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41.
整体桥中台后土压力在温度循环作用下会发生较大变化,这种季节性横向土压力的变化在每次温度循环后会持续增大,其实际所受水平土压力会远大于桥台设计时的压力,同时桥台桩基会产生累积和残余变形,因而有效减少台后土压力与桥台桩基的累积和残余变形至关重要。为此以桥台-H形钢桩试件为研究对象,通过在桥台侧向施加水平位移荷载,开展带膨胀聚苯乙烯(EPS)填料板的整体式桥台-桩-土往复荷载拟静力试验,分析桥台、桩基的骨架曲线、滞回曲线及其沿入土深度方向的水平变形和桥台转角等的变化规律,初步研究EPS填料板的厚度对桥台-桩基-土相互作用受力性能的影响。试验结果表明:在台后埋设EPS填料板能有效减小上部结构变形时桥台所受到的水平力,最大可减小31%;同时,也可减小模型试件的累积变形,其随着EPS厚度的增加而逐渐减小,尤其对桩的累积变形减小最为显著,最大减小了74.3%;在台后埋设EPS填料板也可有效减小台后填土对桥台转角的约束作用;台后埋设EPS填料板会使单步位移荷载作用下产生的变形有所增大,但幅度不大;试验全过程各模型试件均表现出了良好的弹性性能和变形能力。 相似文献
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鉴于我国城际长途慢行交通设施建设快速发展,为提高其交通旅游服务水平,改善游客出行体验和控制建设成本,并为制订相关标准提供基础性指标,对慢行交通驿站设置间距进行了综合性量化研究。首先,构建了基于慢行交通人群出行过程的生理机能、不同情境下的应急需要及驿站设施建设成本等多因素的量化规划模型。然后,利用MATLAB软件求解函数极值,得到综合社会效益较优的驿站设置间距范围。最后,基于计算结果对《绿道规划设计导则》中驿站间距设置标准的合理性进行了验证,提出城际长途慢行交通服务驿站设施最佳间距为2.2~3.4km,并进一步推断出旅游公路服务驿站间距的设置原则。 相似文献
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为给我国科学制定新时期绿色出行和慢行交通发展政策提供支撑,通过实证分析、比较分析等方法,对自行车交通发展已经较为完备,拥有系统化的战略,资金投入和建设管理体系相对完善的丹麦、德国和英国的自行车交通发展战略进行了研究。结合战略编制背景,从发展目标、行动战略和保障措施3个方面系统梳理并总结了国外自行车交通发展的先进经验。在此基础上,考虑我国自行车交通发展的现状和挑战,对如何有效提升自行车出行分担率的启示如下:优化整体自行车道网络布局,分为省、市和县3个层级;复兴自行车文化,培养居民绿色出行意识;明确各部门工作职责,落实管理责任和范围;制定相关技术标准和法律法规,完善自行车交通专有路权;通过设立政府专项资金和鼓励社会投资建立稳定的财政保障机制,集中资金解决重点问题。 相似文献
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Accurate modelling of the health and environmental benefits of non-recreational transport cycling requires information about its effects on the use of other transport modes. Relevant research has not focussed on cycling for transport in a general context (as opposed to bikeshare), nor allowed for multi-modal trips. The influence of trip- and personal-characteristics on whether cycling replaces car-driving have yet to be considered. The present study aimed to address these research gaps. An on-line cross-sectional survey was completed by 1525 Australians who cycle for transport at least once per week. For the most recent trip completed (at least partly) by bicycle participants provided trip distance, and percentage travelled by car, public transport (PT), and walking. They also provided the percentage travelled by each mode for the same trip before taking up transport cycling; and a hypothetical future trip when riding is not possible. Compared to the same trip before, fifty percent of recent trips reduced car use, and around 1/3 eliminated a 100%-car trip. Reduced car use was significantly less likely for trips under 7.5 km, commuting, females, respondents under 55, and regular cyclists. Reduced car use was less likely for respondents who started riding because it is flexible, and more likely for those who started riding to avoid parking. Car-use was reduced by an average of 6.2 km per trip, and each bicycle-km cycled replaced 0.5 car-km. Participants report that since taking up cycling, even when they cannot use their bike, they use cars less and use PT more compared to before they took up cycling. Results suggest that previous studies underestimated the extent to which transport cycling replaces car travel, and highlights trip types and population groups to target with cycling promotion strategies. Information about the per-trip and per-bicycle-km replacement of car, PT and walking may be used for more accurate estimation of the benefits of transport cycling than has hitherto been possible. 相似文献
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Andrea Riedel Christine Michel Michel Gosselin Bernard LeBlanc 《Journal of Marine Systems》2008,74(3-4):918
An understanding of microbial interactions in first-year sea ice on Arctic shelves is essential for identifying potential responses of the Arctic Ocean carbon cycle to changing sea-ice conditions. This study assessed dissolved and particulate organic carbon (DOC, POC), exopolymeric substances (EPS), chlorophyll a, bacteria and protists, in a seasonal (24 February to 20 June 2004) investigation of first-year sea ice and associated surface waters on the Mackenzie Shelf. The dynamics of and relationships between different sea-ice carbon pools were investigated for the periods prior to, during and following the sea-ice-algal bloom, under high and low snow cover. A predominantly heterotrophic sea-ice community was observed prior to the ice-algal bloom under high snow cover only. However, the heterotrophic community persisted throughout the study with bacteria accounting for, on average, 44% of the non-diatom particulate carbon biomass overall the study period. There was an extensive accumulation of sea-ice organic carbon following the onset of the ice-algal bloom, with diatoms driving seasonal and spatial trends in particulate sea-ice biomass. DOC and EPS were also significant sea-ice carbon contributors such that sea-ice DOC concentrations were higher than, or equivalent to, sea-ice-algal carbon concentrations prior to and following the algal bloom, respectively. Sea-ice-algal carbon, DOC and EPS-carbon concentrations were significantly interrelated under high and low snow cover during the algal bloom (r values ≥ 0.74, p < 0.01). These relationships suggest that algae are primarily responsible for the large pools of DOC and EPS-carbon and that similar stressors and/or processes could be involved in regulating their release. This study demonstrates that DOC can play a major role in organic carbon cycling on Arctic shelves. 相似文献
