인 금속복합재료 의 제조방법을 확립하였다. 균일하게 분실되어진 반용융상태의 단섬유강화형 금속복 합재료를 직접 압연하여 박판을 제조할 수 있는 가능성을 검토하였으며, 또한 제조되 어진 박판의 인장시험에 의하여 기계적 성질을 조사하였다.

• Structural Engineering and Mechanics
• /
• 제58권6호
• /
• pp.1127-1143
• /
• 2016

The pounding phenomenon in adjacent structures happens in severing earthquakes that can cause great damages. Connecting neighboring structures with active and semi-active control devices is an effective method to avoid mutual colliding between neighboring buildings. One of the most important issues in control systems is applying online control force. There will be a time delay if the prose of producing control force does not perform on time. This paper proposed a time-delay compensation method in coupled structures control, with semi-active Magnetorheological (MR) damper. This method based on Newmark's integration is adopted to mitigate the time-delay effect. In this study, Lyapunov's direct approach is employed to compute demanded voltage for MR dampers. Using Lyapunov's direct algorithm guarantees the system stability to design a controller based on feedback. Because of the strong nonlinearity of MR dampers, the equation of motion of coupled structures becomes an involved equation, and it is impossible to solve it with the common time step methods. In present paper modified Newmark-Beta integration based on the instantaneous optimal control algorithm, used to solve the involved equation. In this method, the response of a coupled system estimated base on optimal control force. Two MDOF structures with different degrees of freedom are finally considered as a numeric example. The numerical results show, the Newmark compensation is an efficient method to decrease the negative effect of time delay in coupled systems; furthermore, instantaneous optimal control algorithm can estimate the response of structures suitable.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2007년도 하계학술대회 논문집 Vol.8
• /
• pp.162-163
• /
• 2007

The dry etching of Si was investigated using direct dc biasing to the Si substrate. The TCP type etching system with a feed-through for applying a dc bias was used in the etching. The applied dc bias and ICP power was varied to examine the effect on the etching at the fixed chamber pressure and $SF_6$ flow rate of 10 mTorr and 10 sccm during. When the plasma was generated at ICP power of 100 W, the etch rate of Si was increased with the bias for the biased samples. However, the etching of Si for the non-biased sample was enhanced for the increased ICP power.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 1993년도 추계학술대회 논문집
• /
• pp.518-523
• /
• 1993

A computer program has been developed for analyzing the two-dimensional unsteady conservation equations for transport phenomena in the ool region of direct rolling with semi-solid metal in order to describe the velocity and temperature, and the solidification process of the semi-solid metal. The energy equations of cooling roll is solved simultaneously with semi-solid metal in order consider heat transfer through the cooling roll. The FDM(finite difference method) and FEM(finite element method) are used in region of pool and roll, respsctively, to reduce computing time and to improve accuracy of calculation. In the present study, influence of solid fraction and casting speed are investigated in a point of view of strip formability with semi-solid metal.