Evaluation of ultimate strength of rational and economical bridges for performance based design

近年来，为了降低桥梁的建设成本，人们提出了一些合理、经济的桥型。U型钢梁是目前建议的经济合理的桥梁之一。施工中的U型钢梁的极限强度低于施工后的极限强度。但施工中无板U形钢梁的极限强度并不明显，以往的工字形钢梁设计方法是否适用于U形钢梁尚不清楚。为了掌握U形钢梁的极限强度特征，为验证本文所用有限元分析的充分性，进行了U形钢梁的抗弯和抗剪试验。试验试件是根据实际U型钢桥主梁的结构参数制作的。在试验的基础上，对U型钢桥主梁的极限强度特性进行了详细的有限元分析。在试验结果和分析结果的基础上，提出了U型钢桥主梁抗弯强度和抗剪强度的评估方法。通过与实验结果和分析结果的比较，验证了所提出的评估方法的有效性。

Recently, some types of rational and economical bridges are proposed for reducing the construction cost of bridges. U-shaped steel girder is one of proposed rational and economical bridges. The ultimate strength of U-shaped steel bridge girders under construction is inferior to that after construction. But the ultimate strength of U-shaped steel girders without the slab under construction is not obvious and it is not clear whether previous design method for I-shaped steel girders is applicable to the U-shaped steel girders.In this research, the bending and shear experiments of U-shaped steel girders were carried out in order to grasp the feature of ultimate strength and to get the basic data for confirming adequacy of FEM analyses used in this study. The test specimens were made in consideration of the structural parameters of actual U-shaped steel bridge girders. Besides experiments, FEM analyses were conducted for investigating the feature of ultimate strength of U-shaped steel bridge girders in detail. On the basis of experimental results and analysis results, the evaluation method of bending strength shear strength of U-shaped steel bridge girders were proposed. The validity of the proposed evaluation method was confirmed in comparison between calculated values by the proposed evaluation method and not only experimental results but also analysis results.