不同模态振型在梁结构裂缝识别中的差异

采用Gaus2小波对多裂缝梁的不同模态振型进行小波变换,分析了不同模态振型在梁结构裂缝检测中的差别。同时,还采用最小二乘法算出各裂缝处的Lipschitz指数,进而分析了各模态振型函数在裂缝处的奇异性程度。结论表明:梁结构裂缝识别的效果主要由裂缝处的小波系数的模的大小决定。     

不同模态振型在梁结构裂缝识别中的差异

本文采用Gaus2小波对多裂缝梁的不同模态振型进行小波变换,分析了不同模态振型在梁结构裂缝检测中的差别。同时,本文还采用最小二乘法将各裂缝处的Lipschitz指数算得,进而分析了各模态振型函数在裂缝处的奇异性程度。结论表明:梁结构裂缝识别的效果主要由裂缝处的小波系数的模的大小决定。     

一种求解多阶梯悬臂梁自由振动问题的新方法与实验验证

对复合单元法(composite element method,CEM)在多阶梯悬臂梁自由振动问题中的应用进行了实验验证。通过对具有2个阶梯和4个阶梯的悬臂梁进行模态测试,得到了实测的前几阶模态频率和相应的振型。将多阶梯悬臂梁在不同复合单元下的固有频率和振型计算结果与有限单元法所得结果及实测值进行了比较研究。结果表明:复合单元法所得到的频率和振型与实测结果符合得较好,并且具有建模时自由度少,高效高精度的优点。     

基于贝叶斯的钢筋混凝土梁模型修正方法

本文提出了一个基于贝叶斯原理的钢筋混凝土梁有限元模型修正方法。针对钢筋混凝土梁模型修正中的方程病态问题及模态测试中测点信息不完整和模态信息不完备的实际情况,建立了适用于有限测点的目标函数和似然函数,且在目标函数中同时考虑了频率和振型信息。采用延迟拒绝自适应算法(DRAM)对待修正参数的后验概率进行了计算。数值算例表明本方法在仅使用低阶测量模态信息和不完整振型信息的情况下,仍能准确修正结构参数;实验算例表明,修正后的钢筋混凝土梁有限元模型的动力特性和测量结果一致,修正后的模型参数值和梁的轻微裂缝的位置及大小基本对应,说明了本文方法的有效性。     

变截面梁受移动荷载时的动力效应研究

为了计算变截面梁的振型,采用了里兹法对高度沿抛物线变化的简支梁和高度线性变化的悬臂梁进行振型计算,将所得结果与文献[1]中的结果进行比较,得出里兹法在求解变截面梁低阶振型时精度较高,高阶振型误差较大的结论。     

基于模态柔度输入的结构模型智能修正研究

讨论了如何基于输入参数选择和样本收集来进行结构模型的神经网络修正。提出了利用模态频率、模态振型和模态柔度组合指标作为神经网络修正的输入参数。并用悬臂梁数值模拟和巴东长江公路大桥实桥模型来进行分析验证,分别比较了不同输入参数的修正精度。最后验证了结合模态柔度可以有效地对实际结构进行修正,保证模型修正效果。     

基于曲率模态的钢筋混凝土梁多点损伤位置识别

采用曲率模态对钢筋混凝土梁的多点损伤位置进行了识别研究。首先用有限元程序建立结构模型,并计算出位移模态振型,然后用差分法计算出曲率模态;同时对实际结构进行检测,得到结构的振型并计算出曲率模态。通过有限元模型和实际结构的曲率模态计算得到结构损伤因子,通过分析该损伤因子,可以判断实际结构的损伤位置。数值模拟算例分析表明,曲率模态对结构的损伤较敏感,用该方法识别结构的多点损伤位置是行之有效的。     

基于模态应变能的梁结构损伤识别

单元模态应变能法诊断结构损伤时理论上需要完整振型,而实测振型往往是不完备的。本文以梁结构为例,基于理论自由度和实测自由度相匹配的原则,对不完备振型信息进行扩充处理,然后再应用模态应变能的方法进行损伤识别。结果表明,当仅测得不完备的振型信息时,单元模态应变能法能很好应用于结构损伤识别,为实际工程的损伤检测提供了依据。     

受时变分布外力悬臂梁稳态随机振动分析

对于体型较简单的悬臂结构,第一振型占有振动能量的绝大部分,因此可以采用单自由度理论对其进行动力分析.认为结构所受分布随机荷载仅大小随时间随机变化,空间分布形式不随时间变化.用承受与随机荷载具有相同空间分布的静力悬臂梁挠曲线形状作为梁振动时的振型,采用广义单自由度分析方法,详细分析了受分布随机荷载作用的悬臂梁,得到了悬臂...     

