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311. Angular change and secondary stress in main cables of suspension bridges.

Author

Lee, Minjae and Kim, Ho-Kyung

Abstract

Three basic cable equations are proposed for evaluating the deflected shape of the main cables of suspension bridges subject to angular changes near the saddles of the main towers as well as the cable bands. The secondary stress on the tensioned parallel wires can be estimated via the combined use of the three basic cable equations that take into account the free and/or friction slip between wires as a function of the lateral restraints by cable bands and wrapping wires. A series of laboratory loading tests were carried out for a parallel wire strand to validate the proposed procedure. The proposed method was also applied to the Yi Sun-sin Bridge to demonstrate the level of secondary stress in parallel wires and to identify the factors that have an impact on the secondary stress in the completed stage as well as during the construction phase. The residual tension of the wrapping wire, which impacts the frictional resistance between wires of the main cable, was measured from field tests. The evaluated secondary stress was found to exceed 10% of the tensile strength of the wires. The findings reported herein also confirm that the distance between the tower saddle and the first cable band is a critical factor for secondary stress. Based on the experimental validation and application to an actual bridge, the proposed approach, despite being based on simplified formulations, is demonstrated to be useful in predicting the secondary stress that develops in parallel wire cables. [ABSTRACT FROM AUTHOR]

Published
2016
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343. Damping Identification of Bridges Under Nonstationary Ambient Vibration

Author

Kim, Sunjoong and Kim, Ho-Kyung

Abstract

This research focuses on identifying the damping ratio of bridges using nonstationary ambient vibration data. The damping ratios of bridges in service have generally been identified using operational modal analysis (OMA) based on a stationary white noise assumption for input signals. However, most bridges are generally subjected to nonstationary excitations while in service, and this violation of the basic assumption can lead to uncertainties in damping identification. To deal with nonstationarity, an amplitude-modulating function was calculated from measured responses to eliminate global trends caused by nonstationary input. A natural excitation technique (NExT)-eigensystem realization algorithm (ERA) was applied to estimate the damping ratio for a stationarized process. To improve the accuracy of OMA-based damping estimates, a comparative analysis was performed between an extracted stationary process and nonstationary data to assess the effect of eliminating nonstationarity. The mean value and standard deviation of the damping ratio for the first vertical mode decreased after signal stationarization.

Published
2017
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344. Ventilation efficiency in road vehicles and probability of respiratory infection

Author

Kim, Sejin, Jung, Sungmoon, Seyedi, MohammadReza, and Kim, Ho-Kyung

Abstract

•Different ventilation methods were evaluated experimentally for road vehicles.•Ventilation efficiency was quantified through aerosol measurements.•The risk of infectious respiratory disease was estimated for various scenarios.•Moving vehicles with all windows open had the greatest infection risk reduction.

Published
2023
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