EditorialStructural Health Monitoring throughVibration-Based Approaches

Giosue Boscato ,1 Luca Zanotti Fragonara ,2 Antonella Cecchi,1 Emanuele Reccia ,3

and Daniele Baraldi 1

1Iuav University of Venice, Venice, Italy2Cranfield University, Cranfield, UK3Sapienza University of Rome, Rome, Italy

Correspondence should be addressed to Giosue Boscato; gboscato@iuav.it

Received 11 December 2018; Accepted 12 December 2018; Published 17 February 2019

Copyright © 2019Giosue Boscato et al.$is is an open access article distributed under theCreative CommonsAttribution License,which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

A promising method of assessing the safety of vulnerablestructures is the application of vibration-based monitoring(VBM) systems. $ese allow observation of the global re-sponse for a structure, including damage detection, classi-fication, and progressive development. In fact, dynamicmonitoring systems have proven to be particularly suited forsystems whose structural behaviours are strongly influencedby their geometric complexity or the inhomogeneity of theirconstituent materials. Moreover, because of its non-destructive and noninvasive nature, vibration-based moni-toring can be safely applied to historical or damagedstructures, which are potentially dangerous under other testconditions. $us, the analysis of the modal behaviour canreveal structural weaknesses or deficiencies amplified orinduced by unforeseen events. In fact, the monitoring of a setof appropriately chosen features jointly with the identifi-cation of the local and global structural weaknesses mayreveal the effectiveness of safety and retrofitting in-terventions, as well as any progression of structural damage.$anks to their noninvasive characteristics, VBM pro-cedures are widely used, and several studies have addressedstructural identification through the vibration data.

$is special issue aims to explore structural healthmonitoring via vibration-based approaches, especially forcomplex systems. In welcoming interdisciplinary studiesfrom across several scientific communities—including en-gineering, numerical modelling, seismology, and geo-technics—we hope to present studies from the breadth of thefield and provide insights into its future development.

$e main areas are covered by the special issue: (1)dynamic identification for model and data-driven ap-proaches, (2) local and global damage detection, and (3)numerical, experimental, and physical modeling.

Among the 41 researches, which constitute this specialissue, the main research topics addressed were damageidentification, data-driven approaches applied to relevantcase studies, and the operational-experimental modalanalysis for the SHM. In detail, the researches carried outthrough procedures based only on statistical analysis ofexperimental dynamic parameters outline a new trend basedon fast and reliable procedures for structural identification.

P. Zhang et al. study the fracture process of rock withacoustic emission related to sudden inelastic deformations.In detail, the rock stability assessment approach is estab-lished based on the chronological order of the characteristicacoustic emission phenomena, and then the rock stabilitywas assessed using the proposed approach.

$e study of Q. Xiong et al. proposes a method of in-tegrating the vibration monitoring system of the axle boxbearing with the underfloor wheelset lathe, where the in-tegration scheme and work flow of the system are introducedfollowed by the detailed fault diagnosis method and ap-plication examples. Firstly, the band-pass filter and envelopeanalysis are successively performed on the original signalacquired by an accelerometer. Secondly, the alpha-stabledistribution (ASD) and multifractal detrended fluctuationanalysis (MFDFA) of the envelope signal are performed,and five characteristic parameters with significant stability

HindawiShock and VibrationVolume 2019, Article ID 2380616, 5 pageshttps://doi.org/10.1155/2019/2380616

and sensitivity are extracted and then brought into theleast-squares support vectors machine based on particleswarm optimization to determine the state of the bearingquantitatively. $e effectiveness of the method is finallyvalidated by bench test data.

$e work of P. G. Golano et al. focuses on the structuraldesign and performances of a unique optical test system(OTS) used for measuring metre-scale optical surfaces. $einvestigation was carried out using modal identificationprocedures. Two sets of results are presented, and bothmodal analysis of the entire OTS and the transmissibilityfunction related to its use as an optical system are carried outand analysed. $e results of the modal analysis highlight thenatural modes of the entire OTS. Both numerical and ex-perimental modal analyses were applied to the case study,and a model updating procedure was also proposed.

$e energy transmission of the guided waves propa-gating in composite sandwich structures is investigated in awide range of frequencies using numerical simulations by S.Shoja et al. $e effects of different potential defects on theguided wave energy transmission are explored in suchstructures. Furthermore, the accuracy of homogenizationmethods for finite element modelling of guided wavepropagation in sandwich structures is studied with the aimof reducing the computational burden of the simulations inthe low range of frequencies.

