bluuebunny/crossref_metadata_2025 huggingface dataset:
Damage Assessment of Structures Using only Post-Damage Vibration Measurements
Authors: Surace Cecilia
Published: July 2013

Damage to many structural systems (including bridges, offshore platforms, airplanes and aerospace systems) can occur during normal service due to fatigue loading, a corrosive environment, collisions with extraneous objects, etc. For such structures, in order to guarantee safety, periodic inspections and maintenance are essential: Since undetected damage may result in catastrophic structural failure, the realisation of an accurate and trustworthy damage detection technique is fundamental.Vibration-based inspection offers the potential for detecting faults by monitoring the dynamic response of a structure, exploiting the fundamental principle that structural damage affects the stiffness distribution and hence the presence of the fault will change the dynamic properties of the structure under investigation.Many vibration-based inspection techniques have been developed over recent years which require knowledge of the baseline modal responses of the structure in the original undamaged state.However, for the vast majority of existing structures in operation, such data are simply not available. This keynote presentation reviews past and present research studies in which the author has been involved that aim to detect the presence of structural damage and identify its approximate location, using only post-damage vibration measurements. The techniques presented analyse either the mode shapes, operating deflection shapes or principal orthogonal modes and their corresponding derivatives. These features have been found to be good indicators of damage due to the spatial information that can be provided with respect to location of damage. The methodologies proposed are applied to isotropic/orthotropic uni/bi-dimensional structures and corresponding numerical and experimental results are presented.
Comparative Study of Robust Novelty Detection Techniques
Authors: Dervilis Nikolaos , Barthorpe Robert J. , Worden Keith
Published: July 2013

The central target of this work is to provide an alternative to machine learning approaches to structural health monitoring with one of robust multivariate statistic novelty detection. Damage detection and identification is a procedure that is hierarchical in nature. At its most sophisticated, diagnosis of the damage could include localisation, classification and severity assessment and even go so far as to estimate the time-to-failure of the structure. In this paper, robust multivariate statistics were investigated focused mainly on a high level estimation of the outliers which determines only the presence or absence of novelty - something that is of fundamental interest. These methods allow a diagnosis of deviation from normality and the option of identifying the presence of masking effects caused by multiple outliers. This paper is trying to introduce a new scheme for damage detection by adopting simple measurements and exploiting robust multivariate statistics.
Comparison of Full Field Strain Distributions to Predicted Strain Distributions from Limited Sets of Measured Data for SHM Applications
Authors: Avitabile Peter , Harvey Eric , Ruddock Justin
Published: July 2013

Measured data from operating systems are often acquired to predict structural health of a system. With only a few measurement sensors, very limited understanding of the system can be obtained. Utilizing some recent novel expansion results, full field information can be obtained to identify a more complete strain description for the system. Using these results in conjunction with an analytical prediction of the expected strains, comparisons and differences can be identified using time response data. The expected full field stress-strain from the analytical model is compared to the predicted full field dynamic stress strain from limited sets of measured locations due to either operating or imposed loading on the structure. Differences in strain distributions at many time increments can provide indications of regions of possible damage in the structure. The work presented in this paper identifies the methodology as well as some results to illustrate the usefulness of the approach.
Uncertainty Modeling and Quantification for Structural Health Monitoring Features Derived from Frequency Response Estimation
Authors: Mao Zhu , Todd Michael D.
Published: July 2013

System identification in the frequency domain plays a fundamental role in many aspects of mechanical and structural engineering. Frequency domain approaches typically involve estimation of a transfer function, whether it is the usual frequency response function (FRF) or an output-to-output transfer model (transmissibility). The field of structural health monitoring, which involves extracting and classifying features mined from in-sit structural performance data for the purposes of damage condition assessment, has exploited many features for this purpose that inherently are derived from estimations of frequency domain models such as the FRF or transmissibility. Structural health monitoring inevitably involves a hypothesis test at the classification stage such as the (common) binary question: are the features mined from data derived from a reference condition or from data derived from a different (test) condition Inevitably, this decision involves stochastic data, as any such candidate feature is compromised by error, which we categorize as (i) operational and environmental, (ii) measurement, and (iii) computational/estimation. Regardless of source, this noise leads to the propagation of error, resulting in possible false positive (Type I) errors in the classification. As such, the quantification of uncertainty in the estimation of such features is tantamount to making informed decisions based on a hypothesis test. This paper will demonstrate several statistical models that describe the uncertainty in FRF estimation and will compare their performance to features derived from them for the purposes of detecting damage, with ultimate performance evaluated by receiver operating characteristics (ROCs). A simulation and a plate subject to single-input/single-output vibration testing will serve as the comparison testbeds.
Strength Assessment of Deteriorated OHL Conductors and Earth Wires Based on Non-Destructive Testing
Authors: Volokhovskiy Vasily , Sukhorukov Vasily , Tzukanov Victor
Published: July 2013

