A comprehensive review on modal parameter-based damage identification methods for beam- or plate-type structures is presented, and the damage identification algorithms in terms of signal processing ...are particularly emphasized. Based on the vibration features, the damage identification methods are classified into four major categories: natural frequency-based methods, mode shape-based methods, curvature mode shape-based methods, and methods using both mode shapes and frequencies, and their merits and drawbacks are discussed. It is observed that most mode shape-based and curvature mode shape-based methods only focus on damage localization. In order to precisely locate the damage, the mode shape-based methods have to rely on optimization algorithms or signal processing techniques; while the curvature mode shape-based methods are in general a very effective type of damage localization algorithms. As an implementation, a comparative study of five extensively-used damage detection algorithms for beam-type structures is conducted to evaluate and demonstrate the validity and effectiveness of the signal processing algorithms. This brief review aims to help the readers in identifying starting points for research in vibration-based damage identification and structural health monitoring and guides researchers and practitioners in better implementing available damage identification algorithms and signal processing methods for beam- or plate-type structures.
Peridynamics is a nonlocal theory, and it has been applied to a series of fracture problems based on its two main bond failure criteria: the critical stretch criterion and the critical energy density ...criterion. In this paper, a new criterion, the critical skew criterion, corresponding to the shear deformation, is for the first time proposed specifically for ordinary state-based peridynamic mode II fracture analysis. The necessity of the critical skew criterion is demonstrated by limitations and inaccuracy of the existing critical stretch and energy density criteria in theoretical and numerical mode II fracture analysis. The validity of the proposed critical skew criterion is illustrated by quantitative analysis of the captured behaviors of the typical mode II fracture tests. The results obtained by the critical skew criterion agree well with the benchmark data from the linear elastic theory, the virtual crack closure technique, and the Griffith’s theory in different aspects of analysis. A simplified formula of the bond energy density is also derived and verified, and it can serves as a fundamental tool in peridynamic fracture analysis.
•A new method is developed for microstructural crack segmentation of concrete images.•The model architecture and training scheme are designed to achieve high accuracy.•The microstructural crack ...patterns of concrete in freeze-thaw cycles are analyzed.
As a nondestructive imaging technology, X-ray CT has become an effective tool for studying the microstructural damage of concrete. However, autonomous identification and segmentation of microstructural cracks remains a challenge due to the same greyscales of voids and cracks in CT images. To address this problem, this paper develops a new method for microstructural crack segmentation of three-dimensional concrete images based on the deep convolutional neural networks. The model architecture and training scheme of the proposed network are specifically designed to achieve the high accuracy in the segmentation of narrowly opened cracks. Meanwhile, the method can also be used to separate aggregates from mortar with high precision. The segmentation results are compared with manual segmentation to validate the performance of the proposed method, demonstrating that the proposed method is capable of successfully separating microcracks from voids through their shapes and the aggregates from the mortar matrix with high precision. Finally, the three-dimensional concrete microstructure is reconstructed with microcrack patterns dependent on freeze-thaw actions, further manifesting the capability of the proposed method in the internal damage analysis of concrete.
A two-dimensional (2-D) continuous wavelet transform (CWT)-based damage detection algorithm using “Dergauss2d” wavelet for plate-type structures is presented. The 2-D CWT considered in this study is ...based on the formulation by Antoine et al. (2004). A concept of isosurface of 2-D wavelet coefficients is proposed, and it is generated to indicate the location and approximate shape or area of the damage. The proposed algorithm is a response-based damage detection technique which only requires the mode shapes of the damaged plates. This algorithm is applied to the numerical vibration mode shapes of a cantilever plate with different types of damage to illustrate its effectiveness and viability. A comparative study with other two 2-D damage detection algorithms, i.e., 2-D gapped smoothing method (GSM) and 2-D strain energy method (SEM), is performed, and it demonstrates that the proposed 2-D CWT-based algorithm is superior in noise immunity and robust with limited sensor data. The algorithm is further implemented in an experimental modal test to detect impact damage in an FRP composite plate using smart piezoelectric actuators and sensors, demonstrating its applicability to the experimental mode shapes. The present 2-D CWT-based algorithm is among a few limited studies in the literature to explore the application of 2-D wavelets in damage detection, and as demonstrated in this study, it can be used as a viable and effective technique for damage identification of plate- or shell-type structures.