A. Tessler et al. apply the inverse finite element method(iFEM) to reconstruct the displacement field of a shellstructure, which undergoes large deformations using dis-crete strain measurements as the prescribed data. $e iFEMcomputations are carried out using an incremental pro-cedure where, at each load step, the incremental strains areused to evaluate the incremental displacements, which inturn update the geometry of the deformed structure. $eincremental iFEM procedure is demonstrated to be suffi-ciently accurate in terms of reproducing the correct non-linear character of the load-displacement curve even when areduced number of strain sensors are used.

Z. Li and B. Shi propose the stochastic resonance (SR)to extract the weak fault characteristics, which are able toutilize the noise to amplify weak fault characteristics. Al-though classical bistable stochastic resonance (CBSR) canenhance the weak characteristics by adjusting the param-eters of the potential model, when potential barrier heightis adjusted, potential well width is also changed, and viceversa. With the simultaneous change of both potential wellwidth and barrier height is difficult to obtain a suitablepotential model for better weak fault characteristic ex-traction and further fault diagnosis of machinery. For thisreason, the output signal-to-noise ratio (SNR) of CBSR isgreatly reduced, and the corresponding enhancementability of weak fault characteristics is limited. In order toavoid the shortcomings, a new SR method is proposed toextract weak fault characteristics and further diagnose thefaults of rotating machinery, where the classical bistablepotential is replaced with a bistable confining potential toget the optimal SR.

M. B. Bagbanc and O. K. Bagbanc study six historic two-storied timber-framed masonry structures dating from the

nineteenth century in Bursa City. $e physical, mechanical,and dynamic parameters of the studied structures are in-vestigated, and the results are comparatively discussedshowing that the use of different infill materials affects thedynamic behaviours of these structures.

F. Li et al. address the difficulty of fault feature extractionwhen multiple failures occur in the reducer through thevariational mode decomposition that can be performed todecompose the vibration signal according to frequency,enabling separation of the vibration signals of the spur andplanetary gears. $e common fault features of these gearscan be extracted from the spectrum of the amplitude de-modulation envelope. To verify the effectiveness of thismethod, the authors first analysed a simulation signal andthen utilized the experimental signals from a laboratorymultistage reducer for verification.

$e work of D. Wang et al. propose a new method toidentify crack parameters in a rotor-bearing system based ona Kriging surrogate model and an improved nondominatedsorting genetic algorithm-III (NSGA-III).

$e goal of the paper of S.-Y. Ok et al. is to expand themultiobjective optimization approach developed for robustdamage identification in order to facilitate its applications tomore realistic bridge damage identification problems. Spe-cifically, a benchmark problem on highway bridges, de-veloped under the auspices of International Association forBridge Maintenance and Safety (IABMAS), is investigated.Various issues regarding sensor noises, multiple measure-ments, and loading scenarios are addressed to improve therobustness of bridge damage identification.

W. Wan et al. propose a compound risk assessment bycombining probabilistic analysis with a computational fluiddynamics (CFD) technique to numerically predict the po-tential cavitation of a high-speed flow in a chute spillway.Based on the local pressure and flow velocity of the nodes,the traditional cavitation number is introduced to charac-terize the possibility of cavitation. $e distribution of cav-itation numbers was obtained according to the numericalsimulation of the flow field in an open spillway. $e pro-posed numerical approach is economical and saves time;moreover, it can provide greater information about thepotential cavitation region.

M. T. Kashani and S. M. Hashemi apply the Galerkin-weighted residual method to convert the coupled differentialequations of motion of delamination beams to a discreteproblem, where, in addition to the conventional mass andstiffness matrices, a delamination stiffness matrix, repre-senting the extra stiffening effects at the delamination tips, isintroduced. $e linear eigenvalue problem resulting fromthe discretization along the length of the beam is solved todetermine the frequencies and modes of free vibration. Both“free mode” and “constrained mode” delamination modelsare considered in formulation, and it is shown that thecontinuity (both kinematic and force) conditions at thebeam spanwise locations corresponding to the extremities ofthe delaminated region, in particular, play a great role in“free mode” model formulation.

