设置限位器双向隔震铁路桥梁车桥耦合动力响应研究

对铅芯橡胶双向隔震铁路桥梁在列车荷载作用下的力学性能进行了研究,针对双向隔震铁路桥梁中存在的问题,提出了设置限位器的解决方案,并对设置限位器的双向隔震铁路桥梁进行了车桥耦合动力响应分析.研究结果表明,采用常规隔震设计方法的铅芯橡胶支座在横桥向的初始刚度和屈服强度均不能满足规范要求,设置限位器后,双向隔震铁路桥梁的力学性...     

不同墩高下连续刚构桥抗震性能分析

以某大跨连续高墩刚构桥为依托,采用Midas/civil软件建立仿真模型,通过时程分析方法研究双肢薄壁墩参数在地震响应下对高墩连续刚构桥抗震性能的影响.以桥墩高度为主要参数,以模型阵型频率、桥墩墩顶、墩底位移及内力变化三个方面对其抗震性能进行评价.研究结果表明,随着其中一个桥墩高度的增加,桥梁频率不断减小,矮墩墩底及矮...     

河床演变影响下桥区水域通航安全研究

为了科学地设定滩槽易变河段处的桥梁跨径布置方案,针对荆州长江大桥桥区水域河床演变影响通航安全的问题,采用实例调研及历史资料分析的方法,指出滩槽易变河段选址建设的桥梁,其最大风险是滩槽移位导致船舶从通航孔位置移动到非通航孔位置,提出新建桥梁通航孔布置应覆盖深泓和可能成为航道的深槽的摆动范围;根据提出的原则研究拟建的李埠桥...     

桥式起重机典型事故分析及安全管理

分析了桥式起重机典型事故发生机理,运用事故树分析法对桥式起重机事故发生进行了分析,从而为能够找出安全隐患,制定出最优的控制措施提供了理论上的依据.最后根据分析结果,系统地提出了控制危害,降低事故发生率的安全管理措施,提出一些具有可行性的建议.     

Effects of compression ratio,swirl augmentation techniques and ethanol addition on the combustion of CNG–biodiesel in a dual-fuel engine

The diminishing resources and continuously increasing cost of petroleum in association with their alarming pollution levels from diesel engines has led to an interest in finding alternative fuels to diesel. Emission control and engine efficiency are two of the most important parameters in current engine design. The impending introduction of emission standards such as Euro IV and Euro V has forced research towards developing new technologies for combating engine emissions. This paper examines the effects of compression ratio, swirl augmentation techniques and ethanol addition on the combustion of compressed natural gas (CNG) blended with Honge oil methyl esters (HOME) in a dual fuel engine. The present results show that the combustion of HOME and 15% ethanol blend with CNG induction in a dual-fuel engine operated in optimized parameters at an injection timing of 27° Before Top Dead Centre and a compression ratio of 17.5 resulted in acceptable combustion emissions and improved brake thermal efficiencies. The implementation of swirl augmentation techniques increased brake thermal efficiencies (BTEs) and considerably reduced combustion emissions such as smoke, HC, CO and NO_x. The addition of ethanol also increased BTEs. However, at more than 15% of ethanol in HOME, NO_x emissions increased dramatically.     

Method for Rapidly Assessing the Overtopping Risk of Bridges Due to Flooding over a Large Geographic Region

Hydraulic events are a leading cause of bridge failures. While these hydraulic events are accounted for in bridge design, changing environmental and land use conditions require continual updating of this risk. For example, after a bridge has been constructed, streamflow can change in unanticipated ways as a result of land use changes, geomorphic changes, and climate change. The objective of this research was to create a screening method able to quickly and inexpensively estimate overtopping risk across a collection of bridges based on the current streamflow conditions. The method uses a geographic information system, nationally available and standardized datasets, and recent regression equations to quantify bridge vulnerability to overtopping for flooding with varying return periods. This screening method could also be used to assist decision makers in updating the Waterway Adequacy field in the National Bridge Inventory, which indicates the overtopping risk of bridges. The method was applied to a portion of the Hampton Roads region of Virginia, United States that includes 475 bridges. The results of the analysis, when combined with transportation data for bridges, aid decision makers to assign further resources to complete more detailed analyses of bridges identified as being at risk for overtopping.     

