地下结构抗震减震措施与研究方法探讨

由于地下结构一直被认为有较好的抗震性能,所以对其抗震减震的理论研究较少,实际工程中采取的抗震减震措施仅仅停留在经验阶段。通过对地下结构抗震减震措施及其分析方法进行研究,对目前地下结构的震害特点、抗震减震措施和理论分析方法进行了归纳总结。分析表明,地下结构的破坏过程主要受地震位移场的控制,与加速度场的关系不明显,所以应尽快修订《铁路抗震设计规范》中有关隧道抗震部分的条文;高烈度地震区的隧道抗震减震措施的耦合技术、减震机理与随机响应分析及动力可靠度的关系、洞口结构抗减震技术以及不同地震烈度下的设防长度、基础处理技术和减震层参数之间的联系等方面需加强研究。这些成果将为高烈度地震区进行的隧道设计和施工提供理论依据。     

汶川地震公路隧道洞口段震害机理及抗震对策研究

汶川地震中震区公路隧道洞口段破坏严重,严重影响了震区生命线工程的畅通.为提高震区公路隧道洞口段的抗震能力,结合公路隧道洞口段震害情况对其震害机理进行了研究.研究结果表明,洞门、边仰坡及明洞震害主要是地震惯性力作用造成的:软岩隧道洞口段衬砌震害主要是地震惯性力和强制位移造成的.文章根据隧道洞口段的震害机理,提出了相应的抗震对策.研究结果对于进一步研究高烈度地震区公路隧道震害机理及抗震对策都有着重要的意义.     

基于一维土层地震反应分析轨道交通区间隧道横向反应位移法的抗震设计

反应位移法作为一种较合适的地下结构拟静力抗震分析方法,其等效动荷载的确定对地下结构抗震结果的影响较大。借助一维土层地震反应分析,获得土体在地震动荷载作用下的动力反应,从而取得地下结构顶底标高处产生最大相对变形时刻的荷载参数,并以此作为确定反应位移法等效动荷载的依据。结合上海轨道交通圆形区间隧道工程实例,阐述了具体抗震分析过程,可为地下交通隧道结构的抗震设计提供借鉴。     

走滑断层错动量大小对铁路隧道结构安全性影响的数值分析北大核心CSCD

走滑断层错动容易使穿越活动断裂带的隧道结构遭受严重的破坏。以某铁路隧道穿越某断裂带为工程背景,采用有限差分数值模拟手段,通过分析不同走滑断层错动量下隧道结构的位移、应力和应变,对隧道结构的安全性进行评判。研究表明:走滑断层错动时,除纵向位移外,随着错动量的增加,隧道结构位移越大,且走滑断层错动对在断层区和上盘区域的隧道结构影响最大;在走滑断层错动量>0.6 m后,隧道结构应力受错动量的影响较小,且隧道结构开始破坏,随着错动量增加,破坏范围增大。     

汶川地震公路隧道震害规律研究

结合汶川地震灾区公路隧道震害资料,文章制定了公路隧道震害量化指标并进行分级,对汶川地震公路隧道震害规律进行了研究。研究结果表明:隧道衬砌开裂长度占隧道总长度比例最高,二次衬砌垮塌及仰拱错台长度次之;多数震害类型在V级围岩中发生的比例均高于其它级别围岩;X、XI度地震烈度区,断层段破坏程度最严重,其次是洞口段;震害严重程度随震中距增加而迅速衰减,发生严重以上震害的隧道集中于10 km以内,近三分之二发生于20 km范围;坚硬岩体中的隧道,震害程度随埋深增加而减轻,软弱围岩中的隧道,震害程度与埋深关系不明确;发生严重以上震害的隧道,实际地震烈度均高于设防烈度,出现中等震害的隧道,近三分之二的隧道实际地震烈度高于设防烈度;隧道轴线与发震断层交角为60°~90°,震害严重,轴线与发震断层交角为30°~60°,震害相对较轻;防水板致使初期支护和二次衬砌在地震时不能协同工作,增加震害风险。     

龙溪隧道出口段在地震荷载下变形破裂特征及其数值模拟分析

龙溪隧道出口段主要有表层覆盖层和下伏基岩组成.文章根据边坡地形地貌以及地质结构分析了隧道在地震作用下的变形破裂特征.在此基础上,运用ansys有限元软件对龙溪隧道在Ⅺ度地震烈度荷载作用下的动力响应进行分析,并结合5·12地震后的现场调查,将数值模拟结果与现场的破坏现象进行了对比,得出地震作用下隧道洞口横向边坡的动力反应从坡内向坡外、坡底向坡顶整体上呈逐步放大的趋势;从洞口至基岩与崩坡积分界面处,变形主要在隧道管段之间的接缝处发牛相对错动,并且有逐渐减弱的趋势;在隧道基岩与覆盖层分界面上,隧道衬砌变形量发生突变,衬砌开裂方向与基覆界面产状基本一致,从分界面向内,衬砌变形变得不明显.研究这一变形破坏现象,对认识隧道洞口段在地震作用下的变形破坏规律及极震区隧道洞口段的抗震结构设计具有重要意义.     

