• Earthquakes and Structures
• /
• 제10권1호
• /
• pp.105-123
• /
• 2016

In this paper, using the probabilistic methods, the seismic demand of buckling restrained braced frames subjected to earthquake was evaluated. In this regards, 4, 6, 8, 10, 12 and 14-storybuildings with different buckling restrained brace configuration (including diagonal, split X, chevron V and Inverted V bracings) were designed. Because of the inherent uncertainties in the earthquake records, incremental dynamical analysis was used to evaluate seismic performance of the structures. Using the results of incremental dynamical analysis, the "capacity of a structure in terms of first mode spectral acceleration", "fragility curve" and "mean annual frequency of exceeding a limit state" was determined. "Mean annual frequency of exceeding a limit state" has been estimated for immediate occupancy (IO) and collapse prevention (CP) limit states using both Probabilistic Seismic Demand Analysis (PSDA) and solution "based on displacement" in the Demand and Capacity Factor Design (DCFD) form. Based on analysis results, the inverted chevron (${\Lambda}$) buckling restrained braced frame has the largest capacity among the considered buckling restrained braces. Moreover, it has the best performance among the considered buckling restrained braces. Also, from fragility curves, it was observed that the fragility probability has increased with the height.

• Smart Structures and Systems
• /
• 제6권5_6호
• /
• pp.505-524
• /
• 2010

Wireless structural monitoring systems consist of networks of wireless sensors installed to record the loading environment and corresponding response of large-scale civil structures. Wireless monitoring systems are desirable because they eliminate the need for costly and labor intensive installation of coaxial wiring in a structure. However, another advantageous characteristic of wireless sensors is their installation modularity. For example, wireless sensors can be easily and rapidly removed and reinstalled in new locations on a structure if the need arises. In this study, the reconfiguration of a rapid-to-deploy wireless structural monitoring system is proposed for monitoring short- and medium-span highway bridges. Narada wireless sensor nodes using power amplified radios are adopted to achieve long communication ranges. A network of twenty Narada wireless sensors is installed on the Yeondae Bridge (Korea) to measure the global response of the bridge to controlled truck loadings. To attain acceleration measurements in a large number of locations on the bridge, the wireless monitoring system is installed three times, with each installation concentrating sensors in one localized area of the bridge. Analysis of measurement data after installation of the three monitoring system configurations leads to reliable estimation of the bridge modal properties, including mode shapes.

• 한국기계가공학회지
• /
• 제19권10호
• /
• pp.87-97
• /
• 2020

In general, tires require various sensors and power supply devices, such as batteries, to obtain information such as pressure, temperature, acceleration, and the friction coefficient between the tire and the road in real time. However, these sensors have a size limitation because they are mounted on a tire, and their batteries have limited usability due to short replacement cycles, leading to additional replacement costs. Therefore, vibration energy harvesting technology, which converts the dynamic strain energy generated from the tire into electrical energy and then stores the energy in a power supply, is advantageous. In this study, the output voltage and power generated from piezoelectric elements are predicted through finite element analysis under static state and transient state conditions, taking into account the dynamic characteristics of tires. First, the tire and piezoelectric elements are created as a finite element model and then the natural frequency and mode shapes are identified through modal analysis. Next, in the static state, with the piezoelectric element attached to the inside of the tire, the voltage distribution at the contact surface between the tire and the road is examined. Lastly, in the transient state, with the tire rotating at the speeds of 30 km/h and 50 km/h, the output voltage and power characteristics of the piezoelectric elements attached to four locations inside the tire are evaluated.

• Earthquakes and Structures
• /
• 제19권6호
• /
• pp.445-457
• /
• 2020

An ultra-high voltage (UHV) transmission system has the advantages of low circuitry loss, high bulk capacity and long-distance transmission capabilities over conventional transmission systems, but it is easier for this system to cross fault rupture zones and become damaged during earthquakes. This paper experimentally and numerically investigates the seismic responses and collapse failure of a UHV transmission tower-line system crossing a fault. A 1:25 reduced-scale model is constructed and tested by using shaking tables to evaluate the influence of the forward-directivity and fling-step effects on the responses of suspension-type towers. Furthermore, the collapse failure tests of the system under specific cross-fault scenarios are carried out. The corresponding finite element (FE) model is established in ABAQUS software and verified based on the Tian-Ma-Qu material model. The results reveal that the seismic responses of the transmission system under the cross-fault scenario are larger than those under the near-fault scenario, and the permanent ground displacements in the fling-step ground motions tend to magnify the seismic responses of the fault-crossing transmission system. The critical collapse peak ground acceleration (PGA), failure mode and weak position determined by the model experiment and numerical simulation are in relatively good agreement. The sequential failure of the members in Segments 4 and 5 leads to the collapse of the entire model, whereas other segments basically remain in the intact state.