Safety operation of overhead lines depends on many factors including strength of conductors and earth wires. Therefore worn-out or defective conductors or earth wires must be detected. Estimation of conductor technical conditions is based on comparison of revealed flaws with requirements of overhead line project and build documentation. It is well known that conductors are affected by corrosion, friction and fatigue wear. All this factors may cause loss of strength and even breakage of conductor. Steel core is the most important part of conductor when it comes to mechanical loads. That is why it is very important to know actual technical conditions of steel core of conductor. Worn or defective wires must be repaired or replaced. Principles of strength assessment of deteriorated of steel-aluminum conductors and steel earth wires based on magnetic non-destructive testing technique are presented. The retention of overhead line conductor and earth wire is one of the most reasonable ways to eliminate the unacceptable clearances. The allowable magnifying tension, regarding the reliable operation, is set relying upon the non-destructive testing of conductors or earth wires in actual state. The measured loss of metallic cross-section area due to abrasion, corrosion etc. and local wire breaks are treated as input data for mechanical model of objects under test. The residual strength estimates give the specialists network company further information that helps to make a valid decision on testing time-limit and policy. Some results of assessing the strength of overhead line conductors and earth wires according to the NDT data are demonstrated.
Defect Detection Using Pulse Phase Thermography - Repeatability and Reliability of Data
Authors: Waugh Rachael C. , Dulieu-Barton Janice M. , Quinn Simon
Published: July 2013

A study has been carried out to characterize the effect of variation of processing parameters on the phase contrast data between defective and defect-free areas obtained through the use of pulse phase thermography (PPT). Processing parameters used to implement the fast Fourier transform (FFT) have been varied. Phase contrast was maximized when the datum used as the start point for the FFT was taken as the frame just after the pulse. Optimum recording duration was found when the surface temperature had returned to its initial temperature. A truncation shorter than this resulted in a reduced phase contrast. Sampling interval and range is required to be balanced against the quantity of data produced and the computational expense. A sampling frequency of 0.06 Hz was suggested for the sample studied as this allowed peak phase contrast to be captured without unnecessarily increasing data size. Repeatability of tests was also investigated. It was found that PPT phase contrast results have been found to be repeatable with a maximum standard deviation of 6°.
Mechanical Characterization of Hybrid (Organic-Inorganic) Geopolymers
Authors: Lamanna Giuseppe , Soprano Alessandro , Bollino Flavia , Catauro Michelina
Published: July 2013

The mechanical properties of geopolymers can be obtained through different kinds of experimental tests: this paper is focused on the compressive strength (i.e. in a direction parallel to the loading axis) for the case of uniaxial compression. The compressive strength of such materials is traditionally characterized by the 28th-day value, but their strength is expected to increase in time at a continuously decreasing rate. The knowledge of the strength vs. time law is of importance when a structure is subjected to a certain type of loading at a later age. In this work inorganic polymers from activated metakaolin (alumina silicate inorganic polymers, obtained from alkali activation of powders containing SiO2+Al2O3 > 80%wt) are reported. In order to improve their compressive strength a percentage of polyethylene glycol has been added, thus obtaining a hybrid (organic-inorganic) geopolymer. Many factors can influence significantly the compressive strength of such materials e.g. w/c ration, aggregate content, water curing period, polyethylene/glycol ratio. Afterwards experimental compressive tests (performed in a Zwick-Roell® testing machine) have been carried out varying the polyethylene/glycol ratio and the main dimensions of the samples.
Wavespeed Measurement in Buried Water Distribution Pipes and its Significance in Leak Location
Authors: Brennan Michael , de Almeida Fabricio , Joseph Phillip , Dray Simon , Whitfield Stuart
Published: July 2013

To determine the location of leaks in buried water pipes, acoustic methods are often used. These have proven to be very effective in metallic pipes but have been problematic in modern plastic pipes. In this paper the reason why this is so is discussed together with some measurements that were made on a bespoke test rig built by South Staffs Water plc. It is shown that there are significant issues in obtaining an accurate estimate of the wavespeed when a leak is present in the system. A method is proposed that overcomes some of these problems, which is discussed and is demonstrated using some data from the bespoke test-rig.
Detection and Localisation of Structural Damage Based on the Polynomial Annihilation Edge Detection: An Experimental Verification
Authors: Surace Cecilia , Mattone Massimiliano , Gherlone Marco
Published: July 2013