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Matthieu Waeles Ricardo D. Riso Jean-Franois Maguer Jean-Franois Guillaud Pierre Le Corre 《Journal of Marine Systems》2008,72(1-4):358
The dissolved lead was studied in the whole salinity gradient of the system composed of the Loire estuary and the North Biscay continental shelf. About 130 samples were collected in winter 2001 and spring 2002 during Nutrigas and Gasprod campaigns (Programme PNEC-Golfe de Gascogne, RV Thalassa) and metal measurements were conducted on board by Potentiometric Stripping Analysis. In the Loire estuary, levels of dissolved lead ranged from 0.15 to 0.24 nM and from 0.04 to 0.26 nM in winter and spring, respectively. Compared to the concentrations reported in 1987 and 1990 (0.4–1.7 nM; Boutier, B., Chiffoleau, J.F., Auger, D., Truquet, I., 1993. Influence of the Loire river on dissolved lead and cadmium concentrations in coastal waters of Brittany. Estuar. Coast. Shelf S., 36:133–143, Estuarine, Coastal and Shelf Science 36, 133–143) our study indicated much lower values. The fall in concentration in the estuary could be attributed to the stopping of activity of Octel, a big manufacturer of tetra alkyl lead. Discharge in dissolved metal to the continental shelf by the Loire river was assessed as 7.5 and 1.9 kg day− 1 for winter and spring, respectively. On the continental shelf, levels of dissolved lead varied within 0.06 and 0.27 nM in winter (0.15 ± 0.06 nM, sd = 1.96, n = 49), whereas concentrations measured in spring were in the range 0.06–0.17 nM (0.09 ± 0.03 nM, sd = 1.96, n = 60). This difference in metal concentration was related to the amounts of rainfall that have fallen over the continental shelf: estimations of inputs by this way (74 and 32 kg day− 1 in winter and spring, respectively) appeared to be significantly higher than inputs from the Loire river (7.5 and 1.9 kg day− 1 in winter and spring, respectively). The distributions of dissolved metal in the surface waters highlighted the role of suspended particular matter (SPM) for a rapid “trapping” of lead near the mouth of the estuary. The vertical distributions showed, in the stratified area, a biological transfer of lead between winter and spring from surface waters to the halocline. 相似文献
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Carbon cycling in the Weddell Sea was investigated during the ANT X/7 cruise with `FS Polarstern' December 1992–January 1993. Samples were taken on a cross section from Kapp Norvegia to Joinville Island, and on a section from the Larsen Ice Shelf to the northeast. The following quantities were measured: total carbon dioxide (TCO2), fluorescence from humic substances and total organic carbon. The distribution of TCO2 was strongly positively correlated to the time elapsed since the various water masses were last ventilated. In general, humic substance fluorescence was positively correlated with TCO2, with the exception of the productive part of the western Weddell Sea, where the correlation was negative in the surface mixed layer. The increased fluorescence at the surface is suggested to be a result of biological production. The distribution of total organic carbon showed less structure, since this quantity includes a particulate component, which is subject to dispersion processes different from those of the dissolved components TCO2 and humic substances. The mean total organic carbon concentration below the surface mixed layer was 50 μmol l−1. At some stations, a steep TOC maximum around 2000 m depth was observed. This was interpreted to result from mass sinking of phytoplankton blooms. Total organic carbon had a maximum in surface water, and at some stations also a second subsurface maximum. In the Warm Deep Water (WDW), TCO2 and fluorescence had their maximum values, while total organic carbon tended to be low. In low productivity surface water in the eastern part of the Kapp Norvegia–Joinville Island section, the lowest flourescence was found. Surface water is eventually formed from Warm Deep Water, which had the highest fluorescence values, and therefore it is concluded that humic substances were removed in situ from surface water. In the central area of the Weddell Sea, TCO2 and fluorescence showed the highest Warm Deep Water maxima, while total organic carbon was low. The Warm Deep Water in this area is part of the so-called Central Intermediate Water which circulates for a long time within the Weddell Gyre. Reduced total organic carbon, which coincides with the most pronounced Central Intermediate Water characteristics, and high TCO2 can thus both be accounted for by continued degradation of organic matter in this water mass. The associated fluorescence maximum implies that humic substances are also produced during mineralisation. Recently formed bottom water, by contrast, could be seen as patches of low TCO2, low fluorescence and high total organic carbon along the western slope of the Weddell Sea. 相似文献
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以船用铅酸蓄电池工作原理为基础,讨论蓄电池运行机理及性能,提出包括放电深度和放电电流密度、电解液浓度和温度、充电程度等日常使用注意事项,以及维护的具体方法。 相似文献