Non-destructive Vibration Testing Research Articles

The prediction of MOE of bamboo-wood composites by ANN models based on the non-destructive vibration testing

The mechanical properties of bamboo-wood composites (BWC) remain crucial for potential further employment. Nevertheless, the approach to detecting its mechanical properties is time-consuming and wasteful of resources. The goal to this research is to create an artificial neural network (ANN) model to predict the modulus of elasticity (MOE) of BWC using non-destructive testing methods of bending and longitudinal vibration to frequency, and to compare the results of the ANN with multiple linear regression (MLR). In comparison to the ANN model trained using spectrum parameters, the results reveal that the ANN model built using characteristic parameters delivers greater prediction performance. The ANN models had R2 and MAPE values of 0.98 and 3.187%, respectively. Using the findings of this work, the MOE of BWC can be calculated in a short amount of time with a low error rate, allowing researchers to better grasp the practicality of BWC in structural applications. Its artificial neural network model might be used to track the quality of BWC in the production process.

RC beams damaged by cracking and strengthened with NSM CFRP/GFRP rods

The near surface mounted (NSM) method of inserting fiber reinforced polymer (FRP) elements (rods or lamina) into notches has been shown to be a good way for restoring reinforced concrete (RC) elements. The knowledge about the use of Glass-FRP rod following the NSM to reinforce RC beams is limited. This paper deals with the analysis of static and dynamic behaviour of RC beams with and without strengthening. The response of RC beams was assessed at different concrete’s damage level by non-destructive vibration tests. First, a couple of beams have been analysed: one RC beam subjected to bending and under vibration tests; another one beam, damaged by bending and strengthened with NSM Carbon-FRP rods tested again under vibration. Further, one RC beam damage was analysed under bending and vibration tests without strengthening; successively, the beam model with NSM GFRP rod has been tested following the same loading path. Below experimental results are shown and commented; in particular, changes in frequency values are related to the evolution of damage level affected RC beams with NSM CFRP and GFRP rods.

Non-destructive Consolidation Assessment of Historical Camorcanna Ceilings by Scanning Laser Doppler Vibrometry

This paper presents a procedure for the evaluation of the conservation state and restoration efficiency of nineteenth century camorcanna vaults based on the analysis of objective features extrapolated from non-destructive vibration testing data. The camorcanna vault in “Salone Grande” of the ninteenth century Villa Greppi in Monticello Brianza, near Milan, Italy, was chosen as an application example. Non-contact scanning Laser Doppler Vibrometry was exploited for the evaluation of the dynamic behaviour of the vault before and after rehabilitation. In the first section, the frescoed structure in question, a reed ceiling spread with mortar, is described and possible related aging problems, e.g painting detachment, are highlighted. In Sects. 1 and 2, traditional and innovative non-invasive diagnostic techniques are illustrated, with particular attention to Laser Doppler Vibrometry. In Sect.3, the case study of Villa Greppi is illustrated, reporting on the restoration intervention, the equipment used on site and how the measurements were taken. While in Sect.4 the results are shown, objective feature indices are defined and conclusions are drawn.

Vibration-based damage identification for reinforced concrete slab-type structures using fiber-optic sensors and random decrement technique

This paper presents and evaluates a damage identification system for reinforced concrete (RC) slab-type structures based on non-destructive vibration testing, Random decrement (RD) signal processing technique, and embedded smart network of fiber-optic sensors. The proposed system aims to overcome the challenges associated with the use of electrical sensors and signal processing of noisy dynamic data. Two experimental modal analysis investigations have been conducted. First modal testing focuses on investigating the capability of fiber-optic sensors and Multi-channel random decrement (MCRD) processing technique to locate damage in RC slabs through changes in the first mode shape response with damage. The second modal testing focuses on the detection of damage intensity using the RD technique through the change in frequency and damping dynamic parameters.
 The results show that RD technique can be used effectively to extract the free vibration response of RC slab-type structures; fiber-optic sensors are more sensitive to capture damage severity in comparison to electrical accelerometer sensors, especially, at steel yielding and failure load; MCRD technique can be used effectively to generate mode shapes for RC slabs based on fiber-optic grating FBG sensors measurements. On the other hand, electrical strain gauges were noisy and it was difficult to obtain any measurable data; A damage identification system based on non-destructive vibration testing, MCRD processing technique, and using an embedded smart network of fiber-optic sensors can estimate accurately the damage location through changes in the first mode shape.

