• Journal of Sensor Science and Technology
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• v.10 no.1
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• pp.9-15
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• 2001

The extrinsic Fabry-Perot interferometric (EFPI) optical fiber sensor shows good sensitivity and resolution, and has many advantages over optical fiber sensors of other types. However, this EFPI optical fiber sensor has a disadvantage that the distinction of measuring directions is difficult due to the measurement method by using only fringe counting. In this paper, the transmission-type extrinsic Fabry-Perot interferometric (TEFPI) optical fiber sensor was developed, which has been improved by the additional function and whose measuring system is different from that of the conventional EFPI optical fiber sensor. Then the application result of the TEFPI optical fiber sensor to the strain and temperature measurement was explained in detail.

• Smart Structures and Systems
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• v.5 no.1
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• pp.95-117
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• 2009

In this paper, the time series based damage detection algorithms developed by Nair, et al. (2006) and Nair and Kiremidjian (2007) are applied to the benchmark experimental data from the National Center for Research on Earthquake Engineering (NCREE) in Taipei, Taiwan. Both acceleration and strain data are analyzed. The data are modeled as autoregressive (AR) processes, and damage sensitive features (DSF) and feature vectors are defined in terms of the first three AR coefficients. In the first algorithm developed by Nair, et al. (2006), hypothesis tests using the t-statistic are applied to evaluate the damaged state. A damage measure (DM) is defined to measure the damage extent. The results show that the DSF's from the acceleration data can detect damage while the DSF from the strain data can be used to localize the damage. The DM can be used for damage quantification. In the second algorithm developed by Nair and Kiremidjian (2007) a Gaussian Mixture Model (GMM) is used to model the feature vector, and the Mahalanobis distance is defined to measure damage extent. Additional distance measures are defined and applied in this paper to quantify damage. The results show that damage measures can be used to detect, quantify, and localize the damage for the high intensity and the bidirectional loading cases.

• Structural Engineering and Mechanics
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• v.69 no.6
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• pp.615-626
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• 2019

The 3-noded metric Timoshenko beam element with an offset of the internal node from the element centre is used here to demonstrate the best-fit paradigm using function space formulation under locking and mesh distortion. The best-fit paradigm follows from the projection theorem describing finite element analysis which shows that the stresses computed by the displacement finite element procedure are the best approximation of the true stresses at an element level as well as global level. In this paper, closed form best-fit solutions are arrived for the 3-noded Timoshenko beam element through function space formulation by combining field consistency requirements and distortion effects for the element modelled in metric Cartesian coordinates. It is demonstrated through projection theorems how lock-free best-fit solutions are arrived even under mesh distortion by using a consistent definition for the shear strain field. It is shown how the field consistency enforced finite element solution differ from the best-fit solution by an extraneous response resulting from an additional spurious force vector. However, it can be observed that when the extraneous forces vanish fortuitously, the field consistent solution coincides with the best-fit strain solution.

• Journal of Ocean Engineering and Technology
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• v.33 no.2
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• pp.161-167
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• 2019

This paper focuses on a newly designed ice load formula based on the ARAON's 2016 Arctic field data in order to improve a structural design against ice loads. The strain gage signals from ARAON's hull plating were converted to the local ice pressure upon the hull plating using the influence coefficient matrix and finite element analysis. First, a traditional pressure-area relationship is derived by applying probabilistic approaches to handle the strains measured onboard the ARAON. Then, the local ice load prediction formula is re-analyzed after reviewing the ARAON's additional field data to consider information about the ship speed and thickness of the sea ice. It is shown that the newly developed pressure-area relationship well reflects the influence of other design parameters such as the ship speed and ice thickness in the prediction of local ice loads on Arctic vessels.

• Steel and Composite Structures
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• v.39 no.2
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• pp.135-148
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• 2021

Hollow structural section (HSS) columns have been increasingly popular due to their structural and architectural merits. However, practical difficulty lies in developing proper connections. The through-diaphragm connections are considered as suitable connection type that is widely adopted in Asian countries. However, the stress concentration occurs at the location connecting through-diaphragm and steel beam. Furthermore, the actual load path from the beam flange is not uniformly transferred to the HSS column as conventionally assumed. In this paper, tensile tests were further conducted on three additional specimens with beam flange plate to evaluate the load versus displacement response. The load-displacement curves, yield and ultimate capacity, ductility ratio were obtained. Furthermore, the strain development at different loading levels was discussed comprehensively. It is shown that the studied connection configuration significantly reduces the stress concentration. Meanwhile, simplified trilinear load-displacement analytical model for specimen under tensile load was presented. Good agreement was found between the theoretical and experimental results.

