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781.
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783.
梁腹板开圆孔的钢框架抗震节点 总被引:11,自引:1,他引:11
杨庆山 《中国安全科学学报》2005,15(2):45-50,40
介绍了梁腹板开圆孔的钢框架梁柱节点 ,笔者探讨的基本思路是希望通过对梁截面的削弱确保结构在强震作用时的塑性铰远离节点域而出现在梁上 ;同时 ,该节点形式应用于住宅体系时 ,使水暖管线穿梁和降低结构空间占用成为可能。因此 ,笔者对该节点形式的基本受力性能及设计中需要考虑的构造措施进行了较详细的探讨 ,并利用ANSYS对其塑性区分布和剪应力分布进行了分析。研究结果初步表明 ,梁腹板开圆孔的钢框架节点具有理论上的合理性和实用上的可行性 ,可达到塑性铰外移和增加使用功能的目的。 相似文献
784.
大规模客流对我国各大城市铁路车站旅客的安全潜伏着极大的隐患,车站旅客安全保障体系的建设显得十分重要。分析在大规模客流条件下,车站旅客可能发生的主要安全问题,包括拥挤踩踏、灾害、公共卫生、犯罪、自身发病等意外事件;提出建立旅客安全保障体系的层次结构,研究了旅客安全保障体系的流程;从车站客流组织和管理角度、车站设计角度、服务设施角度等方面来研究大规模客流条件下车站安全保障工作中应采取的措施。保障旅客安全是车站工作的重点,必须通过科学的手段,从各方面综合、严密地进行管理和组织,才能实现铁路车站的安全运营。 相似文献
785.
Shailesh Shah Ulrich Fischer Konrad Hungerbühler 《Journal of Loss Prevention in the Process Industries》2005,18(4-6):335-352
A new method called SREST-layer-assessment method with automated software tool is presented that in a hierarchical approach reveals the degree of non-ideality of chemical processes with regard to SHE (safety, health and environment) aspects at different layers: the properties of the chemical substances involved (substance assessment layer (SAL)), possible interactions between the substances (reactivity assessment layer (RAL)), possible hazard scenarios resulting from the combination of substances and operating conditions in the various equipments involved (equipment assessment layer (EAL)), and the safety technologies that are required to run a process safely and in accordance with legal regulations (safety-technology assessment layer (STAL)). In RAL, EAL and STAL the main focus is put on process safety. A case study is used to show the principles of the method. It is demonstrated how the method can be used as a systematic tool to support chemical engineers and chemists in evaluating chemical process safety in early process development stages. 相似文献
786.
787.
以山东省防震减灾信息网站为例 ,介绍了网页设计要点及日常维护的经验和体会 ,进而提出了网页进一步发展的新思路 相似文献
788.
Collins David N. Harrison John Kitcher John M. S. 《Water, Air, & Soil Pollution: Focus》2002,2(2):191-207
Measurements of electrical conductivity and discharge ofmeltwaters in the Gornera, which drains from the 83%glacierised basin containing Gornergletscher, PennineAlps, Switzerland, were undertaken between May andSeptember in both 1979 and 1998. Discharge in theGornera was 43% higher in 1998, average air temperatureduring the ablation season being 2.1 °C warmer andpreceding winter precipitation 28% lower than in 1979. Mean electrical conductivity of meltwater in 1998 wasreduced by 40%. In the same 60 day period in 1998,however, solute flux was augmented by only 2% bycomparison with 1979. Year-to-year climatic variations,reflected in discharge variability, strongly affectsolute concentration in glacial meltwaters, but havelimited impact on solute flux. Climatic conditionstranslate into meltwater quality through inter-relationships between mineral reaction rates, subglacialresidence time in contact with sediment, and discharge. Annual variability in solute flux depends on the extentto which volume of flow can offset decline in soluteconcentration brought about by reducing residence time. 相似文献
789.
Lance R. Williams Christopher M. Taylor Melvin L. Warren Jr. J. Alan Clingenpeel 《Environmental management》2002,29(1):76-87
Using Basin Area Stream Survey (BASS) data from the United States Forest Service, we evaluated how timber harvesting influenced
patterns of variation in physical stream features and regional fish and macroinvertebrate assemblages. Data were collected
for three years (1990–1992) from six hydrologically variable streams in the Ouachita Mountains, Arkansas, USA that were paired
by management regime within three drainage basins. Specifically, we used multivariate techniques to partition variability
in assemblage structure (taxonomic and trophic) that could be explained by timber harvesting, drainage basin differences,
year-to-year variability, and their shared variance components. Most of the variation in fish assemblages was explained by
drainage basin differences, and both basin and year-of-sampling influenced macroinvertebrate assemblages. All three factors
modeled, including interactions between drainage basins and timber harvesting, influenced variability in physical stream features.
Interactions between timber harvesting and drainage basins indicated that differences in physical stream features were important
in determining the effects of logging within a basin. The lack of a logging effect on the biota contradicts predictions for
these small, hydrologically variable streams. We believe this pattern is related to the large scale of this study and the
high levels of natural variability in the streams. Alternatively, there may be time-specific effects we were unable to detect
with our sampling design and analyses. 相似文献
790.
A. Allen Bradley Christa Peters‐Lidard Brian R. Nelson James A. Smith C. Bryan Young 《Journal of the American Water Resources Association》2002,38(5):1393-1407
ABSTRACT: A general framework is proposed for using precipitation estimates from NEXRAD weather radars in raingage network design. NEXRAD precipitation products are used to represent space time rainfall fields, which can be sampled by hypothetical raingage networks. A stochastic model is used to simulate gage observations based on the areal average precipitation for radar grid cells. The stochastic model accounts for subgrid variability of precipitation within the cell and gage measurement errors. The approach is ideally suited to raingage network design in regions with strong climatic variations in rainfall where conventional methods are sometimes lacking. A case study example involving the estimation of areal average precipitation for catchments in the Catskill Mountains illustrates the approach. The case study shows how the simulation approach can be used to quantify the effects of gage density, basin size, spatial variation of precipitation, and gage measurement error, on network estimates of areal average precipitation. Although the quality of NEXRAD precipitation products imposes limitations on their use in network design, weather radars can provide valuable information for empirical assessment of rain‐gage network estimation errors. Still, the biggest challenge in quantifying estimation errors is understanding subgrid spatial variability. The results from the case study show that the spatial correlation of precipitation at subgrid scales (4 km and less) is difficult to quantify, especially for short sampling durations. Network estimation errors for hourly precipitation are extremely sensitive to the uncertainty in subgrid spatial variability, although for storm total accumulation, they are much less sensitive. 相似文献