• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
• /
• pp.538-540
• /
• 1997

A new dual half bridge induction heating cooker circuit with multiple loads is proposed for reducing the acoustics noise which is caused by the difference between operating frequencies q adjacent loads. This circuit has minimum loss due to the zero voltage switching characteristic. According to the mode analysis of the proposed circuit, we explain the operation of the dual half bridge induction heating cooker circuit The proto-type circuit with 2.8kW power consumption is builted and tested to verify the operation q the proposed circuit.

• Structural Engineering and Mechanics
• /
• 제11권1호
• /
• pp.35-48
• /
• 2001

The objective of this study is to investigate the stability behavior of steel cable-stayed bridges by comparing the buckling loads obtained by means of finite element methods with eigen-solver. In recent days, cable-stayed bridges dramatically attract engineers' attention due to their structural characteristics and aesthetics. They require a number of design parameters and present a high degree of static indetermination, especially for long span bridges. Cable-stayed bridges exhibit several nonlinear behaviors concurrently under normal design loads due to the individual nonlinearity of substructures such as the pylons, stay cables, and bridge deck, and their interactions. The geometric nonlinearities arise mainly from large displacements of cables. Strong axial and lateral forces acting on the bridge deck and pylons cause structural nonlinear behaviors. The interaction is among the substructures. In this paper, a typical three-span steel cable-stayed bridge with a variety of design parameters has been investigated. The numerical results indicate that the design parameters such as the ratio of $L_1/L$ and $I_p/I_b$ are important for the structural behavior, where $L_1$ is the main span length, L is the total span length of the bridge, $I_p$ is the moment of inertia of the pylon, and $I_b$ is the moment of inertia of the bridge deck. When the ratio $I_p/I_b$ increases, the critical load decreases due to the lack of interaction among substructures. Cable arrangements and the height of pylon are another important factors for this type of bridge in buckling analysis. According to numerical results, the bridges supported by a pylon with harp-type cable arrangement have higher critical loads than the bridges supported by a pylon with fan-type cable arrangement. On contrary, the shape of the pylon does not significantly affect the critical load of this type of bridge. All numerical results have been non-dimensionalized and presented in both tabular and graphical forms.

• Smart Structures and Systems
• /
• 제23권5호
• /
• pp.449-466
• /
• 2019

Cable-stayed bridges are attractive due to their beauty, reducing material consumption, less harm to the environment and so on, in comparison with other kinds of bridges. As a massive structure with long period and low damping (0.3 to 2%) under many dynamic loads, these bridges are susceptible to fatigue, serviceability disorder, damage or even collapse. Tuned Mass Damper (TMD) is a suitable controlling system to reduce the vibrations and prevent the threats in such bridges. In this paper, Multi Tuned Mass Damper (MTMD) system is added to the Ahvaz cable stayed Bridge in Iran, to reduce its seismic vibrations. First, the bridge is modeled in SAP2000 followed with result verification. Dead and live loads and the moving loads have been assigned to the bridge. Then the finite element model is developed in OpenSees, with the goal of running a nonlinear time-history analysis. Three far-field and three near-field earthquake records are imposed to the model after scaling to the PGA of 0.25 g, 0.4 g, 0.55 g and 0.7 g. Two MTMD systems, passive and active, with the number of TMDs from 1 to 8, are placed in specific points of the main span of bridge, adding a total mass ratio of 1 to 10% to the bridge. The parameters of the TMDs are optimized using Genetic Algorithm (GA). Also, the optimum force for active control is achieved by Fuzzy Logic Control (FLC). The results showed that the maximum displacement of the center of the bridge main span reduced 33% and 48% respectively by adding passive and active MTMD systems. The RMS of displacement reduced 37% and 47%, the velocity 36% and 42% and also the base shear in pylons, 27% and 47%, respectively by adding passive and active systems, in the best cases.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
• /
• pp.3156-3159
• /
• 2011

In case of the continuous welded rail(CWR) track is supported by the railway bridge, the additional axial force is occurred in the CWR due to the track-bridge interaction. In the various design codes such as Korean code, European code, UIC code, etc, three important loads(temperature variation in the bridge-deck, braking/acceleration and the bending of the bridge-deck resulted from the passing train) are treated as the independent loading case. In other words, the additional axial force can be obtained by summing up the three different values calculated by the three independent analysis. However, this analysing method may have an error because the behavior of the longitudinal resistance between the rail and the bridge-deck is under the highly nonlinear. Therefore, in order to exactly analyse the track-bridge interaction, nonlinear loading history and the change of the longitudinal resistance owing to the loading history must be considered in the analysis process. In this study, the loading history effect on the track-bridge interaction is investigated considering the resonable combination of three loads and the longitudinal resistance change.

• Geomechanics and Engineering
• /
• 제13권3호
• /
• pp.431-446
• /
• 2017

Rock bridges in rock masses would increase the bearing capacity of Non-persistent discontinuities. In this paper the effect of ratio of rock bridge surface to joint surface, rock bridge shape and normal load on failure behaviour of intermittent rock joint were investigated. A total of 42 various models with dimensions of $15cm{\times}15cm{\times}15cm$ of plaster specimens were fabricated simulating the open joints possessing rock bridge. The introduced rock bridges have various continuities in shear surface. The area of the rock bridge was $45cm^2$ and $90cm^2$ out of the total fixed area of $225cm^2$ respectively. The fabricated specimens were subjected to shear tests under normal loads of 0.5 MPa, 2 MPa and 4 MPa in order to investigate the shear mechanism of rock bridge. The results indicated that the failure pattern and the failure mechanism were affected by two parameters; i.e., the ratio of joint surface to rock bridge surface and normal load. So that increasing in joint area in front of the rock bridge changes the shear failure mode to tensile failure mode. Also the tensile failure change to shear failure by increasing the normal load.

