• Structural Engineering and Mechanics
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• 제24권3호
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• pp.355-374
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• 2006

Thin walled steel bridge-piers/columns are vulnerable to damage, when subjected to earthquake excitations. Local buckling, global buckling or interaction between local and global buckling usually is the cause of this damage, which results in significant strength reduction of the member. In this study new innovative design concepts, "thin-walled corrugated steel columns" and "thin-walled cellular steel columns" are presented, which allow the column to undergo large plastic deformations without significant strength reduction; hence dissipate energy under cyclic loading. It is shown that, compared with the conventional designs, circular and stiffened box sections, these new innovative concepts might results in cost-effective designs, with improved buckling and ductility properties. Using a finite element model, that takes the non-linear material properties into consideration, it is shown that the corrugations will act like longitudinal stiffeners that are supporting each other, thus improving the buckling behavior and allowing for reduction of the overall wall thickness of the column.

• Smart Structures and Systems
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• 제23권1호
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• pp.45-60
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• 2019

This paper is devoted to proposing a new approach for damage detection of structures. In this technique, the biconjugate gradient method (BCG) is employed. To remedy the noise effects, a new preconditioning algorithm is applied. The proposed preconditioner matrix significantly reduces the condition number of the system. Moreover, based on the characteristics of the damage vector, a new direct search algorithm is employed to increase the efficiency of the suggested damage detection scheme by reducing the number of unknowns. To corroborate the high efficiency and capability of the presented strategy, it is applied for estimating the severity and location of damage in the well-known 31-member and 52-member trusses. For damage detection of these trusses, the time history responses are measured by a limited number of sensors. The results of numerical examples reveal high accuracy and robustness of the proposed method.

• Structural Engineering and Mechanics
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• 제84권2호
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• pp.181-206
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• 2022

This paper presents experimental modal analysis and static load testing results to validate the accuracy of dynamic parameters-based damage locating indices in RC structures. The study investigates the accuracy of different dynamic-based damage locating indices compared to observed crack patterns from static load tests and how different damage levels and scenarios impact them. The damage locating indices based on mode shape curvature and mode shape fourth derivate in their original forms were found to show anomalies along the beam length and at the supports. The modified forms of these indices show higher sensitivity in locating single and multi-cracks at different damage scenarios. The proposed stiffness reduction index shows good sensitivity in detecting single and multi-cracks. The proposed anomalies elimination procedure helps to remove the anomalies along the beam length. Also, the adoption of the proposed weighting method averaging procedure and normalization procedure help to draw the overall crack pattern based on the adopted set of modes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.159.1-159.1
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• 2005

• Nutrition Research and Practice
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• 제11권1호
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• pp.33-42
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• 2017

BACKGROUND/OBJECTIVE: This study aims to measure the in vitro antioxidant capacity of Korean diet (KD) with American diet (AD) as a control group and to examine the ex vivo DNA damage reduction effect on human lymphocytes. MATERIALS/METHODS: The KD applied in this study is the standard one-week meals for Koreans (2,000 kcal/day) suggested by 2010 Dietary Reference Intakes for Koreans. The AD, which is the control group, is a one-week menu (2,000 kcal/day) that consists of foods that Americans would commonly take in according to the National Health and Nutrition Examination Survey. The antioxidant capacity of each menu was measured by means of the total phenolic assay and 3 in vitro antioxidant activity assays (2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, trolox equivalent antioxidant capacity (TEAC), Oxygen radical absorbance capacity ($ORAC_{ROO{\cdot}}$)), while the extent of ex vivo lymphocyte DNA damage was measured by means of the comet assay. RESULTS: When measured by means of TEAC assay, the in vitro antioxidant capacity of the KD of the day was higher than that of the AD (P < 0.05) while there was no significant difference in total phenolic contents and DPPH and ORAC assays. The ex vivo lymphocyte DNA damage protective effect of the KD was significantly higher than that of the AD (P < 0.01). As for the one-week menu combining the menus for 7 days, the total phenolic assay (P < 0.05) and in vitro antioxidant capacity (P < 0.001, DPPH; P < 0.01, TEAC) of the KD menu were significantly higher than those of the AD menu. Likewise, the ex vivo DNA damage reduction rate of the Korean seven-day menu was significantly higher than that of the American menu (P < 0.01). CONCLUSION: This study demonstrates that the high antioxidant capacity and DNA damage protective effect of KD, which consists generally of various plant foods, are higher than those of typical AD.

• Earthquakes and Structures
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• 제17권2호
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• pp.175-189
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• 2019

The aim of the study is to show the results of complex shaking table experimental investigation focused on the response of two models of cylindrical steel tanks under mining tremors and moderate earthquakes, including the aspects of diagnosis of structural damage. Firstly, the impact and the sweep-sine tests have been carried out, so as to determine the dynamic properties of models filled with different levels of liquid. Then, the models have been subjected to seismic and paraseismic excitations. Finally, one fully filled structure has been tested after introducing two different types of damages, so as to verify the method of damage diagnosis. The results of the impact and the sweep-sine tests show that filling the models with liquid leads to substantial reduction in natural frequencies, due to gradually increasing overall mass. Moreover, the results of sweep-sine tests clearly indicate that the increase in the liquid level results in significant increase in the damping structural ratio, which is the effect of damping properties of liquid due to its sloshing. The results of seismic and paraseismic tests indicate that filling the tank with liquid leads initially to considerable reduction in values of acceleration (damping effect of liquid sloshing); however, beyond a certain level of water filling, this regularity is inverted and acceleration values increase (effect of increasing total mass of the structure). Moreover, comparison of the responses under mining tremors and moderate earthquakes indicate that the power amplification factor of the mining tremors may be larger than the seismic power amplification factor. Finally, the results of damage diagnosis of fully filled steel tank model indicate that the forms of the Fourier spectra, together with the frequency and power spectral density values, can be directly related to the specific type of structural damage. They show a decrease in the natural frequencies for the model with unscrewed support bolts (global type of damage), while cutting the welds (local type of damage) has resulted in significant increase in values of the power spectral density for higher vibration modes.

