基于自振频率的悬臂梁损伤识别方法

梁的损伤识别是损伤检测理论中最基本、最具有代表性意义的工作.寻找基于频率的结构损伤识别和定位的参数,并证明这些参数仅与损伤的位置有关,而与结构损伤程度无关.然后建立悬臂梁损伤定位通用频率指纹库,并通过数值算例和具体试验验证该频率指标用于悬臂梁损伤定位的有效性、实用性及其准确性.最终找到一种比较实用的悬臂梁损伤定位方法,从而为结构损伤识别理论在工程实际的应用提供方便.     

基于频率进行简支梁损伤评估的数值研究

基于摄动理论,推导出结构的频变比为结构损伤位置的函数。以一等截面简支梁为例,利用梁损伤前后的频率比来对梁的损伤进行定位与定量。在不同损伤程度下,分析了梁对应的频率及频变比变化,以及由于忽略二阶项带来的影响,并指出了本方法的不足。     

高温下钢筋混凝土梁损伤识别研究

以动力损伤识别理论和火灾损伤识别理论为基础,针对火灾损伤特点引入了横观各向同性梁,同时考虑到简支梁刚度与弹性模量、中性轴和配筋率的关系,建立了火灾下钢筋混凝土简支梁的自由振动方程及其解析解。提出了以刚度为转换变量、以频率为指纹参数的识别损伤的新方法,并利用ABAQUS有限元软件对其进行了模拟验证,得出理论与模拟具有高度一致性。     

基于模态灵敏度分析的框架结构损伤识别:灵敏度分析

结构损伤识别是开发结构安全监测系统中的一个重要课题。由于结构频率容易测试并且有较高的测量精度,因此成为损伤识别中广泛应用的模态参数。基于模态频率的灵敏度分析,提出了一种基于结构损伤前后频率变化测量的损伤参数识别方法,用于确定结构的损伤位置和损伤程度。     

基于频率的网架结构损伤识别模糊系统研究

鉴于频率变化平方比仅是与损伤位置有关的量,利用基于频率变化平方比损伤识别方法不能识别网架结构的损伤程度,本文提出了一种网架结构损伤识别模糊推理方法.该方法以网架结构的前6阶频率变化率作为输入变量,以杆件的损伤程度作为输出变量,通过合理的模糊推理规则使频率变化率与损伤程度建立唯一的联系.经过网架结构的数值模拟分析验证了该...     

模态应变能法结构损伤检测研究

结合摄动理论，通过分析结构参数修改量高阶项的影响，推导了基于单元模态应变能的结构损伤评估方法；经数值仿真结果表明，其损伤定位准确、程度评估可靠，具有实际应用价值。     

基于实测频率的钢筋混凝土柱爆炸损伤快速评估方法

钢筋混凝土柱作为混凝土结构的关键受力构件,在爆炸荷载作用下,其破坏及失效可能进一步引发结构的连续倒塌,加剧灾害的程度.因此,爆炸作用后钢筋混凝土柱的损伤评估对于灾后结构性能评估具有重要意义.但由于灾后爆炸荷载确定困难,爆炸荷载作用下钢筋混凝土柱损伤评估的超压-冲量(P-I)曲线法很难应用于灾后钢筋混凝土构件的爆炸损伤评估.为此,提出了一种基于现场实测频率变化的钢筋混凝土柱爆炸损伤快速评估方法.建立了钢筋混凝土柱模态试验的数值方法,通过数值模态试验提取爆炸前后钢筋混凝土柱的一阶频率,建立钢筋混凝土柱的一阶频率与基于竖向剩余承载力的损伤指标的关系.参数分析结果表明,相同爆炸荷载下,矩形钢筋混凝土柱基于频率变化的损伤指标随配箍率、纵筋配筋率的增大而降低,随长细比的增大而增加.并运用最小二乘曲线拟合方法,得到柱损伤程度与频率变化之间的关系式,从而实现在爆炸现场通过频率测试对矩形钢筋混凝土柱爆炸损伤程度的快速评估.     