基于现场测试的斜拉桥有限元模型修正

由于多年使用,桥的结构材料等都已经发生变化,因此在研究桥的当前工作状态时,必须依照现场测试结果,将初始模型修正为符合现阶段实际情况的有限元模型。本文以黄河胜利大桥为工程背景,根据设计资料建立了该桥初始有限元模型,用ANSYS通用软件开发了索力修正程序,该程序通过调整拉索的初始应变和附加质量块,使模型索力与设计索力之间误差在5%以内。计算发现,有限元模型中的施工顺序对成桥状态有着很大影响,应通过单元生死技术进行施工模拟。本文以各级加载工况下挠度、索力的变化情况作为控制目标,最终建立了能够反映加载工况下挠度变化、索力变化的黄河胜利大桥基准有限元模型,为今后监测桥的索力变化情况进而了解整座桥的工作状态奠定了基础。     

Adaptive Management of Stream Channel Maintenance at Bridge Crossings in the Northern Tier Region,Pennsylvania1

Abstract: An adaptive management framework is applied to the problem of identifying mitigation measures for sediment deposition near bridge crossings in small streams in the Northern Tier region of northern Pennsylvania. The presence of the rigid bridge infrastructure introduces a challenge for applying adaptive management practices, because the integrity of the bridge structure itself has to be maintained regardless of the mitigation practices used in the stream channel near the bridge. In an effort to overcome the unacceptable risk that field‐scale adaptive management experiments present to rigid bridge infrastructure, an adaptive management approach for laboratory‐scale experimentation of mitigation methods at bridge crossings in the Northern Tier region is presented as a way to decrease the level of uncertainty about channel response to mitigation measures and increase the rate of learning about the effectiveness of these measures. Four cycles of adaptive management experiments are discussed to demonstrate that this approach results in fast and efficient learning about channel response to mitigation methods for the given conditions. The value of monitoring and of assessment of monitored data in the overall efficiency of the adaptive management approach is highlighted. Assessment of what was learned in the adaptive management experiment cycles presented here leads to new directions to continually improve management policies and practices in stream channels at bridge crossings in the Northern Tier region. The adaptive management process, rather than continuing with a normally risk‐averse management approach, results in opportunities for learning new information about a system’s response.     

桥梁安全综合评价体系构建及重心法评价研究

目前桥梁安全综合评价研究并不成熟,在分析了桥梁安全综合评价应该考虑的主要因素的基础上,提出并确立了桥梁安全综合评价体系.探讨了应用模糊重心决策法进行桥梁安全综合评价的实现过程,为桥梁安全管理人员和安监部门理性决策提供理论依据.     

Toxicological characterization of the landfill leachate prior/after chemical and electrochemical treatment: A study on human and plant cells

In this research, toxicological safety of two newly developed methods for the treatment of landfill leachate from the Piškornica (Croatia) sanitary landfill was investigated. Chemical treatment procedure combined chemical precipitation with CaO followed by coagulation with ferric chloride and final adsorption by clinoptilolite. Electrochemical treatment approach included pretreatment with ozone followed by electrooxidation/electrocoagulation and final polishing by microwave irradiation. Cell viability of untreated/treated landfill leachate was examined using fluorescence microscopy. Cytotoxic effect of the original leachate was obtained for both exposure periods (4 and 24 h) while treated samples showed no cytotoxic effect even after prolonged exposure time. The potential DNA damage of the untreated/treated landfill leachate was evaluated by the comet assay and cytokinesis-block micronucleus (CBMN) assay using either human or plant cells. The original leachate exhibited significantly higher comet assay parameters compared to negative control after 24 h exposure. On the contrary, there was no significant difference between negative control and chemically/electrochemically treated leachate for any of the parameters tested. There was also no significant increase in either CBMN assay parameter compared to the negative control following the exposure of the lymphocytes to the chemically or electrochemically treated landfill leachate for both exposure periods while the original sample showed significantly higher number of micronuclei, nucleoplasmic bridges and nuclear buds for both exposure times. Results suggest that both methods are suitable for the treatment of such complex waste effluent due to high removal efficiency of all measured parameters and toxicological safety of the treated effluent.