Adequate development of the substrate-to-overlay bond is crucial in repaired concrete structures. Poorly developed bonds may facilitate crack propagation, a concern evaluated through fracture tests. ...However, the scarcity of fracture tests, especially for in-plane shear-type cracks (Mode II), coupled with the reliance on strength-based bond characterizations in field tests, emphasizes the need to understand the relationship between fracture and strength behavior. Therefore, this study compares tensile, shear, and Mode I and Mode II fracture tests in characterizing shotcrete-to-concrete interface bonds with different substrate surface preparation techniques (chipped (C), sandblasted (SB), pressure-washed (PW), and as-cast (AC)). Results indicate that all three test methods are sensitive to the substrate surface preparation technique. The shear bond strengths in C, SB, and AC specimens are over two times the corresponding tensile bond strengths. In contrast, the shear bond strength of PW specimens is about 73% of the corresponding tensile strength. It is also evident that the Mode II fracture and shear behavior closely resemble each other and are more sensitive to surface roughness than the tensile bond strength. The comparative tests conducted in this study can assist in screening surface preparation techniques for cementitious overlays.
A strain energy-based damage identification method for plate-type structures is presented. The concepts of a damage location factor (DLF) matrix and a damage severity correction factor (DSCF) matrix, ...which can be derived from the elemental modal strain energy, are proposed. The damage identification method using the DLF and DSCF is developed for damage localization and quantification in plate-type structures. The method consists of three steps: sensitive mode selection, damage localization, and damage quantification. The proposed method is a response-based damage identification technique which requires the modal frequencies and curvature mode shapes before and after damage. Numerical study demonstrates its viability to correctly detect the damage, approximate the damage area, and estimate the damage severity under high measurement noise and low damage severity conditions. The possibility of damage identification using the partial modal strain energy from the modal strain/curvature mode shape in one direction of plate is also explored based on the numerically simulated data. The method is further implemented on the experimental modal testing data to identify damage at three stages of increasing damage severity on a fiber-reinforced plastic (FRP) sandwich deck panel using a surface-bonded PVDF sensor array. The present DSCF-based damage identification method, as demonstrated in this study, can be used as a viable and effective technique for damage localization and quantification of plate-type structures.
► Novel damage severity correction factor from the elemental modal strain energy is proposed. ► Strain energy-based method is capable of both localizing and quantifying the damage. ► Only using partial modal strain energy makes easier for experimental testing with sensor array.
Based on a boundary layer theory of shell buckling, the semi-analytical solutions for nonlinear stability analysis of anisotropic laminated composite doubly-curved shells with rectangular planform ...subjected to lateral pressure are derived. A new shell model of arbitrary constant curvature and fibre stacking sequences but constant thickness is developed. The governing equations are based on an extended higher-order shear deformation shell theory with von Kármán-type of kinematic nonlinearity and including the effect on stiffness couplings. The nonlinear deformation and initial deflection of shells are both taken into account. The boundary layer equations of buckling for doubly-curved shells are introduced to match the asymptotic solutions satisfying the clamped or simply-supported boundary condition. The closed-form solutions for buckling and postbuckling analysis of an anisotropic shear deformable laminated doubly-curved panel are obtained by the two-step perturbation methods and the boundary layer theory for shell buckling, which is employed to determine interactive buckling loads and postbuckling equilibrium paths. At the same time, the internal quantitative relationship in the asymptotic sense between deflection and rotations of the normal to the middle surface is for the first time obtained. The influences of anisotropic lay-up, change in the stacking sequence, temperature variation, different types of elastic foundation and boundary condition on nonlinear stability behaviour are analysed and discussed. The study provides a good theoretical method for the load-carrying capacity design of composite shell structures.