• 한방안이비인후피부과학회지
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• 제21권1호
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• pp.70-82
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• 2008

Objective : The purpose of this study is to examine the effects of Baickbujasan(BB) on the skin damage and depigmentation. Method : The inhibition of tyrosinase activity, melanogenesis and cell viability in cultured B16 melanoma cells were measured. In order to test effects of reduction of melanogenesis, B16 F-10 mouse melanoma stem line was employed to extract melanin from cultured cell, where BB was added or not, and was dissolved in alkali for colorimetric analysis. Also, in order to test skin alteration in C57BL/6 after UV irradiation, the animals were grouped into a UV urradiation group and UV irradiation after BB application group. Dopa oxidase tissue staining was excuted to invesitage the change in the distribution of active melanin cell. The distribution of active melanin cell in inner skin of iNOS after damage from UVB irradiation and the manifestation condition of P53 which takes part in natural death of keratinocyte were examined. Result : The results indicate that BB has significant effects on tyrosinase activity, and melanogenesis in vivo test. BB seems to reduce C57BL/6, external dermatological damage, for instance, erythematous papule, eczema, loss of keratinocyte, reduction in pus, and relieves dermatological damages. Conclusion : BB can be applied externally for UV protection and depigmentation.

• Structural Engineering and Mechanics
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• 제77권4호
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• pp.495-508
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• 2021

This study devises a novel approach, namely quadruple 1D convolutional neural network, for detecting connection stiffness reduction in steel truss bridge structure using experimental and numerical modal data. The method is developed based on expertise in two domains: firstly, in Structural Health Monitoring, the mode shapes and its high-order derivatives, including second, third, and fourth derivatives, are accurate indicators in assessing damages. Secondly, in the Machine Learning literature, the deep convolutional neural networks are able to extract relevant features from input data, then perform classification tasks with high accuracy and reduced time complexity. The efficacy and effectiveness of the present method are supported through an extensive case study with the railway Nam O bridge. It delivers highly accurate results in assessing damage localization and damage severity for single as well as multiple damage scenarios. In addition, the robustness of this method is tested with the presence of white noise reflecting unavoidable uncertainties in signal processing and modeling in reality. The proposed approach is able to provide stable results with data corrupted by noise up to 10%.

• 한국농림기상학회지
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• 제16권2호
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• pp.146-154
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• 2014

월동기간 동안의 차나무에 대한 차광망 색상과 차광율에 따른 동해경감에 미치는 영향을 조사한 결과, 차광율 변화에 대한 효과는 차광율이 높아질수록 차나무생육이 불량하고 동해 피해율이 높았으며, 무처리구 대비 55% 차광율에서 신초 및 생엽수확량이 좋게 나타났다. 차광망 색상별로 보면, 투명망(차광망 55% 수준) 처리구와 녹색 차광망 처리구가 무처리구와 검정 차광망 처리구에 비해 생엽수확량과 피해면적이 감소하였다. 투명망 처리구가 무처리구에 비해 동해 피해율이 50%이상 감소하고, 생엽수확량은 무처리구보다 투명망 처리구에서 단위면적당(10a) 68kg 더 많았다. 차광망의 색상별 동해경감은 검정<녹색<투명 색상 순으로 동해 경감률이 다소 높게 나타났다. 처리구간의 미기상변화를 보면 처리구가 무처리구에 비해 평균기온은 $0.7^{\circ}C$ 낮았으며, 평균상대습도는 14.9% 높게 관측되었고, 지중온도는 $0.6^{\circ}C$ 낮은 반면에 토양수분은 4.6% 높게 관측 되었다. 또한 차광망 피복물 설치에 의한 평균풍속은 무처리구 대비 0.7m/s 감소하여, 바람에 의한 과잉 증발산과 토양의 건조를 줄여주는 효과가 있었으며, 동해경감의 방안으로 활용이 가능한 것으로 판단되었다.

• Structural Engineering and Mechanics
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• 제38권6호
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• pp.715-732
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• 2011

A novel structural damage detection method with a new damage index has been recently proposed by the authors based on the statistical moments of dynamic responses of shear building structures subject to white noise ground motion. The statistical moment-based damage detection (SMBDD) method is theoretically extended in this paper with general application. The generalized SMBDD method is more versatile and can identify damage locations and damage severities of many types of building structures under various external excitations. In particular, the incomplete measurements can be considered by the proposed method without mode shape expansion or model reduction. Various damage scenarios of two general forms of building structures with incomplete measurements are investigated in consideration of different excitations. The effects of measurement noise are also investigated. The damage locations and damage severities are correctly identified even when a high noise level of 15% and incomplete measurements are considered. The effectiveness and versatility of the generalized SMBDD method are demonstrated.