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毕业设计 论文 外文翻译 题目简支空心板桥静 动力 荷载试验方案设计 专业理论与应用力学 学院土木建筑学院 学号09460114 学生江南 指导教师许羿 重 庆 交 通 大 学 2013 年 研究需要密切观察 J 型梁柱是怎样支撑着宾夕法尼亚的 By By KentKent A A Harries Harries Ph D Ph D FACI FACI P E P E 据报道说配筋接口的基础和干墙在拆除桥的旧桥墩 桥台和剩余的墙体是已经明 显的恶化和颈缩 任何减少在该地区这些接口处的钢材可能会导致基础能力减少 在钢筋面积 显著下降可能导致基础不稳定和阻碍恢复或者维持现有的基础 在宾夕法尼亚州 开展了一项研究一确定在宾夕法尼亚州现有桥梁结构配筋颈缩退化的程度和性 质 其目的是识别风险结构和适当的方法以解决减缓这种恶化的状况 钢筋穿过基础墩或基础干墙界面也许会以 J 型梁的形式出现 典型的就像 钢筋直径较小的有180度锚地的基础 传力杆梁 大直径的梁有笔直的锚地立足点 相对的 L 梁柱是一个90度锚地基础 联系在一起 这些细节通常被称为 起动杆 锚桩的性质不是和基脚接口的恶化直接相关 而且 除了大口径传力杆梁 竖杆 埋置高度高于基础接口也典型的适用于发挥接口处杆梁的作用的 而对于传力杆 梁 不会开发其张力 而是采取适当的埋深开发压力 健康检测 五座坐落在宾夕法尼亚州西部的退役的桥梁被确定以研究较合理的影响桥 梁的可能的因素 这些桥梁的使用时间到拆迁时从35年到53年不等 样品取自路 边的桥墩和桥台 桥台正下方 泄漏 伸缩缝和码头位于溪冲积平原上 采取评 估样品的接口钢筋腐蚀的程度 以确定所使用的钢的等级 干钻混凝土芯样也被 允许界面附近的钢筋氯配置来确定 所有样品均位于一个 B 类 脚跟 和 A 类 墩或茎壁 的具体的接口 在所 有的情况下 这个接口应该有充分的准备 而观察时 混凝土浇筑层之间的死结 应该是显而易见的 包括桥台在内的样品具有4号或5号 J 型杆梁 桥墩和11号传 力杆 样本包括 A615 40和60等级的梁 A408 40和50等级的梁 A431 75等 级的梁和 A432 60等级的梁 除了非常小的表面腐蚀 没有在任何样品中发现 有关于桥墩基础或干墙接口处的腐蚀 可溶于酸的氯化物含量 AASHTO T260 伴随试验的样品取自基础的侧面的接口 有很多强有力的理由 一 基础一般是低质量的混凝土 B 级 而不是 A 类 二 重力往往会导致的下表面的水平的界面具有更大的氯离子浓度 及 c 由于拆卸的实践 是很难获得界面以上的样品 样品粉末从每个核心不同深度回 收 从顶部测量基础 通过钻孔穿过铁心的横向在所需的深度 在一般情况下 覆盖在为约2 2 5英寸的所有情况下的钢筋之上 该酸的水溶性氯的值表示相对较低的氯诱导腐蚀 在基础表面 这些观值对 所有考虑到的桥梁是一致的 平均约0 26 没有测得的氯化物含量值超过0 37 在更深的混凝土的深度 4英寸 的几个测量很可能表示原混凝土混合料的 氯化物含量 大约是在0 20 0 30 附近 这可能是这一时期混凝土的一个经典 值 在一定情况下 氯离子含量不随深度变化 它是不可能有氯化物从环境中被 引入 对于那些有一个明确氯乙烯浓度梯度的样品 它很可能从环境中引入了一 些氯离子 虽然在所有情况下在这些数值很低 所有记录的值相对于的设立在那 些氧气扩散将受到限制且在立足界面下方的基础接口的值都被认为是偏低的 这些意见应被理解为代表有限的样本 虽然已竭尽全力使这个在宾夕法尼亚 州西部的条件尽可能为代表 在这次调查中发现得关于接口梁的腐蚀可能表明了 一个迹象 这种腐蚀是不是特有宾夕法尼亚州桥清单 尽管如此 证据的缺失不 是缺失的证据 进一步观察未来的拆迁项目的一些正式的报告 如照片 才能 扩大定性样品数量 在关于中部和东部的宾夕法尼亚州采样六桥的相关配套研究中 做出了一些 相反的观察 同时对两个桥墩和桥台干墙进行了采样 在这项研究中 三座桥梁 展出了 毫不相关 的恶化 壹桥表现出 温和 的恶化 最大的梁的截面损失 估计为25 其他两座桥梁展出 严重 恶化 一个最大的梁截面损失估计为65 在存根桥台后墙观察到中度的恶化 而严重恶化 在一个存根干墙和一个弯 柱观察到 在至少一种情况下是的显着的观察 即该基脚混凝土的顶部已完成界 面中的 产生相对平滑的关节 那么这将可能缓解 氯化物 水和氧沿关节的侵 入腐蚀 尽管对于恶劣的施工现实来说 这似乎是一个孤立的案件 研究结果表 明需要考虑更多可能的变化和进一步观察的需要 特定条件 进行实地考察 每个结构拆卸前确定了一系列有可能影响腐蚀基础桥墩或干 墙接口的条件 那些处于间歇流或受干湿交替的条件下的桥墩 一旦腐蚀过程开 始 那么其腐蚀速度便会加速 然而 通常情况下 这些地点将不会是高氯加载 除非结构是一个沿海的环境 桥墩 特别是位于巷道处接收经常的 无论是直接 或间接来自盐雾和沉积在春耕作业接触融雪剂的 排水不畅也可以在附近的码头 基地和 或损坏或无法使用的甲板排水 会引导氯沿渠道流向着码头基地接口 排水不畅也会冲刷掉土壤覆盖层 同样地 损坏或磨损的甲板关节也可能会导致 墩台墙氯的浓度 在拆迁过程中 小钢筋腐蚀在任何桥梁上都注意到了 在基础接口上面和下 面的混凝土 听起来在所有观察到的情况下是合理的 钢 当暴露在拆迁过程中 是未腐蚀的和 黑色 的 大多数梁杆保留了一层薄薄的水泥浆体薄膜 是一个 迹象表明梁杆继续被动工作 虽然在本研究中观察到没有梁杆恶化感染的可能性 但对一些被认为是造成 这种腐蚀的潜在因素 进行了鉴定 虽然这些可用于筛选的现有结构的可能的潜 在的这种类型的恶化 但没有因素已被发现到与接口梁处恶化相关 使用黑钢 在本研究中的所有情况下 缺乏防水膜 在本研究中的所有情况下 准备不当造成粘结不良或 平滑 界面裂纹面的施工缝 传闻证据讲述了 一个这样的施工缝 这是失败品 这种做法显然应避免 在这项研究中没有 观察到 施工缝 具有很少或没有土壤覆盖或位于在飞溅区或其它环境中 导致其 处于湿干交替条件 在本研究中的一个例子 暴露氯化物 这可能会导致接近甲板关节 甲板排水或泄水孔或接近一条 行车道 飞溅区 地形位置也有可能导致潜在的氯乙烯污染的水入口 在本 研究中的所有情况下 在这项研究中考虑结构所展出全部 但条件3还没有表现出 J 型梁杆的恶化 因此 单独来看这些条件和恶化时不相关的 它们是简单的指标 可用于指导桥 梁检查员在现场施工 但条件3才是可知 照理 组合多个条件将得出导致恶化 的更大的可能性 因此 所有这些条件都应当在检验报告中指出 接口钢筋锈蚀解决上述五个细节的潜在缓解 条件1 2和3对于在宾夕法尼 亚州的新的建设应该不再是一个问题 条件1是在1995年左右解决 要求所有基 台和翼墙杆和环氧树脂涂层 J 型梁杆 条件2最近已得到纠正 要求所有桥台和 挡土墙 2008年 搭板接头 2011 和码头 弯列 2011年 被使用在干的基础 施工缝防水细节 这些要求被认为最能代表新建设的做法 条件3 必须视为建 设施工误差 因此是罕见的 上浇筑混凝土时 施工缝应粗糙和延迟 土壤覆盖 施工缝当然是非常理想的 但这却并不总是可能的 提供防水应该有类似的效果 必须牢记的是土壤的存在限制的是氧气侵入而不是水分侵入的效果 因此适用于 不同的原则比防水 最后 