• Structural Engineering and Mechanics
• /
• 제77권3호
• /
• pp.369-381
• /
• 2021

The seismic responses of elevated tanks considering liquid-structure interaction are presented under horizontal earthquake. The scaled model tank is fabricated to study the dynamic responses of anchored tank and newly designed uplift tank with replaced dampers. The natural frequencies for structural mode are obtained by modal analysis. The dynamic responses of tanks are completed by finite element method, which are compared with the results from experiment. The displacement parallel and perpendicular to the excitation direction are both gained as well as structural acceleration. The strain of tank walls and the axial strain of columns are also obtained afterwards. The seismic responses of liquid storage tank can be calculated by the finite element model effectively and the results match well with the one measured by experiment. The aim is to provide a new type of tank system with vertical constraint relaxed which leads to lower stress level. With the liquid volume increasing, the structural fundamental frequency has a great reduction and the one of uplift tank are even smaller. Compared with anchored tank, the displacement of uplift tank is magnified, the strain for tank walls and columns parallel to excitation direction reduces obviously, while the one perpendicular to earthquake direction increases a lot, but the values are still small. The stress level of new tank seems to be more even due to uplift effect. The new type of tank can realize recoverable function by replacing dampers after earthquake.

• 한국군사과학기술학회지
• /
• 제25권2호
• /
• pp.196-209
• /
• 2022

Driving dynamic characteristics of semi-trailer loaded with precise equipments are very important to protect them from vibration, impact or other disturbances. In this paper, in order to identify the driving dynamic characteristics of the large scale semi-trailer equipped with swivel axle and hydropneumatic suspension unit, Dynamics Modeling & Simulation(M&S) were performed using general Dynamics Analysis Program(RecurDyn V9R2). The semi-trailer was modeled as two types - one is Multi Rigid Body Dynamics(MRBD) model, and the other Rigid-Flexible Body Dynamics(RFlex) one. The natural vibration mode and frequencies of semi-trailer body, acceleration of dummy-weight, pitch, roll and yaw of dummy-weight, swivel axle and hydropneumatic suspension cylinder support structure, and acting force of hydropneumatic suspensions etc. were obtained from the M&S. Additionally frequency analysis were performed using the data of behavior obtained from above M&S. Generally the quantitative results of RFlex are larger than them of MRBD in view of magnitude of the comparable parametric values.

• Structural Engineering and Mechanics
• /
• 제82권5호
• /
• pp.651-665
• /
• 2022

While the lateral confinement provided by an FRP jacket to a concrete column is passive in nature, confinement is activated when the concrete expands due to additional compression stresses or significant shear deformations. This characteristic of FRP jacketing theoretically leads to similar initial stiffness properties of FRP retrofitted buildings as the buildings without retrofit. In the current study, to validate this theoretical assumption, the initial stiffness characteristics, and thus, the potential seismic demands were investigated through forced vibration tests on two identical full-scale substandard reinforced concrete buildings with or without FRP retrofit. Power spectral density functions obtained using the acceleration response data captured through forced vibration tests were used to estimate the modal characteristics of these buildings. The test results clearly showed that the natural frequencies and the mode shapes of the buildings are quite similar. Since the seismic demand is controlled by the fundamental vibration modes, it is confirmed using vibration-based full-scale tests that the seismic demands of RC buildings remain unchanged after CFRP jacketing of columns. Furthermore, the damping characteristics were also found similar for both structures.

• Nuclear Engineering and Technology
• /
• 제54권11호
• /
• pp.4030-4048
• /
• 2022

In this study, road transportation tests were conducted with surrogate fuel assemblies under normal conditions of transport to evaluate the vibration and shock load characteristics of spent nuclear fuel (SNF). The overall test data analysis was conducted based on the measured acceleration and strain data obtained from the speed bump, lane-change, deceleration, obstacle avoidance, and circular tests. Furthermore, representative shock response spectrums and power spectral densities of each test mode were acquired. Amplification or attenuation characteristics were investigated according to the load transfer path. The load attenuated significantly as it transferred from the trailer to the cask. By contrast, the load amplified as it transferred from the cask to the surrogate SNF assembly. The fuel loading location on the cask disk assembly did not exhibit a significant influence on the strain measured from the fuel rods. The principal strain was in the vertical direction, and relatively large strain values were obtained in spans with large spacing between spacer grids. The influence of the lateral location of fuel rods was also investigated. The fuel rods located at the side exhibited relatively large strain values than those located at the center. Based on the strain data obtained from the test results, a hypothetical road transportation scenario was established. A fatigue evaluation of the SNF rod was performed based on this scenario. The evaluation results indicate that no fatigue damage occurred on the fuel rods.

