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851.
A series of scalar and vector intensity measures is examined to determine their suitability within the seismic risk assessment of liquid storage tanks. Using a surrogate modelling approach on a squat tank that is examined under both anchored and unanchored support conditions, incremental dynamic analysis is adopted to generate the distributions of response parameters conditioned on each of the candidate intensity measures. Efficiency and sufficiency metrics are used in order to perform the intensity measure evaluation for individual failure modes, while a comparison in terms of mean annual frequency of exceedance is performed with respect to a damage state that is mutually governed by the impulsive and convective modes of the tank. The results reveal combinations of spectral acceleration ordinates as adequate predictors, among which the average spectral acceleration is singled out as the optimal solution. The sole exception is found for the sloshing‐controlled modes of failure, where mainly the convective period spectral acceleration is deemed adequate to represent the associated response due to their underlying linear relationship. A computationally efficient method in terms of site hazard analysis is finally proposed to serve in place of the vector‐valued intensity measures, providing a good match for the unanchored tank considered and a more conservative one for the corresponding anchored system. 相似文献
852.
Two new algorithms are presented for efficiently selecting suites of ground motions that match a target multivariate distribution or conditional intensity measure target. The first algorithm is a Markov chain Monte Carlo (MCMC) approach in which records are sequentially added to a selected set such that the joint probability density function (PDF) of the target distribution is progressively approximated by the discrete distribution of the selected records. The second algorithm derives from the concept of the acceptance ratio within MCMC but does not involve any sampling. The first method takes advantage of MCMC's ability to efficiently explore a sampling distribution through the implementation of a traditional MCMC algorithm. This method is shown to enable very good matches to multivariate targets to be obtained when the numbers of records to be selected is relatively large. A weaker performance for fewer records can be circumvented by the second method that uses greedy optimisation to impose additional constraints upon properties of the target distribution. A preselection approach based upon values of the multivariate PDF is proposed that enables near‐optimal record sets to be identified with a very close match to the target. Both methods are applied for a number response analyses associated with different sizes of record sets and rupture scenarios. Comparisons are made throughout with the Generalised Conditional Intensity Measure (GCIM) approach. The first method provides similar results to GCIM but with slightly worse performance for small record sets, while the second method outperforms method 1 and GCIM for all considered cases. 相似文献
853.
管井降水是一种设备简单、排水效率高的降水方法,在地下工程的施工中有广泛的应用。本文结合拉萨京藏交流中心邻河基坑降水项目的施工实践,参考实际施工效果和实际施工条件,研究邻河基坑管井降水的方案优化,分析降水过程中的重点和难点,增强降水方案的科学性,提高降水效率。 相似文献
854.
855.
滇池盆地地质条件复杂,多处分布可溶岩,岩溶问题突出,对昆明轨道交通工程影响很大。轨道交通工程岩溶的勘察需经过多阶段采用综合勘察技术才能查清其特征、性质及危害。经勘察及分析,昆明轨道交通4号线大河埂站-大塘子站段、呈贡东站（含）-昆明火车南站段岩溶弱发育,联大街站-呈贡东站区间、白龙潭停车场及出入段线岩溶中等发育,金鼎山站-小菜园站段岩溶强烈发育。4号线为覆盖型岩溶,岩溶主要发育于基岩面下15m范围,并以0.5~3.0m洞高的充填型溶洞为主,钻孔平均遇洞率21%,平均线岩溶率3.29%。综合将岩溶区划分为稳定区、次不稳定区和不稳定区。岩溶治理应针对不同的工程类型和岩溶特征采取相应的处理原则和工程措施。岩溶治理一般采用注浆加固措施,对于埋深较小的岩溶可采取开挖揭露回填注浆进行加固处理,桩基需穿过岩溶置于下部稳定地层中。文章对昆明地区轨道交通岩溶勘察及治理具有一定指导作用。 相似文献
856.