悬臂梁随机振动的最优控制

本文采用模态分析方法,导出了受控弹性悬臂梁的状态方程,研究了单振型单点控制模型,并求得其状态变量的方差与结构参数间的解析关系式。最后,对多振型多点控制模型进行了数值分析,并探讨了选择控制点个数和位置的方法。     

Wavelet‐Based Detection of Beam Cracks Using Modal Shape and Frequency Measurements

Abstract: When a structure is subjected to dynamic or static loads, cracks may develop and the modal shapes and frequencies of the cracked structure may change accordingly. Based on this, a new method is proposed to locate beam cracks and to estimate their depths. The fault‐induced modal shape and frequency changes of cracked structures are taken into account to construct a new hybrid crack detection method. The method includes two steps: crack localization and depth estimation. The locations of the cracks are determined by applying the wavelet transform to the modal shape. Using the measured natural frequencies as inputs, the depths of the cracks are estimated from a database established by wavelet finite element method. The effectiveness of the proposed hybrid two‐step method is demonstrated by numerical simulation and experimental investigation of a cantilever beam with two cracks. Our analyses also indicate that the proposed method performed reasonably well at certain level of noise.     

Crack Detection from the Slope of the Mode Shape Using Complex Continuous Wavelet Transform

Abstract: A new method for cracks detection in beams is proposed by using the slope of the mode shape to detect cracks, and by introducing the angle coefficients of complex continuous wavelet transform. This study is aimed at detecting the location of the nonpropagating transverse crack. A series of beams with cracks that are simulated by rotational springs with equivalent stiffness are analyzed. The mode shape and the slope of this lumped crack model are calculated. Through complex continuous wavelet transform of the slope of the mode shape using Complex Gaus1 wavelet (CGau1), the locations of cracks are detected from the modulus line and the angle line of wavelet coefficients. By comparison, the singularity is much more apparent from the angle line of complex continuous wavelet transform. This demonstrates that the proposed method outperforms the existing method of wavelet transform of the mode shape with real wavelets. Also, this method can detect cracks in beams with different boundary conditions. The influence of crack locations and crack depth on crack detection is discussed. Finally, the noise effect is studied. Through the multiscale analysis, the locations of cracks may be detected from the angle of wavelet coefficients.     

带挑梁剪力墙结构局部强度破坏

采用ANSYS程序,建立三维有限元模型,对带挑梁剪力墙结构进行数值模拟计算.深入分析了主体结构剪力墙在强配筋挑梁处局部区域的复杂应力状态,包括混凝土局部区域的应力变化规律及主应力的分布、伸入钢筋的应力分布以及钢筋与混凝土之间的粘结应力的变化规律,同时也详细论述了混凝土中裂缝的分布及开展规律.在此基础上进一步研究了混凝土的局部强度破坏模式,总结归纳出了混凝土的锥形破坏模式,并对该破坏模式的形状通过数值模拟计算进行了参数分析.     

从受力角度谈PC斜拉桥主梁横向裂纹产生原因

采用平面有限元法对斜拉桥主梁悬臂施工中正应力变化规律进行了分析,对施工工序、挂篮重量对主梁正应力分布的影响进行了研究,从受力角度分析了PC宽主梁边缘横向裂纹产生的原因,以更好地处理裂缝,从而保证结构的安全。     

Higher Order Coherences for fatigue crack detection

Higher Order Coherences (normalized Higher Order Spectra) are the tools to identify the relationship between the different harmonic components in a signal. The vibration of a structure having a crack also generates several harmonics of the exciting frequency due to its breathing (closing and opening) behaviour which is a non-linear phenomenon. Presently two types of the HOC — namely, the Bicoherence and the Tricoherence, are used for the fatigue crack detection. This paper presents the observations made on the HOC on the numerically simulated experiment of a cantilever beam with and without cracks. The robustness of the HOC in the crack detection even for the noisy response vibration data has also been brought out.     

