Search

Data-driven damage detection methods are widely researched and implemented due to the availability of advanced sensing and cloud technologies, where machine learning models are used to process the various data collected from the sensors for damage diagnosis. Supervised methods have shown to be accurate in identifying damages given that they are trained with sufficient historical damage samples. As damage events are rare, supervised methods often face the cold-start problem, that is, insufficient labelled damage samples to initiate model training. Unsupervised methods do not require training and have shown to be practical up to detecting damage presence, but prior knowledge or labelled historical damage samples are still required as references to further locate and quantify the damage. To solve the cold-start issue, a modal-based method, which relates the modal parameters with damages, is proposed to bridge the gap between the unsupervised and supervised methods. Therefore, this work proposes an integration strategy of a modal-based method into a hybrid machine learning-based method for damage detection and localisation of beam-like structures. A two-stage scheme with unsupervised, supervised, and modal-based methods is proposed. The first stage detects damage presence using PCA-FRF as the damage-sensitive feature in an unsupervised manner, and the second stage locates the damages using the first mode shape. Mode shape assessment-based damage localisation is performed at the second stage when no trained model is available due to zero or limited damage samples for training to solve the cold-start and manual labelling issue. Supervised model training starts once there are at least two classes of damage, and the trained model is only used for damage localisation when it surpasses the 90% validation accuracy benchmark. Results showed accuracies of 100%, 100%, and 95.85% for the first stage unsupervised detection, second stage mode shape assessment-based damage localisation and the supervised model-based damage localisation, respectively. [ABSTRACT FROM AUTHOR]

This study aims to make investigation for the free vibration problem of simply supported axial-FGB by applying the Rayleigh method. The model of (power law) is adopted to describe the change in physical mechanical and properties through the axial direction. The computer program is built in this work. The accuracy of Rayleigh method is checked by comparison of the results of Rayleigh method with the results available in literatures and a very good accuracy was found. The combined effects of power-law index, modulus-ratio and density-ratio on the fundamental frequency and mode shapes of axial-FGBs are investigated. The results explain that the non-dimensional frequency parameter at any modulus-ratio is approximately constant when the power-law index increases. When the power-law index is smaller than (1), the effect of modulus-ratio is greater than the effect of density-ratio. While the effect of modulus-ratio is smaller than the effect of density-ratio when the power-law index is greater than (1). Also, when density-ratio equals (1), the dimensionless deflection (or amplitude) increases with reducing of power-law index (β). When the modulus-ratio is smaller than (1), the dimensionless deflection increases with increasing the power-law index (β). From results, the Rayleigh method is able to calculate the natural frequency and mode shape of simply supported axial-FGM beam. [ABSTRACT FROM AUTHOR]

A prevalent issue in rotors is mass unbalance, which leads to synchronous lateral vibrations. In this paper, the critical whirling speeds and global responses of an unbalanced rotor-bearing system with viscoelastic boundary condition are computed using the relationships between the vectors of solution coefficients of differential equations governing the transverse displacements. The mathematical formulation is based on the matrix form of the aforementioned relationships and boundary conditions in the resonance case. The Timoshenko beam model, including the effects of gyroscopic moments is employed. It was found that the presented approach in comparison with the transfer matrix method reduces the matrix product when shaft segments have the same geometric and mechanical properties. A good agreement is found between the results of this study and the findings of studies available in the literature. Furthermore, the eigenvectors for free vibrations of the system were calculated by combining Natanson's technique with the presented approach while considering the derived rotor's characteristic equation after removing the forced term in the equation that describes the forced vibrations. Each obtained forward whirling mode shape describes perfectly the global response in the vicinity of the corresponding forward critical speed. The presented approach can, therefore, be applied to obtain the unbalance responses, whirling speeds, and associated mode shapes of rotor-bearing systems with complex boundary conditions. [ABSTRACT FROM AUTHOR]