The present paper describes an experimental validation of a new structural damage detection method based on the Polynomial Annihilation Edge Detection (PAED) technique. It is well known that concentrated damage such as a crack, causes a discontinuity in the rotations and consequently in the first derivatives of the mode shapes. On this basis, the PAED, a numerical method for detecting discontinuities in smooth piecewise functions and their derivatives, can be applied to the problem of damage detection and localisation in beam-like structures for which only post-damage mode shapes are available. As described in this paper, in order to verify this approach experimentally (a numerical assessment having already been documented in previous papers), vibration tests on a cantilever steel beam with a saw-cut have been performed and the Operational Deflection Shapes (ODS) determined. As the approach requires a reasonably high spatial resolution of the ODS, a scanning laser vibrometer, capable of acquiring data rapidly at a very large number of observation points, was used.
Development of a Remote Collaborative Visual Inspection System for Road Condition Assessment
Authors: Miyamoto Ayaho
Published: July 2013

This paper describes a Remote Collaborative Visual Inspection System for integrated management by linking digital movie captured by a running vehicle and online road drawings. The newly developed road condition assessment system consists of commercially available on-board high-resolution video cameras during the visual inspection of road pavements and road appurtenances and a Web connection system. The system enables users to select a road section in a road register on an on-screen map and visually observe not only pavements but also road facilities, slopes, the state of vegetation, and road-occupying structures. The system, therefore, can be expected to help reduce visual detection failures compared with conventional visual observation from moving vehicles and make highly objective evaluation possible through observation by two or more persons. By using image data, the system also provides basic data that can be used for not only maintenance but also road planning.
Polymeric Bearings – A New Base Isolation System to Reduce Structural Damage during Earthquakes
Authors: Falborski Tomasz , Jankowski Robert
Published: July 2013

Base isolators, like lead rubber bearings, high damping rubber bearings or friction pendulum systems are extensively used in practice in many seismically active regions to protect structures against earthquake forces. The present paper reports the results obtained from the experimental study aimed to determine the effectiveness of the Polymeric Bearings in suppressing structural vibrations during dynamic excitations and therefore to minimize structural damage. The response of the analyzed two-storey structure model both fixed and supported by the Polymeric Bearings under different earthquake excitations was studied. The reduction in lateral response due to seismic events was measured by comparing the peak accelerations of the two-storey steel structure models – with and without base isolation system. The results of the study have shown that the use of the Polymeric Bearings leads to significant improvement in dynamic properties by suppressing structural vibrations. The results have indicated that the Polymeric Bearings can be successfully used to reduce damage of structures during seismic events.
Finite Element Analysis for Structural Performance of Offshore Platforms under Environmental Loads
Authors: Abdel Raheem Shehata E. , Abdel Aal Elsayed M.A.
Published: July 2013

Offshore structures for oil and gas exploitation are subjected to various ocean environmental phenomena which can cause highly nonlinear action effects. Offshore structures should be designed for severe environmental loads and strict requirements should set for the optimum performance. The structural design requirements of an offshore platform subjected to wave induced forces and moments in the jacket can play a major role in the design of the offshore structures. For an economic and reliable design; good estimation of wave loadings are essential. The structure is discretized using the finite element method, wave force is determined according to linearized Morison equation. Hydrodynamic loading on horizontal and vertical tubular members and the dynamic response of fixed offshore structure together with the distribution of displacement, axial force and bending moment along the leg are investigated for regular and extreme conditions, where the structure should keep production capability in conditions of the one year return period wave and must be able to survive the 100 year return period storm conditions. The results show that the nonlinear response analysis is quite crucial for safe design and operation of offshore platform. Fixed Jacket type offshore platforms under extreme wave loading conditions may exhibit significant nonlinear behavior. The effect of current with different angles when hitting the offshore structure with the wave and wind forces, is very important for calculate the stress, the response displacement and deformation shapes. As the current increase or decrease the effect of wave force according to the hitting angle of current.
NDT Data Fusion for the Enhancement of Defect Visualization in Concrete
Authors: Cotič Patricia , Niederleithinger Ernst , Bosiljkov Vlatko , Jagliċiċ Zvonko
Published: July 2013

Ground penetrating radar (GPR) and active thermography are well known non-destructive testing (NDT) methods for structural visualization and defect detection in concrete. However, for both methods, the probability of detection is strongly depth-dependent and each method suffers from an almost blind region at a specific depth. In this study we propose the use of unsupervised clustering techniques for the fusion of GPR and thermographic phase contrast data to enhance defect visualization in concrete. The evaluation was carried out on the basis of experimental data acquired on laboratory concrete test specimens, which contain inbuilt anomalies varying in shape, material and position. To achieve an optimal fusion of radar depth slices and thermographic phase contrast images along the depth axis, we derive sensitivity curves for both NDT methods and use the probability mass information to further improve the fusion results. Results show that the fuzzy c-means algorithm may contribute to an enhanced detection probability of defects below high density reinforcement. For defects with a concrete cover from 1.5 to 2 cm, the use of weighted clustering is particularly suggested. In general, complex defect types and shapes could be better resolved by using the Gustafson-Kessel algorithm or noise clustering. In addition, we demonstrate the application of the Dempster-Shafer theory to quantitatively evaluate the effectiveness of fused data on the basis of joint mass probability.
Investigating the Use of Moving Force Identification Theory in Bridge Damage Detection
Authors: Carey Ciaran H. , O'Brien Eugene J. , Keenahan Jennifer
Published: July 2013