Natural Frequencies Reduction of RC Slab Subjected to Incremental Concentrated Loads

Reinforced concrete slabs are frequently used in many engineering structures such as buildings and bridges. Damages in an engineering structure including reinforced concrete slab are classified as light, moderate, and severe cracks. A special treatment is required for every typical crack-damage to strengthen its structure. The reinforced concrete slab experiencing cracks reduce stiffness as well as its strength. An experimental program was set up to establish a relation between cracks and changes of a dynamic system characteristics of the slab through natural frequencies. The aim is to perform experimental modal analysis (EMA) as a non-destructive vibration testing method for diagnosing the structural integrity of the slab. For this purpose, two RC square slabs specimens of dimensions 1200mm x 1200mm x 40mm were used. As a first part of the project, a reinforced concrete slab was subjected to an increasing partially concentrated loads at the slab’s center to introduce cracks. After each incremental load steps (5, 10, 12kN) the slab was unloaded. Then, a free-free set-up for the slab was established by using the flexible elastic ropes (bungee cords). After the dynamic test of 5, 10 and 12kN loads, the slab was strengthened using external CFRP sheets (type TR30S). Next, experimental modal analysis was performed to establish a relation between cracks and changes in natural frequencies of the slab. The overall trend of frequency decrease after occurring damage that would be expected for all modes. However, it is not guaranteed all modes have same sensitivity to the applied load that inflicts severe cracks.

Operational modal analysis of a high-rise multi-function building with dampers by a Bayesian approach

The field non-destructive vibration test plays an important role in the area of structural health monitoring. It assists in monitoring the health status and reducing the risk caused by the poor performance of structures. As the most economic field test among the various vibration tests, the ambient vibration test is the most popular and is widely used to assess the physical condition of a structure under operational service. Based on the ambient vibration data, modal identification can help provide significant previous study for model updating and damage detection during the service life of a structure. It has been proved that modal identification works well in the investigation of the dynamic performance of different kinds of structures. In this paper, the objective structure is a high-rise multi-function office building. The whole building is composed of seven three-story structural units. Each unit comprises one complete floor and two L shaped floors to form large spaces along the vertical direction. There are 56 viscous dampers installed in the building to improve the energy dissipation capacity. Due to the special feature of the structure, field vibration tests and further modal identification were performed to investigate its dynamic performance. Twenty-nine setups were designed to cover all the degrees of freedom of interest. About two years later, another field test was carried out to measure the building for 48h to investigate the performance variance and the distribution of the modal parameters. A Fast Bayesian FFT method was employed to perform the modal identification. This Bayesian method not only provides the most probable values of the modal parameters but also assesses the associated posterior uncertainty analytically, which is especially relevant in field vibration tests arising due to measurement noise, sensor alignment error, modelling error, etc. A shaking table test was also implemented including cases with and without dampers, which assists in investigating the effect of dampers. The modal parameters obtained from different tests were investigated separately and then compared with each other.

Inverse method to identify crack parameters in multi-span beam using genetic algorithm

The increased flexibility due to the presence of an open crack in the multi-span beam is made bases for identification of crack location and size. The genetic algorithm is coupled with the inverse dynamics of the cracked beam to get effective solution. The modal parameters, obtained through non-destructive vibration testing, are the input to the code and the location and size of crack are the output. The crack is modeled as rotational spring, and support conditions are generalized in the formulation for cracked multi-span beam.

A method for nondestructive mechanical testing of tissues and implants.

