基于模态分析技术的大跨度斜拉桥主梁损伤识别

根据模态曲率的概念,构造结构损伤指标。采用有限元方法,对1座设定主梁不同位置发生损伤的大跨度预应力混凝土斜拉桥进行动力特性分析,利用构造的结构损伤指标对结构损伤进行识别研究。结果表明:结构损伤指标对结构损伤的识别精度与参与计算的模态振型及节点间距有关。应选择在损伤位置振幅较大的模态振型,而避免平衡位置处于损伤位置或附近的模态振型。该方法对结构的早期损伤可进行定性判断,结构损伤指标随结构的早期损伤程度的增大而增大,且增长幅度逐渐变小,当结构损伤达到一定程度后,损伤指标不再增大,而在渐近线附近波动。节点间距在一定范围内增大时,不影响损伤位置的识别,甚至可以确定损伤程度,但可能会反映不出损伤对其临近区域的影响;节点间距过大,可能发生漏判。

Damage Identification for the Main Girders of Large-Span Cable-Stayed Bridge Based on Modal Analysis Technique

Based on the concept of modal curvature,a damage locating index was constructed.The dynamic properties of a prestressed concrete cable-stayed bridge with various damage cases set in different positions of the main girder were analyzed by finite element method.The constructed damage index was applied to identify the damage set in different positions of the main girder.The conclusions indicate that the mode shapes involved in the calculation and the distance of nodes have influence on the precision of the damage index.The mode shapes have a large amplification in the damage position should be selected and others should be avoided.This damage identification method can detect qualitatively the early damage occurred in the structures.The index increases with the degree of damage but the increasing gets smaller and smaller.When the damage in the structures is very severe,the index will not increase and has a perturbation along the asymptote.When the distance of nodes increases within certain range,it will not influence the identification of damage location.It even can determine damage degree but may not reflect the influence of damage to the regions near the damage positions.If the distance of nodes is too long,the damage may not be reflected.