This study examined the vibration behavior of a beam with linear spring attachments using finite element analysis. It aims to determine the natural frequency with both consistent/coupled mass and lumped mass matrices. The natural frequencies and corresponding mode shapes were correctly determined which formed the basis of any further noise vibration and severity calculations and impact or crash analysis. In order to obtain eigenfrequencies subject to the attached spring, the characteristic equation was obtained by eigenfunctions expansion whose roots were extracted using the root-finding technique. The finite element method by coupled and lumped mass matrices was then used to determine complete mode shapes against various eigenfrequencies. The mode shapes were then analyzed subject to supports with varying stiffness thereby comparing the analytical and numerical results in case of consistent and lumped masses matrices so as to demonstrate how the present analysis could prove more valuable in mathematical and engineering contexts. Utilizing a consistent mass matrix significantly enhanced accuracy compared to a lumped mass matrix, thereby validating the preference for the former, even with a limited number of beam elements. The results indicated that substantial deflection occurred at the beam's endpoints, supporting the dynamic behavior of the spring-beam system. [ABSTRACT FROM AUTHOR]

This study examined the vibration behavior of a beam with linear spring attachments using finite element analysis. It aims to determine the natural frequency with both consistent/coupled mass and lumped mass matrices. The natural frequencies and corresponding mode shapes were correctly determined which formed the basis of any further noise vibration and severity calculations and impact or crash analysis. In order to obtain eigenfrequencies subject to the attached spring, the characteristic equation was obtained by eigenfunctions expansion whose roots were extracted using the root-finding technique. The finite element method by coupled and lumped mass matrices was then used to determine complete mode shapes against various eigenfrequencies. The mode shapes were then analyzed subject to supports with varying stiffness thereby comparing the analytical and numerical results in case of consistent and lumped masses matrices so as to demonstrate how the present analysis could prove more valuable in mathematical and engineering contexts. Utilizing a consistent mass matrix significantly enhanced accuracy compared to a lumped mass matrix, thereby validating the preference for the former, even with a limited number of beam elements. The results indicated that substantial deflection occurred at the beam's endpoints, supporting the dynamic behavior of the spring-beam system.

The first goal of this research was to document the process of using the MODAL analysis system of the ANSYS 2024R1 student edition to create a finite element model of the modes and frequencies of vibration of one basketball rim and backboard design. This finite element model included the use of steel for the rim and its mount, a tempered glass backboard, and an aluminum frame behind the backboard. After a mesh was created, fixed support boundary conditions were applied to the four corners of the aluminum frame, followed by the theoretical modal analysis. The second goal was to validate this model by comparing the finite element calculated mode shapes and frequencies to the empirical modal analysis previously measured at the United States Military Academy at West Point, New York. Five mode shapes and frequencies agreed rather well between the theoretical finite element analysis and previously published empirical modal analysis, specifically where the rim was vibrating in the vertical direction, which was the direction that the accelerometer was aligned for the empirical modal analysis. These five modes were addressed from a finite element model validation standpoint by a 99.5% confidence in a 98.09% cross-correlation with empirical modal analysis data, and from a verification standpoint by employing a refined-mesh. However, three theoretical mode shapes missed by the empirical modal analysis were found where the vibration of the rim was confined to the horizontal plane, which was orthogonal to the orientation of our accelerometer.

This study aims to analyze the in-plane free vibrations of arches comprising the laterally symmetric functionally graded materials. Emphasis is placed on the circular arch whose material properties vary laterally symmetrically about the centroidal axis by a power-law function. The differential equations governing the mode shape of the arch were derived under the boundary conditions and were numerically solved to calculate the natural frequencies using the Runge–Kutta and Regula–Falsi methods. Calculation results of this study for natural frequencies compare well with those of the finite element method. The effects of various arch parameters on natural frequencies are highlighted and discussed in detail. [ABSTRACT FROM AUTHOR]

Full-field optical techniques provide valuable information for the analysis of mode shapes thanks to their high density of measurement points, providing very detailed maps, in a non-invasive way that avoids alterations of the dynamic behaviour of the specimen. Digital image correlation and thermoelastic stress analysis are two of the most interesting ones. The first provides displacement fields that can be three-dimensional if a calibrated stereoscopic system is used. The second uses a thermographic camera to determine the stress invariant. Given the complementary nature of these magnitudes, this study deals with the integration of the displacement and stress fields by means of a calibrated set of a stereoscopic system and a thermographic camera which, through spatial triangulation, allow the association of the measurements to the same spatial point on the specimen. For this purpose, typical laboratory setups have been carried out for the characterisation of operational modal shapes of resonances. The integration has allowed a more accurate interpretation of the behaviour of the specimen, identifying the regions with the highest mechanical stress. This shows the advantages of integration compared to the isolated analysis of displacement and/or stress measurements that are usually carried out and proves the potential for the development of optical techniques at a scientific and industrial level, opening up new avenues of study. [ABSTRACT FROM AUTHOR]

