【作者】 李冬生；

【导师】 欧进萍；

【作者基本信息】 哈尔滨工业大学 ， 防灾减灾工程及防护工程， 2007， 博士

【摘要】 在拱桥结构中,吊杆是关键的受力构件,但由于长期处于恶劣的环境和疲劳受力状态,吊杆往往因为环境腐蚀和疲劳损伤以及锚头锚锭磨损而发生断裂,导致桥梁倒塌,并因此造成严重的交通事故和人员伤亡以及带来巨大的经济损失和极坏的社会影响。因此发展一套吊杆损伤监测和安全评定方法,具有重要意义。本文对吊杆内力、疲劳腐蚀、防腐砂浆失效等损伤进行了监测,提出了一套较为实用的监测、评定和腐蚀疲劳寿命预测方法,并通过实际工程检验了所提方法有效性和正确性。其主要研究内容如下:首先,针对吊杆内力识别的频率测试法都是基于弦振动理论、在实际应用中可能带来不可接受误差的弊端,提出了一种基于频率测试的吊杆内力识别的神经网络方法,给出了神经网络的具体设计步骤和优化方法。运用20多座桥梁的200多组数据对设计好的网络进行了训练,得到了吊杆内力预测较为精确的神经网络模型,并通过工程实例验证了本方法的正确性。其次,提出了拱桥吊杆应力变化的光纤光栅传感器监测方法。对现役拱桥提出对吊杆开窗直接布设裸光纤光栅传感器,并对它的波长与应变和温度的关系进行了理论分析,通过标定试验,得到传感器的应变与温度灵敏系数,提出并实施了现役拱桥吊杆光纤光栅传感器的布设工艺、布设后吊杆的修复方法以及光纤光栅传感器温度补偿方法;对新建拱桥吊杆提出用玻璃纤维-光纤光栅智能复合筋监测吊杆应力变化的方法,对复合筋在吊杆中布设工艺、根数、温度和应变灵敏系数以及如何与钢绞线协同变形进行了系统的研究;比较了不同直径纤维智能复合筋的极限应变,得出φ7mm的智能筋适用于监测吊杆应力变化;最后开发了取代式和粘结式两种智能吊杆,并通过张拉实验表明它们都能很好地监测张拉全过程的应力变化。第三,提出吊杆拉伸损伤的声发射监测方法,得到了新旧钢绞线、单根吊杆拉伸损伤的声发射特征。首先根据声发射特征参数图提出了断丝信号和非断丝信号的判断方法,运用声发射直线定位技术准确定出了断丝的位置;其次,由声发射累积能量相关图,动态分析了钢绞线损伤演化过程和规律,判断了断丝的根数和发生的时刻;最后,基于得到的声发射参数,导出了声发射参数同损伤变量的关系,建立了用声发射累积能量相对变化表示的钢绞线拉伸损伤演化方程,采用声发射特征参数时间序列分形理论研究了钢绞线的损伤演化规律,并提出将分形维数变化图中“最大-最小”变化模式作为为钢绞线临界损伤破坏的判断依据。第四,提出了吊杆防腐砂浆损伤全过程的声发射监测方法。首先,通过三点弯曲试验,得到了水泥砂浆梁破坏全过程力学特征和声发射特征,发现声发射计数的包罗曲线和荷载曲线具有良好的对应关系。然后,提出三种方法来预测它的损伤演化过程:1)速率过程分析方法,它的统计模型能有效预测声发射事件数和判断结构的状态;2)声发射信号幅值与声发射事件数关系图分析方法,声发射信号幅值包络线形状变化可以判断损伤的极限状态和损伤演化过程;3)分形算法,声发射特征参数在不同应力状态下时间序列分形维数变化规律能很好预测水泥砂浆临界破坏。最后,通过声发射机理分析,利用声发射能量的相对变化来定义水泥砂浆损伤因子,提出了用声发射参数表示水泥砂浆损伤演化方程的方法,并试验证明了损伤演化方程的正确性。第五,提出了基于监测数据的拱桥吊杆疲劳累积损伤寿命评估方法。对危桥和正常运营两种不同状态的拱桥提出采用不同的方法来获得它的疲劳应力谱,结合实际桥梁监测的数据,给出了拱桥吊杆腐蚀疲劳累积损伤计算公式、步骤及数据处理方法;并对实际桥梁的某一根吊杆腐蚀疲劳累积损伤进行了预测,比较了有无腐蚀钢绞线累积损伤寿命,其评估结果与实际结果基本吻合。最后,把上述监测和评定方法在四川峨边大渡河拱桥吊杆(系杆)得到了具体实施和应用,成功测试了各吊杆内力和监测了吊杆常见类型的损伤,基于光纤光栅监测数据正确地评价了吊杆安全状况,并根据测试结果分析了不同长度吊杆和同根吊杆不同钢绞线的受力特征;提出了基于监测数据识别车辆荷载大小的方法;利用布设在系杆中的玻璃纤维-光纤光栅智能复合筋成功地监测了系杆整个张拉过程,并指导了工程施工。更多还原

