【作者】 陈晓强；

【导师】 朱宏平；

【作者基本信息】 华中科技大学 ， 结构工程， 2009， 博士

【摘要】 随着社会发展、科技进步以及人们对安全需求的提升,结构损伤识别吸引了众多学者的目光,已经成为土木工程领域的一个研究热点。土木工程结构损伤识别技术对保护人民的生命财产安全有着重大的作用,开展这方面的研究具有重要的意义。现有的基于振动的结构损伤识别方法主要是频域的,在实际应用中具有局限性。时域损伤识别方法,利用时域测量信号,直接在时域内进行损伤识别,不需要完备的模态信息,不会丢失信号的时域信息,有利于应用在实时、在线的健康监测中;基于能量的结构损伤识别方法,将局部的损伤信息与结构局部能量的变化联系起来,对损伤更为敏感,而且不需要阵型求解、结构建模。基于此,本论文在国家自然科学基金(No.50378041,50778077)的资助下,进行了基于能量指标的结构损伤识别理论与试验研究。本文在如下几个方面进行了研究,综合应用理论分析、数值模拟以及试验验证等手段,取得了一些结论和成果:(1)统计矩实质上是一种时域能量指标,具有很好的抗噪声干扰能力,对剪切型结构效果很好,但是不适合弯曲型结构。为此,针对弯曲型梁结构,提出了损伤识别两步法:先识别损伤单元位置,再针对已识别的损伤单元利用模型修正得到其损伤程度。同时提出了位移4阶统计矩曲率指标,用来完成损伤定位工作。数值算例表明,位移4阶统计矩曲率指标具有很好的定位能力,该方法可以有效识别弯曲型结构的损伤,具有很好的抗噪能力。(2)提出了基于加速度测试数据的动能密度指标,并建立了损伤识别方法。利用该方法进行了简支梁结构的损伤定位,结合弯曲弹簧模型,识别了梁的裂纹深度。针对动能密度指标的局限性,利用基线修正、小波包变换等技术对该方法进行修正。通过连续梁数值模拟和一空间钢框架的试验,证明了该方法的损伤识别能力及抗噪能力。(3)结合一悬臂梁结构,通过理论推导表明:应变变化与结构的损伤单元位置一一对应,局部的损伤仅能引起对应部位应变的变化,远离损伤地方的应变不发生变化;而位移则不具备此特性,一处的损伤可以引起另一处位移的很大变化。因此,应变类参数非常适合于损伤定位。(4)提出了基于结构应变响应的伪比能指标,能够准确地指示结构的损伤部位。通过缺口平滑拟合(GSM)技术,可以通过损伤后的伪比能曲线拟合出未损伤的伪比能指标值,这样,该方法就不需要未损伤时的信息作为基准,这对于大部分现役结构的损伤识别意义重大。另外,发展了统计伪比能指标与伪比能灰色关联系数指标,拓展了伪比能指标的形式,提高了其识别效力。通过与遗传算法的结合,该方法可以在识别出损伤位置的基础上定量得到损伤单元的损伤程度,与传统的单一优化算法相比,该方法大大降低了计算时间,提高了识别效率。(5)小波(包)变换是进行信号预处理的强大工具,原始测试信号通过小波(包)分解与重构,选择其中最有效的信号成分,可以提高信号对损伤的敏感性、剔除引发误判的潜在因素,同时可以降低噪声的影响。(6)通过理论推导表明,压电薄膜能够用于一维梁结构、二维板结构的动态应变测量工作,压电薄膜的测量电荷与结构被测部位的应变有着确定的正比关系,可以通过测量电荷直接得到应变大小。试验结果也表明了压电薄膜可以用于分布测量结构各部位的动态应变响应。(7)利用压电薄膜测量了铝梁、铝板试件各工况下的动态应变信号,将其用于伪比能法的损伤识别中;尽管试验中还存在一些问题,但结果总体上还是可以接受的,这也进一步验证了该损伤识别方法的有效性和实用性。更多还原

