温度波动对螺栓法兰连接系统垫片应力的影响

温度波动会造成螺栓法兰连接系统中垫片应力松弛,从而影响其密封性能。文章以DN80法兰接头为研究对象,通过ABAQUS软件建立了三维有限元模型,分析了温度波动对垫片应力的变化,研究了垫片与螺栓载荷变化的机理。结果表明,螺栓法兰连接系统在温度变化时存在着一定的温度滞后现象;当温度波动时,垫片应力随温度的降低而减小,随温度的升高而增大,波动结束后垫片表现出“内紧外松”的应力分布现象。在这一过程中,垫片的热膨胀与温度场的滞后性是垫片应力变化的主要因素。研究结果为螺栓法兰连接系统的进一步优化和改进提供了有力支持。     

弯头与直管连接截面及边缘区应力分析

以弯头与直管连接结构边缘区及连接截面为主要研究对象,应用有限元方法建立弯头与直管连接结构数值计算模型,通过与ASME中的弯管应力计算公式进行比较,验证模拟结果的准确性。在此基础上分析结构在内压、弯矩以及2种载荷共同作用下的边缘区和连接截面应力分布特点和规律,提出了连接截面应力计算方法,并证明公式计算结果的可靠性,可用于弯头与直管连接结构安全评定时,计算含面型缺陷的连接面的应力。     

法兰接头预紧过程中垫片应力场数值模拟分析

螺栓法兰接头安装过程中的螺栓弹性交互作用会造成各螺栓预紧载荷不均匀,从而影响其密封性能。文中考虑垫片压缩回弹曲线的非线性和迟滞性,建立了DN80的法兰接头三维有限元模型。以ASME PCC-1标准中螺栓传统星形预紧方式为例,分析了预紧过程中螺栓载荷及垫片应力的变化。结果表明:即使按照标准中规定的螺栓加载方式,预紧后螺栓载荷仍有较大的分散性;螺栓载荷的分散性会造成垫片接触应力沿周向分布不均匀;垫片应力最小值出现在6#和7#螺栓之间,其大小仅为目标应力的74.3%,表明法兰接头最容易在此处发生泄漏。     

低温环境下管道法兰连接的应力分析

文中在考虑温度作用的前提下,对低温管道中的法兰进行了不同螺栓强度等级和螺栓预紧力下的"拉伸+弯曲"组合工况的有限元分析。研究表明:法兰最大应力出现在螺栓上,螺栓的预紧力和强度等级的降低都将对法兰应力分布产生重要的影响。同时,文中也给出了法兰外侧的位移随螺栓预紧力和强度等级的变化规律。最后,通过现场测试验证了数值模拟的准确性。该研究结果可以为输油管线法兰连接的预紧力设定提供参考。     

可控移热变换炉设备法兰结构的设计与应力分析

文中设计的可控移热变换炉中的设备法兰连接结构上连球形封头,下连筒体,是无垫片焊接密封法兰结构,并采用Ω密封环和O形密封圈组合密封,以保障其密封的可靠性。在对其进行初步应力分析后,运用有限元软件ANSYS建立了相关的力学计算模型,在边界载荷及位移的约束和内部载荷的施加后,计算了设计工况下上封头和上法兰、筒体和下法兰的第三强度当量应力和转角。按照JB 4732—1995(2005年确认)及文献,对法兰及其连接的各部位进行了应力强度评定和刚度评定,并认为主要是强度评定起决定作用。     

连续重整再生单元高温对夹止回阀失效分析

针对连续重整再生单元还原区高温工况下对夹式止回阀泄漏的问题,对该法兰连接系统的主要部件(垫片、螺栓、阀门)连接形式进行了分析。其中,从垫片填充材料——柔性石墨因高温氧化而造成的热失重、高温回弹性下降等分析了高温工况下柔性石墨缠绕垫失效原因;从高温蠕变松弛、脆断及预紧力等方面分析了螺栓失效的原因;从对夹式止回阀的连接特点分析了该连接形式用在高温工况下存在的弊端。最后提出了阀门失效的解决措施。     

