• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2010년도 추계 학술발표회
• /
• pp.49-59
• /
• 2010

Earthquake-induced liquefaction on saturated loose sand is well known in the world. Since Saemangeum Dike Project has a plan to be reclaimed with dredged sand on wide river, possibility of liquefaction should be checked. Section Dongjin5 was selected to evaluate possibility of liquefaction. Estimating method follows as 1) determination of PL value with SPT results, passing curve, and soil properties, 2) prediction for maximum earthquake acceleration, 3) calculation for FL value on depth with Korean specification for highway bridges, 4) visualization for possibility of liquefaction on all of project area with GIS 5) comparison with Japanese specification for highway bridges, Youd and Idriss method, and Andrus and Stokoe II method for verification, 6) ascertainment for the potential liquefaction with cyclic triaxial test. 7) establishing for countermeasure if needed. From the results, even though most of area covered with sand, no potential liquefaction exists except some areas. Those need to soil improvement with grout or attaching measurement on substructure.

• 한국자동차공학회논문집
• /
• 제22권1호
• /
• pp.20-28
• /
• 2014

This paper presents static output feedback LQ and $H_{\infty}$ controllers for rollover prevention. Linear quadratic static output feedback controllers have been proposed for rollover prevention in such a way to minimize the lateral acceleration and the roll angle. Rollover prevention capability can be enhanced if $H_{\infty}$ controller is designed. To avoid full-state measurement for feedback requirement or sensitiveness of an observer to nonlinear model error, static output feedback is adopted. To design static output feedback controllers, Kosut's method is adopted because it is simple to calculate. Differential braking and active anti-roll bar are adopted as actuators that generate yaw and roll moments, respectively. The proposed method is shown to be effective in preventing rollover through the simulations on nonlinear multi-body dynamic simulation software, CarSim.

• 한국안전학회지
• /
• 제27권5호
• /
• pp.185-189
• /
• 2012

While there is no standards on slip risk for contaminants on surface, glycerol is described in standard contaminant for measuring coefficient of friction(COF) and slip resistance such as ISO 13287. But that is just used to measure the slip resistance of surface materials and shoes not to evaluate the contaminant materials. Therefore the objective of this study was to find out the relationship between standard contaminant and the contaminants used usually at the workplaces. For this, some measurement criteria were acquired from the analysis based on biomechanics and kinetics of human gait during slips. The slip resistance according to viscosity of the contaminants was measured applying the criteria and slip probability was determined by the gait analysis. Some factors which should be considered when measuring the slip resistance were identified. The velocity, acceleration, contact time and contact pressure should be 1 m/sec, 10 $m/sec^2$, 350 kPa and less than 0.5sec respectively. The variation of viscosity according to temperature for working oils was different from that of standard contaminant. The static coefficient of friction (SCOF) of working oils was almost 0.5 times as large as the SCOF of standard contaminant. So it was assumed to be difficult to compare the contaminants at the workplaces with the glycerol as a standard contaminant for estimating the slip risk.

• Coupled systems mechanics
• /
• 제1권4호
• /
• pp.311-324
• /
• 2012

Previous investigations have demonstrated that strong earthquakes can cause severe damage or collapse to storage tanks. Theoretical studies by other researchers have shown that allowing the tank to uplift generally reduces the base shear and the base moment. This paper provides the necessary experimental confirmation of some of the numerical finding by other researchers. This paper reports on a series of experiments of a model tank containing water using a shake table. A comparison of the seismic behaviour of a fixed base system (tank with anchorage) and a system free to uplift (tank without anchorage) is considered. The six ground motions are scaled to the design spectrum provided by New Zealand Standard 1170.5 (2004) and a range of aspect ratios (height/radius) is considered. Measurements were made of the impulsive acceleration, the horizontal displacement of the top of the tank and uplift of the base plate. A preliminary comparison between the experimental results and the recommendations provided by the liquid storage tank design recommendations of the New Zealand Society for Earthquake Engineering is included. The measurement of anchorage forces required to avoid uplift under varying conditions will be discussed.

• Smart Structures and Systems
• /
• 제1권1호
• /
• pp.29-46
• /
• 2005

In this study, a wavelet packet based method is proposed for identifying damage occurrence and damage location for beam-like structures. This method assumes that the displacement or the acceleration response time histories at various locations along a beam-like structure both before and after damage are available for damage assessment. These responses are processed through a proper level of wavelet packet decomposition. The wavelet packet signature (WPS) that consists of wavelet packet component signal energies is calculated. The change of the WPS curvature between the baseline state and the current state is then used to identify the locations of possible damage in the structure. Two numerical studies, one on a 15-storey shear-beam building frame and another on a simply-supported steel beam, and an experimental study on a simply-supported reinforced concrete beam are performed to validate the proposed method. Results show the WPS curvature change can be used to locate both single and sparsely-distributed multiple damages that exist in the structure. Also the accuracy of assessment does not seem to be affected by the presence of 20-15dB measurement noise. One advantage of the proposed method is that it does not require any mathematical model for the structure being monitored and hence can potentially be used for practical application.