瑞利波作用下隧道洞口段的抗震设防长度

隧道洞口段是隧道抗震设计的薄弱部位,文章从瑞利波动方程出发,推导了洞口段地层在瑞利波作用下的峰值位移、峰值加速度和地层曲率的计算公式,并探讨了洞口段抗震设防长度。分析结果表明:在瑞利波作用下,地层位移、曲率和加速度随隧道埋深的增大而迅速减小,因此当洞口埋深达到一定程度后,地层对隧道的强加位移已很小,无需再设防;现行隧道设计规范规定的洞口段抗震设防长度偏短,应延长。最后,结合汶川地震隧道洞口段破坏长度,进行了分析验证,分析结论可供隧道抗震设计、灾后重建和今后有关规范修订参考。     

地下结构抗震设计方法的比较与分析

在日本阪神大地震中,地下结构遭到了严重破坏,因此地下结构的地震反应及抗震设计和安全性评价越来越被重视。首先采用矩形地下结构的两种抗震设计方法——拟静力法和反应位移法对北京地铁北宫门车站进行了抗震计算,并使用计算软件FLAC4.0对北宫门车站进行了时程分析,发现拟静力法对地震荷载过于简化,致使其过低估计了地震对地下结构的影响;而反应位移法较合理地反应了地震荷载对地下结构的影响;地震中的惯性力对地下结构的内力影响不大,地震剪应力对结构的内力影响最大;并且,通过软件FLAC时程分析,得到的位移等反应规律与反应位移法的假设相同,计算得到的弯矩值与采用反应位移法计算得到的弯矩值相近。因此,推荐首先采用反应位移法进行地下结构的抗震设计。     

浅埋黄土隧道破坏模式的探讨

根据郑西客运专线黄土隧道地表裂缝的现场调查,推断黄土隧道隐形破裂面;结合UDEC程序,根据黄土垂直节理及推断的隧道隐形破裂面,计算模拟埋深20m情况下不同开挖跨度的隧道毛洞开挖,以分析、研究节理黄土的破坏过程及破坏模式.结果表明.黄土隧道的稳定跨度为8m,隧道剪切开裂面与水平方向成β角,并非直接与节理面重合;浅埋大跨条件下的黄土隧道破坏由β面先破坏渐进发展为土体的垂直剪切破坏.     

隧道掌子面地震动力响应特性及加固方法

文章以雅沪高速公路石棉隧道为工程背景,研究分析了地震动力作用对隧道掌子面稳定性能的影响及加固措施。首先,阐述了隧道震害的主要形式及隧道掌子面的力学平衡机理,并采用FLAC3D有限差分软件,针对不同地层中的隧道掌子面进行了地震动力响应分析;其次,通过对比静力和动力下掌子面的稳定状况,分析地震对不同地层中隧道掌子面稳定性的影响,总结出了掌子面挤出变形和约束压力随地震时程的变换规律,并通过掌子面平均塑性剪切应变、掌子面挤出变形、掌子面约束压力等参数评估了加固效果。分析结果表明,与隧道衬砌相比,隧道掌子面更容易受到地震的破坏;地震动力作用对不同地层条件中隧道掌子面的影响程度是截然不同的,岩质地层中隧道掌子面受到的影响较小,而土质地层中隧道掌子面所受影响则很大;锚杆的加固作用能显著提高隧道掌子面的抗震性能。     

Survey of R&D in PRT systems

A survey of research and development in advanced transit has been made by Chalmers University of Technology in Gothenburg in cooperation with Trans21 in Boston. Summary findings are reported for fourteen academic research programs and ten development programs for PRT. An earlier version of this paper was presented at the International Conference of PRT and other Emerging Systems held in Minneapolis in 1996.     

Determinants of modal choice in freight transport

In the next few years, exciting developments in the field of freight transport are likely to occur. The Channel Tunnel will be perceived as giving railways much greater distance of operation, compared to the current train ferry to/from Great Britain. The further development of swap-body technology will allow easier modal transfer and the creation, in 1992, of a single market in Europe will transform the pattern of trade. All of these are likely to have significant impacts on modal choice, and hence modal split, in freight transport. Reappraisal by many firms of the modes of transport used is likely but will it result in a net transfer of freight from road to rail and, if so, to what extent? To answer such questions, an accurate and reliable method of predicting modal split is required. Research in the past has concentrated on the development of modal split models based on generalised costs. These fail to explain adequately the prevalence of road freight in the UK. From surveys of freight managers within industry, it is clear that models to date rely too heavily on the economic cost factor and too little on behavioural factors (Jeffs 1985). This paper derives from a recent study of freight transport modal choice from the standpoint of the transport decision-maker within the firm. It attempts to shed light on the actual parameters which should be incorporated into a modal split model. Many variables appear to exert an influence on modal choice decision-making process. However, it is possible to categorise them into six main groups, namely: customer-requirements; product-characteristics; company structure/organisation; government interventions; available transport facilities; and perceptions of the decision-maker him/herself. It is the interactions and inter-relationships between these which ultimately determine freight modal split. This study has shown that the relationship between the outcome of the transport decision process and the values of particular determinants of modal split is not straight-forward, due to the complexity and variety of interactions involved. Perhaps one of the main reasons for researchers' failure hitherto to develop a successful modal-split model has been the preoccupation with techniques that rely on the development of common metric (e.g. generalised cost), which has led to the exclusion of some important explanatory variables along quite different dimensions. Another important issue concerns the appropriate level of aggregation. In order not to reduce the explanatory power of the key variables, it is important to work at a disaggregate level, although this does make substantial demands on data. The use of factor analysis enables both the aggregation of information without loss of behavioural reality and the specification of variables in terms of a common metric. In conclusion, freight transport has usually been examined within too narrow a framework. It must be placed firmly within the context of the total industrial process. The demand for freight transport is directly influenced by the level, composition and geographical distribution of production and consumption activities. Freight flows are complex and so it is highly unlikely that a universal mode-choice model can ever be developed. Future research should, therefore, be directed towards developing partial models in response to specific needs of those involved in decision-taking in the freight sector.     

