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Electrochemical characterization and time-variant structural reliability assessment of post-tensioned, segmental concrete bridges.

机译：后张拉分段混凝土桥梁的电化学表征和时变结构可靠性评估。

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摘要

In post-tensioned (PT) bridges, prestressing steel tendons are the major load carrying components. These tendons consist of strands, ducts, and cementitious grout that fill the interstitial space between the strands and ducts. However, inspections on PT bridges have reported the presence of voids, moisture, and chlorides inside grouted ducts as the major cause of accelerated corrosion of strands. Corrosion of the strands has resulted in PT bridge failures in Europe and tendon failures in the United States. As most of the PT bridges have high importance measures and the consequences of failure are significant, it is important to maintain high levels of safety and serviceability for these bridges. To meet this goal, bridge management authorities are in dire need of tools to quantify the long-term performance of these bridges. Time-variant structural reliability models can be useful tools to quantify the long-term performance of PT bridges.;This doctoral dissertation presents the following results obtained from a comprehensive experimental and analytical program on the performance of PT bridges. (1) Electrochemical characteristics of PT systems; (2) Probabilistic models for tension capacity of PT strands and wires exposed to various void and environmental conditions; (3) Time-variant structural reliability models (based on bending moment and stress limit states) for PT bridges; (4) Time-variant strength and service reliabilities of a typical PT bridge experiencing HS20 and HL93 loading conditions and different exposure conditions for a period of 75 years.;The experimental program included exposure of strand specimens to wet-dry and continuous-atmospheric conditions. These strand specimens were fabricated to mimic void and/or grout-air-strand (GAS) conditions inside the tendons. It was found that the GAS interface plays a major role in strand corrosion. The GAS interfaces that are typically located in the anchorage zones of harped PT girders or vertical PT columns can cause aggressive strand corrosion. At these locations, if voids are present and the environment is relatively dry, then limited corrosion of the strands occurs. However, if the presence of high relative humidity or uncontaminated and chloride-contaminated water exists at these interfaces, then corrosion activity can be high. The strands were exposed for a period of 12, 16, and 21 months, after which the remaining tension capacity was determined.;The analytical program included the development of probabilistic strand capacity models (based on the experimental data) and the structural reliability models. The time-variant tension capacity predicted using the developed probabilistic models were reasonably consistent with the tendon failures observed in PT bridges in Florida and Virginia. The strength reliability model was developed based on the moment capacity and demand at midspan. Service reliability model was developed based on the allowable and applied stresses at midspan. Using these models, the time-variant strength and service reliabilities of a typical PT bridge were determined based on a set of pre-defined constant and random parameters representing void, material, exposure, prestress, structural loading, and other conditions. The strength and service reliabilities of PT bridges exposed to aggressive environmental conditions can drop below the recommended values at relatively young ages. In addition, under similar conditions the service reliability drops at a faster rate than the strength reliability.
机译：在后张式（PT）桥梁中，预应力钢腱是主要的承载部件。这些肌腱由股线，导管和胶结水泥浆组成，填充了股线与导管之间的间隙。但是，对PT桥的检查表明，在灌浆管道内存在空隙，湿气和氯化物，这是加速钢绞线腐蚀的主要原因。股线的腐蚀已导致欧洲的PT桥断裂和美国的腱断裂。由于大多数PT桥梁都具有高度重要的措施，并且故障后果十分严重，因此，对于这些桥梁而言，保持高水平的安全性和可维修性非常重要。为了实现此目标，桥梁管理机构迫切需要使用工具来量化这些桥梁的长期性能。时变结构可靠性模型可以作为量化PT桥梁长期性能的有用工具。该博士论文提出了从PT桥梁性能综合实验和分析程序获得的以下结果。 （1）PT体系的电化学特性； （2）暴露于各种空隙和环境条件下的PT绞线和钢丝的拉伸能力的概率模型； （3）PT桥梁的时变结构可靠性模型（基于弯矩和应力极限状态）； （4）典型的PT桥在经历HS20和HL93载荷条件以及不同暴露条件的情况下持续75年的时变强度和使用寿命可靠性;该实验程序包括将钢绞线样品暴露在干湿和连续大气条件下。这些钢绞线标本的制作是为了模拟肌腱内部的空隙和/或灌浆-空气钢绞线（GAS）条件。发现GAS界面在钢绞线腐蚀中起主要作用。通常位于竖向PT大梁或垂直PT柱的锚固区域中的GAS界面可能会导致股线腐蚀。在这些位置，如果存在空隙且环境相对干燥，则股线会受到有限的腐蚀。但是，如果在这些界面处存在较高的相对湿度或未受污染且受氯化物污染的水，则腐蚀活性可能很高。将钢绞线暴露12个月，16个月和21个月，然后确定剩余的抗拉能力。分析程序包括开发概率钢绞线能力模型（基于实验数据）和结构可靠性模型。使用已开发的概率模型预测的时变张力能力与在佛罗里达州和弗吉尼亚州的PT桥中观察到的腱断裂合理地一致。强度可靠性模型是根据中跨的弯矩能力和需求而开发的。基于中跨的允许应力和应用应力，开发了服务可靠性模型。使用这些模型，可以基于一组预定义的常数和随机参数（它们代表空隙，材料，暴露，预应力，结构载荷和其他条件）来确定典型PT桥的时变强度和服务可靠性。暴露于恶劣环境条件下的PT桥的强度和服务可靠性在相对较小的年龄时可能会低于建议值。另外，在类似条件下，服务可靠性下降的速度比强度可靠性下降的速度快。

著录项

  • 作者

    Pillai Gopalakrishnan, Radhakrishna.;

  • 作者单位

    Texas A&M University.;

  • 授予单位 Texas A&M University.;
  • 学科 Engineering Civil.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 399 p.
  • 总页数 399
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

  • 入库时间 2022-08-17 11:38:19

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