• 한국산학기술학회논문지
• /
• 제19권5호
• /
• pp.611-617
• /
• 2018

대형구조물의 효과적인 구조 안전성 확보를 위해서는 결함탐지기술을 포함한 건전성 모니터링의 적용이 필요하다. 본 연구에서는 보 구조물에 발생하는 균열위치와 균열크기를 추정하기 위하여 다음과 같은 2단계의 균열추정방법을 제안한다. 우선, 보 구조물의 분포 국부 변형률 계측결과를 이용하여 변형률 모드형상을 구하고, 이에 대한 수정 라플라시안(Laplacian) 연산을 통하여 균열발생 영역을 추정한다. 이후, 가속도 측정을 통하여 구한 고유주파수와 신경망기법을 이용하여, 미리 추정된 균열발생 영역을 대상으로 균열위치와 균열크기를 추정한다. 이때, 신경망을 훈련시키기 위하여, 에너지법에 의해 유도된 균열보의 등가휨강성을 이용하여 균열보의 고유주파수를 해석적으로 구한다. 기법을 검증하기 위하여 알루미늄 캔틸레버 보에 대한 손상실험을 수행하였다. 인위적으로 실험체에 균열을 가한 후 자유진동실험을 수행하여 동적 변형률과 가속도를 계측하고 이를 이용하여 변형률 모드형상과 고유주파수를 구하였다. 변형률 모드형상에 대한 수정 라플라시안 연산을 통하여 균열발생 영역을 추정하고, 고유주파수와 신경망기법을 이용하여, 미리 추정된 균열발생 영역에 대하여 균열위치와 균열크기를 판정하였다. 3가지 손상경우에 대한 균열발생 영역의 추정결과는 실제 영역과 잘 일치하였으며, 균열위치와 균열크기 추정결과의 정확성을 상당히 향상시킬 수 있었다. 제안된 기법은 장대구조물에 대한 구조물 건전성 모니터링에 효과적으로 활용될 수 있을 것으로 판단된다.

• 한국응용과학기술학회지
• /
• 제35권4호
• /
• pp.1108-1119
• /
• 2018

대기오염에 대한 관심은 국내 외에서 점진적으로 상승하고 있으며, 자동차 및 연료 연구자들은 청정(친환경 대체연료) 연료와 연료품질 향상 등을 위해 새로운 엔진 설계, 혁신적인 후 처리 시스템 등의 많은 접근을 통하여 차량 배출가스와 온실가스를 감소시키려고 노력하고 있다. 이러한 연구들은 주로 차량의 배출가스 (규제 및 미규제물질, PM 입자 배출 등)와 온실가스의 두 가지 이슈로 진행되고 있다. 자동차의 배출가스는 환경오염과 인체에 악영향을 주는 많은 문제를 일으키고 있다. 이러한 배출가스를 줄이기 위하여 각국에서는 배출가스 시험모드를 새로 만들어 규제하고 있다. 2007 년부터 UN ECE의 WP.29 포럼에서 배출가스 인증을 위한 전 세계의 조화된 light-duty 차량 시험 절차 (WLTP)가 개발되었다. 이 시험 절차는 유럽과 동시에 국내 light-duty 디젤 차량에도 적용되어졌다. Light-duty 차량의 대기오염 물질 배출량은 거리 당 무게로 규제되어 있어 주행주기가 결과에 영향을 미칠 수 있다. 차량의 배출가스는 주행 및 환경조건, 주행습관 등에 따라 크게 달라진다. 극단적인 외기온도는 배출가스를 증가시키는데, 이것은 더 많은 연료가 실내를 가열하거나 냉각해야하기 때문이다. 또한 높은 주행속도는 증가된 항력을 극복하기 위해 필요한 에너지로 인해 배출가스 량을 증가시킨다. 일반적으로 상승하는 차량속도와 비교할 때, 급격한 차량가속도도 배출가스를 증가시킨다. 부가적인 장치 (에어컨 또는 히터)와 도로경사 또한 배출가스를 증가시킨다. 본 연구에서는 3대의 light-duty 차량을 가지고 light-duty 차량의 배출가스 규제에 사용되는 WLTP, NEDC 및 FTP-75로 시험을 하였으며, 배출가스가 다른 주행 사이클에 의해 얼마나 많은 영향을 받을 수 있는지를 측정하였다. 배출 가스는 통계적으로 의미있는 차이를 보이지 않았다. 최대 배출 가스는 주로 냉각 된 엔진 조건에 의해 야기되는 WLTP의 저속 단계에서 발견된다. 냉각 된 엔진 상태에서 배출가스의 양은 시험 차량과 크게 다르다. 이는 WLTP 구동 사이클에 대처하기 위해 다른 기술적 솔루션이 필요하다는 것을 의미한다.