• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.253-259
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• 2002

The rigid body characteristics (value of mass, Position of center of mass, moments and products of inertia) of mechanical systems can be identified from FRF data or vibration spectra of rigid body motion. Therefore the accuracy of rigid body characteristics is connected directly with the accuracy of measured data for rigid body motions. In this paper, a method of improving accuracy of measurement of rigid body motion is presented. Applying rigid body theory, ail translational and rotational displacements at a tentative point on the rigid body are calculated using the measured translational displacements for several points and transfer matrix. Then the estimated displacements for the identical points are calculated using the 6 displacements of the tentative Point and transfer matrix. By using correlation coefficient between measured and estimated displacements, we can detect the existence of errors that are contained in a certain measured displacement. Consequently, the improved rigid body motion with respect to a tentative point can be obtained by eliminating the contaminated data.

• Structural Engineering and Mechanics
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• 제42권2호
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• pp.229-245
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• 2012

Bridge vibration displacements have been directly measured by LVDTs (Linear Variable Differential Transformers) or laser equipment and have also been indirectly estimated by an algorithm of integrating measured acceleration. However, LVDT measurement cannot be applied for a bridge crossing over a river or channel and the laser technique cannot be applied when the weather condition is poor. Also, double integration of accelerations may cause serious numerical deviation if the initial condition or a regression process is not carefully controlled. This paper presents an algorithm of estimating bridge vibration displacements using vibration strains measured by FBG (Fiber Bragg Grating) sensors and theoretical mode shapes of a simply supported beam. Since theoretically defined mode shapes are applied, even high modes can be used regardless of the quality of the measured data. In the proposed algorithm, the number of theoretical modes is limited by the number of sensors used for a field test to prevent a mathematical rank deficiency from occurring in computing vibration displacements.89The proposed algorithm has been applied to various types of bridges and its efficacy has been verified. The closeness of the estimated vibration displacements to measured ones has been evaluated by computing the correlation coefficient and by comparing FRFs (Frequency Response Functions) and the maximum displacements.

• 지질공학
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• 제17권2호
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• pp.217-224
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• 2007

터널이 굴착되면 응력이 재분배되는 과정동안 변위가 발생한다. 터널의 변위는 굴착 전 선행변위, 굴착 후 미측정 변위, 계측변위로 구분할 수 있다. 일반적으로 굴착 전 선행변위와 굴착 후 미측정 변위의 현장 측정은 어렵기 때문에 터널 굴착에 따른 전변위의 크기와 변화 양상을 산정하기 위한 연구가 많이 수행되어왔다. 본 연구에서는 퇴적암을 기반으로 하는 터널의 지반등급별 전변위를 산정하고 이들의 특성을 파악하기 위하여 역해석 기법을 사용하였다. 계측변위와 3차원 수치해석에 의해 계산된 변위의 오차를 최소한으로 줄여 지반등급별 물성치를 추정하였으며, 굴착에 따른 전변위 분포 양상을 산정하였다. 최종적으로 logistic 모형을 따르는 지반등급별 굴착에 따른 변위의 비선형 회귀식을 산정하였다.

• Smart Structures and Systems
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• 제20권5호
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• pp.549-562
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• 2017

The US railroad network carries 40% of the nation's total freight. Railroad bridges are the most critical part of the network infrastructure and, therefore, must be properly maintained for the operational safety. Railroad managers inspect bridges by measuring displacements under train crossing events to assess their structural condition and prioritize bridge management and safety decisions accordingly. The displacement of a railroad bridge under train crossings is one parameter of interest to railroad bridge owners, as it quantifies a bridge's ability to perform safely and addresses its serviceability. Railroad bridges with poor track conditions will have amplified displacements under heavy loads due to impacts between the wheels and rail joints. Under these circumstances, vehicle-track-bridge interactions could cause excessive bridge displacements, and hence, unsafe train crossings. If displacements during train crossings could be measured objectively, owners could repair or replace less safe bridges first. However, data on bridge displacements is difficult to collect in the field as a fixed point of reference is required for measurement. Accelerations can be used to estimate dynamic displacements, but to date, the pseudo-static displacements cannot be measured using reference-free sensors. This study proposes a method to estimate total transverse displacements of a railroad bridge under live train loads using acceleration and tilt data at the top of the exterior pile bent of a standard timber trestle, where train derailment due to excessive lateral movement is the main concern. Researchers used real bridge transverse displacement data under train traffic from varying bridge serviceability levels. This study explores the design of a new bridge deck-pier experimental model that simulates the vibrations of railroad bridges under traffic using a shake table for the input of train crossing data collected from the field into a laboratory model of a standard timber railroad pile bent. Reference-free sensors measured both the inclination angle and accelerations of the pile cap. Various readings are used to estimate the total displacements of the bridge using data filtering. The estimated displacements are then compared to the true responses of the model measured with displacement sensors. An average peak error of 10% and a root mean square error average of 5% resulted, concluding that this method can cost-effectively measure the total displacement of railroad bridges without a fixed reference.

