【作者】 王丹生；

【导师】 朱宏平；

【作者基本信息】 华中科技大学 ， 结构工程， 2006， 博士

【摘要】 近年来,随着世界经济和现代科学技术的迅速发展以及人们安全意识和安全需求的逐渐提高,那些关系国计民生的重要工程结构的损伤识别和健康监测问题逐渐被人们所重视,工程结构的损伤识别和健康监测也成为了当前结构工程学科十分活跃的研究领域。本文在国家自然科学基金(No.50378041)、教育部博士点基金(No.20030487016)以及华中科技大学优秀博士论文基金(No.2004-23)的资助下进行了基于反共振频率和压电阻抗的结构损伤检测数值与试验研究。本文所开展的主要研究工作和取得的主要成果为:(1)提出了一类基于反共振频率信息的损伤识别方法,即基于反共振频率曲线、反共振频率曲线斜率以及反共振频率曲线曲率的裂纹损伤检测方法。该方法的基本思想是:通过获取结构各驱动点阻抗(或导纳)响应和第一阶反共振频率曲线、反共振频率曲线斜率以及反共振频率曲线曲率,并观察曲线的弯折和突变情况来识别损伤的发生并对损伤定位;在裂纹位置确定之后,结合结构固有频率和裂纹梁频率方程识别裂纹损伤大小。(2)介绍了两种模拟梁裂纹的弯曲弹簧模型,并通过数值计算和试验验证了这两种模型的有效性。利用上述裂纹模型对裂纹混凝土梁进行了动力特性分析,分析结果表明:裂纹的产生会引起梁固有频率减小,但低阶固有频率对梁裂纹损伤并不敏感,而且简支梁对称位置的裂纹会引起相同的固有频率变化,因此单纯利用低阶固有频率对结构进行损伤识别是不可靠的。(3)推导了单裂纹简支梁、双裂纹简支梁的频率方程;利用基于反共振频率信息的损伤识别技术对单裂纹梁、双裂纹梁和多裂纹梁进行了振动分析和损伤识别数值研究。数值研究结果表明:利用梁结构的第一阶反共振频率曲线,不仅可以判断损伤的发生、准确识别中等深度以上梁裂纹的位置,而且能定性识别裂纹损伤程度;利用第一阶反共振频率曲线斜率和曲率可以对小裂纹损伤进行准确定位;结合裂纹梁频率方程和固有频率,对单裂纹梁和双裂纹梁裂纹尺寸进行了定量识别,识别误差较小。(4)基于反共振频率曲线的损伤识别技术对单裂纹梁、双裂纹梁和多裂纹梁进行了损伤识别试验研究。研究结果发现:反共振频率测量值与计算值是基本吻合的;基于测量得到的第一阶反共振频率曲线可以较好地识别出中等深度以上裂纹的位置;随着梁裂纹个数的增多,反共振频率曲线上的弯折或不连续现象变得不明显。(5)对表面粘贴有单压电片的钢梁进行了阻抗分析,在此基础上对单压电片智能钢梁的压电阻抗进行了数值计算和实验验证,二者结果基本吻合。利用压电阻抗技术,通过测量单压电片的电导纳变化成功识别了钢梁裂纹损伤;将三个压电片分布在钢梁的不同部位,通过监测各个压电片的电导纳变化,并结合各压电片处的反共振频率成功识别了梁裂纹损伤位置。(6)利用压电阻抗技术对钢框架结构进行了健康监测试验研究。通过监测粘贴在框架节点处的各压电片的电导纳变化发现,在不同损伤工况下,直接与螺栓连接的连接板上的压电片的电导纳变化最大,与连接板相连的下斜撑上的压电片的电导纳也有变化,而与连接板不直接相连的上斜撑上压电片的电导纳几乎没有变化。由此表明,利用压电阻抗技术能识别钢框架结构损伤;压电阻抗技术具有局部检测能力。分别建立了基于压电导纳实部和虚部的损伤程度识别指标RMSDR和RMSDI,研究结果发现,利用RMSDR指标能较好地对钢框架螺栓松动损伤程度进行定性识别,而利用RMSDI指标对螺栓松动损伤程度识别则不可靠。(7)利用压电阻抗技术对混凝土立方块固化过程进行了监测。监测结果发现,随着混凝土龄期的增加,粘贴在试块表面的压电片的电导纳曲线峰值频率逐渐增大,并且在混凝土龄期3-6天增幅较大,在随后的龄期增幅较小。由压电片的机电耦合特性可知,压电导纳曲线峰值频率与混凝土的固有频率具有对应关系,由此可间接预测龄期内混凝土刚度变化规律。(8)基于多压电片分布传感和压电阻抗技术,对裂纹混凝土梁进行了损伤定位试验研究。试验结果发现,靠近裂纹的压电传感器对梁裂纹损伤较为敏感,而远离裂纹的压电传感器则几乎不受裂纹损伤的影响,这进一步证实了压电传感器的局部检测能力和损伤定位能力;结合损伤程度识别指标RMSDR,实现了对不同损伤工况下混凝土梁裂纹的损伤定位。(9)利用压电阻抗技术对钢筋混凝土梁加载过程进行了监测实验。利用分配梁对钢筋混凝土梁进行两点加载,将压电片分布粘贴在梁的下表面来监测由于外加荷载所导致的结构开裂以及刚度损失。实验结果表明利用压电阻抗技术可以判断钢筋混凝土结构开裂荷载,能较直观地反映梁裂纹扩展过程及其刚度损失状态。更多还原