基于实测频率的钢筋混凝土柱爆炸损伤快速评估方法

钢筋混凝土柱作为混凝土结构的关键受力构件,在爆炸荷载作用下,其破坏及失效可能进一步引发结构的连续倒塌,加剧灾害的程度.因此,爆炸作用后钢筋混凝土柱的损伤评估对于灾后结构性能评估具有重要意义.但由于灾后爆炸荷载确定困难,爆炸荷载作用下钢筋混凝土柱损伤评估的超压-冲量(P-I)曲线法很难应用于灾后钢筋混凝土构件的爆炸损伤评估.为此,提出了一种基于现场实测频率变化的钢筋混凝土柱爆炸损伤快速评估方法.建立了钢筋混凝土柱模态试验的数值方法,通过数值模态试验提取爆炸前后钢筋混凝土柱的一阶频率,建立钢筋混凝土柱的一阶频率与基于竖向剩余承载力的损伤指标的关系.参数分析结果表明,相同爆炸荷载下,矩形钢筋混凝土柱基于频率变化的损伤指标随配箍率、纵筋配筋率的增大而降低,随长细比的增大而增加.并运用最小二乘曲线拟合方法,得到柱损伤程度与频率变化之间的关系式,从而实现在爆炸现场通过频率测试对矩形钢筋混凝土柱爆炸损伤程度的快速评估.     

复杂边界条件下基于频率法的吊杆张力测定研究

考虑吊杆两端弹性支承及拱肋、系杆梁里设置的减振垫减振作用和拱肋、系杆梁附加质量等的影响,基于Euler-Bernoulli梁理论建立了复杂边界条件下吊杆张力与其横向振动频率之间关系的隐式解析表达式,给出表达式中各参数的确定方法,分析边界参数的灵敏度,以京港澳高速公路郑州黄河二桥为实例对计算公式进行验证。计算结果表明:该表达式比较全面地考虑了吊杆实际边界条件,无论对于短吊杆还是长吊杆,计算结果都比较准确;当不考虑拱肋或系杆梁对吊杆的转动约束时,对于短吊杆来说,其边界条件更类似于固接;对于刚性系杆梁刚性拱类型的中、下承式拱桥,吊杆边界约束条件更接近于固接。     

模式识别的斜拉桥损伤诊断动力指纹与识别算法

为有效并准确诊断出斜拉桥损伤,对基于模式识别的斜拉桥损伤诊断方法进行了研究。选取易于测试出的低阶模态频率和部分关键点竖向振型数据为动力指纹,无需模态扩展或模型缩聚。研究并采用全因子设计进行动力指纹库的创建,可精确评估设定的损伤因子及其交互作用对损伤识别结果的影响。设计并增加了带随机误差的动力指纹库样本集。编制了基于Matlab的模式识别的多种算法,重点研究了精确度高的多层感知器识别算法及其提高该算法预测准确率的装袋集成算法。最后给出一座单塔双跨双索面斜拉桥的多种识别算法的损伤诊断过程和结果,得到一种可包容测试随机误差的高精确度斜拉桥损伤诊断评估模型。     

Use of Ritz method for damage detection of reinforced and post-tensioned concrete beams

Damage-induced changes in modal characteristics can be detected using experimental modal analysis. In this article, based on changes in natural frequency, mode shapes, and damping ratios, a methodology for detecting damage location and severity is presented. The damage was induced by application of point load at half span location on the reinforced and post-tensioned concrete beams. The load was gradually increased to obtain different crack patterns to be used in simulation of damage scenarios. Experimental modal analysis was performed on the undamaged and damaged beams. The natural frequency and mode shapes were used to determine the location of damage. The approach is developed at an element level with a conventional finite element (FE) model by Ritz method, which is called Ritz damage detection method (RDDM). The mathematical model for both damped and undamped damaged structures have been established through the eigenvalue equations. The singular value decomposition (SVD) technique is used for determination of damage or sound index. These indexes are sensitive to the change of dynamic characteristics due to damages. This approach is applied to five simply supported post-tensioned concrete beams. The numerical results show that the exact location and severity of damage for different simulated damage scenarios could be efficiency found by the present methodology.     