This paper investigates the use of Moving Force Identification as a method of bridge damage detection. It identifies changes in the predicted axle force histories that occur as a result of loss in bridge element stiffness, i.e. as a result of bridge damage. A 2-dimensional Vehicle-Bridge Interaction model is used in numerical simulations to assess the effectiveness of the method in detecting changes in stiffness. Fleets of similar vehicles are simulated and the mean force pattern is used as the damage indicator. Results show that the method is more sensitive to damage than direct measurements of displacement. The paper also explores the use of the force history as an indicator of damage location.
Testing and Monitoring for a Large Scale Truss Bridge Using Long-Gauge Fiber Optic Sensors
Authors: Wan Chun Feng , Hong Wan , Wu Zhi Shen , Sato Tadanobu
Published: July 2013

Fiber optic sensors become very popular for structural testing and monitoring in civil engineering nowadays, due to its advantage of high resolution and environment durability. In this paper, long-gauge fiber optic bragg grating sensors will be introduced. Structural damage detection stratagem using the micro-strain mode will be studied. Then its application to a structural testing and monitoring for a real long span truss bridge will be discussed in detail. In the testing, 23 long-gauge fiber optic bragg grating sensors were deployed on the mid span of the bridge. Testing were made under conditions either there is train on the bridge or no train on it. Corresponding dynamic characteristics were analyzed and discussed. Results of the testing show that long-gauge fiber optic sensors can work well for structural testing and also damage detection for truss bridges.
The Impact of the Gigacycle Fatigue on Steel Bridges
Authors: Bandara Chaminda S. , Dissanayake Ranjith
Published: July 2013

Recent studies have proved that there is no fatigue limit for metallic materials; the stress life curve continuously drops even after 107 cycles. However, existing design codes assume that there is a fatigue limit. Therefore, it is important to use appropriate safety factors if existing codes are used for life evaluations. This paper first describes a method to extend high cycle fatigue stress life curves which are developed using tests on small scale specimens, to the gigacycle regime. Then the difference between the stress life curves of small scale specimens and full scale tests related to steel bridges are explained. Finally, the paper presents a case study on a fatigue critical element of a steel railway bridge to show the significance of the gigacycle regime for fatigue life evaluation.
Simulation of Impact Damage in Foam-Based Sandwich Composites
Authors: Feng Dian Shi , Aymerich Francesco
Published: July 2013

The paper describes the application of a 3D finite element model for prediction of impact induced damage in sandwich composites consisting of laminated skins bonded to a closed cell foam core. The major damage and fracture mechanisms typically developing in transversally loaded sandwich composites were simulated in the model. The model was implemented in the FE package ABAQUS/Explicit and used to predict the impact damage resistance of sandwich panels with different core densities, core thicknesses, and skins layups. Numerical results obtained by FE simulations were compared with experimental data and observations collected through impact tests carried out at various impact energies.
On the Seismic Performance of Elevated Water Tanks and their Control Using TLDs
Authors: Ghosh Aparna Dey , Bhattacharyya Soumi , Roy Anuja
Published: July 2013

The post-earthquake function of elevated water tank structures so as respond to the civil water requirements is of extreme significance. These structures are, however, extremely vulnerable to seismic conditions and there has been substantial damage/failure of several such structures during major earthquakes. A review of the damage and performance of some elevated water tanks subjected to earthquakes is presented in this paper. An investigation is also made on the seismic vibration control of elevated water tank structures by using Tuned Liquid Dampers (TLDs). A frequency domain formulation for the transfer function of the elevated water tank with attached TLDs is developed. Numerical studies on a reinforced concrete elevated water tank with shaft type support are carried out. The effect of detuning on the performance of the TLDs due to the change in the structural frequencies resulting from the fluctuating water level in the water tank is also examined. Results indicate that it is possible to design a fairly robust and effective TLD system for the seismic vibration mitigation of the considered elevated water tank.
Sustainable Design of Smart Health Facilities in Seismically Prone Areas
Authors: Rainieri Carlo , Fabbrocino Giovanni
Published: July 2013

