• Smart Structures and Systems
• /
• v.10 no.2
• /
• pp.131-154
• /
• 2012

In this paper, it is aimed to determine the seismic behaviour of highway bridges by nondestructive testing using ambient vibration measurements. Eynel Highway Bridge which has arch type structural system with a total length of 216 m and located in the Ayvaclk county of Samsun, Turkey is selected as an application. The bridge connects the villages which are separated with Suat U$\breve{g}$urlu Dam Lake. A three dimensional finite element model is first established for a highway bridge using project drawings and an analytical modal analysis is then performed to generate natural frequencies and mode shapes in the three orthogonal directions. The ambient vibration measurements are carried out on the bridge deck under natural excitation such as traffic, human walking and wind loads using Operational Modal Analysis. Sensitive seismic accelerometers are used to collect signals obtained from the experimental tests. To obtain experimental dynamic characteristics, two output-only system identification techniques are employed namely, Enhanced Frequency Domain Decomposition technique in the frequency domain and Stochastic Subspace Identification technique in time domain. Analytical and experimental dynamic characteristic are compared with each other and finite element model of the bridge is updated by changing of boundary conditions to reduce the differences between the results. It is demonstrated that the ambient vibration measurements are enough to identify the most significant modes of highway bridges. After finite element model updating, maximum differences between the natural frequencies are reduced averagely from 23% to 3%. The updated finite element model reflects the dynamic characteristics of the bridge better, and it can be used to predict the dynamic response under complex external forces. It is also helpful for further damage identification and health condition monitoring. Analytical model of the bridge before and after model updating is analyzed using 1992 Erzincan earthquake record to determine the seismic behaviour. It can be seen from the analysis results that displacements increase by the height of bridge columns and along to middle point of the deck and main arches. Bending moments have an increasing trend along to first and last 50 m and have a decreasing trend long to the middle of the main arches.

• Journal of Environmental Science International
• /
• v.19 no.4
• /
• pp.447-457
• /
• 2010

This study aims to monitor the variation of concentration of PCDD/DFs between the gaseous phase-particulate phases in the ambient air of urban area in Korea. This monitoring is evaluated by using the Junge-Pankow model and the Koa absorption model with the application of the Octanol-air partition coefficient. In this study, the ambient air samples were analyzed according to each congener group of the PCDD/DFs by HRGC/HRMS, which have been investigated for the past 5 years. In the results, the annual variation in the concentration level of $\Sigma$PCDD/DFs in TSP was increased from $1588\;fg/m^3$ in 1998 to $5123\;fg/m^3$ in 2002, and from 31 fg I-TEQ/$m^3$ to 94 fg I-TEQ/$m^3$ in the $\Sigma$I-TEQ. In the case of PUF of gaseous phase sample, their variation was increased from $1615\;fg/m^3$ in 1998 to $2237\;fg/m^3$ in 2002, and in the $\Sigma$I-TEQ from 12 fg I-TEQ/$m^3$ to 17 fg I-TEQ/$m^3$. The relative coefficient between the gas phase concentration of PCDD/DFs and the temperature was a value of 0.744; the contributive rate of the temperature to the gaseous phase concentration was 0.554. According to the results, the pattern of the coefficient of distribution based on log $p_L^0$ is similar to the ambient air of the urban areas.

• Journal of Korean Society for Atmospheric Environment
• /
• v.31 no.3
• /
• pp.209-222
• /
• 2015

Fine and coarse PM had been collected by LVCI (low volume cascade impactor) and HVAS (high volume air sampler) during January 1989 to April 2012 at Kyung Hee University, Global Campus located on the boarder of Yongin and Suwon. The database of PM mass concentration was constructed and then intensively and extensively investigated to understand monthly, seasonal, and annual patterns of each PM behavior. Especially the study separated all the PM data into the 5 Period Zones, which were classified on the basis of social, political, and environmental issues that might be influencing local ambient air quality during the monitoring period. The overall $PM_{10}$ level had been continuously decreased until 2005 and after then was staggering due to rapidly increasing $PM_{2.5}$ level in $PM_{10}$. The annual average of $PM_{2.5}$ concentration varied from $34.3{\mu}g/m^3$ to $59.0{\mu}g/m^3$, which were much higher than the 2015 ambient air quality standard. The $PM_{2.5}$ level was strongly associated with haze events, while both $PM_{10}$ and $PM_{2.5}$ levels were associated with Yellow storm events. Daily concentrations of $PM_{2.5}$ were ranged $13.1{\sim}212.9{\mu}g/m^3$ in haze days and $33.6{\sim}124.6{\mu}g/m^3$ in Asian dust days. The study also intensively investigated annual and seasonal patterns of $PM_{2.5}/PM_{10}$ ratios.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.26 no.4
• /
• pp.20-29
• /
• 2022

