Damage and repair classification in reinforced concrete beams using frequency domain data

This research aims at developing a new vibration-based damage classification technique that can efficiently be applied to a real-time large data. Statistical pattern recognition paradigm is relevant to perform a reliable site-location damage diagnosis system. By adopting such paradigm, the finite element and other inverse models with their intensive computations, corrections and inherent inaccuracies can be avoided. In this research, a two-stage combination between principal component analysis and Karhunen-Loéve transformation (also known as canonical correlation analysis) was proposed as a statistical-based damage classification technique. Vibration measurements from frequency domain were tested as possible damage-sensitive features. The performance of the proposed system was tested and verified on real vibration measurements collected from five laboratory-scale reinforced concrete beams modelled with various ranges of defects. The results of the system helped in distinguishing between normal and damaged patterns in structural vibration data. Most importantly, the system further dissected reasonably each main damage group into subgroups according to their severity of damage. Its efficiency was conclusively proved on data from both frequency response functions and response-only functions. The outcomes of this two-stage system showed a realistic detection and classification and outperform results from the principal component analysis-only. The success of this classification model is substantially tenable because the observed clusters come from well-controlled and known state conditions

Vibration fatigue analysis of circumferentially notched specimens under coupled multiaxial random vibration environments

<p>The time-domain critical plane-based Carpinteri et al. criterion and the Theory of the Critical Distance are here combined together so as to propose a novel procedure for vibration fatigue analysis of circumferentially notched specimens subjected to coupled multiaxial random vibration environments.  A novel metallic testing equipment is specially devised for notched specimen, meanwhile biaxial random vibration environment fatigue test is specially implemented on notched specimen in order to investigate how both coherence and phase shift between the ASD auto-spectral density functions in different directions influence the specimen fatigue life.  The location of the verification point where to perform the fatigue damage estimation is determined by applying both the point method and the Carpinteri et al. criterion (for damage evaluation).  The obtained results prove that the proposed procedure can provide satisfactory fatigue life estimations.</p&gt

Experimental Assessment of a Modal-Based Multi-Parameter Method for Locating Damage in Composite Laminates

The low specific weight of composite materials, together with their excellent mechanical properties, make them suitable to be widely used in many modern engineering structures. However, composite materials are quite sensitive to impacts: a specific kind of damage, called Barely Visible Impact Damage (BVID), may occur, constituting an unsafe failure of difficult assessment. In the past few years several methods have been developed aiming at assessing this type of damage. In this paper, a vibration-based technique that combines both the natural frequencies and the modal damping factors as damage sensitive features is tested for locating impact damage in carbon fibre reinforced laminates. The method is intended to be used for locating damage in real laminated composite structures that undergo in-service impacts, such as an airplane's fuselage or wings. Assessing a minimum of one response coordinate is the strict requirement during each inspection, because it uses the dynamic global parameters of the structure as damage features. This is possible because the method assumes that, at least for BVID, the mode shapes remain practically unchanged. The theory is summarized and the method is tested using experimental setups where damage is introduced at different locations. Additionally, the hypothesis that different damage morphologies on composite materials have different contributions to the damage features is addressed.Peer reviewedFinal Accepted Versio