良好的维护桥梁排水系统应有助于减轻条件5 可能的处理办法 由于构造几何形状 仅仅只有几个可行的办法来修复恶化的 J 型梁杆区域 截面扩张 本质是将一个恶化的接口包围在一个新的混凝土桥墩内 这是用于 当桥墩必须保持下来的情形 由于几何形状 截面扩张是不太可能适用于干墙 对于局部恶化的几个梁杆 外侧肩带的安装 重置了恶化的梁杆和核心混凝 土锚固可以用来控制和传输接口基础和桥墩干墙之间的力 这样的带可安装在桥 墩的表面或 近表面贴装 应用程序 嵌入在盖混凝土的吊带 不应该被锚定在 任何情况下 通过该接口传输的力而使其没有过度变形 对于大型梁杆来说可 能是一个挑战 在这个位置上需要一个筋角来确定 对于 J 型梁杆区要求拆除盖混凝土的最后一个选项 即钻孔起动杆进入一个 新的立足点 改革封面混凝土和地区提供外部约束 这种方法似对于桥墩是唯一 实用的方法 因为约束可能会由外部护套 纤维增强聚合物材料在这方面提供了 一个合理的选择 对于干墙 的钻孔和环氧树脂发夹围条可能是一种选择 虽 然这些必须通过小的壁厚而开发 在任何情况下 从现有的腐蚀的原因和现存的损害应当被减轻而作为修复的 一部分 但据笔者所知 没用任何已知能应对 J 型梁杆区的维修的方法 Not evidence of absence 这句只能意会 确实翻译不出来 同时对于新建筑和结构修复两个方面 环氧树脂涂层和其他耐腐蚀钢筋跨越 的基础接口 加上防水的接口 是减缓潜在的在干墙和桥墩附近 J 型梁杆或传 力杆恶化的最佳实际方案 对于现有建筑 有没有一个放之四海而皆准 的做法 每个结构必须视具体 情况而决定 这里总结 有一定程度的指导识别 减轻和修复潜在的恶化情况 值得注意的是 这份报告还提供了关于在接口恶化部分建模的指导 本次调查中发现的情况下 J 型梁杆和传开杆的腐蚀可能是一个迹象表明 这 种腐蚀是不是宾夕法尼亚州桥梁所特有的 然而 没有证据的情况下是不是没有 证据 进一步观察未来的拆迁项目 一些正式的报告 如照片 以扩大定性样 品的大小 BRIDGE MAINTENANCE Patient J Study takes close look at how J bars hold up in Pa By By By By KentKentKentKent A A A A Harries Harries Harries Harries Ph D Ph D Ph D Ph D FACI FACI FACI FACI P E P E P E P E Deterioration and necking of reinforcing bars has been reportedly observed at the interface of the footing and stem wall during the demolition of older bridge piers abutments and retaining walls Any decrease in the area of steel at these interfaces may result in reduction of foundation capacity and significant decrease in steel area may result in foundation instability and hamper efforts to rehabilitate or preserve existing foundations A study was carried out to determine the extent and nature of deterioration and or necking of interface reinforcing bars in existing bridge structures in Pennsylvania The objective was to identify at risk structures and appropriate methods of mitigating such deterioration Reinforcing steel crossing the footing pier or footing stem wall interface may take the form of J bars typically small diameter reinforcing bars having a 180 anchorage in the footing dowel bars usually large diameter bars having a straight anchorage into the footing or L bars having a 90 anchorage Together these details are often referred to as starter bars The nature of the anchorage is not immediately relevant to the deterioration at the footing interface With the exception of large diameter dowel bars embedment into the footing is typically more than adequate to develop the bar in tension at the footing interface Again with the exception of large diameter dowel bars straight bar embedment length above the footing interface also is typically adequate to develop the bar at the interface Dowel bars while not developed for tension will usually have adequate embedment to be developed for compression Physical exam Five decommissioned bridges located throughout western Pennsylvania were identified for study representing a reasonable snapshot of potentially affected bridges The bridges ranged in age from 35 to 53 years at their time of demolition Samples were taken from roadside piers and abutments abutments immediately beneath leaking expansion joints and piers located on a creek flood plain Samples of the interface reinforcing bars were taken to