Functionally graded materials are innovative composites of hybrid ceramics and metals that exhibit excellent mechanical performance in harsh temperature environments and under various external loads. In this study, the free vibrations of Timoshenko circular arches, made of functionally graded materials in the axial direction, are investigated. The material properties of Young's modulus and mass density of the arch vary according to a symmetric quadratic function along the arch axis. Differential equations governing the free vibration of the arch including the rotatory inertia and shear deformation, called the Timoshenko arch, are derived. A novel numerical solution method is developed to calculate the natural frequencies and mode shapes of the arch. Parametric studies of the modular ratio, shear correction factor, shear modulus ratio, and slenderness ratio on the natural frequencies are conducted, and the results are reported in the tables and figures. [ABSTRACT FROM AUTHOR]

The effect of structure on the vibration response was explored for four piano soundboards with different but commonly adopted structures. The vibration response was obtained using the free-vibration method, and the values of the dynamic modulus of elasticity and dynamic shear modulus obtained using the free-vibration frequency method (EF and GF) were compared with the dynamic modulus of elasticity obtained using the Euler beam method (EE) and dynamic shear modulus obtained using the free-plate torsional vibration method (GT), respectively. It was found that the soundboards with different structures had different vibration modes and that excitation at different locations highlighted different vibration modes. For all the soundboards analyzed, the EE and GT were higher than EF and GF by 2.2% and 24.3%, respectively. However, the trends of the results of these methods were the same. The four piano soundboards with different structures possessed varying dynamic moduli of elasticity and dynamic shear moduli. These rules are consistent with the grain directions of the soundboards and the anisotropy of the wood (the direction of the units of the soundboards). The results show that the vibration mode of the piano soundboard is complex. The dynamic elastic modulus of the soundboard can be calculated using the Euler beam method. The results provide a reference for studies on the vibration response, material selection, production technology, and testing of piano soundboards. [ABSTRACT FROM AUTHOR]

The development of operational modal analysis (OMA) techniques has enabled the monitoring of large civil engineering structures, such as long-span bridges and high-rise buildings. However, implementing these techniques in real-world testing sites with limited resources remains a challenge. This study introduces a novel approach to obtain the modal characteristics of a box girder bridge in a more cost-effective and simplified manner, with experiments performed in a gap of more than 4 years (Years: 2018 and 2023). The study proposes two output-only frequency domain system identification techniques, namely roving reference normalized power spectrum and roving reference frequency domain decomposition, as part of the OMA-based approach. These techniques involve measuring responses from a pair of roving accelerometers. The collected vibration data records the concrete bridge's response to various external factors, including vehicular traffic on the carriageway, pedestrian movement, river flow, and wind. Despite weak environmental excitations and sensor noise, the findings suggest that accurate modal properties can still be extracted. The two proposed OMA approaches yielded five mode shapes and modal frequencies with closely matching results. When these experimental findings are compared with the numerical results, they exhibit a notable level of consistency. The paper identifies the dynamic characteristics of bridge structures from ambient vibration responses using only two accelerometers with two-point roving technique. This is especially important in real-world testing sites where data are inevitably noisy, unlike in laboratory environments. Additionally, it significantly reduces the cost of the bridge health monitoring. [ABSTRACT FROM AUTHOR]

To study the impact of the trailing-edge wear on the vibrational behavior of wind-turbine blades, unworn blades and trailing-edge worn blades have been assessed through relevant modal tests. According to these experiments, the natural frequencies of trailing-edge worn blades -1, -2, and -3 increase the most in the second to fourth order, the fifth order increases in the middle, and the first order increases the least. The damping ratio data indicate that, in general, the first five-order damping ratios of trailing-edge worn blades -1 and trailing-edge worn blades -2 are reduced, and the first five-order damping ratios of trailing-edge worn blades -3 are slightly improved. The mode shape diagram shows that the trailing-edge worn blades -1 and -2 have a large swing in the tip and the blade, whereas the second- and third-order vibration shapes of the trailing edge-worn blade -3 tend to be improved. Overall, all these results reveal that the blade's mass and the wear area are the main factors affecting the vibration characteristics of wind turbine blades. [ABSTRACT FROM AUTHOR]