D. Tao et al. detect seismic damage of moment-resistingframe (MRF) structures through a data-driven method using

2 Shock and Vibration

the fractal dimension (FD) of time-frequency feature (TFF)of structural seismic dynamic responses at measured stories.$e TFF is defined as the real part of Gabor wavelettransform of translational interstory displacement, and FD isused to give a quantitative value to describe the calculatedTFF. Static condensation method is first used to reduce thedegrees of freedom (DOFs) of MRF and to express therotational displacements using translational displacements.For linear MRF, the FDs of TFFs at all stories are the sameusing the definition of TFF and modal superpositionprinciple. For damaged MRF with plastic hinges at the endsof beams and columns, the force analogy method isimplemented to establish the transformation matrix fromplastic hinge rotations to translational interstory inelasticdisplacements.

G. Boscato et al. identify the intrinsic discontinuity andthe damage of multileaf masonry walls through thevibration-based approach. In the first step, the character-ization of initial conditions based on the investigation of theintrinsic discontinuity and the manufacturing imperfectionshas been done. In the second step, starting from the iden-tification of the undamaged condition, the damage effects onchanges of the dynamic parameters have been recorded. $eincoherent response between the leaves affects the dynamicparameters.

In the work of M. B. Bagbancı and O. K. Bagbancı, fivehistoric timber minarets in Sakarya City are experimentallyand computationally examined to determine the effects ofthe construction techniques and geometrical properties onthe dynamic behaviour of the minarets. Ambient vibrationtests of timber minarets are performed, and the constructiontechniques and geometrical features are examined. Anempirical formula is derived from the relationships for arapid estimation of the fundamental period of timberminarets.

X. Guan et al. investigate the effects of snow load to themodal parameters of the steel structure roof of the HarbinRailway Station. A single-span simply supported beam isanalysed from the theoretical perspective to study theprinciples. FEM-based analyses are conducted for the steelstructure roof to illustrate the significance of the snow loadeffects to modal parameters.

In the F. Jiang et al. study, the improved permutationentropy (IPE) is defined as a feature for bearing fault di-agnosis. In this method, the ensemble empirical mode de-composition (EEMD), a self-adaptive time-frequencyanalysis method, is used to process the vibration signals, anda set of intrinsic mode functions (IMFs) can thus be ob-tained. A feature extraction strategy based on statisticalanalysis is then presented for IPE, where the so-called op-timal number of permutation entropy (PE) values used foran IPE is adaptively selected.

$e work of Q. Zhang and Z. Xiong proposes a newsensing system combining BOFDA (Brillouin opticalfrequency-domain analysis) and FBG (fiber Bragg grating)technology, which are used to detect internal and surfacecracks and their development in reinforced concretestructures, and an attempt is made to estimate the width ofsurface cracks.

P. Gueguen and A. Tiganescu, after analyzing the cor-relation of resonance frequency values with temperature forone building, used a data mining procedure called “asso-ciation rule learning” (ARL) to predict future frequenciesaccording to temperature measurements. $e study thenproposes an anomaly interpretation strategy using the“traffic light” method.

J. Tian et al. propose a newmethod for the fault diagnosisof intershaft bearings. $e fusion information exergy dis-tance method (FIEDM) is proposed by fusing four in-formation exergies, such as singular spectrum exergy, powerspectrum exergy, wavelet energy spectrum exergy, andwavelet space spectrum exergy, which are extracted fromacoustic emission (AE) signals under multiple rotationalspeeds and multimeasuring points.

$e work of M. Romero et al. shows operational modalanalysis (OMA) capabilities for evaluating the effectivenessof intervention works on the health state of a historicalmasonry structure. In detail, this work reports the evaluationof the effects that the strengthening intervention has on thestructural health state of the Jura Chapel, in Jerez de laFrontera (Spain), using nondestructive techniques based onambient vibration tests (AVT) and operational modalanalysis (OMA). $e AVT are performed for both prere-stored and restored states and under environmental loads. Adiscussion about the validity of doing AVT from extradoswhen a vault presents disconnection between ribs and web isincluded in the paper.

S. R. Borneman and S. M. Hashemi present a method fordetection of multiple cracks present in laminated compositebending-torsion coupled cantilevered beams using naturalfrequency data. $is methodology relies on both experi-mentally collected natural frequencies and frequencies cal-culated using amathematical model. An algorithm is devisedbased on the Adam–Cawley criterion and extended tolaminated composites with multiple cracks. $is method hasshown exceptional convergence on the size and location ofcracks using a number of modes of free vibration with andwithout errors in measured frequencies.