【Abstract】 With the social development, scientific progress and aggrandizement of people’s safety requirement, structural damage identification is attracting more attention and becomes a new research focus in the field of civil engineering, because it does play an important role in the operation of protecting people’s life and property. Therefore, it is a significant work to study on this subject.Many damage identification methods have been developed and, most of them are frequency-domain ones which possess some limitations in practical applications. In contrast, time-domain methods utilize the measured signals to detect structural damage in time-domain directly, requiring no perfect structural modal parameters and preserving the original time-domain information of tested signals. As a result, they are suitable for the real-time and online structural health monitoring. At the same time, energy indexes are sensitive to structural damages which induce the structural local energy changes. Thereby, energy indexes-based methods do well in this subject and they do not need structural model building and modal shape analyzing. Based on aforementioned background and supported by the National Natural Science Foundation of China (No. 50378041 & 50778077), in this dissertation, theoretical and experimental studies of structural damage identification based on energy indexes have been implemented.In this dissertation, following aspects have been studied theoretically, numerically and experimentally and, some important results and conclusions have been acquired:(1) The statistical moment, which has been used to develop a new damage detection method for shear building structures, is a time-domain energy index essentially. It is a good damage index with strong noise robustness. However, it is only effective for shear type structures but ineffective for bending type ones. A progress is made to the index for damage identification in bending type structures here using a two-step method: first, the locations of damaged elements are detected utilizing a new index proposed here, named statistical moment curvature; then, the damage extent of these elements is identified with a model updating method. The effectiveness of this new method is verified with a numerical example.(2) A new damage detection technique based on kinetic energy density, which is firstly developed applying the tested acceleration signals, is presented here. Associating with the rotational spring model, it identifies both the crack location and depth in a beam model successfully. Then, the limitation of this method is pointed out and, overcomed with some techniques such as wavelet packet transform and correction of datum line. The diagnosis results of a numerical continuous beam and a 3D steel frame confirm the damage detection ability and noise robustness of this new method.(3) A theoretical analysis based on a cantilever is accomplished to prove the following argues: structural damages cause strain changes in the corresponding locations, which implies a one-to-one correspondence between the strain changes and damage locations; however, displacement changes do not possess this property because a damage occurring in one element could induce displacement variation of another element. Thus, not the displacement type parameters but the strain ones are good for damage localization.(4) A strategy using strain test data for damage detection is proposed by defining a new index named "Pseudo Strain Energy Density (PSED)". Applying the gapped-smoothing method, the undamaged PSED curve can be obtained from the damaged one and this new strategy becomes a non-baseline one which is significant to the damage estimation when lacking the undamaged information. Furthermore, two other indexes, the statistical PSED and PSED grey relation coefficient, are addressed for damage localization. By combining the PSED method with the genetic algorithm, both the damage location and damage extent can be identified and the analysis time decreases sharply.(5) Wavelet packet transform is proved to be a strong tool for signal preprocessing. In these damage identification methods, it is utilized to accomplish signal decomposition and recomposition. During this process, the most useful signal components are extracted and used for damage detection. Meanwhile, the noise effect is lightened.(6) A theoretical analysis is accomplished to prove that the polyvinylidene fluoride (PVDF) can be used to measure the structural dynamic strain. And the expressions about the structural strain and the tested PVDF electric charges for both 1D beam structures and 2D plate structures are deduced theoretically. A PVDF-based dynamic strain measurement experiment is designed and accomplished. The experimental results confirm the strain measuring ability of PVDF.(7) Decades of PVDF patches are used to measure dynamic strains of both an aluminum beam and plate in different damaged cases. The experimental data are obtained for damage identification using the PSED-based method. The results are acceptable although there are some defects in the experiment, which also confirms the practical effectiveness of the PSED-based method.更多还原