Damage identification in a lightly reinforced concrete beam based on changes in the power spectral density

This paper deals with the detection of damage in a lightly reinforced concrete beam using dynamic measurements. An algorithm based on changes in the power spectral density (PSD) is presented. The algorithm is used to detect damage, predict the location and assess the extent of damage in the reinforced concrete beam. The method is based on the measured data on the beam after introducing some damage at salient locations. A tuneable piezoelectric actuator was used to produce additional peaks in the dynamic response of the system in the frequency domain. These additional peaks were adjusted over the frequency band by tuning the actuator. It was noticed from the results, that the PSD method detected the damage, determine the location and could monitor the increase in damage in the beam     

基于模型修正理论和频响函数模式置信准则的简支梁损伤动力评估方法

提出了一种基于频响函数模式置信准则的改进模型修正方法,用以识别各部位的损伤指数,从而对简支梁的损伤进行定量评估。加工制作了4片模型简支钢梁,用切割截面的方式模拟了损伤,进行了动力测试,并利用所提方法进行了损伤识别。简支钢梁数值模拟和模型试验结果表明：利用相邻测点间频响函数模式置信准则指数构造目标函数时,可有效增加识别变量的个数;第1阶频率和第2阶频率之间的区段内频响函数对损伤灵敏度较高,可用SAC指数计算和简支梁损伤识别;所提损伤评估方法对测试系统误差和噪声不敏感,可实现对多个位置损伤的同步定位和定量识别;在传感器数量有限的情况下,采用分步识别法可以实现对损伤位置的逐步接近和损伤程度的精细化识别。     

悬索桥损伤指标的适用性分析

依据精细的悬索桥有限元模型,分析比较了在无噪声情况下频变比指标、模态曲率差指标和静态应变差指标对悬索桥不同位置损伤的适用性.对主梁和吊索两种常见损伤类型的数值模拟发现,主梁损伤时,由于各阶指标之间信息的互补性,模态曲率差指标识别效果最好;吊索损伤则对结构整体频率的影响极其微小,无法用频变比指标来定位,此时静态应变差指标最为敏感.在试验的基础上,提出了根据损伤类型来综合运用频率变化比、主梁竖弯振型模态曲率变化以及静态应变差进行悬索桥的损伤定位的方法.     

On free vibration of nonsymmetrical thin-walled beams

In this paper, a numerical–experimental study about natural frequencies of doubly unsymmetrical thin-walled and open cross-section beams is presented. The equations of motion are based on Vlasov's theory of thin-walled beams, which is modified to include the effects of shear flexibility, rotatory inertia in the stress resultants and variable cross-sectional properties. The formulation is also applicable to solid beams, constituting therefore a general theory of coupled flexure and torsion of straight beams. The differential equations are shown to be particularly suitable for analysis in the frequency domain using a state variables approach. A simplified theory, which excludes the analysis the warping constraint, is presented leading to a more simple theory that is used for comparison purposes in this paper. Finally, free vibration experimental tests about unsymmetrical beams are presented which allow to verify the theory presented in this paper and provide good quality data that can be used for checking the accuracy and reliability of different theories.     

On free vibration analysis of thin-walled beams axially loaded

In this paper, a numerical–experimental study about natural frequencies of thin-walled beams axially loaded is presented. Moreover, the influence of axial load in the frequencies is studied. The equations of motion are based on Vlasov’s theory of thin-walled beams, which were modified previously to include the effects of shear flexibility, rotatory inertia in the stress resultants. Moreover, a constant axial load is incorporated to the formulation, both in the time and frequency domain. The differential equations are shown to be particularly suitable for analysis in the frequency domain using a state variables approach. A numerical investigation is carried out to reveal the influence of the axial load in several boundary conditions. Finally, free vibration experimental tests are presented, which allow verify the theory presented in this paper and provide good quality data that can be used for checking the accuracy and reliability of different theories.     

钢筋锈蚀对钢筋混凝土结构固有频率和阻尼比影响的试验研究

针对钢筋锈蚀使钢筋混凝土结构的抗震性能和耐久性能退化,并且对结构动力特性产生影响的现象,采用电化学加速锈蚀方法,通过法拉第定律控制锈蚀程度,将钢筋的理论锈蚀率分为5%,10%,15%三个锈蚀阶段,在实验室中模拟了钢筋混凝土梁中钢筋的锈蚀过程。根据悬臂梁的自由振动衰减特性,采用自由衰减法采集了钢筋混凝土梁的固有频率和阻尼比,研究了钢筋锈蚀对钢筋混凝土梁固有频率和阻尼比的影响。结果表明:钢筋锈蚀对钢筋混凝土梁的固有频率和阻尼比有显著影响,钢筋混凝土梁的固有频率随着钢筋锈蚀程度的加深而呈减小趋势,阻尼比随着钢筋锈蚀程度的加深而呈增大趋势,因此阻尼比可以作为损伤指标用于混凝土结构腐蚀损伤检测。