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Prediction of long-term prestress loss in concrete box girder bridges.

机译：混凝土箱梁桥长期预应力损失的预测。

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摘要

Post-tensioned cast-in-place concrete box girder bridges are the most popular type for new bridge construction in California since this class of bridges shows an increased ability to resist and dissipate seismic loads for long-span structures. However, due to the long-term behavior of the construction materials .i.e. concrete and steel, tension forces induced by prestressing decrease over time as a result of creep and shrinkage of concrete and steel relaxation, which is called long-term prestress loss. This loss is one of the most important factors to consider in designing and analyzing this type of bridges. Although the inaccurate prediction of the loss is not considered to impose severe effects on the ultimate capacity of the structures, it is known to lead to critical problems at the design and service stages. Underestimating the prestress loss can cause cracking and excessive deflection during service stage and overestimating it could lead to uneconomic design.;A number of bridge specifications use varied approximations currently to predict the long-term prestress losses. However, they show significant scatter in values of their estimates even under the same environmental conditions. This diversity of prediction mainly results from two sources of error. The first source of the error is related to inaccurate material characteristics: the coefficients for creep and shrinkage of concrete. The other comes from excessive simplification in the method of analysis in the specifications.;Consequently, the goals of this research are to verify which specifications can provide more accurate creep and shrinkage strains and to propose a simple yet more comprehensive analysis procedure to predict the long-term prestress losses including effects from important structural- and material-level parameters. To meet these objectives, monitoring responses from bridges in service and investigating material characteristics from cylinder specimens are in progress on four bridge spans of I5-I805 and I215-CA91 in San Diego and Riverside, California, respectively. Also, a simple analysis method which could be easily applied in the design is improved by incorporating the effects from the five parameters: transverse shear deformation, loading events, and horizontal reinforcements as structural-level parameters, compressive strength of concrete and thermal creep from accumulation of temperature variation as material-level parameters. The results from this research are validated by comparing with the predictions in current specifications and data from the monitored spans on I5- I805 and I215-CA91.
机译：后张预应力现浇混凝土箱梁桥在加利福尼亚州的新建桥梁中是最受欢迎的类型，因为这类桥梁显示出更大的抵抗和消散大跨度结构的地震荷载的能力。但是，由于建筑材料的长期行为，即混凝土和钢，由于混凝土和钢松弛的蠕变和收缩，预应力引起的拉力会随着时间的推移而降低，这称为长期预应力损失。这种损耗是设计和分析此类桥时要考虑的最重要因素之一。尽管不认为损失的不准确预测会对结构的极限承载力产生严重影响，但已知在设计和使用阶段会导致严重问题。低估预应力损失可能会导致在服务阶段出现开裂和过度挠曲，高估可能会导致设计不经济。目前，许多桥梁规格使用各种近似值来预测长期预应力损失。但是，即使在相同的环境条件下，它们的估计值也显示出很大的分散性。这种预测的多样性主要来自两个误差源。误差的第一个来源与不准确的材料特性有关：混凝土的蠕变和收缩系数。另一个来自规范中分析方法的过度简化。因此，本研究的目的是验证哪些规范可以提供更准确的蠕变和收缩应变，并提出一种简单但更全面的分析程序来预测长长期预应力损失，包括重要的结构和材料水平参数的影响。为了达到这些目标，分别在加利福尼亚州圣地亚哥和里弗赛德市的I5-I805和I215-CA91的四个桥跨上，正在进行对在役桥梁的响应进行监测并研究圆柱试样的材料特性的研究。此外，通过结合以下五个参数的影响，改进了一种易于在设计中应用的简单分析方法：横向剪切变形，荷载事件和水平钢筋作为结构层参数，混凝土的抗压强度和累积热蠕变温度变化作为材料级参数。通过与当前规格中的预测以及I5-I805和I215-CA91上受监视跨度的数据进行比较，可以验证这项研究的结果。

著录项

  • 作者

    Kim, Seung Dae.;

  • 作者单位

    University of California, San Diego.;

  • 授予单位 University of California, San Diego.;
  • 学科 Engineering Civil.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 376 p.
  • 总页数 376
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 建筑科学;
  • 关键词

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