以青岛海湾大桥沧口斜拉桥为背景，采用多尺度有限元模型对钢箱梁局部裂缝进行损伤分析和识别.首先，采用小尺度的壳单元和大尺度的梁单元建立钢箱梁的多尺度模型，并根据实际监测数据对整桥模型进行模型修正；然后，对小尺度钢箱梁易损截面进行小损伤模拟，研究断面应变响应的变化规律和损伤敏感性；最后，采用BP神经网络法进行损伤位置和程度识别.分析结果表明：多尺度模型使小损伤模拟与计算效率得到较理想的协调；顺桥向应变对钢箱梁小损伤具有较好的敏感性，应变变化具有显著的局部化特征；基于合理的应变测点布置，采用顺桥向应变的BP网络方法能较好地识别损伤位置及损伤程度，且具有较强的抗噪能力.

Based on the Cangkou cable-stayed bridge of Qingdao Bay bridge, the multi-scale finite element model was used to analyze and identify the local crack damage of the steel box girder. Firstly, a multi-scale model of steel box girder was established by using small-scale shell elements and large-scale beam elements, and the whole bridge model was modified according to actual monitoring data. Then, the small damage simulation of the vulnerable section of small-scale steel box girder was carried out, and the variation law and damage sensitivity of the section strain response were studied. Finally, the BP neural network method was used to identify the location and extent of the damage. The analysis results show that the multi-scale model makes the small damage simulation and calculation efficiency get better coordination; the strain along the direction of the bridge has better sensitivity to small damage of the steel box girder, and the strain change has significant localized characteristics; the BP network method of strain along the bridge direction can better identify the damage location and damage degree, and has strong anti-noise ability based on the reasonable strain point arrangement.