The operational modal analysis (OMA) technique, which extracts the modal parameters of a structural system using ambient vibrations, has been actively developed as a field of structural health monitoring of cable-supported bridges. In this paper, the short and long-term modal parameters of a cable-stayed bridge were evaluated using the acceleration data obtained from the two ambient vibration tests (AVTs) and three years of continuous measurements. A total of 27 vertical modes and 1 lateral mode in the range 0.1 ~ 2.5 Hz were extracted from the high-resolution AVTs which were conducted in the 6th and 19th years after its completion. Existing OMA methods such as Peak-Picking (PP), Eigensystem Realization Algorithm with Data Correlation (ERADC), Frequency Domain Decomposition (FDD) and Time Domain Decomposition (TDD) were applied for modal parameters extraction, and it was confirmed that there was no significant difference between the applied methods. From the correlation analysis between long-term natural frequencies and environmental factors, it was confirmed that temperature change is the dominant factor influencing natural frequency fluctuations. It was revealed that the decreased natural frequencies of the bridge were not due to changes in structural performance and integrity, but to the environmental effects caused by the temperature difference between the two AVTs. In addition, when the TDD technique is applied, the accuracy of extracted mode shapes is improved by adding a proposed algorithm that normalizes the sequence so that the autocorrelations at zero lag equal 1.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.9
• /
• pp.5877-5884
• /
• 2014

Recently, abnormally cold weather has been reported more frequently in winter due to the climate change and abnormal weather changes. On the other hand, the heating capacity of a railcar may be not enough to warm the cabin under severe cold climatic conditions, which is one of the reasons for the passengers' complaints about heating. In this study, the effects of ambient temperature and heater power on the cabin temperature was investigated to obtain the minimum ambient temperature for the tested railcar. The test railcar was placed in a large-climatic chamber, and various ambient temperature conditions were simulated. The effects of the heater output were investigated by monitoring the cabin temperature under a range of heater output conditions. The mean cabin temperature was $14.0^{\circ}C$, which was far lower than the required minimum temperature of $18^{\circ}C$, under a $-10^{\circ}C$ ambient temperature condition with the maximum heat power. When the ambient temperature was set to $0^{\circ}C$ and $10^{\circ}C$, the maximum achievable cabin temperature was $26.1^{\circ}C$ and $34.0^{\circ}C$. Through calculations using the interpolation method, the minimum ambient temperature to maintain an $18^{\circ}C$ cabin temperature was $-6.7^{\circ}C$ for this car. The vertical temperature difference was higher with a higher power output and higher ambient temperature. The maximum vertical temperature difference was higher than $10^{\circ}C$ in some cases. However, the horizontal temperature difference vs. low temperature (< $2^{\circ}C$) was independent of the power output and ambient temperature. As a result, it is very important to reduce the vertical temperature difference to achieve good heating performance.

• Journal of the Korea institute for structural maintenance and inspection
• /
• v.9 no.4
• /
• pp.227-234
• /
• 2005

In this paper, a smart wireless MEMS-based accelerometer(MA) system has been designed and experimented for smart monitoring system of civil structures. Various performance and experimental tests have been carried out to evaluate whether this system is suitable for monitoring system of civil structures. First, we examined its sensitivity, resolution, and noise, specifically to evaluate the performance of the smart wireless MA system. The results of experiments enabled us to estimate performance of the MA in SWMAS in comparison to the value of data sheet from MA. Second, characteristics of model structure were analyzed by the ambient vibration test based on the NExT combined with ERA. Finally, this analysis was compared to the one that was made by FE results, and the comparison proved that a smart wireless MA system was fitted in smart monitoring system effectively.

• Journal of Korean Society for Atmospheric Environment
• /
• v.20 no.2
• /
• pp.215-224
• /
• 2004

We report the high concentration episodes for PM$_{10}$, SO$_2$, NO$_2$, and $O_3$ in many urban areas Korea during 2002. The high concentration episodes are identified based on the National Ambient Air Quality Standards and the observations obtained from the Regional Air Monitoring Network composed of approximately 160 air pollution monitoring stations located in a number of major or big cities in South Korea including Seoul, Pusan, Daegu, and Incheon cities. The results show that the twenty cases of high concentration episodes in 2002 consists of both ozone warning episodes (6 cases) and high PM$_{10}$ concentration cases (14 cases), and one half of the latter are found to occur in association with the Yellow Sand (Asian Dust) phenomena. The most outstanding characteristics of the reported episodes are the excessively high levels of maximum PM$_{10}$ concentrations during the Yellow Sand period (i.e., exceeding 3,000$\mu\textrm{g}$/㎥ in April, 2002) and their variable occurrence frequencies across seasons. The high ozone concentration episode days are mainly resulting from both the high photochemical reactions and poor ventilations. The high PM$_{10}$ concentration days during non Yellow Sand periods, however, mostly occurred under the influence of synoptic meteorological conditions such as stagnant or slowly passing high pressure centers, and consequently prevailing weak wind speeds over the Korean peninsula. The overall results of our study thus suggest the importance of both synoptic and local meteorological factors for high concentration levels in the major and/or big cities in Korea.n Korea.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.66 no.7
• /
• pp.1141-1148
• /
• 2017