To predict the cycle and propulsive performance, and further instruct the integral engine design, an ideal power cycle model for a two-phase underwater ramjet is established. Four performance parameters are defined to evaluate overall performance of the two-phase underwater ramjet systems: transmission efficiency, propulsive efficiency, overall efficiency and specific impulse. Then, a scaled-down experimental ramjet engine was tested in a direct-connect ground testing system to validate the present model, and the predictions with present model compare favorably with experimental results. Subsequently, the influences of cruise velocity, air/water mass ratio and cruising depth on the theoretical performance of the two-phase underwater ramjet are discussed. The results indicate that one of the most outstanding advantages of two-phase underwater ramjet is its high propulsive efficiency with the order of 50–95%. As a result, the overall efficiency magnitude are as high as 30% at cruise speed of 100 m/s. Furthermore, regarding rules of specific impulse vs cruise velocity under a certain air/water mass ratio, the occurrence of peak specific impulse of order 400 s is observed. 相似文献
857.
Anne J. Jefferson Aditi S. Bhaskar Kristina G. Hopkins Rosemary Fanelli Pedro M. Avellaneda Sara K. McMillan 《水文研究》2017,31(23):4056-4080
Deleterious effects of urban stormwater are widely recognized. In several countries, regulations have been put into place to improve the conditions of receiving water bodies, but planning and engineering of stormwater control is typically carried out at smaller scales. Quantifying cumulative effectiveness of many stormwater control measures on a watershed scale is critical to understanding how small‐scale practices translate to urban river health. We review 100 empirical and modelling studies of stormwater management effectiveness at the watershed scale in diverse physiographic settings. Effects of networks with stormwater control measures (SCMs) that promote infiltration and harvest have been more intensively studied than have detention‐based SCM networks. Studies of peak flows and flow volumes are common, whereas baseflow, groundwater recharge, and evapotranspiration have received comparatively little attention. Export of nutrients and suspended sediments have been the primary water quality focus in the United States, whereas metals, particularly those associated with sediments, have received greater attention in Europe and Australia. Often, quantifying cumulative effects of stormwater management is complicated by needing to separate its signal from the signal of urbanization itself, innate watershed characteristics that lead to a range of hydrologic and water quality responses, and the varying functions of multiple types of SCMs. Biases in geographic distribution of study areas, and size and impervious surface cover of watersheds studied also limit our understanding of responses. We propose hysteretic trajectories for how watershed function responds to increasing imperviousness and stormwater management. Even where impervious area is treated with SCMs, watershed function may not be restored to its predevelopment condition because of the lack of treatment of all stormwater generated from impervious surfaces; non‐additive effects of individual SCMs; and persistence of urban effects beyond impervious surfaces. In most cases, pollutant load decreases largely result from run‐off reductions rather than lowered solute or particulate concentrations. Understanding interactions between natural and built landscapes, including stormwater management strategies, is critical for successfully managing detrimental impacts of stormwater at the watershed scale. 相似文献
858.
本文从6个方面详细分析探讨了地震重点监视防御区信息公开的必要性和意义,并以行业专项课题“地震重点监视防御区工作指南和发布方案”执行过程中专门设计的“重防区管理办法和工作指南调查问卷”为基础,针对被访者对重防区信息公开的态度、信息公开途径、发布形式、发布内容、防震减灾工作应当加强的环节以及采取的强化措施进行了系统调查。通过对数据进行分析研究得出以下结论和建议:地震重防区信息应当采取逐级公开、逐步公开的方式进行,建议由国务院颁布地震重点监视防御区管理办法和工作指南,同时以政府文件下发重防区县级行政单元名单,不加密级。本文最后提出了为减轻信息公开后引起的负面影响所应实行的一些配套措施。 相似文献
859.
宁夏南部地区湿陷性黄土厚度较大,湿陷性系数较大,压缩性高,相应地地基处理难度大,费用高,尤以该地区的低层建筑物地基处理安全性和经济性两者矛盾最为突出,已成为制约该地区开发建设的一大阻碍因素。针对此问题,采用经验总结和专家论证的研究方法,提出采用垫层法部分消除湿陷性,同时采取严格防水措施和结构措施的综合处理方案,以科学、安全、经济和适用为宗旨,经该地区采用此地基处理方案的工程实践证明,此方案能够很好地解决该地区低层建筑物地基处理中安全和经济两者的巨大矛盾,使两者达到协调统一。 相似文献
860.