Background: Failure of the structure may be avoided if, the damage is noticed at an early stage and proper remedial work is performed. In this context, this paper presents a detection of structural damage in steel beams, which are major load carrying members in bridges and buildings. Method: In the present study, the Generalized Flexibility Energy Quotient Difference Index (χ) is determined at various locations of the beam by introducing the damage by means of a cut by 0.5 mm to 2.5 mm at an interval of 0.25 mm. In practice, it is very difficult to capture all the modes of vibration. Hence, the method followed uses the first mode of vibration only for quantifying the magnitude of damage and its location. The validation is done between numerical simulations and experimental works for the estimation of first frequency. The efficiency of the method is tested by inducing the damage very close to the support. In ANN, the depth of cut at various locations of the beam and χ is utilized in the input layer. Results: The predicted depth of cut or severity of damage from the output layer of ANN model is compared with the actual depth of cut induced in the beam. Finally, the polynomial equations are formulated for the damaged elements, which are the major contribution of the present study. These equations can be used as a ready reckoner to estimate the actual depth of cut in the beam. This approach is validated through a beam with fixed ends and two-span beam, and the results indicate that this method is very much beneficial in preventing the structural failure. [ABSTRACT FROM AUTHOR]

Structures are subjected to a variety of environmental and loading conditions over time, and minor damage to structural elements may occur. By timely identifying damage and repairing damaged locations, it is possible to prevent the spread and development of damage to other elements and, as a result, the overall destruction of the structure. This article discusses the identification and determination of the location of damage in steel plates based on the use of the primary and secondary shapes of vibration modes and the analytical method of two-dimensional wavelet analysis. Modelling and frequency analysis of the plate were performed in ABAQUS software, and the primary and secondary mode shapes were extracted. To determine the location of the damage, a damage detection index (DDI) was proposed based on the angle between the primary and secondary mode shape vectors and the diagonal detail coefficients obtained from the wavelet analysis of the primary and secondary mode shapes. The results showed that by using this index, damage can be identified by identifying peaks resulting from irregularities and disturbances. Also, the DDI value of the damage was dependent on the severity of damage occurring in a damaged situation, and the height of the disorder peaks increased with increased damage only at that damage position.

The integration of Operational Modal Analysis (OMA) and Finite Element Model (FEM) techniques has proven to be a valuable approach for evaluating and maintaining the health of such structures. OMA extracts dynamic characteristics from a bridge's responses to ambient vibrations, while FEM employs computational models to simulate and compare these dynamic behaviours. This comprehensive methodology ensures an accurate representation of the bridge's behaviour and its correlation with real-world conditions. However, a significant challenge arises in assessing the Ultra High Performance Fiber Reinforced Concrete (UHPFRC) pedestrian bridge in Klang, Selangor, launched in October 2022, due to limited available information about OMA and FEM on UHPFRC. This research aims to develop FEM and conduct ambient vibration tests to obtain modal parameters. Moreover, the study investigates OMA techniques in the context of weak excitation sources, filling a critical knowledge gap. By comparing experimental results with FEM, this research provides insights into the feasibility and reliability of OMA under challenging environmental conditions. The principal results reveal significant percentage differences in natural frequencies between FEM and OMA, with the most notable disparities occurring in the first mode. Nevertheless, the mode shapes extracted from OMA closely resemble those from FEM. In conclusion, this research enhances the understanding of UHPFRC pedestrian bridge behaviour and modal analysis techniques. [ABSTRACT FROM AUTHOR]

Purpose: This paper investigates into the existence of the second frequency spectrum of an uniform Timoshenko beam, which has been debated in the literature. The equivalence of the fourth order partial differential equation to two second-order partial differential equations of an uniform Timoshenko beam from the perspective of boundary conditions, another topic of debate in the literature, is examined by using the concept of observability of a state space model. Methods: Natural frequencies and mode shapes are computed using the new approach developed by the author in his previous papers, which is based on the spatial state space analysis. Results: Numerical results are presented for pinned-pinned, clamped-free, clamped-clamped and clamped-pinned Timoshenko beams. Conclusions: It has been found that the second frequency spectrum exists irrespective of boundary conditions. Also, boundary conditions for the fourth-order partial differential equation can be derived from the boundary conditions for two original second-order partial differential equations. [ABSTRACT FROM AUTHOR]