【Abstract】 Suspenders are arguably the most crucial elements of the arch bridge structure. However, they are often suffered from damage due to corrosion, fatigue and anchor head abrasion, what is more, these damages will perhaps cause arch bridge collapse, engendered severe casualties and economic loss, brought great bad social effect. It is very important to develop a series of methods that are monitored and assessed suspender damage.In this dissertation, the suspender tension, fatigue corrosion and anticorrosion cement mortar damage were monitored, and a systemic monitoring and corrosion fatigue life evaluating method was introduced and developed. A field application was examined through these methods.The main contributions of the thesis are given as follows:Firstly, the measurement of suspender tension using vibration menthod is mostly considered that the suspender is idealized as taut strings.This idealization simplifies the analysis may introduce unacceptable errors in many applications. The neural network intelligent methodology was proposed to compute suspenders tension, and design steps and optimization methods of neural network were given. In order to get correct neural network predictive model, 200 data of 20 bridges was used to train the neural network. The applicability of the proposed intelligent methodology was verified by comprasion with the others method through a case study.Secondly, the application of fiber Bragg gratting (FBG) sensors monitored arch bridge suspender stress was inventigated. The bare FBG sensors were directly installed in in-service arch bridge suspender by opening window. Its wavelength shift due to strain and temperature change has been studied theoretically, and theirs sensitivity coefficient was gotten through calibrating experiment. Techniques of installation of FBG sensors, suspender windows repairing and sensors temperature compensation have been explored in-service arch bridge. A new kind of smart glass fiber reinforced polymer optical fiber Bragg gratting (GFRP-OFBG) composite bar was developed to monitor the new constructing arch bridge suspender strain. The GFRP-OFBG sensors installation technology, number, strain and temperature sensitivity coefficient and how to setup transmission line were systemically studied. The different diameter GFRP-OFBG sensor’s limit strain was compared. It was verified that diameter 7mm GFRP-OFBG sensor was suit for the application of suspender strain monitoring. Based on these methods and technology, adhere intelligent suspender and replaceable intelligent suspender have been exploited. It was found that the two intelligent suspenders could well monitor the whole tensile process.Thirdly, the suspender tensile damage was monitored using acoustic emission (AE) technique, and AE characteristic parameters of tensile damage were investigated by the new and old steel strand, single suspender tensile experiment. Multiparameter analysis method based on correlation figure was proposed to recognize steel strand break and localization. According to the correlation figure of AE accumulative energy, the steel strand damage evolution process and law can be dynamically analyzed and broken strand numbers and time are judged. Based on the monitoring data, the relationship between AE parameter and damage variables was derived, and the steel strand tensile damage evolution equation is defined with AE accumulative energy relative change. The steel strand damage evolution law was studied applying the AE characteristic parameter time series fractal theory. In the initial stage of loading,the fractal value of steel strand is unsteady. When the cable crack begins its fast propagation, the fractal dimension appears the“increase-decrease”pattern, which could be used to identify the steel strand critical failure.Fourthly, AE monitoring systems for anticorrosion cement motar damage were established. AE characteristics of anticorrosion cement mortar were studied with three-point bending test. Compared with AE counts embraceable curve and load curve, it was found they had a good corresponding connection. Three damage evaluation methods were proposed: 1) Rate process analysis, its statistic model can correctly predict the AE event number and judge anticorrosion cement mortar damage state. 2) AE signal amplitude versus hits correlation figure analysis, in the different stress state embraceable curve of AE signal amplitude versus hits correlation figure can express anticorrosion cement mortar damage evolution process. 3) Fractal theory, the fractal dimension change of the whole damage process can be predicted the anticorrosion cement mortar critical failure. Based on the experiment, analyzed AE mechanics, damage factors were ?defined as variation of AE energy, the equation of damage evolution and the constitutive equations presented by AE parameters were derived. The evolution equation has been verified through experiments. ?Fifthly, the arch bridge suspender fatigue accumulative damage life assessment method was proposed using monitored data. The fatigue stress spectrum of different state arch bridge suspender was otained using different computing method. According to the data of arch bridge suspender monitoring and fatigue model experiment, the computing formulas and steps of suspender corrosion fatigue accumulative damage were given. The fatigue life of corrosive and noncorrosive steel wires was compared, the estimating results were well coincided with the practical case.Lastly, the above monitoring method and assessment criterion were applied in Sichuan E Bian Dadu river arch bridge suspenders and tie cables. The suspender tension and damage was successfully monitored. The different length suspender and different steel strand of the same suspender stress was analysed based on the monitoring data. The tie cables tensile process was successfully monitored utilizing GFRP-OFBG intelligent sensors, which supplied a great reference meaning to construction.更多还原