assess the extent of corrosion and in order to determine the grade of steel used Dry drilled concrete core samples also were taken to permit the chloride profile near the interface reinforcing steel to be determined All samples were located at an interface of Class B footing and Class A pier or stem wall concrete In all cases this interface appeared to be well prepared and when observable sound bond between concrete lifts was evident Samples included abutment walls having No 4 or No 5 J bars and piers having No 11 dowel bars The samples included A615 Grades 40 and 60 bars A408 Grades 40 and 50 bars A431 Grade 75 bars and A432 Grade 60 bars Beyond very minor surface corrosion no evidence of corrosion at the pier footing or stem wall footing interfaces was observed in any sample Companion tests of acid soluble chloride content AASHTO T260 were conducted on samples taken from the footing side of the interface There are a number of compelling reasons for this a the footing is generally the lower quality concrete Class B rather than Class A b gravity will tend to result in the lower face of the horizontal interface having a greater chloride concentration and c due to demolition practice it is difficult to obtain samples above the interface Powdered samples were recovered from each core at various depths measured from the top of the footing by drilling transversely through the core at the desired depth In general there was approximately a 2 to 2 5 in cover to the reinforcing bars in all cases The acid soluble chloride values indicated a relatively low susceptibility to chloride induced corrosion At the footing surface values were consistent for all bridges considered averaging about 0 26 No measured chloride content values exceeded 0 37 The few measurements taken at deeper concrete depths 4 in were likely indicative of chloride content of the original concrete mixes and found to be in the vicinity of 0 20 0 30 This would be a typical value for concrete of this vintage In cases where chloride content did not vary with depth it is unlikely that there were chlorides being introduced from the environment For those samples with a clear chloride gradient it is likely that some chloride had been introduced from the environment although the values were low in all cases All recorded values are believed to fall below any reasonable value for the chloride corrosion threshold for a footing interface located below grade where oxygen diffusion will be limited These observations should be understood to represent a limited sample although every effort was made to make this as representative of conditions in western Pennsylvania as possible The absence of interface bar corrosion found in this investigation may be an indication that such corrosion is not endemic to the Pennsylvania bridge inventory Nonetheless the absence of evidence is not evidence of absence Further observation of future demolition projects with some formal reporting such as photographs is warranted to expand the qualitative sample size Somewhat contrary observations were made in a related companion study which sampled six bridges