In this study, the modified first-order shear deformable theory (FSDT) is applied to analyze the resonant characteristics of piezoelectric (PZT) moderately thick plate vibrators with different thicknesses. A simple and straightforward simplification method between mechanical and electrical functions is also proposed based on the modified FSDT. The natural frequencies and associated mode shapes of piezoelectric plates with completely free boundary are analyzed. The displacement fields of the flexural modes are presented based on the superposition method. This analytical method provides a strong-form novel solution for the flexural-dominated motion's out-of-plane and in-plane coupling displacement fields. The solutions of displacement functions, which are obtained from the superposition method, show excellent convergence for numerical calculation. To verify the validity of the theoretical solution, the resonant frequencies and the corresponding mode shapes are compared with that obtained by the finite element method (FEM) and experimental measurements using the amplitude-fluctuation electronic speckle pattern interferometer (AF-ESPI) technique. According to the electromechanical formula and the derived theoretical solution, four types of electrode are designed to excite the moderately thick PZT specimen for examining the application feasibility of the proposed method. It is shown in this study that the theoretical analysis, numerical calculation, and experimental measurement are fully compared, and excellent agreements of the piezoelectric moderately thick plate are also obtained. [ABSTRACT FROM AUTHOR]

This study numerically examines the changes in dynamic properties of fire-damaged steel trusses made of square hollow sections subjected to uniform and non-uniform heating scenarios. After verifying the numerical models at both ambient and elevated temperatures, a vast number of the simulations were analysed using non-linear finite element software to evaluate the effects of fire scenarios, truss types, and fire-damaged levels on the fire dynamic characteristics of square hollow section Warren, Howe, and Pratt trusses. The results indicated that the natural frequency of steel trusses significantly decreased as the fire-damaged level increased. In the case of local fire, the natural frequencies of the trusses began to drop suddenly at temperatures above 550 °C. Whereas the drop in the natural frequency of the uniformly heated trusses started at even much lower temperature levels. Moreover, the decrease in the natural fundamental frequencies of the uniformly heated trusses was lower than the reduction rate of the modulus of elasticity at high temperatures due to the large non-linear deformations. Since the modification of the stiffness of the truss by simply the reduction factor of the elastic modulus of the steel may be inappropriate to calculate the fundamental frequency of the trusses in the local and global fires, a new method was introduced to calculate the fundamental frequency value of the steel trusses in the fire. [ABSTRACT FROM AUTHOR]

It is crucial to perform routine bridge maintenance in order to evaluate the structure's current state. As a result, it is possible to guarantee that the bridge structure can offer services that are both comfortable and secure. The bridge structure being able to reach the service life as planned is another goal that can be accomplished. Visual inspection or the use of some currently popular sensors can be used to monitor the condition of the bridge. The dynamic properties of a structure including modal frequency and mode shape will be used to determine the structure's present and potential future conditions. Using a velocitymeter, vibration data collection is conducted as the first step. The next step is analyzing data to determine natural frequency. The fundamental frequency of the Tugu Suharto bridge structure in Semarang was determined to be 3.995 Hz. Future bridge structure condition monitoring can be done using frequency data and finite element model. The condition of bridge infrastructure in the future for one city is an important thing that must be considered. Some bridges are classified as structurally deficient, and many bridges are nearing the end of their design lives. The next generation of Semarang highway bridges is currently being designed and built, but existing bridges still need to be maintained through proper inspection and load rating. In order to incorporate structural modeling, instrumentation, and nondestructive testing into the design, construction, and management of bridges, this study proposes an objective load rating protocol. Using information gathered from structural health monitoring (SHM), a baseline structural model is developed and verified. The load rating factors of the bridge are then determined using the structural model under both real-condition and simulated damaged conditions. [ABSTRACT FROM AUTHOR]