• Structural Engineering and Mechanics
• /
• 제15권3호
• /
• pp.299-314
• /
• 2003

This investigation presents an efficient method for identifying modal characteristics from the measured displacement, velocity and acceleration signals of multiple channels on structural systems. A Vector Backward Auto-Regressive model (VBAR) that describes the relationship between the output information in different time steps is used to establish a backward state equation. Generally, the accuracy of the identified dynamic characteristics can be improved by increasing the order of the Auto-Regressive model (AR) in cases of measurement of data under noisy circumstances. However, a higher-order AR model also induces more numerical modes, only some of which are the system modes. The proposed VBAR model provides a clear characteristic boundary to separate the system modes from the spurious modes. A numerical example of a lumped-mass model with three DOFs was established to verify the applicability and effectiveness of the proposed method. Finally, an offshore platform model was experimentally employed as an application case to confirm the proposed VBAR method can be applied to real-world structures.

• 한국전자통신학회논문지
• /
• 제7권3호
• /
• pp.585-590
• /
• 2012

본 논문에서는 구조물의 안전한 관리를 위하여 진동현방식 센서를 이용하여 변형을 측정하고 Zigbee 무선 네트워크를 통하여 원격 모니터링할 수 있는 시스템을 구현하였다. 구현한 변형측정기는 진동현방식 센서를 구동하여 출력되는 신호의 주파수를 측정하여 변형을 계산하고, 변형 측정에 있어 요구되는 온도 보상을 위한 온도를 측정한다. 2축 가속도센서를 이용하여 변형의 방향을 측정할 수 있다. 개발한 변형측정기에는 보다 효율적인 모니터링을 위하여 유무선 통신 기능이 있다. 실험을 통하여 개발한 진동현방식 변형측정 시스템이 원격모니터링에 효과적임을 확인한다.

• International Journal of Concrete Structures and Materials
• /
• 제2권2호
• /
• pp.91-98
• /
• 2008

Curved bridges are important components of a highway transportation network for connecting local roads and highways, but very few data have been collected in terms of their field performance. This paper presents two-years monitoring and system identification results of a curved concrete box-girder bridge, the West St. On-Ramp, under ambient traffic excitations. The authors permanently installed accelerometers on the bridge from the beginning of the bridge life. From the ambient vibration data sets collected over the two years, the element stiffness correction factors for the columns, the girder, and boundary springs were identified using the back-propagation neural network. The results showed that the element stiffness values were nearly 10% different from the initial design values. It was also observed that the traffic conditions heavily influence the dynamic characteristics of this curved bridge. Furthermore, a probability distribution model of the element stiffness was established for long-term monitoring and analysis of the bridge stiffness change.

• 대한토목학회논문집
• /
• 제9권1호
• /
• pp.71-78
• /
• 1989

본(本) 논문(論文)은 주거(住居) 및 상가구조물(商街構造物)이 밀집(密集)된 지역(地域)에서 구조물(構造物)의 말뚝기초공사(基礎工事)를 위한 항타작업시(抗打作業時) 야기되는 지반진동(地盤振動)의 영향(影響)을 평가(平價)하기 위해서 디젤해머로 PC콘크리트말뚝을 항타(抗打)하는 동안 발생(發生)되는 지반진동(地盤振動)을 항타지점(抗打地點)으로부터 진동측정거리(振動測定距離)를 변경시키면서 측정(測定) 분석(分析)하였다. 본(本) 논문(論文)의 측정(測定)과 분석(分析)을 통하여 항타진동(抗打振動)의 감소(減素) 및 주파수특성(周波數特性)이 파악되었으며, 이로부터 항타진동(抗打振動)의 크기를 사전(事前)에 예측(豫測)할 수 있는 진동추정식(振動推定式)의 유도 및 항타기(抗打機) 선정(選定)을 비롯한 제반문제에 대하여 고찰(考察)하였다.

• 대한기계학회논문집A
• /
• 제24권8호
• /
• pp.1931-1939
• /
• 2000

Operating excitation forces of the linear vibratory system are normally determined by direct measurement techniques using load cells, strain gauges, etc. But, hydraulic forces of the rotating turbomachinery such as centrifugal pumps are exerted on an impeller due to asymmety of the flow by the interaction between pump impeller and volute. So, investigations of wide range of hydraulic designs and geometric deviations are difficult by direct method. This paper presents a hybrid approach for fourier transformed operational excitation forces, which uses pseudo-inverse matrix of the transfer matrix for the system and the measured vibrational data with standard installed pump. The determination of the transfer function matrix is based on a linear rotor/stationary system and steady state harmonic response in finite element analysis. And, vibrational data is collected in both vertical and horizontal directions at inboard and outboard bearing housings. The results of the process may be enhanced by making acceleration measurements at many more locations than there are forces to be determined.