Excessive Bridge Deflections: Inverse Analysis to Identify Multi-Decade Creep Properties of Concrete

桥梁过度挠度：通过反演分析来识别混凝土的数十年蠕变特性

• 批准号: 1129449
• 负责人: Zdenek Bazant
• 金额: $ 34.71万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-09-01 至 2015-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1129449&HistoricalAwards=false
• 关键词: Excessive; Bridge; Deflections; Inverse; Analysis

The resaerch objective of this project is to use actual data on excessive creep deflections to find a realistic multi-decade concrete creep law. The fatal collapse of KB Bridge in Palau, a segmental box-girder bridge of world record span, called attention to the preceding creep deflections, which attained 1.61m, nearly 5-times the design deflection. Forced unsealing of the technical data on this bridge allowed Northwestern University researchers to conclude that the standard design recommendations were obsolete. This motivated a broad search which has so far led to a collection of 64 large-span bridges deflecting excessively within 20 to 40 years, while supposed to serve 100 years. The main cause of this obsoleteness is that most laboratory creep data have durations 6 years. The bridge deflection data are combined in one aggregate database, and an inverse three-dimensional finite-element creep analysis of box-girder deflections is combined with the lab database to calibrate an improved material law for creep of concrete. Sophisticated statistical concepts and a genetic algorithm are used to predict the parameters of material creep law from the concrete composition characteristics and strength. The results will be proposed for standard design recommendations of engineering societies.Although the societal costs of retrofits or closings of numerous excessive deflecting bridges are enormous, their data represent a gold mine for progress. The research will clarify how to avoid repetitions, which causes serviceability losses and cracking with corrosion. An improved creep model will also be important for design against differential shortening of columns in modern super-tall buildings.

本计画的研究目的是利用实际的徐变挠度资料，找出一个符合实际的混凝土徐变规律。帕劳的KB桥是一座世界纪录跨度的节段箱梁桥，该桥的坍塌引起了人们对徐变挠度的关注，徐变挠度达到了1.61 m，几乎是设计挠度的5倍。 这座桥的技术数据被强制解封，使得西北大学的研究人员得出结论，标准设计建议已经过时。这激发了广泛的研究，到目前为止，已经收集了64座大跨度桥梁，这些桥梁在20到40年内过度偏转，而应该使用100年。这种过时的主要原因是大多数实验室蠕变数据的持续时间为6年。将桥梁挠度数据合并到一个汇总数据库中，并将箱梁挠度的三维有限元徐变反分析与实验室数据库相结合，以校准混凝土徐变的改进材料法。采用先进的统计概念和遗传算法，从混凝土的组成特性和强度出发，预测材料徐变规律的参数。结果将被提出为工程学会的标准设计建议。尽管改造或关闭许多过度偏转桥梁的社会成本是巨大的，但他们的数据代表了进步的金矿。该研究将阐明如何避免重复，这会导致使用性能损失和腐蚀开裂。一个改进的徐变模型也将是重要的设计，以防止在现代超高层建筑柱的差异缩短。