This study investigates the feasibility of an alternative structural health monitoring (SHM) technique for an existing, post-tensioned, prestressed concrete bridge in Niigata, Japan. Currently, a static SHM system is in place to detect the progress of damages within the bridge. However, the existing system cannot properly monitor the structural health of the bridge including the periodic vibration, which is one of the damage-sensitive features of interest. Therefore, to effectively detect the real-time performances of the bridge, a three-dimensional (3D) Finite Element (FE) model was developed as a reference and verified using on-site loaddeflection test results. After validating the reference FE model, different damage scenarios, such as degradation of concrete, corrosion & rupture of steel tendons and missing tendons, were incorporated in the FE models. Based on non-linear structural and Eigenvalue analyses, natural frequencies and mode shapes of the bridge remain constant even after careful consideration of all types of damages in the FE model. However, vertical displacements are observed to increase for the damage scenarios. Although the effect of tendon rupture and corrosion showed negligible influences on the vertical displacement, the deterioration of the concrete largely influenced the vertical displacement. Additionally, crack widths were found to vary with damage types. Brifely, this study recommends some effective indicators to monitor the structural conditions of the bridge using FE analysis (FEA). [ABSTRACT FROM AUTHOR]

Analytical equations that describe the dynamic behavior of beams with a soft clamped end are very little treated in the literature. The paper aims to solve this problem by introducing a stiffness in the hinged end of the beam, respectively by comparing the bending moment in the clamped end with the slope in the hinge of the same end of the beam. The other end of the beam is permanently hinged. The characteristic equation for determining the eigenvalues and the modal function is deduced. The results show the first four vibration modes for seven stiffness values and the eigenvalues for eleven cases of soft clamped end. [ABSTRACT FROM AUTHOR]

Structures are subjected to a variety of environmental and loading conditions over time, and minor damage to structural elements may occur. By timely identifying damage and repairing damaged locations, it is possible to prevent the spread and development of damage to other elements and, as a result, the overall destruction of the structure. This article discusses the identification and determination of the location of damage in steel plates based on the use of the primary and secondary shapes of vibration modes and the analytical method of two-dimensional wavelet analysis. Modelling and frequency analysis of the plate were performed in ABAQUS software, and the primary and secondary mode shapes were extracted. To determine the location of the damage, a damage detection index (DDI) was proposed based on the angle between the primary and secondary mode shape vectors and the diagonal detail coefficients obtained from the wavelet analysis of the primary and secondary mode shapes. The results showed that by using this index, damage can be identified by identifying peaks resulting from irregularities and disturbances. Also, the DDI value of the damage was dependent on the severity of damage occurring in a damaged situation, and the height of the disorder peaks increased with increased damage only at that damage position. [ABSTRACT FROM AUTHOR]

Bridge inspections performed by the response of the moving vehicle have been widely studied because of its mobility and efficiency, whereas mode shapes extracted by the moving vehicle have low order and limited accuracy in existing studies. In this study, experimental studies are conducted in which a stationary shaker is used to excite the steady-state-forced vibration of the bridge, and the bridge vibration is collected by an accelerometer installed on a moving vehicle. Accurate multiorder mode shapes are obtained by extracting the vehicle acceleration envelope. First, a theoretical derivation of the method is provided, and an extraction process for field tests is proposed. Then, a model test of a three-span continuous beam bridge and a field test of a two-span continuous girder bridge are conducted. To verify the accuracy of the mode shapes extracted by the moving vehicle, reference data are obtained by finite-element modal analysis and by using the hammer test. Through a difference analysis of accelerations between the parked vehicle and the bridge deck under the test vehicle, the ability of the designed test vehicle to collect bridge vibration in different frequency bands is evaluated. Finally, the first five mode shapes of the bridge model and the first six mode shapes of the field bridge are extracted by a moving test vehicle, and the effects of vehicle speed and excitation amplitude on mode shape extraction are analyzed. The results show that multiorder mode shapes can be accurately extracted by a moving test vehicle. [ABSTRACT FROM AUTHOR]

This research extends a method for direct estimation of Poisson's ratio from mode shapes of plates with hinged-hinged boundary conditions to include combinations of clamped and free boundary conditions. Using finite element simulations, we observe the effects of boundary conditions on the estimate of Poisson's ratio using the combination of Time-Average Scanning Digital Holography and Cornu's method. First, we introduce the abstraction of the span-to-width ratio to an effective antinode region. This abstraction enables us to extend the direct estimation technique to plates with various boundary conditions. Second, for long and thin enough plates, the effects of boundary conditions become negligible and Cornu's method is sufficient for direct estimation of the true value of Poisson's ratio from an out-of-plane bending mode shape. We note that for many situations, the necessary plate dimensions could be a limitation. Therefore, as a third concept, we discuss the behavior of the direct estimate of Poisson's ratio with respect to each type of boundary condition. Ultimately, this research initiates a path forward for a common processing technique for making a direct estimate of Poisson's ratio across different types of opposing boundary conditions for thin plates.

