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61.
厚软场地上大跨径桥梁设计反应谱研究 总被引：1，自引：0，他引：1
大跨径桥梁塔高、跨径大、自振周期长,深厚、软弱场地的长周期地震动对桥体结构影响较大。我国《公路工程抗震设计规范(JT J004-89)》也只适用主跨不超过150 m的梁桥和拱桥,国内长期以来没有一个适用于大跨径桥梁的抗震设计规范或指南。本文结合大跨径桥梁工程实例,根据场地土层静、动力性能参数的原位测试和动三轴试验结果,进行厚软场地土层地震反应分析,研究厚软场地的地震动效应,讨论了不同地震动强度时厚软场地的设计反应谱特征,分析了现行规范设计反应谱应用的局限性,成果对相关工程有重要指导意义,对大跨径桥梁抗震设计规范的制定也有借鉴作用。 相似文献
62.
Urban renewal in Hong Kong plays an important role in stimulating local economy by optimizing development potential of disturbed site and introducing new activities/businesses with large profit margins. However, past and current urban renewal practices put too much emphasis on achieving economic objectives, and overlook the environmental and social needs of the community, which violates the global trend to promote sustainable development in the urban areas. In view of it, this paper has reviewed the property‐led/ market‐led urban renewal approach continuously adopted in Hong Kong, and suggested a more sustainable approach to meet economic objectives. In order to facilitate such approach, this paper has highlighted a list of urban design considerations contributing to sustainable development and identified key design factors improving economic sustainability of the urban renewal projects. Copyright © 2008 John Wiley & Sons, Ltd and ERP Environment. 相似文献
63.
The purpose of this research is to obtain optimal processing conditions for the adsorption of Remazol Brilliant Violet-5R (RBV-5R) dye onto activated carbon prepared from periwinkle shells (PSAC) by chemical activation with KOH using response surface methodology. Central composite design (CCD) was used to determine the effects of three preparation variables; CO2 activation temperature, CO2 activation time and KOH:char impregnation ratio (IR) on two responses; percentage RBV-5R dye removal and PSAC yield. Based on the CCD, two quadratic models were developed for percentage RBV-5R dye removal and PSAC yield, respectively. The most influential factor on each experimental design response was identified from the analysis of variance (ANOVA). The optimum conditions for the adsorption of RBV-5R dye onto PSAC were CO2 activation temperature of 811 °C, CO2 activation time of 1.70 h and IR of 3.0, resulting in 81.28% RBV-5R dye removal and 28.18% PSAC yield. PSAC prepared under optimum conditions was mesoporous with a Brunauer–Emmett–Teller surface area of 1894 m2·g?1, total pore volume of 1.107 cm3·g?1 and average pore diameter of 2.32 nm. The surface morphology and functional groups of the activated carbon were respectively determined from the scanning electron microscopy and Fourier transform infrared analysis. 相似文献
64.
本文介绍了一种新型正压空气呼吸器面罩的结构设计。分别从数据采集、曲面重构及实体建模等方面对面罩的数字化设计步骤进行了详细阐述,并对面罩视野进行了初步校核。 相似文献
65.
环境温度在容器设计中不仅影响设计压力的合理确定,而且更影响最低设计金属温度的确定直至影响材料的正确选择。通过对规程标准的解读,结合液化石油气储罐设计对此进行了讨论,认为环境温度应视为容器的特例工况条件,容器设计应将与其对应的设计压力一起作为设计载荷条件,不仅要对容器的壁厚进行校核,而且尚需根据容器的一次应力判断并确认是否需要修订完善容器设计的选材、制造及检验等技术要求,使容器设计文件正确完整,保证容器制造的安全可靠性。 相似文献
66.
Most highways in urban China are tolled to finance their construction. During the eight-day National Day holiday in 2012, highway tolls were waived nationwide for passenger vehicles. We use this to identify the effects of highway tolls on air pollution. Using daily pollution and weather data for 98 Chinese cities in 2011 and 2012 and employing both a regression discontinuity design and differences-in-differences method with the 2011 National Day holiday as a control, we find that eliminating tolls increases pollution by 20% and decreases visibility by one kilometer. We also estimate that the toll elasticity of air pollution is −0.15. These findings complement the scant literature on the environmental impact of road pricing. 相似文献
67.
We describe designs for the temporal aspect of sampling in an experiment that estimates the population mean growth of an organism that can be modeled using a Weibull or von Bertalanffy growth curve. First, the properties of the Weibull growth curve are explained. Next, using the shape parameter (v), the Weibull growth curve can be categorized into two shape categories: sigmoid and saturation. D‐optimization and shape classification are used to determine the optimal sampling occasions and the effect of a sampling schedule on the precision of the size estimates. Finally, the results are used to recommend a generalized sampling design to best determine the shape and size of a growth curve. 相似文献
68.
In this study, we develop a model for Antarctic surface mass balance (SMB), which allows us to assess regional and global uncertainty in SMB estimation and carry out a model‐based design to propose new measurement sites. For this analysis, we use a quality‐controlled aggregate data set of SMB field measurements with significantly more observations than previous analyses; however, many of the measurements in this data set lack quality ratings. In addition, these data demonstrate spatial autocorrelation, heteroscedasticity, and non‐Gaussianity. To account for these data attributes, we pose a Bayesian Gaussian process generalized linear model for SMB. To address missing reliability ratings, we use a mixture model with different variances to add robustness to our model. In addition, we present a novel approach for modeling the variance as a function of the mean to account for the heteroscedasticity in the data. Using this model, we predict Antarctic SMB and compare our estimates with previous estimates. In addition, we create prediction maps with uncertainty to visualize spatial patterns in SMB and to identify regions of high SMB uncertainty. Our model estimates the total SMB to be 2,156 Gton/yr over the range of our data, with 95% credible interval (2,081, 2,234) Gton/yr. Overall, our results suggest lower Antarctic SMB than previously reported. This lower SMB estimate may be indicative of a more dire diagnosis of the long‐term health of the Antarctic ice sheets. Lastly, we use our model to propose 25 new measurement sites for the field study utilizing a sequential design, minimizing the integrated mean squared error. 相似文献
69.
S. Kim 《国际发展与全球生态学杂志》2019,26(2):141-153
The impact of large-scale urban development on land resources has long been debated by urban planners and designers. This study investigated the extent to which different urban characteristics are associated with land-cover change. The Yangtze River Delta region in China, forming one of the largest sprawling urban landscapes among the regions around the world, was chosen for the study area. Spatial analysis and multiple regression methods were applied to empirically investigate the pattern of resource sites lost to urban development in the area between the 1950s and 2017. The results showed that contrary to the widespread notion that large-sized cities are predominantly responsible for a region’s environmental degradation, city size was not a significant factor in determining the rate of resource loss. Large-sized cities gained their populations with far lesser impacts on land than small-sized cities and towns if normalized to the same number of populations. One explanation for the diminishing effect of city size on land-cover change relates to the degree of spatial dispersion of urban development and local differences in social valuation of diversified lands by cities. 相似文献
70.