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

本项目的研究目标是利用实际的徐变挠度数据来寻找一个真实的几十年的混凝土徐变规律。帕劳KB桥是一座跨度创世界纪录的节段式箱梁桥，该桥的致命坍塌引起了人们对之前蠕变挠度的关注，蠕变挠度达到1.61米，几乎是设计挠度的5倍。强行打开这座桥的技术数据，使西北大学的研究人员得出结论，标准设计建议已经过时。这引发了广泛的研究，到目前为止，已经导致一批大跨度桥梁在20至40年内过度挠曲，而本应服役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集合体数据库中，并将箱梁挠度的三维有限元反分析与实验室数据库相结合，对混凝土徐变的改进材料定律进行了标定。利用复杂的统计概念和遗传算法，从混凝土的组成特征和强度预测材料徐变规律的参数。这些结果将作为工程学会的标准设计建议提出。尽管许多过度偏转的桥梁的改造或关闭的社会成本是巨大的，但他们的数据是进步的金矿。这项研究将阐明如何避免重复，因为重复会导致适用性损失和因腐蚀而破裂。改进的徐变模型对于现代超高层建筑中柱的抗差异缩短设计也将是重要的。

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.