$e research of X. Fukun et al. adopts the FrenchROCK600-50 three-axis experiment instrument and SH-IIsystem to evaluate the acoustic emission (AE) peak of therear axle of yellow sandstone by carrying out the confiningpressure synchronous unloading experiment and evolutionof mechanical properties and characteristics of energytransformation and damage of a yellow sandstone.

E. Lenticchia et al. propose a seismic assessment of thestructures of Hall B of Turin Exhibition Centre, consideringthe potential seismic damage and the related consequencesto global behaviour of nonstructural elements. $e appli-cation of an optimal sensor placement strategy is describedwith reference to two different scenarios: the first onecorresponding to the undamaged structure and the secondone that considers a possible damage to the infill walls. Anovel damage-scenario-driven sensor placement strategybased on a combination of the two abovementioned sce-narios is proposed and discussed.

In the research of S. Tashakori et al., two different SHMmethods are used to evaluate the strength of composite

Shock and Vibration 3

bonds by using two separate experimental setups. First, theheterodyne effect method is used for assessing the separationin the composite joint. $en, the surface response to exci-tation (SuRE) method is used for studying various simulatedcontamination levels.

A. Concha and L. Alvarez-Icaza propose a parameteridentification method and a high gain observer to identifythe model and to recover the state of a seismically excitedshear building using acceleration responses of the groundand instrumented floors levels, as well as the responses atnoninstrumented floors, which are reconstructed by meansof cubic spline shape functions.

X. Zhang et al. present a novel fault diagnosis approachfor rotating machinery by combining improved local meandecomposition (LMD) with support vector machine-recursive feature elimination with minimum redundancymaximum relevance (SVM-RFE-MRMR). Firstly, an im-proved LMD method is developed to decompose vibrationsignals into a subset of amplitude modulation/frequencymodulation (AM-FM) product functions (PFs). $en, time-and frequency-domain features are extracted from the se-lected PFs, and the complicated faults can be thus identifiedefficiently.

M. Regni et al. analyze the effect of temperature andwind velocity on the natural frequencies andmodal dampingratios of the Faculty of Engineering Tower at the UniversitaPolitecnica delle Marche, a 10-story reinforced concreteframe building, permanently monitored with low-noiseaccelerometers. $e data recorded over the first 5monthsof monitoring demonstrate that temperature variations andwind intensity have a clear effect on the first three naturalfrequencies and the corresponding damping ratios. A me-chanical explanation of these phenomena is offered, basedon a critical review of literature case studies.

M. R. Kaloop et al. develop and apply four advancedheuristic regression methods to estimate raft foundations’settlement, namely, multivariate adaptive regression splines(MARS), M5 model tree (M5Tree), generalized regressionneural networks (GRNN), and support vector regression(SVR) techniques. Simulation of raft pile foundations isutilized to calculate the settlements of piles under the effectof static and dynamic loads. $e results show that the fourmodels can be used to accurately predict foundations’ set-tlements in the training stage.

X. Wang et al. address the damping identification withacceleration measurements based on the sensitivity en-hancement method. To reduce the measurement noiseeffect and enhance the effectiveness of the response sen-sitivity method, an enhanced sensitivity analysis method isproposed to identify the structural damping based on theprincipal component analysis (PCA) method. $e pro-posed damping identification method is numerically val-idated with a planar truss structure at first, and then theexperimental study is conducted with a steel planar framestructure.

Br. Joyce et al. outline the design of an experimental testbed with user-selectable parameters that can change rapidlyduring the system’s response to external forces. $e test bedconsists of a cantilever beam with electronically detachable

added masses and roller constraints that move along thebeam. Both controllable system changes can simulate systemdamage. Experimental results from the test bed are shown inboth fixed and changing configurations.

A. Malekjafarian et al. investigate the feasibility ofdetecting local damage in a bridge using laser Dopplervibrometer (LDV) measurements taken from a vehicle as itpasses over the bridge. It is shown that instantaneouscurvature (IC) at a moving reference, which is the curvatureof the bridge at an instant in time, is sensitive to localdamage. $e vehicle measures the rate of instantaneouscurvature (RIC), defined as the first derivative of IC withrespect to time. A comparison of filtered RIC measurementsin healthy and damaged bridges shows that local damage canbe detected well with noise-free measurements and can stillbe detected in the presence of noise.