• International journal of steel structures
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• v.18 no.5
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• pp.1577-1588
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• 2018

As the excellent mechanical performance and easy construction of concrete filled steel tubes (CFST) composite structure, it has the potential to be used to strengthen RC pier columns. Therefore, tests were conducted on 2 reinforcement concrete (RC) stub columns and 9 RC columns strengthened with circular CFST under axial loading. The test results show that the circular CFST strengthening method is effective since the mean bearing capacity of the RC columns is increased at least 3.69 times and the ductility index is significantly improved more than 30%. One of the reasons for enhancement is obvious confinement provided by steel tube besides the additional bearing capacity supplied by the strengthening materials. From the analysis of the enhancement ratio, the strengthening structure has at least an extra 20% amplification except for taking full advantage of the strength of the strengthening material. Through the analysis of confining stress provided by steel tube and the stress-strain relationship of confined concrete, it is found that the strength of the core concrete can be increased by 21-33% and the ultimate strain can be enhanced to beyond $15,000{\mu}{\varepsilon}$.

• Geomechanics and Engineering
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• v.32 no.3
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• pp.245-254
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• 2023

Through qualitative analysis and quantitative analysis, the contradictory conclusions about the stability of the settled goaf with two-layer coal seams subject to building load were obtained. Therefore, it is necessary to combine the additional stress method and numerical simulation to further analyze the foundation stability. Through borehole analysis and empirical formula analogy, the height of water-conducting fracture zone in No.4 coal and No.9 coal were obtained, providing the calculation range of water-conducting fracture zone for numerical simulation. To ensure the accuracy of the elastic modulus of broken gangue, the stress-strain curve were obtained by broken gangue compression test in dried state of No.4 coal seam and in soaking state of No.9 coal seam. To ensure the rationality of the numerical simulation results, the actual measured subsidence data were retrieved by numerical simulation. FISH language was used to analyze the maximum building load on the surface and determine the influence depth of building load on the foundation. The critical building load was 0.16 MPa of No.4 settled goaf and was 1.6 MPa of No.9 settled goaf. The additional stress affected the water-conducting fracture zone obviously, resulted in the subsidence of water-conducting fracture zone was greater than that of bending subsidence zone. In this paper, the additional stress method was analyzed by numerical simulation method, which can provide a new analysis method for the treatment and utilization of the settled goaf.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.16 no.4
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• pp.191-195
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• 2004

This study investigated the effect of deep-sea environment on the compressive characteristics of polymer matrix composite. The specimens used in the experiment were thick Carbon-Epoxy composites that were made from Carbon-Epoxy prepregs. The specimens were immersed into seawater for thirteen months. The seawater content at saturation was about 1.2% of the specimen weight. The hydrostatic pressures applied were 0.1 MPa, 100 MPa, 200 MPa, and 270 MPa. It was found that the compressive elastic modulus increased about 10% as the hydrostatic pressure increased from 0.1 MPa to 200 MPa. The modulus increased additional 2.3％ as the pressure increased to 270 MPa. It was also found that compressive fracture strength and compressive fracture strain increased with pressure in a linear behavior. Compressive fracture strength increased 28％ and compressive fracture strain increased 8.5％ as the hydrostatic pressure increased from 0.1 MPa to 270 MPa.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.7
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• pp.841-849
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• 2013

In this study, a 2-step stamping model with an additional 1st stamping tool is proposed to reduce stamping flaws in the curved parts of a dimple in a nuclear fuel spacer grid. First, the strains of curved part of dimple are characterized via a comparison with strain solutions in pure bending. A reference 2D finite element (FE) model of 1-step stamping is then established, and the corresponding maximum strain is obtained. By varying the values of design variables of the 1st stamping tool in the 2-step stamping model, FE solutions are obtained to express the strain as a function of process variables, which provides the optimum values of process variables. Finally, applying these optimum values to a 3D FE model, we demonstrate the enhanced formability of the proposed 2-step stamping model.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.147-157
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• 2002

In this paper, the testing cell and the related theory far the interpretation of constant rate of strain (CRS) consolidation test results in case of radial drainage were developed. The proposed method makes it possible to evaluate consolidation characteristics of clayey soil rapidly and accurately. To investigate the application of the developed testing device and theory, CRS consolidation tests and incremental loading(IL) tests in radial drainage condition with remolded and undisturbed samples were performed. Comparisons of consolidation parameters from consolidation curves including coefficient of consolidation values show the applicability and the reliability of the suggested method. The experimental data were compared with additional vertical drainage CRS tests and IL tests, and then were analyzed considering the effect of the drainage direction. In addition, the effect of excess pore water pressure generated during CRS consolidation test was investigated.