Safety ofhealth facilities (hospitals) is only partially related to the performance ofprimary structural members. Modern seismic codes provide strict requirements toboth structural and non-structural components, since the latterare alsocritical to ensure that the system remains fully operational in the case offrequent earthquakes. Thus, performance and safety checks apply also to electro-mechanicaland medical equipment,elevators, tanks, power supply systems, distributionsystems, heating, ventilation and air-conditioning systems.In the present paperattention is focusedon the analysis of the factors which make health facilities vulnerable and onthe issues related to a rational and objective assessment of performance andhealth state of structural and non-structural components. This is not a trivialtask, since functions and resilience of the system as a whole depend also onthe ability of inspectors and managers to integrate theoretical evaluationswith field measurements and their physical meaning.In this context, strategies and recommendations for a sustainableimplementation of Smart Health Facilities, which fulfilAtoE characteristics (Accuracy, Budget compliance, Computational burden,Durability, Ease of use)on a long term basis, are discussed, taking into account the specific requirementsand characteristics of the different subsystems in a hospital.
Seismic Damage Assessment of Regular Gravity Design Buildings
Authors: Negulescu Caterina , Wijesundara Kushan K. , Foerster Evelyne
Published: July 2013

During the past earthquakes, different low ductile failure modes are observed in the gravity design structures and thus, the most of existing damage indices may fail to assess the damage of gravity design structures accurately in referring to the two main performance levels: immediate occupancy and ultimate limit state. Therefore, this study investigates the possible damage indices for the damage assessment of gravity design frames. For this purpose, among the existing damage indices in the literature, this study considers the inter-story drift and the natural period based damage indices. In addition, two new damage indices based on the wavelet based energy and the dominant inelastic period of a building are also considered in this study. Furthermore, the damage assessment results from the four damage indices for three gravity design buildings are compared and discussed.
From the comparison, linear correlations between the inter-storey drift based damage index and the wavelet energy based index, and dominant inelastic period based damage index are observed. Finally, this study concludes based on the observations that no significant effects of number of inelastic cycles to the damage assessment results for low ductile structures. However, this study also highlights the effects of number of inelastic cycles to the damage for medium and high ductile structures.
Post-Earthquake Damage Assessment Process and Problems in Turkey – A Case Study in Van Province
Authors: Yilmaz Didem Gunes , von Meding Jason , Erk Gul Kacmaz
Published: July 2013

This paper presents the current post-earthquake damage assessment procedure in Turkey, and is based on the authors experience in the province of Van after the earthquakes in late 2011. The damage assessments were conducted mainly by the state with the collaboration of the Chamber of Architects in Turkey. It is aimed at explaining how the damage surveys are conducted and what problems occurred during and after the completion of the assessments. The differences and similarities between other countries post-earthquake damage assessment practices are also examined by comparing them and giving some examples.
PolyVinyliDene Fluoride (PVDF) Material Based Energy Harvesting from Train and Damaged Bridge Interaction
Authors: Cahill Paul , Jackson Nathan , Mathewson Alan , Pakrashi Vikram
Published: July 2013

This paper investigates the potential use of PolyVinyliDene Fluoride (PVDF) for the purposes of damage detection for infrastructural elements, primarily for bridge elements. PVDF based sensors have been created and characterised in the laboratory in this regard. Finite element analysis of vehicle-bridge interactions with varying damage are carried out. The energy harvesting signatures of realistic trains are assessed and quantified for the modelled bridge. The effect of localized damage on the finite element model and its subsequent relationship with energy harvesting from the calibrated PVDF based sensors are investigated using the harvesting signatures of realistic trains. This approach is useful in terms of designing new generation smart bridge structures and for possible retrofit of existing structures. The use of train-bridge interaction ensures that the damage detection is carried out while the bridge is under operational conditions. Consequently, there is minimal to no impact on the existing operation of the bridge or the transport network during damage detection. The paper is expected to be useful for practicing engineers and researchers in the field of application of new materials in the next generation of bridge structures.
Assessment of Structural Reliability of Bridge Beams Based on Measured Symptoms
Authors: Quattrone Antonino , Matta E. , Zanotti Fragonara L. , Ceravolo Rosario , de Stefano Alessandro
Published: July 2013

The evaluation of the safety and the estimation of the remaining service life of existing structures need a thorough knowledge of the effective operational conditions, achievable implementing a health monitoring system. The measured quantities, if opportunely chosen, allow to follow the evolution of the structural behavior in the lifetime and to recognize the occurrence of damages. Hence the collected data can be considered as symptoms and used to assess the reliability and the prognosis of the monitored structure.
This paper presents the application of symptom-based reliability formulation to a real case study: a set of precast bonded post-tensioned concrete bridge beams, recently dismounted after a service life of 50 years. Both static and dynamic tests were carried out at the aim of evaluating the residual load-bearing capacity and investigating the effects of deterioration on their dynamic properties. The experimental results of test campaigns have been used as symptoms in order to estimate the reliability function of the beams and the evolution of their resistance in time.
A Seismic Reliability Assessment of Reinforced Concrete Integral Bridges Subject to Corrosion
Authors: Choine Mairéad Ní , O’Connor Alan , Padgett Jamie E.
Published: July 2013