Numerous tests have been used to elucidate mechanical properties of tissues and implants including tensile, compressive, shear, hydrostatic compression, and three-point bending in one or more axial directions. The development of a nondestructive test that could be applied to tissues and materials in vivo would promote the analysis of tissue pathology as well as the design of implant materials. The purpose of this article is to present the results of preliminary studies demonstrating nondestructive in vitro testing of a tissue model, decellularized human dermis, and a model implant, silicone rubber, using a combination of optical coherence tomography (OCT), and vibrational analysis. The results presented suggest that nondestructive vibrational testing of tissues and materials can be used to determine the modulus of polymeric materials and the results are similar to those found using tensile stress-strain measurements. The advantage of this method is that the modulus can be obtained from vibrational methods without having to approximate the tangent to the stress-strain curve, which is difficult for nonlinear materials that have a rapidly changing slope. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 15-22, 2017.

Non-Destructive Vibration Tests on Reinforced Concrete Structures

The purpose of this paper is looking at the dynamic response of existing reinforced concrete structures which have possibly sustained various levels of damage, a set of tests need to be identified that will be able to detect damage and quantify the damage if damage exists. In this work it is presented a further study on the effect of damage on the behavior of reinforced concrete beams. In particular, the non-linear behavior of these beams is considered once significant cracking has been introduced, outlining the stage of testing carried out in dynamic field.

A Vibration-Based Approach for the Estimation of the Loss of Composite Action in Timber Composite Systems

This paper presents a novel approach for the determination of the loss of composite action for timber composite systems using only measurements from non-destructive vibration testing. Traditionally, the composite action of a system is evaluated from static load testing using deflection measurements. However, static load testing is expensive, time consuming and inappropriate for existing flooring systems. The method proposed in this paper is based on the Damage Index (DI) method, which uses changes in modal strain energies, to detect locations and severities of damage. In the proposed method, a new Loss of Composite Action Index (LCAI), which is derived from direct mode shape measurements obtained from dynamic testing, is introduced to evaluate the loss of composite action. The proposed method is tested and validated on numerical and experimental models of a timber composite beam structure, which consists of two timber components that are connected with different numbers of screws to simulate various degrees of partial composite states. The results obtained from the new method are very encouraging and show a clear trend of the proposed dynamic-based LCAI in indicating the loss of composite action in the investigated timber composite structure.

Structural Steel Plate Damage Detection using Non Destructive Testing, Frame Energy based Statistical Features and Artificial Neural Networks

Abstract This paper discusses about the detection of damages present in the steel plates using nondestructive vibration testing. A simple experimental model has been developed to hold the steel plate complying with the simply supported boundary condition. Vibration patterns from the steel structure are captured based on the impact testing using a simple protocol. The vibration signals in normal condition of the steel plate are recorded. The damages of size 512 |x m to 1852 |j, m are simulated manually on the steel plate using drill bits. The vibration signals in the fault condition of the steel plate are collected. The captured vibration signals are preprocessed and time domain based feature extraction algorithms are developed to extract features from the vibration signals. The conditions of the steel plate namely healthy and faulty are associated with the extracted features to establish input output mapping. A feed-forward neural network is modeled to classify the condition. The neural network parameters are adjusted to train the network. The performance of the network is calculated using Falhman criterion.

Dynamic characteristics and model updating of damaged slab from ambient vibration measurements

This paper reports a field investigation using ambient vibration testing on a damaged floor slab of a reinforced concrete frame building. Due to unexpected heavy rainfall, the hill slope at the rear of building failed triggering a major landslide and causing major damage to the perimeter beams and parts of the slab on the first floor. The modal parameters namely natural frequencies and mode shapes were acquired using output only identification technique and the results obtained from the undamaged and damaged floor slabs were compared. It was observed that there was a 25–53% drop in natural frequencies of the damaged slab compared to the undamaged slab, with a much bigger drop for the lower modes. The irregularities in mode shapes identified correlates with the location of the cracks as revealed from visual examination on the damaged slab. Two finite element models of the slab were created using a finite element software package. The damaged slab was updated manually so as to match the modal parameters obtained experimentally. The results from this study further highlight the possibility and feasibility of using non-destructive vibration testing for condition monitoring of structures over more conventional testing techniques.