• Structural Engineering and Mechanics
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• 제39권6호
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• pp.751-765
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• 2011

The present paper deals with the identification of a concentrated damage in an elastic parabolic arch through the minimization of an objective function which measures the differences between numerical and experimental values of static displacements. The damage consists in a notch that reduces the height of the cross section at a given abscissa and therefore causes a variation in the flexural stiffness of the structure. The analytical values of static displacements due to applied loads are calculated by means of the principle of virtual work for both the undamaged and damaged arch. First, pseudo-experimental data are used to study the inverse problem and investigate whether a unique solution can occur or not. Various damage intensities are considered to assess the reliability of the identification procedure. Then, the identification procedure is applied to an experimental case, where displacements are measured on a prototype arch. The identified values of damage parameters, i.e., location and intensity, are compared to those obtained by means of a dynamic identification technique performed on the same structure.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.275-282
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• 1999

In this study, the algorithm which can estimate displacements from the acceleration data is developed. For proving the validity of this study, the calculated displacements are compared with the measured displacements through the forced vibration tests in the laboratory. So the sampling frequency and filtering range for the estimation of the displacements are proposed. Finally, these results are applied to estimate displacements from the acceleration data obtained from the real bridge.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2007년도 정기 학술대회 논문집
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• pp.199-204
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• 2007

This research aimed at to develop a quantitative assesment technique which uses the measured displacements at the excavated plane during tunnel construction. Tunnel structure has a feature with long extents comparing to the excavated section so that the tunnel safety assesment is more effective by using the measured data of displacements. Tunnel structures show different structural behaviors due to the mechanical characteristics of ground and supports themselves, excavation methods and construction methods of supports, etc. From this point of view, it has very important meanings on the practical aspects that the measured data from the construction cite represent the features of the interaction effects between ground and supports as they are. In this study, both the stress state and the properties of surrounding ground are analyzed by newly incorporated feedback analysis technique which can use the measured displacements directly. Then, the stress state and the properties of ground will be used to obtain the strain distribution of surrounding ground. Finally the tunnel safety can be assessed by comparing the estimated strain through the analysis to the allowable strain of ground quantitatively.

• Smart Structures and Systems
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• 제19권6호
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• pp.679-694
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• 2017

The complexity, enlargement and irregularity of structures and multi-directional dynamic loads acting on the structures can lead to unexpected structural behavior, such as torsion. Continuous torsion of the structure causes unexpected changes in the structure's stress distribution, reduces the performance of the structural members, and shortens the structure's lifespan. Therefore, a method of monitoring the torsional behavior is required to ensure structural safety. Structural torsion typically occurs accompanied by displacement, but no model has yet been developed to measure this type of structural response. This research proposes a model for measuring dynamic torsional response of structure accompanied by displacement and for identifying the torsional modal parameter using vision-based displacement measurement equipment, a motion capture system (MCS). In the present model, dynamic torsional responses including pure rotation and translation displacements are measured and used to calculate the torsional angle and displacements. To apply the proposed model, vibration tests for a shear-type structure were performed. The torsional responses were obtained from measured dynamic displacements. The torsional angle and displacements obtained by the proposed model using MCS were compared with the torsional response measured using laser displacement sensors (LDSs), which have been widely used for displacement measurement. In addition, torsional modal parameters were obtained using the dynamic torsional angle and displacements obtained from the tests.

• 터널과지하공간
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• 제9권4호
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• pp.296-305
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• 1999

많은 터널 현장에서 계측을 수행하고 있지만, 일반적인 역해석 방법으로 이 계측자료를 통해 라이닝에 작용하는 변형율과 응력 등의 역학량을 추정하기는 어렵다. 그 이유는 현장에서 계측이 가능한 적은 변위수로부터 라이닝의 응력상태를 추정할 수 없기 때문이다. 계측의 시간과 비용을 고려해 볼 때, 계측자료를 이용할 수 있는 기법의 개발은 시급한 연구과제라 할 수 있다. 본 연구에서는 터널계측에서 계측 가능한 소수의 변위로 전테 라이닝의 변위와 응력 등의 역학량을 계산할 수 있는 역해석 모델을 개발하였다. 역해석 방법으로서 복공 외면에 작용하는 외력의 자승이 최소화될 때 해를 구하는 방법을 사용하였다. 라이닝 외면에 작용하는 하중을 가정하여 유한요소법으로 변위와 응력을 계산하고, 여기서 얻은 몇개의 변위를 계측 변위로 가정하여 역해석 모델에 입력함으로써 절점 변위, 요소의 변형율 및 응력 등을 다시 구하였다. 처음 계산된 변위와 역계산으로 구한 변위를 비교함으로써 모델의 신뢰성을 평가하였다. 자동계측으로 라이닝의 비교적 정확한 계측을 수행하고 있는 지하철 한강 하저터널 현장에서 얻은 계측변위를 개발한 역해석 모델을 적용하여 실제 계측한 응력과 유사한 결과를 얻었다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1998년도 가을 학술발표회 논문집
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• pp.167-174
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• 1998

It is important to measure e dynamic behaviors of the structures and determine the safety and serviceability of those structures by analyzing the gathered data. It is very much easier and more economical to measure the accelerations than displacements in order to obtain the dynamic responses of a structure, but the physical meanings of the displacements are more clear and definite than those of accelerations. In this study, the algorithm which can evaluate the displacements from the measured acceleration data by integration are developed. The calculated displacements are compared with measured data through the laboratory test and the results represent good agreements. This algorithm is applied to the data of real structures.