【作者】 李苗；

【导师】 任伟新；

【作者基本信息】 中南大学 ， 土木工程， 2013， 博士

【摘要】 随着桥梁分析理论、施工技术、材料性能的迅速发展,桥梁跨度越来越大,结构越来越柔,不仅要求精确严密的计算与施工技术,而且对桥梁建成后的安全运营提出了更高的要求。对这些大跨度结构进行健康监测与安全评估具有重要意义。桥梁健康监测是在一段较长的时间内通过传感器对结构的响应进行采集,从响应信号中提取出对结构损伤比较敏感的特征,进而区别无损或异常的结构,达到健康监测的目的。基于结构动力学参数的结构损伤识别方法,采用模拟的信号可取得比较好的识别结果,但应用到实际结构和实测信号当中,往往得不到较好的效果。其主要原因之一是,环境因素对结构损伤特征参数的影响有时会淹没掉因结构真实损伤造成的损伤特征参数的改变。因此,对桥梁进行健康监测不应忽略环境因素的影响,结构实际工作环境因素对损伤特征的影响,已成为结构健康监测领域研究的热点和难点。本文以贵州坝陵河大桥健康监测实测数据为工程背景,采用理论、分析和实测的方法,分析环境温度变化对大跨度悬索桥结构长期性能的影响,重点研究环境温度对动应变实测数据的影响。论文的主要研究工作和结论包括：1.根据坝陵河悬索桥长期监测数据,分析了环境温度对主梁挠度、塔的倾角、伸缩缝位移和主缆、吊索索力的影响,得到了悬索桥主塔和主跨跨中截面结构的温度变化情况。结果表明,反映桥梁结构物几何线形变化的数据(挠度、倾角和伸缩缝位移)以及吊索索力与温度都有较明显的相关性。2.分别采用温度应变片和工作应变片,对坝陵河大桥跨中主桁杆件应变响应进行了长期测试。结果显示应变时程中的温度效应成分表现为趋势形式,其形成时间较长；车辆荷载引起的应变时程曲线表现为脉冲形式,历时很短。在此基础上,提出了采用信号分解的方法对应变时程中的温度效应成分和活载效应成分进行分离：首先根据工作应变片和温度应变片信号的功率分布情况确定了信号分离的截止频率。然后,采用解析模式分解法,根据截止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,快变成分较好地保留了桥梁动荷载产生的应变信息。3.通过分解出的快变成分得到测试期间各测点的最大应力幅值,对比可知1月份和4月份测试期内通过坝陵河大桥的车辆最大载重情况差别不大。分解出的慢变成分中剔除变温度引起的应变片自身的应变,余下的应变成分反映了各测点结构温度应力的变化情况。4月测试期日温差较大,导致测点温度应力较1月份有大幅增长,且各测点日温差产生的结构温度应力要大于车辆活载产生的最大应力幅。4.定义了动应变相关函数,证明了结构在白噪声激励下,应变时程的相关函数幅值向量仅与结构的固有频率、模态振型和阻尼比有关,规范化后的相关函数幅值向量具有较固定的比例形态。采用坝陵河大桥监测实测数据,研究了温度对动应变相关函数的影响,证明了以上结论。5.提出了基于主成分分析的环境温度影响剔除方法,即对测点原始应变时程进行主成分分析,找出主要反映温度信息的特征子空间,将原始应变时程投影至温度特征子空间后再重构时程数据,得到原始应变时程的温度效应成分,由此来消除温度对应变信号的影响。坝陵河大桥动应变监测数据分析结果表明,第一主成分反映了动应变时程绝大部分的波动信息。通过第一主成分特征向量对实测数据进行重构,得到了应变时程中的温度效应成分。6.基于实测应变数据的相关函数幅值向量在各时段的比例形态均存在差异,对坝陵河大桥动应变监测数据剔除温度效应成分后,所得到的相关函数幅值向量均呈现出一致的比例线形。结果表明,应变时程中的温度效应成分会导致相关函数幅值向量的比例线形发生改变,因此,若不考虑环境温度对应变时程相关函数幅值向量的影响,易对桥梁结构的健康状况产生误判。更多还原