This paper seeks to determine the effect deterioration has on the seismic vulnerability of a 3 span integral concrete bridge. Traditionally it has been common to neglect the effects of deterioration when assessing the seismic vulnerability of bridges. However, since a lot of the bridges currently being assessed for retrofit are approaching the end of their design life, deterioration is often significant. Furthermore, since deterioration affects the main force resisting components of a bridge, it is reasonable to assume that it might affect its performance during an earthquake. For this paper, chloride induced corrosion of the reinforcing steel in the columns and in the deck has been considered. Corrosion is represented by a loss of steel cross section and strength. A 3 dimensional non-linear finite element model is created using the finite element platform Opensees. A full probabilistic analysis is conducted to develop time-dependent fragility curves. These fragility curves give the probability of reaching or exceeding a defined damage limit state, for a given ground motion intensity measure taken as Peak Ground Acceleration (PGA). This analysis accounts for variation in ground motion, material and corrosion parameters when assessing its overall seismic performance as well as the performance of its most critical components. The results of the study show that all components experience an increase in fragility with age, but that the columns are the most sensitive component to aging and dominate the system fragility for this bridge type.
Diagnosis of Damage in a Steel Tank with Self-Supported Roof through Numerical Analysis
Authors: Burkacki Daniel , Wójcik Michał , Jankowski Robert
Published: July 2013

The safety of civil engineering structures is one of the most important issues of building industry. That is why the assessment of the damage-involved structural response has recently become of major concern to engineers. Among a number of different approaches to diagnosis of damage, the method of measuring the changes in natural frequencies is considered to be one of the most effective indicators of global damage. From the practical point of view, the method has been successfully applied to relatively small structures, while in-situ tests on large structures, such as bridges, tanks or dams, are very difficult. The aim of the present paper is to show the results of the numerical analysis concerning the diagnosis of damage in a cylindrical steel tank with self-supported roof which is filled with liquid. The tests have been conducted for various stages of damage, introduced in the numerical model by reducing the stiffness of tank-soil system as well as by cutting the connection between the shell and roof of the tank as well as between roof elements. The results of the numerical analysis have shown the characteristic decrease in the natural frequencies for the case of tank-soil system with reduced stiffness, which is the global type of damage. On the other hand, cutting the welds, which can be considered as the local type of damage, has not lead to the differences in the natural frequency values, although differences in local deformations of shell in the vicinity of cuts have been observed in vibration modes.
Non-Destructive Tests for the Structural Assessment of a Historical Bridge over the Tua River
Authors: Valente Isabel , Ramos Luís F. , Vasquez Kevin , Guimarães Paulo , Lourenço Paulo B.
Published: July 2013

Paradela Bridge is a metallic bridge located along the bank of the Tua River in northern Portugal. While the bridge is not currently in service, its structure is representative of many metallic truss structures built across the continent between the XIX and the XX century. Tua Line belongs to the Douro area that UNESCO recently declared as world heritage. This study acquires its importance since it might serve as an insight for the study of many other similar structures all over the country. This paper comprises a historic investigation of archived documents, an on-site survey to evaluate its present conditions, a dynamic testing and the construction and calibration of numerical models in finite element analysis (FEA) software, structural assessment and capacity rating estimation. The purpose of constructing numerical models was to evaluate the suitability of the bridge under the original loading and in accordance to modern design standards. The historical research revealed that the truss bridge was designed as a simply supported element and that a series of hand calculations were carried out on individual structural elements (e.g. main trusses, stringers and floor beams). Furthermore, a dynamic test was conducted in order to identify the global dynamic properties of the structure and to calibrate numerical models that ensure reliability and representativeness. FE models served through the structural assessment of the bridge in accordance with modern design codes and to estimate the safety of the bridge. Likewise, a nonlinear failure analysis was also conducted in order to estimate the capacity rate of the bridge and the likely failure modes.
Experimental Analysis of Bending and Axial Crush Behaviour of Single Hat Longitudinal Rail
Authors: Husain Nurulakmar Abu , Pang Chi Loog
Published: July 2013

This paper deals with experimental investigations of single hat longitudinal rail under quasi-static crush loading. A set of identical specimen which was simplified from actual automotive longitudinal rail was fabricated, and quasi-static testing (i.e., compression and bending test) were conducted. The main objective of this research was to study the failure mode, bending and tensile behaviour of the structure under bending and axial compression. In order to get the compressive load-displacement response and its corresponding deformation pattern, the compression test was carried out using a Universal Testing Machine. Stress-strain curve and energy absorption of the specimen were derived from the compressive load-displacement response. It was found that the quasi-static response of the specimen in compression case was affected by the number and position of spot welds. For the bending test, the bending load was found to be fluctuated with the displacement in a way analogous to the folding behaviour and deformation of the cross-section of the specimen. Bending moment-rotation characteristic was derived from bending load-displacement curve to investigate the energy absorption of the specimen in bending case. Lastly, the von Mises stress at the top and bottom surface of the specimen is increased with increment of the punch head travel distance.
On the Assessment of Fatigue Damage in Railway Bridges
Authors: O'Dwyer Dermot W.
Published: July 2013