• Smart Structures and Systems
• /
• 제9권6호
• /
• pp.473-487
• /
• 2012

GPS has become an established technique in structural health monitoring. This paper presents the application of an on-line GPS RTK system on the Zhujiang Huangpu Bridge (China) for monitoring bridge deck and towers movements. In this study, both the form and functions of movements of the deck and towers of the bridge under affecting loads were monitored in lateral, longitudinal and vertical directions. Such movements were described in time and frequency domains by determining the trend, torsion, periodical of the series using probability density function (PDF). The results of the time series GPS data are practical and useful to bridge health monitoring.

• 콘크리트학회논문집
• /
• 제15권5호
• /
• pp.635-642
• /
• 2003

최근들어 노후화된 교량의 증가에 따라 바닥판의 보강효과에 대한 많은 연구가 이루어지고 있으나 대부분의 연구는 실험실 수준에 국한되어 있으며, 구조물의 피로거동은 이동하중이 아닌 고정반복하중에 의한 연구가 집중적으로 시행되고 있다. 본 연구에서는 이동하중의 영향을 반영하기 위하여 국내에서 실측된 축하중으로 활하중 모델을 제시하였다. 확률론적 해석과 신뢰성 해석을 적용하여 탄소섬유쉬트와 격자형 탄소섬유로 성능향상된 바닥판의 보강효과 및 연장수명을 예측한 결과 성능향상 된 설계 2등급의 교량바닥판은 일반적인 증가 차량하중에 대하여 사용기간동안 충분한 내하력뿐만 아니라 충분한 피로거항성을 갖는 것으로 나타났다.

• Smart Structures and Systems
• /
• 제15권1호
• /
• pp.99-117
• /
• 2015

The Stonecutters Bridge (SCB) in Hong Kong is the third-longest cable-stayed bridge in the world with a main span stretching 1,018 m between two 298 m high single-leg tapering composite towers. A Wind and Structural Health Monitoring System (WASHMS) is being implemented on SCB by the Highways Department of The Hong Kong SAR Government, and the SCB-WASHMS is composed of more than 1,300 sensors in 15 types. In order to establish a linkage between structural health monitoring and maintenance management, a Structural Health Rating System (SHRS) with relevant rating tools and indices is devised. On the basis of a 3D space frame finite element model (FEM) of SCB and model updating, this paper presents the development of an SHR-oriented 3D multi-scale FEM for the purpose of load-resistance analysis and damage evaluation in structural element level, including modeling, refinement and validation of the multi-scale FEM. The refined 3D structural segments at deck and towers are established in critical segment positions corresponding to maximum cable forces. The components in the critical segment region are modeled as a full 3D FEM and fitted into the 3D space frame FEM. The boundary conditions between beam and shell elements are performed conforming to equivalent stiffness, effective mass and compatibility of deformation. The 3D multi-scale FEM is verified by the in-situ measured dynamic characteristics and static response. A good agreement between the FEM and measurement results indicates that the 3D multi-scale FEM is precise and efficient for WASHMS and SHRS of SCB. In addition, stress distribution and concentration of the critical segments in the 3D multi-scale FEM under temperature loads, static wind loads and equivalent seismic loads are investigated. Stress concentration elements under equivalent seismic loads exist in the anchor zone in steel/concrete beam and the anchor plate edge in steel anchor box of the towers.

• Steel and Composite Structures
• /
• 제31권5호
• /
• pp.437-452
• /
• 2019

In this study, in-situ static and dynamic tests of four pre-stressed concrete (PC) track beams with different span lengths and curvatures in a straddle monorail transit system were reported. In the static load tests, the strain and deflection at critical sections of the PC track beams were measured to determine the load bearing capacity and stiffness. The dynamic responses of strain, deflection, acceleration, and displacement at key positions of the PC track beams were measured under different train speeds and train loads to systematically study the dynamic behaviors of the PC track beams. A three-dimensional finite element model of the track beam-vehicle coupled vibration system was established to help understand the dynamic behavior of the system, and the model was verified using the test results. The research results show that the curvature, span length, train speed, and train loads have significant influence on the dynamic responses of the PC track beams. The dynamic performance of the PC track beams in the curve section is susceptible to dynamic loads. Appropriate train loads can effectively reduce the impact of the train on the PC track beam. The PC track beams allow good riding comfort.

• 한국전산구조공학회논문집
• /
• 제23권5호
• /
• pp.543-550
• /
• 2010

내진설계는 타 설계의 요구사항, 즉 각 구조부재의 설계강도가 소요강도 이상이어야 한다는 것을 만족해야 하는 동시에 지진발생시 구조물의 항복과정을 규명하여 제시하여야 한다. 이러한 요구사항이 추가되는 이유는 타 하중과는 차별되는 지진하중의 불확실성이다. 이 연구에서는 일반교량을 해석대상교량으로 선정하고 연결부분의 설계를 수행하여 연성파괴메카니즘을 확보하는 과정을 제시하였다. 이와 같은 과정으로부터 구조부재의 강도 증가 또는 지진저감장치 도입 등의 비용증가 없이 타 설계에서 요구되는 구조부재의 강도 이내에서 내진성능을 확보할 수 있다는 것을 확인하였다.