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Stress intensity factors under combined bending and torsion moments
Al Emran Ismail, Ahmad Kamal Ariffin, Shahrum Abdullah, Mariyam Jameelah Ghazali, Mohammed Abdulrazzaq, Ruslizam Daud
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2012, 13(1): 1-8.
https://doi.org/10.1631/jzus.A1100040
This paper discusses stress intensity factor (SIF) calculations for surface cracks in round bars subjected to combined torsion and bending loadings. Different crack aspect ratios, a/b, ranging from 0.0 to 1.2 and relative crack depths, a/D, ranging from 0.1 to 0.6 were considered. Since the loading was non-symmetrical for torsion loadings, a whole finite element model was constructed. Then, the individual and combined bending and torsion loadings were remotely applied to the model. The equivalent SIF method, F*EQ, was then used explicitly to combine the individual SIFs from the bending and torsion loadings. A comparison was then carried out with the combined SIF, F*FE, obtained using the finite element analysis (FEA) under similar loadings. It was found that the equivalent SIF method successfully predicted the combined SIF for Mode I. However, discrepancies between the results determined from the different approaches occurred when FIII was involved. It was also noted that the predicted F*FE using FEA was higher than the F*EQ predicted through the equivalent SIF method due to the difference in crack face interactions.
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Statistical extremes and peak factors in wind-induced vibration of tall buildings
Ming-feng Huang, Chun-man Chan, Wen-juan Lou, Kenny Chung-Siu Kwok
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2012, 13(1): 18-32.
https://doi.org/10.1631/jzus.A1100136
In the structural design of tall buildings, peak factors have been widely used to predict mean extreme responses of tall buildings under wind excitations. Vanmarcke’s peak factor is directly related to an explicit measure of structural reliability against a Gaussian response process. We review the use of this factor for time-variant reliability design by comparing it to the conventional Davenport’s peak factor. Based on the asymptotic theory of statistical extremes, a new closed-form peak factor, the so-called Gamma peak factor, can be obtained for a non-Gaussian resultant response characterized by a Rayleigh distribution process. Using the Gamma peak factor, a combined peak factor method was developed for predicting the expected maximum resultant responses of a building undergoing lateral-torsional vibration. The effects of the standard deviation ratio of two sway components and the inter-component correlation on the evaluation of peak resultant response were also investigated. Utilizing wind tunnel data derived from synchronous multi-pressure measurements, we carried out a wind-induced time history response analysis of the Commonwealth Advisory Aeronautical Research Council (CAARC) standard tall building to validate the applicability of the Gamma peak factor to the prediction of the peak resultant acceleration. Results from the building example indicated that the use of the Gamma peak factor enables accurate predictions to be made of the mean extreme resultant acceleration responses for dynamic serviceability performance design of modern tall buildings.
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Dispersion modeling and health risk assessment of dioxin emissions from a municipal solid waste incinerator in Hangzhou, China
Xiao-jun Ma, Xu-guang Jiang, Yu-qi Jin, Hong-mei Liu, Xiao-dong Li, Tong Chen, Jian-hua Yan
Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 2012, 13(1): 69-78.
https://doi.org/10.1631/jzus.A1100201
The emission of dioxins from municipal solid waste incinerators (MSWIs) has become a widespread concern. The effect of meteorological parameters (wind speed, atmospheric stability and mixing height) on the hourly ground level concentration (GLC) of dioxins was estimated using air dispersion models. Moreover, the health risks of dioxin exposure were evaluated for children and adults using the Nouwen equation. The total environmental exposure via air inhalation and food ingestion was calculated, based on linear fit equations. The results indicate that potentially severe pollution from dioxins occurs at a wind speed of 1.5 m/s with atmospheric stability class F. In addition, local residents in the study area are exposed to severe weather conditions most of the time, and the risk exposures for children are far higher than those for adults. The total exposure for children far exceeds the tolerable daily intake of dioxin recommended by the World Health Organization (WHO) of 1–4 pg TEQ/(kg·d) under severe weather conditions. Results from modeling calculations of health risk assessment were consistent with dioxin levels obtained during actual monitoring of emissions.
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7 articles
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