基于解析模态分解法的桥梁动态应变监测数据温度影响的分离

Separating temperature effect from dynamic strain measurements of a bridge based on analytical mode decomposition method

对于大跨度桥梁结构,温度荷载会对结构应变产生显著影响。为得到桥梁在动荷载下的真实应变,对其运营状况做出正确评估,有必要将温度变化对应变的影响从结构应变中剔除。对比分析了悬索桥钢桁架跨中上弦杆的温度应变片和工作应变片数据的功率谱密度,得到应变片输出信号在各频段的能量分布特征,确定了工作应变片数据中温度应变信息和动荷载应变信息的分界频率;采用解析模态分解法,根据分界频率将工作片原始应变时程分离为慢变成分和快变成分两部分。结果表明,由温度变化产生的应变时程波动(慢变成分)得到有效分离,该方法不仅能去除温度变化引起的应变片自身的应变,同时温度应力引起的应变亦得到有效剔除;通过雨流计数法对提取出的快变成分进行检验分析。结果表明,快变成分较好地保留了桥梁动荷载产生的应变信息,具有较高的工程利用价值。

Under temperature load, structural stress of a long-span bridge changes and its strain is affected remarkably. For proper assessment of bridge operation condition, it＇s highly necessary to remove the effect of varying temperature on the strain data and get the structure strain induced by dynamic load on the bridge. Here, dynamic strains of the active strain gauges fixed on chord of steel truss at mid span of a suspension bridge and inactive strain gauges not sensing mechanical surface strains but temperature variation induced strains were analyzed. According to normalized power spectral density （PSD） ratio, the information in strain data of the active gauges were separated into two parts in frequency domain, they were respectively dominated by varying temperature and dynamic load and the value of dividing frequency was obtained. After the a nalytial mode decomposition method was applied to the strain data, the slow-varying component and fast-varying component were obtained. It was shown that the fast-varying component does not fluctuate periodically; the slow-varying component including strain of gauges themselves and structural strain induced by temperature variation can be effectively eliminated from the strain data of the active strain gauges. Through test analysis with the rain-flow counting method, it was indicated that the strain amplitude information of the fast-varying component and that of the original data from active gauges are similar; the fast-varying component properly retains the strain information produced by dynamic load and has some practical engineering value.