管道风险分析指数评分法中分值调整初探

管道风险分析指数评分法中重要步骤之一就是确定影响管道事故因素的权重,各个管道风险因素在整个管道事故中所占的权重是不相同的。针对目前管道风险分析指数评分法基本假设之一（各因素的分值范围都是0～100分）,为了更加客观、准确、合理地反映各个风险因素对于管道事故的影响程度,提出并论述了依据层次分析法的数学逻辑性进行综合计算得出管道风险因素的权重,然后对评分法中各个因素的最高分值,根据其权重不同进行相应调整,从而增强评价者对风险因素的认识和评判能力,提高管道风险评价结果的准确性。     

天然气站往复式压缩机活塞失效分析

针对天然气站往复式压缩机活塞的断裂事故,运用失效分析方法,开展了活塞断口扫描电镜分析、能谱和金相分析。根据断口形貌的电镜和金相观察结果,结合理论知识,分析确定了该活塞发生断裂事故的主要原因,即在特定工况下该活塞的材料缺陷是造成断裂的主要因素。     

中国城市道路规划方位性问题研究

文章结合中国的传统建筑文化理念和现代科学原理,从历史文化、能源节约、环境保护、房地产定价、交通安全等多方面分析研究了城市道路在规划和设计时所应遵从的定向规则。     

A century of evolution of the accessibility concept

The concept of accessibility has acquired numerous meanings along multiple dimensions during the century of its evolution. This essay argues for the salience of two dimensions: application-based and definition-based. In its application, accessibility has incorporated positive and normative dimensions which have varied in prominence over time. In its definition, accessibility has varied between a mode of evaluation incorporating measured mobility and proximity, on the one hand, and a predefined market basket of urbanist improvements to transportation and land use systems, on the other. Advocates of the accessibility shift should emphasize both the measured approach to accessibility and accessibility’s normative side.     

Predicting queue variability to enable analysis of overload risk

ABSTRACT

Predicting the risk of traffic demands and delays exceeding critical limits at road junctions, airports, hospitals, etc., requires knowing how both mean and variance of queue size vary over time. Microscopic simulation can explore variability but is computationally demanding and gives only sample results. A computationally efficient approximation to the mean is used in many modelling tools, but only empirical extensions for variance in particular situations have been available. The paper derives theoretical formulae for time-dependent and equilibrium variance, believed to be novel and to apply generally to queues covered by the Pollaczek–Khinchin mean formula, and offering possible structural insights. These are applied in an extended approximation giving mutually consistent mean and variance estimates with improved accuracy. Tests on oversaturated peak demand cases are compared with Markov probabilistic simulation, demonstrating accuracy (R^2?>?0.99) for typical random, priority-like (M/M/1) and traffic-signal-like (M/D/1) queues. Implications for risk analysis, planning and policy are considered.     

Planning guidelines for metro–bus interchanges by means of a pedestrian microsimulation model

The big paradigm for cities nowadays is to study the movement of pedestrians at the interface between metro and bus systems – metro–bus interchanges. When these interchanges are not well designed, walking is inefficient and can be unsafe for pedestrians. This paper analyses, by means of a pedestrian microsimulation model, metro–bus interchange spaces in order to propose planning guidelines for the city of Santiago de Chile. Specific objectives are (1) to identify the variables that provide efficiency and safety in those spaces; (2) to simulate different scenarios using the pedestrian simulation model LEGION; (3) to propose planning and design guidelines for pedestrian spaces at metro–bus interchanges; and (4) to contrast the recommendations in the recently opened terminal station on Line 1 of Metro de Santiago: Los Dominicos Station.     

生命大过天

文章介绍了广西壮族自治区公路管理局开展专项行动,治理以桥梁为重点的交通基础设施安全隐患的情况,针对在役桥梁、在建桥梁和农村公路桥梁存在的安全隐患提出了相应的治理措施。