【Abstract】 With the rapid developing global economy and modern science and technologies, as well as the improving safety consciousness and safety demands of people, the problems concerning damage detection and health monitoring of many important engineering structures have attracted wide attention in recent years, and the study on damage detection and health monitoring has become one of the most active research fields in structural engineering community. Supported jointly by the National Natural Science Foundation of China (No.50378041), the Specialized Research Fund for Doctoral Program of Higher Education (No.20030487016) and the Excellent PhD Dissertation Foundation of Huazhong University of Science and Technology (No.2004-23), in this dissertation, the studies on structural crack identification and health monitoring based on the anti-resonant frequency information and piezoelectric impedance (or admittance) have been implemented numerically and experimentally.In this dissertation, the main research works and results include:(1) A kind of damage identification techniques based on the first anti-resonance curve and its slope and curvature is proposed. The basic idea of the proposed method is: when the driving point impedances (or admittances), and the first anti-resonance curve of the beam structure, as well as the slope and curvature of the first anti-resonance curve are acquired, the presence and the location of crack damage can be identified by monitoring the presences of the breaks or jumps of the first anti-resonance curve. Once the crack locations are determined, integrated with the identified natural frequencies and frequency equation of cracked beam, the sizes of the beam cracks can also be identified.(2) Two rotational spring models used to represent beam cracks are introduced, and the validity of the models is subsequently verified by numerical and experimental examples. The vibration characteristics analysis of a cracked concrete beam based on one of the two rotational spring models is performed, and the analytical results indicate that the presence of the beam crack results in the decrease of natural frequencies, the lower natural frequencies, however, are insensitive to the beam crack, and the crack at a position induces the same change in natural frequencies as its symmetrical position of the beam. It seems to be deduced that it is not reliable to detect damage of beams only depending on the lower natural frequencies.(3) The frequency equation of simple supported beams with one crack or two cracks is deduced. Based on the antiresonance information vibration analysis and damage identification of single-crack and double-crack and multi-crack beams are numerically implemented. The results indicate that not only the presence of the crack damage and the location of moderate crack damage are identified, but also the extent of crack damage is qualitatively evaluated by using the first anti-resonance curve; the small crack damage is located by using the slope and curvature of the first anti-resonance curve; integrated with the first two identified natural frequencies and the frequency equation, the sizes of the beam cracks are also identified with a high degree of accuracy.(4) Damage identification of single-crack and double-crack and multi-crack beams based on the first antiresonance curve vibration analysis is experimentally implemented. It is concluded that the measured first antiresonance curve is close to the caculated one in genaral; by the use of the measured first antiresonance curve the moderate crack damage is identificated, however, when the number of the cracks increase, the breaks or jumps of the measued first antiresonance curve become not visible.(5) Impedance of a piezoelectric smart steel beam with a single PZT sheet is implemented theoretically. On the basis, the piezoelectric impedance of a smart steel beam with free boundary conditions at both ends is verified numerically and experimentally, and the numerical and experimental results are comparable. Experimental study on damage identification of cracked steel beams is performed based on the piezoelectric impedance technique. The presence of the crack of a steel beam with a PZT sheet is detected via monitoring the variations of piezoelectric admittances. Further, when the steel beam is furnished with three PZT sheets in different positions, integrated the antiresonant frequency in the scaning frequency range, the crack location is also identified successfully.(6) Experimental study on a steel frame structure for health monitoring is implemented based on the piezoelectric impedance technique. By monitoring the changes in piezoelectric admittances of different PZT sheets in different damage cases, it is found that the electric admittances of the PZT bonded on the joint plate vary obviously, and those of the PZT bonded on the low diagonal support vary a little, and those of the PZT bonded on the top diagonal support hardly vary. So it is concluded that the damage of the steel frame structure can be identified by using the piezoelectric impedance technique, and the piezoelectric impedance technique has the ability to detect the local damage. Subsequently, the two damage indexes, i.e. RMSDR and RMSDI, are used to qualitatively evaluate the damage extent of the steel frame structure, and the results show that the damage extent can be preferably evaluated by the use of the RMSDR index.(7) Curing process of concrete samples is monitored based on the piezoelectric impedance technique. It is found from the experimental results that with the increase of concrete ages, the resonance of electric admittance curve of the PZT sheet bonded on the concrete block gradually increases, and the extent of increase is larger in 3-6 day ages than in the next ages. From the electromechanical coupled characteristic of PZT it is known that the resonance of piezoelectric admittance is corresponding to the natural frequency of the concrete block, so the variations of rigidity of concrete block in concrete ages can be forecasted indirectly. (8) Based on distributed sensing of multi-PZT and piezoelectric impedance technique, the experimental study on crack location of a concrete beam is performed. From the experimental results it is found that the PZT sheet near to the crack is sensitive to the crack, the PZT sheet far from the crack, however, is insensitive to the crack, which further verifies the ability of PZT to detect local damage transducer and the ability to damage location. Integrated the RMSDR index the crack locations of the concrete beam are determined in different damage cases.(9) Experimental strudy on a reinfored concrete beam for load process monitoring is conducted. The RC beam is loaded on two sites of beam by the use of a distribution beam, and several PZT sheets are bonded to the bottom surface of the RC beam with certain interval, and are used to monitor the presence of cracking and the loss of rigidity of the RC beam. The experimental results indicate that the load value of cracking of the RC beam under the vertical loads can be estimated, and the cracking propagation and the loss status of rigidity of the RC beam can also intuitively reflected based on the piezoelectric impedance technique.更多还原