Crack detection of the cantilever beam using new triple hybrid algorithms based on Particle Swarm Optimization

The presence of cracks in a concrete structure reduces its performance and increases in the size of cracks result in the failure of the structure. Therefore, the accurate determination of crack characteristics, such as location and depth, is one of the key engineering issues for assessment of the reliability of structures. This paper deals with the inverse analysis of the crack detection problems using triple hybrid algorithms based on Particle Swarm Optimization (PSO); these hybrids are Particle Swarm Optimization-Genetic Algorithm-Firefly Algorithm (PSO-GA-FA), Particle Swarm Optimization-Grey Wolf Optimization-Firefly Algorithm (PSO-GWO-FA), and Particle Swarm Optimization-Genetic Algorithm-Grey Wolf Optimization (PSO-GA-GWO). A strong correlation exists between the changes in the natural frequency of a concrete beam and the crack parameters. Thus, the location and depth of a crack in a beam can be predicted by measuring its natural frequency. Hence, the measured natural frequency can be used as the input parameter of the algorithm. In this paper, this is applied to identify crack location and depth in a cantilever beam using the new hybrid algorithms. The results show that among the proposed triple hybrid algorithms, the PSO-GA-FA and PSO-GWO-FA algorithms are much more effective than PSO-GA-GWO algorithm for the crack detection.     

Crack identification method for tapered cantilever pipe-type beam using natural frequencies

A method to detect location and size of a crack in tapered cantilever pipe-type beam using changes in natural frequencies is presented. The boundary conditions of cantilever beam are applied to a general solution for vibrating tapered beam. Then, an equivalent bending stiffness for cracked beam is used to obtain the natural frequencies. Numerical simulations are carried out to construct a set of training patterns of a neural network, and committee of neural networks is employed to identify the crack. Crack identifications are carried out for the 16 damage cases numerically and for the 3 damage cases experimentally. The identified crack locations and sizes agree reasonably well with the exact values.     

再生骨料混凝土梁受剪性能试验研究

通过对混凝土强度等级为C30、再生骨料替代率为0%、50%、70%配置的9根HRB500钢筋混凝土梁的试验,研究不同再生骨料替代率、不同剪跨比下,混凝土梁的破坏形式以及裂缝最终形态、宽度、变形、钢筋应变及受剪承载力等性能。试验表明:当剪跨比λ=1.5时,再生混凝土梁的破坏过程、形态和裂缝发展破坏形态与普通混凝土梁相同;当剪跨比λ=2.5,3.0时,破坏过程与裂缝发展相似,但破坏形态趋向塑性破坏,再生骨料混凝土梁斜截面受剪能力没有降低,且再生骨料替代率的大小对梁斜截面承载力影响不大;现行规范中斜截面受剪承载力的理论公式对再生混凝土梁是适用的,安全储备较高。建议再生混凝土梁设计剪跨比在2.5左右。     

Damage detection method for large structures using static and dynamic strain data from distributed fiber optic sensor

A method for damage detection applicable to large slender steel structures such as towers of large-scale wind turbines, long-span bridges, and high-rise buildings is presented. This method is based on continuous strain data obtained by distributed fiber optic sensor (FOS) and neural network (NN) analysis. An analytical model for cracked beam based on an energy balance approach was used to train a NN. The continuous static strains and the natural frequencies obtained from the distributed FOSs were used as the input to the trained NN to estimate the crack depths and locations. An experimental study was carried out on a cracked cantilever beam to verify the present method for damage identification. The cracks were inflicted on the beam, and static and free vibration tests were performed for the intact case and the damage cases. The distributed FOSs were used to measure the continuous strains. The damage estimation was carried out for the 5 damage cases using the NN technique. It has been found that the identified crack depths and locations agree reasonably well with the inflicted cracks on the structure.