http://hdl.handle.net/10397/510 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/5748 Title: Finite element modeling of reinforced concrete beams exposed to fire<br/><br/>Authors: Gao, W. Y.; Dai, J. G.; Teng, Jin-guang; Chen, G. M.<br/><br/>Abstract: The practical implementation of performance-based fire safety design of reinforced concrete (RC) structures hinges on the availability of accurate numerical simulation tools for the behavior of RC members exposed to fire. This paper presents a three-dimensional (3D) finite element (FE) model for the accurate prediction of both the thermal and the mechanical behavior of RC beams exposed to fire. In this FE model, particular attention is paid to the modeling of interfacial bond-slip behavior between the reinforcing steel and the concrete, an aspect which has rarely been considered by previous numerical studies. Results obtained from this FE model are compared with existing test data to examine the accuracy of the model. This comparison shows that the inclusion of the steel-to-concrete interfacial behavior leads to more accurate predictions of the deflection of RC beams exposed to fire. Predictions from this FE model also allow the complex distribution and evolution of stresses in the reinforcing steel and the concrete to be examined in detail, leading to a better understanding of the local responses of RC beams exposed to fire. The FE model presented in the paper can be used directly in performance-based fire safety design of RC beams; it can also be employed in parametric studies aimed at developing simple design rules.<br/><br/>Description: DOI: 10.1016/j.engstruct.2013.03.017 Mon, 01 Jul 2013 00:00:00 GMT http://hdl.handle.net/10397/5614 Title: A case study on the biomass burning in Southeast Asia and enhancement of tropospheric ozone over Hong Kong <br/><br/>Authors: Chan, L. Y.; Chan, C. Y.; Liu, H. Y.; Christopher, S.; Oltmans, S. J.; Harris, J. M.<br/><br/>Abstract: Substantial enhancement of ozone was frequently observed in the lower troposphere (2.5–6.0 km) over Hong Kong (22.2°N, 114.3°E). Most of these enhanced ozone layers (with peak concentration up to 138 ppbv) feature moderate and high relative humidity (50–100%) and a temperature inversion at the bottom of the layer. These phenomena predominantly occur in spring (late February to mid April) coinciding with the dry season in Southeast Asia. Back air trajectories showed that these ozone‐rich air masses had passed through the Indo‐Burma region of Southeast Asia, where large‐scale fires were recorded at the time. A case study is presented and evidence from the fire count derived from AVHRR satellite images and carbon monoxide concentration derived from space shuttle during the MAPS experiment was used. We have illustrated with this case study that biomass‐burning emissions are the source of the elevated ozone observed.<br/><br/>Description: DOI: 10.1029/1999GL010855 Mon, 15 May 2000 00:00:00 GMT http://hdl.handle.net/10397/5613 Title: An ozone episode in the Pearl River Delta: field observation and model simulation<br/><br/>Authors: Jiang, F.; Guo, Hai; Wang, T. J.; Cheng, H. R.; Wang, X. M.; Simpson, I. J.; Ding, Aijun; Saunders, S. M.; Lam, S. H. M.; Blake, D. R.<br/><br/>Abstract: In the fall of 2007 concurrent air sampling field measurements were conducted for the first time in Guangzhou (at Wan Qing Sha (WQS)) and Hong Kong (at Tung Chung (TC)), two cities in the rapidly developing Pearl River Delta region of China that are only 62 km apart. This region is known to suffer from poor air quality, especially during the autumn and winter months, when the prevailing meteorological conditions bring an outflow of continental air to the region. An interesting multiday O₃ pollution event (daily maximum O₃ > 122 ppbv) was captured during 9–17 November at WQS, while only one O₃ episode day (10 November) was observed at TC during this time. The mean O₃ mixing ratios at TC and WQS during the episode were 38 ± 3 (mean ± 95% confidence interval) and 51 ± 7 ppbv, respectively, with a mean difference of 13 ppbv and a maximum hourly difference of 150 ppbv. We further divided this event into two periods: 9–11 November as Period 1 and 12–17 November as Period 2. The mixing ratios of O₃ and its precursors (NOₓ and CO) showed significant differences between the two periods at TC. By contrast, no obvious difference was found at WQS, indicating that different air masses arrived at TC for the two periods, as opposed to similar air masses at WQS for both periods. The analysis of VOC ratios and their relationship with O3 revealed strong O₃ production at WQS during Period 2, in contrast to relatively weak photochemical O₃ formation at TC. The weather conditions implied regional transport of O₃ pollution during Period 1 at both sites. Furthermore, a comprehensive air quality model system (Weather Research and Forecasting–Community Multiscale Air Quality model (WRF-CMAQ)) was used to simulate this O₃ pollution event. The model system generally reproduced the variations of weather conditions, simulated well the continuous high O₃ episode event at WQS, and captured fairly well the elevated O₃ mixing ratios in Period 1 and low O₃ levels in Period 2 at TC. The modeled surface O₃ distributions and flow structures clearly illustrated the occurrence of O₃ formation and the impact of regional transport on O₃ levels in Period 1 in the Pearl River Delta. Further analysis of O₃ formation indicated that horizontal transport was the main contributor to the O₃ increase at TC during Period 1, while at WQS O₃ levels were dominated by photochemical production during both periods. The low O₃ levels at TC during Period 2 were attributable to lower temperatures and the arrival of fresh maritime air masses brought in by strong easterly winds. This study highlights how contrasting precursor concentrations and photochemical conditions can occur over a very small distance, and it provides a rare opportunity to better understand ozone production and precursor source origins on a finer scale in this region.<br/><br/>Description: DOI: 10.1029/2009JD013583 Mon, 01 Nov 2010 00:00:00 GMT http://hdl.handle.net/10397/5612 Title: Asian emissions of CO and NOₓ: constraints from aircraft and Chinese station data<br/><br/>Authors: Wang, Yuxuan X.; McElroy, Michael B.; Wang, Tao; Palmer, Paul I.<br/><br/>Abstract: Observations of CO and NO [sub y] from the Transport and Chemical Evolution over the Pacific (TRACE-P) aircraft mission over the northwest Pacific and from two Chinese ground stations (Hong Kong and Lin An) during spring 2001 are used in conjunction with an optimal estimation inverse model to constrain estimates of Asian emissions of CO and NOₓ . A priori emissions are based on a detailed bottom-up inventory for the observation period. The inversion analysis requires 43% and 47% increases in Chinese emissions of CO and NOₓ , respectively, distributed heterogeneously, with the largest adjustments required for central China. A posteriori estimates of emissions from biomass burning in Southeast Asia are much lower than a priori values. Inversion results for NOₓ emissions are consistent with CO emissions in terms of the sense of the adjustments. Inclusion of the station data in the inversion analysis significantly improves estimates for emissions from central and south China. A large increase in NOₓ emissions inferred for central China (a factor of 3) is attributed to decomposition of organic wastes associated with the human-animal food chain and extensive applications of chemical fertilizer. An analysis of emission ratios for CO relative to NOₓ for different sectors indicates that emissions attributed to industry and transportation may be underestimated in the bottom-up inventory for central China, while emissions from the domestic sector may be underestimated for south China. An increase in emission factors could help reconcile results from the inversion analysis with the “bottom-up” approach. Detailed analysis of the surface observations using a posteriori emissions indicates the importance of meteorological phenomena, notably cold fronts in March and small-scale high- and low-pressure systems in April in modulating concentrations of CO, with the latter most evident in the data from Lin An.<br/><br/>Description: DOI: 10.1029/2004JD005250 Wed, 01 Dec 2004 00:00:00 GMT