Modal curvature is more sensitive to structural damage than directly measured mode shape, and the standard Laplace operator is commonly used to acquire the modal curvatures from the mode shapes. ...However, the standard Laplace operator is very prone to noise, which often leads to the degraded modal curvatures incapable of identifying damage. To overcome this problem, a novel Laplacian scheme is proposed, from which an improved damage identification algorithm is developed. The proposed step-by-step procedures in the algorithm include: (1) By progressively upsampling the standard Laplace operator, a new Laplace operator is constructed, from which a Laplace operator array is formed; (2) by applying the Laplace operator array to the retrieved mode shape of a damaged structure, the multiresolution curvature mode shapes are produced, on which the damage trait, previously shadowed under the standard Laplace operator, can be revealed by a ridge of multiresolution modal curvatures; (3) a Gaussian filter is then incorporated into the new Laplace operator to produce a more versatile Laplace operator with properties of both the smoothness and differential capabilities, in which the damage feature is effectively strengthened; and (4) a smoothened nonlinear energy operator is introduced to further enhance the damage feature by eliminating the trend interference of the multiresolution modal curvatures, and it results in a significantly improved damage trait. The proposed algorithm is tested using the data generated by an analytical crack beam model, and its applicability is validated with an experimental program of a delaminated composite beam using scanning laser vibrometer (SLV) to acquire mode shapes. The results are compared in each step, showing increasing degree of improvement for damage effect. Numerical and experimental results demonstrate that the proposed novel Laplacian scheme provides a promising damage identification algorithm, which exhibits apparent advantages (e.g., high-noise insusceptibility, insightful in damage revealment, and visualized damage presentation) over the standard Laplace operator.
A general solution of the vibration of an Euler–Bernoulli beam with arbitrary type of discontinuity at arbitrary number of locations is presented in this paper. To account for the discontinuity term ...induced by various additional elements on the beam, Heaviside's function is used to express the modal displacement of the whole beam by a single function. This general modal displacement function is then solved by using Laplace transformation. This general solution consists of four types of basic modal shapes induced by four corresponding types of discontinuity terms at the discontinuity points. Various discontinuity terms are obtained and expressed by the boundary values of the modal displacement in a recursive way. Consequently, the modal displacement can be determined by examining only the conditions on the boundary. In such a way, the present solution reduces the vibration of beams with arbitrary discontinuities to the same order of the case without discontinuity point. To demonstrate the efficiency and applicability of the present method, three application examples are presented. Calculation example shows that the lead–zirconate–titanate (PZT) actuator should be placed as close to the fixed end as possible to achieve the best excitation effect on a cantilever beam. A new method to calculate the driving-point anti-resonance frequency is also proposed. Numerical results suggest that the variation of driving-point anti-resonance frequency can be used to determine the location and size of crack in beams. Due to the generic nature of the solution and the problem, the present method can be utilized in smart structures modeling and structural health monitoring of beam-type structures.
•Degradation of concrete due to freeze/thaw action is characterized by cohesive fracture test.•The relationship between damage and the number of F/T cycles is established using the nonlinear ...regression analysis.•Probabilistic damage model is established to predict the cyclic freeze/thaw life of concrete.
The durability of concrete with low-degradation aggregates due to cyclic freezing and thawing effect is experimentally studied by characterizing the variance of fracture energy with respect to the number of freeze/thaw (F/T) cycles. Cohesive fracture test is conducted for notched concrete beams subjected to different F/T cycles, and the fictitious crack model-based approach is employed to calculate the fracture energy from the testing data. The relationship between the relative fracture energy and the number of F/T cycles is established using the nonlinear regression analyses. Based on the three-parameter Weibull distribution model, the probabilistic damage analysis is conducted, and the life distribution diagrams are produced according to the probability of reliability/survival concept. The relationships between the life (i.e., the number of F/T cycles) and damage parameter for different probabilities of reliability are obtained, from which the service life of concrete due to cyclic freezing and thawing actions can be determined at any given reliability index. The validation and accuracy of the present models are demonstrated through comparisons between the predicted data by the present models and the test data. The present probabilistic damage model can serve as a reference for maintenance, design and life prediction of concrete structures with low-degradation aggregates in cold regions subjected to cyclic freezing and thawing actions.
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