D. Han et al. propose a new method to solve detectionproblems of multifrequency weak signals in noisy back-ground; a novel weak signal detection method based onvariational mode decomposition (VMD) and rescalingfrequency-shifted multistable stochastic resonance(RFMSR) with analytical mode decomposition (AMD) isproposed. In this method, different signal frequency bandsare processed by rescaling subsampling compression tomake each frequency band meet the conditions of sto-chastic resonance.

S. Yang et al. investigate the damage evolution ofsandstone specimens under two types of cyclic loading bymonitoring and analyzing changes in the elastic moduli andthe ultrasonic velocities during loading. A crack densityparameter is introduced in order to interpret the changes inthe tangential modulus and the ultrasonic velocities.

J. Gai and Y. Hu propose a method based on singularvalue decomposition (SVD) and fuzzy neural network(FNN) to extract and diagnose the fault features of dieselengine crankshaft bearings efficiently and accurately.

J. Qian et al. analyze a method to identify strand tensionsbased on scale energy entropy spectra of ultrasonic-guidedwaves (UGWs).

S. Quqa et al. investigate the usability of easily obtainableparameters instead of the modal traditional ones, in thecontext of a flexibility-based damage detection procedure,under the assumption of unknown structural masses. To thisaim, a comparison is made between two different ap-proaches: the first involves the calculation of the flexibilitymatrix by using traditional modal parameters, while thesecond involves the use of singular vectors, obtained througha simple matrix factorization.$e modal parameters and thesingular vectors necessary for the implementation of thedamage detection procedure are evaluated through twodifferent techniques: the eigensystem realization algorithmand a wavelet-based procedure, for which a variant isproposed by introducing the energy reassignment conceptinto the original algorithm.

W. Shan et al. study a procedure to eliminate thetemperature effect on modal frequency, an effective methodto construct quantitative models which accurately predictthe modal frequency corresponding to temperature varia-tion. In this paper, principal component analysis (PCA) is

4 Shock and Vibration

conducted on the temperatures taken from all embeddedthermocouples for extracting input parameters of regressionmodels. $ree regression-based numerical models usingmultiple linear regression (MLR), backpropagation neuralnetwork (BPNN), and support vector regression (SVR)techniques are constructed to capture the relationshipsbetween modal frequencies and temperature distributionsfrommeasurements of a concrete beam during a period of 40days of monitoring.

$e paper of H. Kordestani et al. provides a simple anddirect output-only baseline-free method to detect damagefrom the noisy acceleration data by using moving averagefilter (MAF). MAF is a convolution approach based on asimple filter kernel (rectangular shape) that works as anaveraging method to smooth signal and remove in-corporated noise. In this paper, a method is proposed toemployMAF to smooth acceleration signals obtained from aseries of accelerometers and determine the damage locationalong a steel beam.

L. Gang et al. investigate the acoustic emission (AE)characteristics of dry and saturated columnar joints basaltunder uniaxial compression and tensile damage process byusing the TAW-2000 rock experiment system and SH-IIAE system for the whole loading. Dry sample of uniaxialcompression in the process at the beginning of loadingproduces a large number of AE signals, and the AE signalhas shown steady growth along with the load increase, butthe sample destroy appears during the blank period thatcan be used as a precursor of instability. From the am-plitude-time-energy diagram, it can be found that whenamplitude increases with hit, the related energy decreases.

$e paper of Marco Buzzoni et al. focuses on the de-velopment of a novel condition indicator specificallydesigned for the damage assessment in rolling elementsbearings. $e proposed indicator allows to track the bearingdegradation process taking into account three differentpossible positions: outer race, inner race, and rolling ele-ment. $e validation of the proposed indicator has beencarried out by means of both simulated signal and a run-to-failure experiment. $e results highlight that the proposedindicator is able to detect more efficiently the fault occur-rence and, most importantly, earlier than other establishedtechniques.

We hope that this special issue updates scientific evi-dences in SHM integrative research based on vibrationaldata contributing to a scientific and practical improvementof the SHM topic.

Conflicts of Interest

$e editors declare that they have no conflicts of interestregarding the publication of this special issue.

Acknowledgments

We express our great appreciation to all authors for theirexcellent contributions and reviewers for their valuable help.We express our sincere thanks to the Editorial Board ofSHMV for their approval on this topic and continuous

support in successful publication of this special issue.$e Lead Guest Editor would like to thank the three GuestEditors for their dedicated cooperation.

Giosue BoscatoLuca Zanotti Fragonara

Antonella CecchiEmanuele RecciaDaniele Baraldi

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