Damage location vector: A non-destructive structural damage detection technique

This paper presents a method for structural damage detection using frequency response functions (FRF) obtained from non-destructive vibration tests. It investigates the case of early structural damage in which there is no appreciable change in mass and damping. The resulting change in structural stiffness matrix is reflected in changes of FRF data which can be exemplified by the evaluation of damage location vector (DLV). This evaluation requires the dynamic stiffness matrix of the undamaged (virgin) structure and the change in frequency response functions of the currently damaged structure. In this paper the former is obtained from a finite element model of the virgin structure and the latter are obtained from the finite element modelling (FEM) and from impact hammer test. The method is applied to a space truss structure and a plate structure. Effects of noise, both numerically simulated and measured are also investigated. Preliminary results show that this method of Damage Location Vector can overcome the problems of coordinate incompatibility and noise and deliver encouraging results on damage detection.

Temperature-controlled fiber Bragg grating dynamic strain detection system

A fiber Bragg grating (FBG) measurement system for dynamic strain detection has been developed. It exploits a temperature-controlled FBG as a small-band filter to measure the strain-induced wavelength shift of structurally integrated FBG sensors. This interrogation method realizes an optimal dynamic performance of the sensor also under the influence of environmental temperature changes. This has been confirmed relative to a conventional reference sensor under simulated in situ conditions in a laboratory test. The FBG system can be applied for nondestructive vibration testing of geotechnical structures, e.g. bridges and borepiles.

Nondestructive Evaluation of Tuned-Mass-Damper-Type Vibration Absorbers Using Vibration Signatures

Nondestructive evaluation methods are often essential in order to objectively assess the condition of structural and ancillary systems for bridges, particularly in cases where visual methods provide only limited or subjective data and the function of the systems being evaluated may not be disturbed using destructive evaluation techniques. This paper describes a nondestructive evaluation procedure that was developed to objectively assess the current condition of a system of 920 aged vibration absorbers installed on a long span cantilever truss bridge. The vibration absorbers, which are essentially tuned mass dampers consisting of a steel weight attached to the end of a viscoelastic rubber stem, were installed soon after the bridge was opened to mitigate the effects of excessive wind-induced vibrations that had occurred in many of the truss members. A nondestructive evaluation procedure was developed because the vibration absorbers had to remain in service during the evaluation process, and there were only a limited number of spare absorbers that could be used to replace any that might be destructively tested. The complete evaluation program included nondestructive vibration testing in the laboratory using impact methods to determine the current dynamic properties of the absorbers, and field testing to evaluate the energy dissipation characteristics of the installed vibration absorbers as they were actually operating. In addition, a limited number of destructive material tests were conducted in order to corroborate the results of the nondestructive tests. This evaluation program revealed that the current performance characteristics of the aged vibration absorbers were within the limits of the original design specifications, and that the synthetic rubber material used for the vibration absorbers had experienced no appreciable deterioration after nearly 25 years of continuous service.

Dynamic deformation signatures in reinforced concrete slabs for condition monitoring

We examine the use of ordinary steel and concrete strain gauges to monitor the dynamic response of reinforced concrete (RC) slabs excited in non-destructive vibrational testing. Plots of measured dynamic strains in the embedded steel reinforcement bars and on the concrete surface, as well as of mid-span deflection, are presented at different levels of load-induced damage. The plots show unique strain and deflection signatures that vary with the internal state of the slab, and could be used for condition monitoring and residual strength identification. It is feasible that the techniques outlined could be used in AI-based evaluation tools for RC slabs and other RC structures.