in central and eastern Pennsylvania Both piers and abutment stem walls were sampled In this study three bridges exhibited insignificant deterioration One bridge exhibited moderate deterioration with the maximum bar section loss estimated to be 25 The other two bridges exhibited severe deterioration with a maximum bar section loss estimated to be 65 The moderate deterioration was observed in a stub abutment backwall while the severe deterioration was observed in one stub abutment stem wall and one bent column A significant observation in at least one case was that the top of the footing concrete had been finished in the interface resulting in a relatively smooth joint which would likely ease the ingress of chloride laden water and oxygen along this joint While poor construction practice this appeared to be an isolated case The results of the study indicate the possible variation of the phenomena considered and the need for further observation Certain conditions Site visits to each structure prior to demolition identified a number of conditions that have the potential to affect corrosion at footing pier or footing stem wall interfaces Piers located in intermittent streams or on flood plains are subject to alternating wet dry conditions which may accelerate the corrosion process once it begins Generally however these locations will not be subject to high chloride loading unless the structure is in a coastal environment Piers in particular may be located sufficiently close to the roadway to receive regular exposure to deicing salt either directly or indirectly from salt spray and deposition during plowing operations Poor drainage in the vicinity of pier bases and or broken or inoperable deck drainage also may channel chloride laden water toward the pier base interface Poor drainage also may wash out some of the soil cover Similarly damaged or deteriorated deck joints may lead to a concentration of chloride laden water at an abutment wall During the demolition process little reinforcing bar corrosion was noted at any bridge Concrete both above and below the footing interface was sound in all observed cases Steel when exposed during demolition was uncorroded and black Most bars retained a thin layer of adhered cement paste an indication of continued passivity of thebar Possibilities of infection While no interface bar deterioration was observed in this study a number of factors that are believed to contribute to the potential for such corrosion were identified While these may be used to screen existing structures for the potential for this type of deterioration no factor has been found to correlate with interface bar deterioration The use of black steel all cases in this study Lack of waterproofing membrane all cases in this study Improperly prepared construction joints resulting in poor bond or a smoother interface cracksurface Anecdotalevidencetellsofonesuchconstructionjoint whichwas trowel finished clearly such practice should be avoided not observed in this study Construction joints having little or no soil cover or that are located in splash zones or other environments resulting