This paper discusses the benefits to using direct strain measurements when undertaking a fatigue assessment of a railway bridge. The paper gives a brief overview of the assessment methodology for assessing fatigue in a bridge carrying a single track before outlining a method suitable for assessing multi-track bridges. The accuracy of a fatigue assessment depends on the level of knowledge of many different parameters including: an accurate loading history comprising axle loads and train frequencies over its service life; details of changes to the track form, including changes in the depth of ballast; and changes to the structure including damage or repairs. Many of these parameters are not known with certainty. However, using monitoring systems to measure the strain cycles in a bridge helps to address some of these uncertainties and hence improves the accuracy of the assessment.
Gear Fault Diagnosis Using Synchro-Squeezing Transform Based Feature Analysis
Authors: Hazra Budhaditya , Narasimhan Sriram
Published: July 2013

Synchro-squeezing transform has recently emerged as a powerful signal processing tool in non-stationary signal processing. Premised upon the concept of time-frequency (TF) reassignment, its basic objective is to provide a sharper representation of signals in the TF plane and extract the individual components of a non-stationary multi-component signal, akin to empirical mode decomposition (EMD). The rich mathematical structure based on continuous wavelet transform (CWT) makes synchro-squeezing powerful for gear fault diagnosis, as faulty gear signal is frequently constituted out of multiple amplitude-modulated and frequency-modulated signals embedded in noise. This work utilizes the decomposing power of synchro-squeezing transform to extract the IMFs from a gear signal followed by the application of standard gearbox condition indicators which promises greater prognostic power than that can be achieved by applying condition indictors directly to the inherently complex gear signals. The efficacy and the robustness of the algorithm are demonstrated with the aid of practical experimental data obtained from a helicopter gear box.
Bearings Fault Detection in Gas Compressor in Presence of High Level of Non-Gaussian Impulsive Noise
Authors: Barszcz Tomasz , Zimroz Radoslaw , Urbanek Jacek , Jabłoński Adam , Bartelmus Walter
Published: July 2013

The paper deals with the local damage detection in rolling element bearings in presence of a high level non-Gaussian noise. In many theoretical signal processing papers and engineering application related to damage detection, a simple model of the vibration is assumed. Basically it consists of signal of interest (SOI) and some unwanted (deterministic and/or random) components masking SOI in acquired observation. So, damage detection problem has to concern filtering, decomposition or extraction issue. Unfortunately, in the most of the industrial systems mentioned unwanted sources are in fact not Gaussian, so many of de-noising techniques cannot be applied directly or at least might give unexpected results. In this paper an industrial example will be discussed and novel approach based on advanced cyclostationary-based technique will be proposed. In the paper disturbances include periodic impacts in reciprocating compressor on an oil rig. Existing classical detection techniques (statistics in time domain, analysis of envelope spectrum, time-frequency decompositions) are insufficient to perform the task due to high power of disturbance contribution in comparison to damage signature. In the proposed technique, the Spectral Coherence Density Map (SCDM) is estimated first. Next step is related to analysis of SCDM contents and selection of informative part. If informative and non-informative components lay in separate frequency regions, such selection should fix the problem immediately
Virtual Structural Monitoring of Wind Turbines Using Operational Modal Analysis Techniques
Authors: di Lorenzo Emilio , Manzato Simone , Peeters Bart , van der Auweraer Herman
Published: July 2013

Operational Modal Analysis (OMA), also known as output-only modal analysis, allows identifying modal parameters only by using the response measurements of the structures in operational conditions when the input forces cannot be measured. These information can then be used to improve numerical models in order to monitor the operating and structural conditions of the system. This is a critical aspect both for condition monitoring and maintenance of large wind turbines, particularly in the off-shore sector where operation and maintenance represent a high percentage of total costs. Although OMA is widely applied, the wind turbine case still remains an open issue. Numerical aeroelastic models could be used, once they have been validated, to introduce virtual damages to the structures in order to analyze the generated data. Results from such models can then be used as baseline to monitor the operating and structural condition of the machine.
Advanced Tools for Damage Detection in Wind Turbines
Authors: Antoniadou Ifigeneia , Dervilis Nikolaos , Barthorpe Robert J. , Manson Graeme , Worden Keith
Published: July 2013