DYNAMIC BENDING AND TORSION STIFFNESS DERIVATION FROM MODAL CURVATURES AND TORSION RATES

In order to maintain the reliability of civil engineering structures, considerable effort is currently spent on developing a non-destructive vibration testing method for monitoring the structural integrity of constructions. The technique must be able to observe damage, secondly to localize the damage; and finally to give an idea of the severity of the damage. Within the framework of relating changes of measured modal parameters to changes in the integrity of the structure, it is important to be able to determine the dynamic stiffness in each section of the structure from measured modal characteristics.A damaged structure results in a dynamic stiffness reduction of the cracked sections. The dynamic stiffnesses provide directly an indication of the extension of the cracked zones in the structure. The dynamic stiffness reduction can also be associated with a degree of cracking in a particular zone.In an experimental programme, a concrete beam of 6 m length is subjected to an increasing static load to produce cracks. After each static perload, the beam is tested dynamically in a free–free set-up. The change in modal parameters is then related to damage in the beam.The technique that will be presented in the paper to predict the damage location and intensity is a direct stiffness derivation from measured modal displacement derivatives. Using the bending modes, the dynamic bending stiffness can be derived from modal curvatures. Using the torsional modes, the dynamic torsion stiffness can be derived from modal torsion rates.

Assessment of the directional elastic moduli of ewe vertebral cancellous bone by vibrational testing.

The ovariectomized ewe is being used as an animal model for postmenopausal osteoporosis. Data on the mechanical properties of ewe vertebral cancellous bone is needed to assess its effectiveness as a model for vertebral osteoporosis. This study utilized traditional compression testing and a novel nondestructive vibrational testing method to assess the directional mechanical properties of ewe vertebral cancellous bone. Composition and density properties were also assessed. It was hypothesized that vibrational testing would have utility in that it would allow for the anisotropic stiffness of cancellous bone to be assessed nondestructively. The present study has found that ewe vertebral cancellous bone has similar physical and mechanical properties to humans. The vibrational testing method described was able to nondestructively provide a valid measure of stiffness that was correlated with stiffness estimates from traditional compression testing. Furthermore, the stiffness measure from the vibration test was found to be sensitive to the architecture of cancellous bone. These results suggest the promise of this testing method for the nondestructive mechanical assessment of skeletal tissue.

PREDICTION OF GLOBAL AND LOCALIZED DAMAGE AND FUTURE RELIABILITY FOR RC STRUCTURES SUBJECT TO EARTHQUAKES

This paper deals with the prediction of global and localized damage and the future reliability estimation of partly damaged reinforced concrete structures under seismic excitation. Initially, a global maximum softening damage indicator is considered based on the variation of the eigenfrequency of the first mode due to the stiffness and strength deterioration of the structure. The hysteretic behaviour of the first mode is modeled by a Clough and Johnston hysteretic oscillator with degrading elastic restoring force. The linear parameters of the model are assumed to be known, measured before the arrival of the first earthquake by non-destructive vibration tests or by means of structural analysis. The previous excitation and displacement response time series are employed for the identification of the instantaneous softening using an ARMA model. The hysteresis parameters are updated after each earthquake. The proposed model is next generalized for a MDOF system. Using the calibrated model for the structure and the global damage state, the global damage in a future earthquake can then be estimated when a suitable earthquake simulation model is applied. The performance of the SDOF hysteretic model is illustrated on RC frames which were tested by Sözen and his associates. © 1997 by John Wiley & Sons, Ltd.

VIBRATION TECHNIQUES TO TEST AVIAN BONE IN VIVO

Non-destructive vibrational material testing has been used to monitor changes in chicken wing bone stiffnessas altered by a calcium deficient diet. A mechanical inertance spectrum was obtained for the radii of the test birds andwas analyzed as a single degree of freedom mass-spring-damper system. Statistical analysis of the data indicated that thenatural frequency of the bone was reduced as well as the bones stiffness. Calculations of viscous parameters were notvery successful and more study is needed. Geometrical changes in the radii were determined using imaging techniquesand were used to insure that the calcium deficient diet affects the skeletal system.