Vibration-based damage detection is a range of methods that utilizes the dynamic response of a structure to evaluate its condition and detect damage. It is an important approach for structural health monitoring and has drawn much attention from researchers. While multiple reviews have been published focusing on different aspects of this field, there has not been a study specifically examining the recent development across the range of methods, including natural frequency, mode shape, modal curvature, modal strain energy, and modal flexibility-based damage detection methods. This paper aims to fill this gap by reviewing the recent application of these methods in civil structures, including beams, plates, trusses, frames, and composite structural members. The merits and limitations of each method are discussed, and research opportunities are presented. This broader review also provides an opportunity for critical comparison across this range of methods. While predominantly reviewing experiment-based studies, this review also considers some numerical studies that may motivate further research.

In this study the primary objective is to design prediction model for the free vibration analysis of thin circular cylindrical steel silos having various aspect ratios in empty and varying filled conditions for different types of closures. A finite element method (FEM) is used to carry out the free vibration analysis of steel silos. It is found that the effect of different aspect ratios slender, intermediate slender and squat steel silos is very significant for dynamic response of silo. The silos are considered having open, flat and cone type of closures at its top end. The clamped-free (cantilever) boundary condition is taken for this approach as actual silos are fixed at flat-base. The structural mass of thin cylindrical shell steel silo is made constant for a particular height and diameter. The eigenvalues of the thin cylindrical shell steel silos are extracted by using block Lanczos method. The free vibrations of thin cylindrical shell steel silo with different aspect ratios, radius to thickness ratio are studied. From the present studies it is seen that as aspect ratio increases the fundamental frequency is reduced in empty silo. It is more in the case of squat silo. It can be seen that the fundamental frequency is less in the case of flat closure in all the aspect ratios of the silo. The frequency values are more in the case of cone closure is observed. Also as the mode number increases the modal frequency value increases. Further, as the filling level is increased the modal frequency also increases. Finally, regression approach is adopted for predicting the mode frequency of empty and filled silos for wide range of aspect ratios.

Usually, only one surface or one side of 3D structures is measured in Scanning Laser Doppler Vibrometer (SLDV) tests due to test setup and instrumentation limitations. However, in this work, we demonstrate an approach to overcome these limitations while also using an SLDV that provides high spatial resolution measurement. In the case of a wind turbine blade, only one surface is typically measured. In most scenarios, only focusing on one surface of the blade is sufficient to characterize the dynamics of the global blade modes. However, as we show measurement of both surfaces offers valuable insights to explore both the global blade modes and the relative motions of the two surfaces of the blade. This work proposes and applies a new method of experimental modal testing on both surfaces of the wind turbine blade using a high spatial resolution 3D SLDV. The two surfaces of the wind turbine blade are scanned by the 3D SLDV respectively under the same global test coordinate system defined by several alignment objects. Then the two surfaces are stitched together to build the blade mode shapes of both surfaces. In the current testing, a total of over 1,500 points (4,500 response degrees of freedom for the 3D measurement) are scanned from both surfaces of the blade in a non-contact fashion to obtain the flap-wise, edge-wise, and torsional mode shapes of the blade. The orthogonality of the measured mode shapes, either one surface or both surfaces, is validated by the correlation tool, Modal Assurance Criterion (MAC). The effectiveness of the two-surface measurement is demonstrated by comparing the drive point Frequency Response Function and by correlating the mode shapes from the two surfaces. With the high spatial resolution 3D SLDV measurement, local panel modes of the wind turbine blade are observed from the mode shapes. Especially the panel breathing mode can only be revealed due to the two-surface measurement. This work also provides a useful reference for the wind turbine blade designers and researchers for design, structural analysis, and reliability study on the wind turbine blade. The two-surface measurement technique proposed in this work is demonstrated on a wind turbine blade, and it will also be applicable for other types of two-surface shell-type structures. [ABSTRACT FROM AUTHOR]