The paper summarises some advanced damage detection approaches used for Structural Health Monitoring (SHM) and Condition Monitoring (CM) of wind turbine systems. In the signal processing part, recent time-frequency analysis methods will be presented and examples of their application on condition monitoring of gearboxes will be given. In the pattern recognition part, examples of damage detection in blades will be used to introduce different algorithms for novelty detection.
Dynamic Responses of a Scaled Tension Leg Platform, Wind Turbine Support Structure in a Wave Tank
Authors: Murphy Jimmy , O’Shea Richard , O’Sullivan Keith , Pakrashi Vikram
Published: July 2013

Understanding the dynamic behaviour of offshore wind and wave energy devices is extremely important in relation to the maintenance and management of these marine assets. Since experimentation in sea may often be difficult, expensive or unnecessary at a conceptual or at pre-commercial stage, scaled experimentation in wave tanks can be central to the understanding and assessment of their dynamic responses. This paper presents scaled dynamic testing in a wave tank of a tension leg platform for supporting a wind turbine for different regular wave conditions and sea states characterised by the Bretschneider spectra. The dynamic response of the device was monitored at different locations on the device using load cells and with a camera based motion recognition system. For the analysis, a frequency response function based approach was considered to illustrate the response of the device under varied wave loading conditions. The experimentation does not assume any underlying theoretical model, apart from the consideration of Froude scaling conditions to attempt to link experimentation conditions with actual conditions. The results are important for characterisation of theoretical models and fitting parameters of such theoretical models, while identifying the limits and potential challenges of applying linear dynamic analysis in these situations. The findings are also important for establishing system identification and control strategies for undesirable levels of dynamic response. The fitted models based on physical modelling, when combined with scaled experimental responses, can also be helpful in better estimating extreme responses of the devices.
Simulation of the Stochastic Wave Loads Using a Physical Modeling Approach
Authors: Liu W.F. , Sichani M.T. , Nielsen S.R.K. , Peng Y.B. , Chen J.B. , Li J.
Published: July 2013

In analyzing stochastic dynamic systems, analysis of the system uncertainty due to randomness in the loads plays a crucial role. Typically time series of the stochastic loads are simulated using traditional random phase method. This approach combined with fast Fourier transform algorithm makes an efficient way of simulating realizations of the stochastic load processes. However it requires many random variables, i.e. in the order of magnitude of 1000, to be included in the load model. Unfortunately having too many random variables in the problem makes considerable difficulties in analyzing system reliability or its uncertainty. Moreover applicability of the probability density evolution method on engineering problems faces critical difficulties when the system embeds too many random variables. Hence it is useful to devise a method which can make realization of the stochastic load processes with low, say less than 20, number of random variables. In this article we introduce an approach, so-called "physical modeling of stochastic processes", and show its applicability for simulation of the wave surface elevation.
Generalized Stochastic Constraint TARMA Models for In-Operation Identification of Wind Turbine Non-Stationary Dynamics
Authors: Avendaño-Valencia Luis David , Fassois Spilios D.
Published: July 2013

The identification of the operational Wind Turbine (WT) dynamics is a challenging problem, due to both the complex dynamics and the non-stationarity of the vibration response. In this study the novel class of Generalized Stochastic Constraint (GSC) Time-dependent ARMA models is used for the identification of the non-stationary characteristics of acceleration vibration signals acquired in the tower top of an operating WT, in the fore-aft and lateral directions. The results demonstrate the improved performance of GSC-TARMA models compared to their conventional Smoothness Priors (SP) and Functional Series (FS) counterparts. The obtained models confirm the presence of cyclo-stationary and broader non-stationary behavior in WT vibration. The model based frozen time-varying modes of vibration are analyzed, and the modal components of the vibration accelerations are pictorially presented on the plane defined by the fore-aft and lateral axes.
Dynamic Stall on Rotating Airfoils: A Look at the N-Sequence Data from the NREL Phase VI Experiment
Authors: Guntur Srinivas , Sørensen Niels N. , Schreck Scott
Published: July 2013

This paper presents an investigation on the combined effect of dynamic stall and rotational augmentation on wind turbine blades. Dynamic stall and rotational augmentation have previously been studied independently. The NREL Phase VI experiment was one large scale experiment that recorded 3D measurements on rotating and pitching airfoils, and using some these data the behaviour of the unsteady CL-α polars under the influence of rotation is investigated. Unsteady DES CFD computations of the Phase VI rotor in axial operation and continuous pitching conditions (reproducing conditions similar to the N-sequence experiments) for select cases have also been carried out using the in-house flow solver EllipSys3D. The resulting set of CL-α curves for the airfoils in rotation operating at various values of the frequency, the mean, and the amplitude of the angle of attack resulting from the CFD computations as well as those from the experiments are presented and discussed. Qualitative differences between dynamic stall occurrence on rotating and stationary airfoils are highlighted, procedures employed to extract the mean angle of attack from the available experimental data are discussed, and comments are made on the application of dynamic stall models in conjunction with 3D augmentation models on the rotating wind turbine blades.