Generally, a thermistor made by sintering a metal oxide is widely used to measure the ambient temperature. This thermistor is widely used not only for industrial use but also for medical use because of its excellent sensitivity, durability, temperature change characteristics and low cost. In particular, the normal body temperature is 36.9 degrees relative to the armpit temperature, and it is most closely related to the circulating blood flow. Previous studies have shown that body temperature changes during biomechanical changes and body temperature changes by anomalous signs or illnesses. Therefore, in this study, we propose a Lock-In-Amp design to detect minute temperature changes of clothing and thermistor wired by a preacher as a method to regularly measure body temperature in daily life. Especially, it is designed to measure the minute resistance change of the thermistor according to body temperature change even in a low-cost microprocessor environment by using a micro-processor-based Lock-In-Amp, and a jacquard and the thermistor is arranged so as to be close to the side, so that the reference body temperature can be easily measured. The temperature was measured and stored in real time using short-range wireless communication for non - restraint temperature monitoring. A baby vest was made to verify its performance through temperature experiments for infants. The measurement of infant body temperature through the existing skin sensor or thermometer has limitations in monitoring infant body temperature for a long time without restriction. However, it can be overcome by using the embroidery fabric based micro temperature monitoring wireless monitoring device proposed in this study.

• Smart Structures and Systems
• /
• v.30 no.6
• /
• pp.687-701
• /
• 2022

Inevitable response loss under complex operational conditions significantly affects the integrity and quality of measured data, leading the structural health monitoring (SHM) ineffective. To remedy the impact of data loss, a common way is to transfer the recorded response of available measure point to where the data loss occurred by establishing the response mapping from measured data. However, the current research has yet addressed the structural condition changes afterward and response mapping learning from a small sample. So, this paper proposes a novel data driven structural response reconstruction method based on a sophisticated designed generating adversarial network (UAGAN). Advanced deep learning techniques including U-shaped dense blocks, self-attention and a customized loss function are specialized and embedded in UAGAN to improve the universal and representative features extraction and generalized responses mapping establishment. In numerical validation, UAGAN efficiently and accurately captures the distinguished features of structural response from only 40 training samples of the intact structure. Besides, the established response mapping is universal, which effectively reconstructs responses of the structure suffered up to 10% random stiffness reduction or structural damage. In the experimental validation, UAGAN is trained with ambient response and applied to reconstruct response measured under earthquake. The reconstruction losses of response in the time and frequency domains reached 16% and 17%, that is better than the previous research, demonstrating the leading performance of the sophisticated designed network. In addition, the identified modal parameters from reconstructed and the corresponding true responses are highly consistent indicates that the proposed UAGAN is very potential to be applied to practical civil engineering.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.10 no.2
• /
• pp.124-139
• /
• 2000

This study was performed to investigate monoacetylbenzidine(MABZ) and benzidine(BZ) hemoglobin adducts among workers who worked at benzidine based dye manufacturing company, and exposed by benzidine and benzidine based dye. The hemoglobin adducts were compared with work environment assessment result for evaluating the usefulness of biological monitoring. The mean BZ hemoglobin adducts among the first synthesis worker's hemoglobin adducts were $40.69{\mu}gBZ/g$ Hb and those of dry and packing workers were $22.14{\mu}gBZ/g$ Hb. The mean of MABZ hemoglobin adducts among 1st synthesis workers were $255.84{\mu}gMABZ/g$ Hb, dispersion worker's hemoglobin adducts were $76.17{\mu}gMABZ/g$ Hb and synthesis worker's hemoglogin adducts were $28.66{\mu}gMABZ/g$ Hb. Work environment assessment results during past 3 years were $0.0065mg/m^3$ and $0.5659mg/m^3$ of benzidine based dye concentration in ambient air of drying and packing only. Dye producing process was categorized by the possibility of exposure to benzidine and benzidine based dye. BZ and MABZ hemoglobin adducts were $19.55{\mu}gBZ/g$ Hb, $119.80{\mu}gMABZ/g$ Hb among workers who exposed by benzidine dihydrochloride and $16.32{\mu}gBZ/g$ Hb, $316.56{\mu}gMABZ/g$ Hb among workers who exposed by benzidine based dye. BZ hemoglobin adducts were not detected among control group and MABZ hemoglobin adducts were $5.33{\mu}gMABZ/g$ Hb. The differences between control and other exposed group was statistically significant. But there was no statistically significant differences between benzidine dihydrochloride exposed process and benzidine based dye exposed group. BZ and MABZ hemoglobin adducts were $2.23{\mu}gBZ/g$ Hb, $76.17{\mu}gMABZ/g$ Hb and $3.46{\mu}gBZ/g$ Hb, $21.33{\mu}gMABZ/g$ Hb. So hemoglobin adducts of MABZ were 5 ~ 30 time higher than those of BZ(P<0.003). Above results indicate that work environment assessment didn't detected benzidine and benzidine based dye in ambient air but biological monitoring detected those of hemoglobin adducts. Two group's hemoglobin adducts exposed benzidine dihydrochloride and benzidine based dye were high level but wasn't statistically significant and those were not detected in control group.