in wet dry conditions one example in this study and Exposure to chlorides This may result from proximity to a deck joint deck drain or scupper or from proximity to a carriageway splash zone Topography also may lead to the potential for chloride contaminated water ingress all cases in this study Structures considered in this study exhibited all but condition 3 yet exhibited no J bar deterioration Thus these conditions alone are not correlated to deterioration they are simply possible indicators that may be used to guide bridge inspectors during field views All but condition 3 are knowable and one would anticipate that compounding multiple conditions would result in a greater likelihood of deterioration thus all such conditions should be noted in inspection reports Mitigation of the potential for interface bar corrosion amounts to addressing the five details described above Conditions 1 2 and 3 should no longer be an issue for new construction in Pennsylvania Condition 1 was addressed in about 1995 by requiring epoxy coated J bars for all abutment and wingwall stems and pier bent columns Condition 2 was corrected more recently by requiring waterproofing details to be used at stem to footing construction joints for all abutments and retaining walls 2008 approach slab joints 2011 and pier bent columns 2011 These requirements are believed to represent best practice for new construction Condition 3 must be considered a construction error and is therefore rare Construction joints should be roughened and free of latency when the upper concrete is placed Soil cover over a construction joint is certainly desirable but not always possible The provision for waterproofing should have a similar effect It must be kept in mind that the presence of soil has the effect of limiting the ingress of oxygen rather than moisture and therefore works on a different principle than waterproofing Finally good maintenance of bridge drainage systems should help to mitigate condition 5 Possible prescriptions Because of the structure geometry there are few practical ways to repair deteriorated J bar regions Section enlargement essentially encasing a pier having deteriorated interface bars in a new reinforced concrete pier is an option in cases where the pier must be maintained Due to geometry section enlargement is not likely practical for stem walls For local deterioration of a few bars the installation of exterior straps duplicating the deteriorated bars and anchoring into the core concrete can be used to control interface gap opening and transmit forces between footing and pier stem wall Such straps could be installed on the pier face or in a near surface mounted application embedding the strap in the cover concrete which should not be anchored to in any event Transmitting forces across the interface without excessive distortion may be a challenge for large bars requiring a stiffened angle at this location A final option when the J bar region is accessible requires removal of cover concrete drilling a new starter bar into the footing reforming the cover concrete and providing external confinement to t