【Abstract】 With the rapid development of the structural analysis theory, construction techniques and building materials on bridges, the span is increasing and structure tends to be lightweight. Therefore, not only rigorous calculation and construction technology are required, but also higher standard for security operation of the finished bridge. Health monitoring and safety assessment on the large span structure is of great significance. In order to achieve the aim of health monitoring, the structure responses are collected through sensors in a long period, and damage sensitive features are extracted from response signals, then judge whether the structure is abnormal. When damage detection method based on the structural dynamic parameters is applied to simulant signals, the detection result may be good. However, the method in the application of the actual structure and the measured signal is difficult to obtain good results. The change in operating and environmental condition is one of the important factors. Effect of environmental factors on damage indices sometimes may cover the change of damage indices caused by real structure damage, and health monitoring should not ignore the influence of environmental factors. The environmental effect on damage indices has become a hot and difficult point in the research field.In the thesis, effect of ambient temperature change on long term performance of large span suspension bridge, especially temperature effect on dynamic strain measured data, were analyzed based on the engineering background of Baling River Bridge in Guizhou. The main tasks and conclusions are as follows:1. Through the long term measured data of Baling River Bridge, temperature effect on deflection of main girder, inclination of tower, displacement of expansion joints and force of the hanger and the cable strand were analyzed. Temperature changes of tower and structure in middle cross section of main span were understood. The results showed that the data reflecting the change of structural geometric configuration (deflection, inclination and displacement) and hanger force had obvious correlation with temperature.2. Dynamic strains of the active strain gauges fixed on chord of steel truss at mid span of suspension bridge and inactive strain gauges, that didn’t sense strains produced by stress but temperature variation induced strains, were measured for a long time. Temperature effect components of strain history showed trend form that experience in a long time. While the components of dynamic load effect, such as vehicle, presented impulse form that lasted shortly. Signal decomposition method was proposed to separate the information in strain data of the active gauges into temperature effect component and live-load effect component. According to power distribution of signals of the active and inactive strain gauges, the cut-off frequency was obtained for signal decomposition. Then, the measured strain data of active strain gauges were separated into the slow-varying component and fast-varying component by analytical mode decomposition method based on the cut-off frequency. It was shown that strain history fluctuation (slow-varying component) induced by varying temperature was extracted. Through the method, all of the gauges strain and stress-induced strain under temperature variation could be effectively eliminated. Via analysis of fast-varying component using rain-flow counting method, fast-varying component properly retained the strain information produced by dynamic load.3. Maximum stress amplitudes of measuring points were obtained through the extracted fast-varying component during the test. According to amplitudes, it’s concluded that maximum vehicle loads of test period in January and April on Baling River Bridge showed little difference. After eliminating the temperature variation-induced gauge strain from slow-varying component, the remaining component reflected the change of structure temperature stress of measuring points. In April, a larger daily temperature difference leaded to much higher temperature stress of measuring points than January and temperature stress produced by daily temperature difference was greater than maximum stress amplitude induced by vehicle load.4. Correlation function of dynamic strain was defined. It was verified that under white noise excitation, the correlation function amplitude vector (Vcf) of strain history was only related to the natural frequency, mode shape and damping ratio of structure. After Vcf being normalized, it showed a fixed ratio shape. This conclusion was proved by studying temperature effect on correlation function of dynamic strain based on test data.5. Based on principal component analysis, a method for eliminating the effect of environmental temperature was proposed. The principal component analysis was applied to the measured strain response, and the feature subspace mainly reflecting the temperature information was obtained. Through projecting the measured strain history into feature subspace of temperature and data reconstruction, temperature effect component was extracted. Then, temperature effect on strain signals could be removed. The analysis results of test data showed that the first principal component indicated most of the volatility of information. Through reconstruction of measured data with eigenvector of the first principal component, the temperature effect components of strain history were effectively extracted.6. In different time period, the shapes of Vcf based on measured data were distinct. After temperature effect component being eliminated from test data, the shapes of Vcf performed consistent. It was showed that temperature effect component in test data leaded to various shapes of Vcf. Therefore, ignoring the temperature effect on the Vcf of strain history was prone to get the false judgment on the real operation condition of structure.更多还原