发夹式换热器异形法兰及封头的设计

发夹式换热器后端壳程连接处常采用异形法兰和封头的结构,标准中并未列出相关结构设计和计算方法,给设计带来很多困难。文中结合一台壳程压力7.3 MPa并伴有温度疲劳载荷作用的发夹式换热器,首先对其异形法兰和封头进行结构优化设计,再利用规则设计方法确定结构的初步尺寸,最终按GB/T 151—2014确定计算工况后进行有限元应力校核。结果表明,规则设计方法计算出的结构应力偏低;尤其对异形封头,因异形法兰对其影响,其结构尺寸必须通过有限元分析进行校核。     

放空阀法兰焊缝断裂失效原因分析

针对某压气站压缩机下游放空阀法兰焊缝断裂的情况,采用外观检测、无损检测、化学分析、金相分析和有限元计算等方法,对该失效法兰进行了失效原因分析。结果表明:该焊缝断裂属于多源断裂,焊缝上部放空装置较重,在较大风力的作用下,在立管焊缝附近产生很大弯曲载荷,内焊趾处产生应力集中,最终导致裂纹扩展并发生断裂。结合现场施工和设计情况,提出了防止发生类似事故的建议。     

车辆载荷碾压作用下管道的安全性测试与分析

通过对重车碾压的土层压力进行试验,总结计算出了车辆载荷引起土层应力的分布规律,综合土层应力的分布规律、土层参数和钢材参数,建立了重车碾压对管道应力影响的有限元分析模型,提出了应力在土壤中沿深度方向变化的计算公式,通过静载和动载分析,计算出了管道安全的最低埋设深度,对埋深大于1．5m且管道上覆土层均匀密实的管道,由车辆载荷而导致的管道附加应力与管道强度及管道内气压相比,不会危及管道安全,也不会造成管道的疲劳破坏。     

承受管道载荷的切向接管有限元分析

由于承受管道载荷的压力容器切向接管结构无法按照常规的设计方法进行开孔补强计算,文中以1台带切向接管的压力容器为例,对筒体与切向接管连接区域进行三维有限元分析,得到了筒体与接管连接区域详细的应力分布。应力分布云图表明：在连接区域产生明显的应力集中,应力强度最大值发生在筒体与接管连接处的外侧,是该结构失效的危险区域。根据JB4732-1995《钢制压力容器—分析设计标准》（2005年确认版）的规定,对该连接区域进行了强度评定,评定结果表明该设备的结构尺寸完全满足强度要求,为进行详细工程设计提供了理论依据。     

滨州黄河大桥钢结构的连接方式

结合滨州黄河大桥维修方案,分别阐述了焊缝连接和高强螺栓连接的施工工艺,并提出了具体的施工质量控制措施,以探讨钢结构桥梁的连接方式。     

龙岩市南环路边坡滑坡综合治理技术

不良地质、路基开挖和水害是边坡滑坡的主要因素,减载、固脚、强腰、排水等综合措施是滑坡治理的有效方法。文章阐述了边坡滑坡的综合治理措施,介绍了预应力锚杆框架锚孔钻造、锚筋制安、锚孔注浆、锚筋张拉锁定和验收封锚的施工方法和注意事项。     

Anti-seismic reinforcement strategy for an urban road network

This paper provides a novel practical method for analyzing an anti-seismic reinforcement (ASR) problem involving hundreds of transportation facilities on an urban road network subject to multiple earthquake risks. The relevant properties of the present method are: (i) it evaluates the performance of an ASR strategy, taking into account traffic congestion and travelers’ trip-making or route-choice behavior; (ii) it estimates the realistic damage patterns on the road network and their occurrence probabilities on the basis of recent advances in structural and earthquake engineering; (iii) it has clear, sensible logic and includes neither a black-box nor a “lottery” in the necessary procedures. We examine the computational efficiency and whether the present method is reasonable by applying it to a test scenario of the Kobe urban and suburban area.     

