Magdalena Rucka

Damage Location in Beam and Plate Structures by Wavelet Analysis of Experimentally Determined Mode Shapes

In this paper a method for estimating the damage location in beam and plate structures is presented. A plexiglas cantilever beam and a plexiglas plate with one fixed boundary condition are tested experimentally. The dynamic response of the structures is analyzed using one and twodimensional continuous wavelet transforms of the structural mode shapes. The location of the crack is indicated by a peak in the spatial variation of the transformed response. The proposed wavelet analysis can effectively identify the crack position without knowledge of either the structure characteristics or its mathematical model. The practical application of the technique for civil engineering structures requires only the response of the structure.

Research on assessment of bolted joint state using elastic wave propagation

The work contains results of experimental investigation of elastic wave propagation in a bolted single-lap joint. Tests were carried out for the excitation perpendicular to the connection plane. In experimental studies, PZT transducers were used for both excitation and registration of ultrasonic waves. The analyses took into account varying contact conditions between the elements of the connection depending on the value of the prestressing force. The influence of loosening/tightening of bolts on the energy dissipation was analysed. The experimental results proved the influence of bolt torque on quantitative characteristics of the signals. To improve the diagnostic possibilities only the initial parts of signals were analysed.

DAMAGE DETECTION OF A T-SHAPED PANEL BY WAVE PROPAGATION ANALYSIS IN THE PLANE STRESS

Abstract A computational approach to analysis of wave propagation in plane stress problems is presented. The initial-boundary value problem is spatially approximated by the multi-node C0 displacement-based isoparametric quadrilateral finite elements. To integrate the element matrices the multi-node Gauss-Legendre-Lobatto quadrature rule is employed. The temporal discretization is carried out by the Newmark type algorithm reformulated to accommodate the structure of local element matrices. Numerical simulations are conducted for a T-shaped steel panel for different cases of initial excitation. For diagnostic purposes, the uniformly distributed loads subjected to an edge of the T-joint are found to be the most appropriate for design of ultrasonic devices for monitoring the structural element integrity Streszczenie W pracy zaprezentowano podejscie obliczeniowe do analizy propagacji fal w płaskim stanie naprezenia. Problem brzegowo-poczatkowy podlega przestrzennej aproksymacji z uzyciem wielowezłowych, izoparametrycznych, czworobocznych elementów klasy C0. Macierze elementowe sa całkowane numerycznie za pomoca kwadratury Gauss-Legendre-Lobatto. Aproksymacje w dziedzinie czasu wykonano za pomoca algorytmu Newmarka. Symulacje numeryczne przeprowadzono dla tarczy w kształcie litery T dla róznych przypadków wzbudzania fali. W pracy wykazano, ze dla celów diagnostyki najlepszym rodzajem obciazenia jest obciazenie liniowe równomiernie przyłozone do krawedzi tarczy.

Wave propagation in damage assessment of ground anchors

The inspection possibilities of ground anchors are limited to destructive test such as pull-out test. Guided wave propagation gives an opportunity to develop an inspection system dedicated to determine the condition of inspected element without violation of their integrity. In this paper the experimental study on wave propagation in laboratory models of ground anchors are presented. Experiments were conducted for different bonding lengths and different frequencies of excitation. Waves were generated by a piezoelectric actuator and the laser vibrometry technique was used to register velocity signals. For all tested anchors it was possible to identify the boundary between steel and concrete based on the registered reflections in wave propagation signals.

Application of guided wave propagation in diagnostics of steel bridge components

Abstract Early detection of potential defects and identification of their location are necessary to ensure safe, reliable and long-term use of engineering structures. Non-destructive diagnostic tests based on guided wave propagation are becoming more popular because of the possibility to inspect large areas during a single measurement with a small number of sensors. The aim of this study is the application of guided wave propagation in non-destructive diagnostics of steel bridges. The paper contains results of numerical analyses for a typical railway bridge. The ability of damage detection using guided Lamb waves was demonstrated on the example of a part of a plate girder as well as a bolted connection. In addition, laboratory tests were performed to investigate the practical application of wave propagation for a steel plate and a prestressed bolted joint.

Diagnostics of pillars in St. Mary’s Church (Gdańsk, Poland) using the GPR method

ABSTRACT The main goal of this study was non-destructive evaluation of pillars in the St. Mary’s Church (Gdańsk, Poland) using the ground penetrating radar (GPR) technique. The GPR inspection was conducted on four brick masonry pillars and five pillars strengthened by reinforced concrete jacketing. Data were acquired with a 2 GHz antenna along longitudinal and transverse profiles. The study involved the estimation of the electromagnetic wave velocity in both brick and concrete, the inspection of the internal structure of the pillars, and the precise identification of reinforcement bars. To determine the wave velocity in bricks, a novel mathematical model was developed. Finite-difference time-domain (FDTD) simulations were used to verify and assess the feasibility of the proposed model. Finally, GPR maps were processed using the hyperbolic summation method to visualize the reinforcement distribution in the concrete jacket.

Lamb wave-based monitoring of shear failure of an adhesive lap joint

The paper presents a study on the elastic wave propagation in adhesive joints of steel plates subjected to tensile loading. A single lap joint was chosen for analysis because of its simplicity and plurality of applications. Experimental investigations consisted of the uniaxial extension of prepared specimens. Force and displacement values were recorded by a testing machine. Simultaneously, guided Lamb waves were excited and signals of their propagation were collected in a number of points by piezoelectric transducers attached to the specimen surface. Further processing of signals allowed to determine some disturbances in gathered data. The continuous wavelet transform revealed discontinuities in force-displacement relations. The Fourier transform showed changes in frequency values of recorded signals. Large disturbances of the root mean square values was also observed. The results of all analyses allowed to conclude that the identification of partial degradation state before the sample destruction was possible.

A concept of heterogeneous numerical model of concrete for GPR simulations

The Ground Penetrating Radar (GPR) method, which is increasingly being used in the non-destructive diagnostics of reinforced concrete structures, often needs more accurate interpretation tools for analysis of experimental data. Recently, there has been growing interest in developing of various numerical models for exhaustive understanding of GPR data. This paper presents the concept of a heterogeneous numerical model of concrete, in which individual components of concrete are separate materials and their location in the model is pseudo-random. The numerical model was validated with the Complex Refractive Index Model (CRIM). In addition, experimental surveys were conducted on a reinforced concrete footbridge with high saturation of water. Experimental radargrams were compared with numerical GPR maps, calculated using both homogeneous and heterogeneous models of concrete.

Dynamic Response of Forum Gdansk Structure due to Rail Traffic

Abstract This paper presents the study of the impact of vibration induced by the movement of the railway rolling stock on the Forum Gdańsk structure. This object is currently under construction and is located over the railway tracks in the vicinity of the Gdańsk Głowny and Gdańsk Środmieście railway stations. The analysis covers the influence of vibrations on the structure itself and on the people within. The in situ measurements on existing parts of the structure allow us to determine environmental excitations used for validation and verification of the derived FEM model. The numerical calculations made the estimates of the vibration amplitudes propagating throughout the whole structure possible.

Guided Waves in Steel Rails – Experimental Works and Wavelet Signal Processing

This paper presents experimental study on dispersive waves propagation in steel rails. The propagation of longitudinal and transverse waves was generated by an impulse hammer and measured in three points. Wavelet transform (WT) and short time Fourier transform (STFT) were applied to analyze the time signals. Analysis of signal by STFT does not provide a proper timefrequency representation due to a fixed size window. The wavelet transform can effectively identify the time-frequency components in waves. The wavelet signal processing of the experimental wave propagation signals is intended to be used for rail flaw detection.