Quantitative evaluation of passenger terminal orientation

When passenger terminal layout is being decided, one of the important aspects to consider is how the passenger orients himself during his visit to the terminal and his movements through it, i.e. terminal orientation. Among other things, this terminal characteristic results from visibility, or the visual connectivity between elements and spaces. The paper proposes an amendment and modification to the known method for the quantitative evaluation of terminal orientation which uses an oriented network to describe the connectivity of elements (terminal orientation). The amendment and modification of the method consists of proposing that during evaluation only visual connections that have functional meaning should be considered, rather than all visual connections. A further modification is the introduction of different weights for different connections. The example presented in the paper considers an airport terminal building.     

Precise estimation of connections of metro passengers from Smart Card data

The aim of this study is to estimate both the physical and schedule-based connections of metro passengers from their entry and exit times at the gates and the stations, a data set available from Smart Card transactions in a majority of train networks. By examining the Smart Card data, we will observe a set of transit behaviors of metro passengers, which is manifested by the time intervals that identifies the boarding, transferring, or alighting train at a station. The authenticity of the time intervals is ensured by separating a set of passengers whose trip has a unique connection that is predominantly better by all respects than any alternative connection. Since the connections of such passengers, known as reference passengers, can be readily determined and hence their gate times and stations can be used to derive reliable time intervals. To detect an unknown path of a passenger, the proposed method checks, for each alternative connection, if it admits a sequence of boarding, middle train(s), and alighting trains, whose time intervals are all consistent with the gate times and stations of the passenger, a necessary condition of a true connection. Tested on weekly 32 million trips, the proposed method detected unique connections satisfying the necessary condition, which are, therefore, most likely true physical and schedule-based connections in 92.6 and 83.4 %, respectively, of the cases.     

Testing the decentralization effects of rail systems: Empirical findings from Israel

Many sustainable urban development approaches are based on mass public transportation ventures, especially railway development, which has been considered a panacea for the unfavorable effects of suburban development. But rail transit also improves accessibility to the fringes, thus encouraging an exodus to the suburbs. This paper explores suburbanization and sprawling effect of commuter rail transit on the rural exurbia of the Tel Aviv metropolis by analyzing its effect on residential location decisions. The findings indicate that the suburban rail system was a determinant factor in the location choice of households which migrated from the inner parts of the Tel Aviv metropolis, since it allowed them to maintain strong commuting connections to their residential origin. This suggests that rail transit, along with its potential to strengthen the inner cities, also accelerates suburbanization and counter urbanization.     

实行计重收费,促进广西高速公路和谐发展

文章通过目前广西高速公路现行收费模式,提出了实行计重收费,改变车辆由人工判别车型的收费方式,克服空车、重车及超载超限车仍按同一标准收费的弊端,同时对实行计重收费模式应注意的问题提出了相关建议。     

A case study on the coordination of last trains for the Beijing subway network

Passengers may make several transfers between different lines to reach their destinations in urban railway transit networks. Coordination of last trains in feeding lines and connecting lines at transfer stations is especially important because it is the last chance for many travellers to transfer. In this paper, a mathematical method is used to reveal the relationships between passenger transfer connection time (PTCT) and passenger transfer waiting time (PTWT). A last-train network transfer model (LNTM) is established to maximize passenger transfer connection headways (PTCH), which reflect last-train connections and transfer waiting time. Additionally, a genetic algorithm (GA) is developed based upon this LNTM model and used to test a numerical example to verify its effectiveness. Finally, the Beijing subway network is taken as a case study. The results of the numerical example show that the model improves five connections and reduces to zero the number of cases when a feeder train arrives within one headway’s time after the connecting train departed.     

沥青混合料抗剪切验算方法

文章借鉴城市道路的抗剪验算方法和步骤,提出了适用于沥青混合料的抗剪验算方法,并采用沥青路面应力计算BISAR程序与三轴试验进行实例分析,验算了该方法的可行性。     

指数平滑法在路面使用性能预测中的应用

文章分析了路面使用性能的发展规律及其特点,指出了传统预测方法的不足,介绍采用指数平滑法来提高预测精度,可解决我国路面使用性能预测模型,预测精度不高的问题。