Damage Assessment of Structures VII

Paper Title Page

Authors: Chun Sheng Wang, Hui Qian, Ang Zhan, Yue Xu, Da Lin Hu
Abstract: Nen’jiang No.1 Bridge has been used for 70 year, so fatigue, fracture and corrosion dominate the remaining life of this bridge. Obviously the designer did not take into consideration the fatigue problem at that time. In order to keep this bridge in service economically as long as possible, bridge owner decides to take measures to preserve its service safety. Thus the remaining fatigue life and fracture failure risk need to be evaluated. The analytical results according to the fracture mechanic based concept show that the diagonal edge members U0L1 and U9L8 have the shortest remaining fatigue life, and some members have a potential risk of brittle failure. The fracture failure risk evaluation results show that the toughness of main truss member steel is lower than the code requirement, and members such as U0L1 and U9L8 have brittle fracture failure risk in cold winter. So this bridge should be temporarily closed traffic in winter.
Authors: Seong Wook Lee, Tae Won Ahn, Dong Seop Han, Tae Hyung Kim, Geun Jo Han
Abstract: In this study we carried out to analyze the effect of wind load on the structural stability of a container crane according to the change of the boom shape using wind tunnel test and provided a container crane designer with data which can be used in a wind resistance design of a container crane assuming that a wind load at 75m/s wind velocity is applied on a container crane. Data acquisition conditions for this experiment were established in accordance with the similarity. The scale of a container crane dimension, wind velocity and time were chosen as 1/200, 1/13.3 and 1/15. And this experiment was implemented in an Eiffel type atmospheric boundary-layer wind tunnel with 11.52m2 cross-section area. Each directional drag and overturning moment coefficients were investigated.
Authors: Alessandro Fasana, Luigi Garibaldi
Abstract: The acoustic emission (AE) technique, whose modern roots are found in the early 50’s, analyses the elastic waves generated into solid materials in a frequency range usually well above the human ears limit. AE are sound waves emitted when abrupt variations occur in the local distribution of strain in a medium. These variations are generally associated with, for example, the growth of fractures, phase transformations and corrosion under various loading conditions. This is why the AE technique can be applied as a non destructive and passive tool in condition monitoring of structures, a typical application being the pressure vessels and piping field. In this paper, after a short summary on wave propagation, the AE is simulated by a pulse generator, acting on a bar and a plate. The aim is to highlight the effects of the sensors positioning on some of the parameters frequently adopted to describe the AE activity, e.g. its amplitude and strength.
Authors: Rhys Pullin, Pete T. Theobald, Karen M. Holford, S.L. Evans
Abstract: This paper reports on a method for numerically modelling acoustic emission signals in simple plate geometries using dispersion curves. It is demonstrated how, by using a known source to sensor distance, it is possible to determine the arrival of the frequencies of the individual AE modes at the sensor face. Assumptions based on sensor frequency response and the amplitude of individual modes allow for an approximation of each mode arriving at the sensor face. These modes are then summed to provide a numerical model of the expected signal. Results of the model are compared with a recorded signal and show good correlation, this is further demonstrated by comparing the wavelet transforms of the modelled and recorded signal.
Authors: P. Kraemer, Claus Peter Fritzen
Abstract: This paper presents a combined approach for sensor fault identification looking for changes within one channel on one hand and for changes between the different channels on the other hand. The first method is based on the identification of autoregressive (AR) models from the reference time signals for each sensor channel separately. The reference models are then used for the prediction of the future sensors signals. The statistical properties of the residuals between this prediction and the true measurement allow a statement about changes of the sensor signals. The second method is based on the concept of mutual information between two signals X and Y from two different sensors. Mutual information or transinformation measures the information about the channel X that is shared by Y. This requires a certain redundancy of information represented in the different sensor signals. It can be seen that the mutual information changes as soon as a sensor fault occurs because the sensor fault information is not present in the other sensor signals.
Authors: Cristiana Delprete, Carlo Rosso
Abstract: The paper presents the design of a new optic fibre sensor that simultaneously measures normal deformation, cross-sectional deformation and temperature with the minimum number of sensible elements. It is based on two assembled in phase quadrature traditional Fabry-Perot sensors. Lightness and the extreme compactness make the proposed sensor suitable to equipe composite materials with low specific weight and various percentage in fibre volume, that it can be used for aeronautical and/or automotive applications without modifying mechanical characteristics. The example host material is Ti-6Al-4V/SiC composite characterized with the volume fraction of carbon fibres of 35%; it permits to insert the sensor at low temperature by means of Cold-Gas Spray technology. Sensor construction is quite easy and does not require great economical effort in comparison with other types of optic fibre sensors reported in literature. The sensor has the capability of independently measuring the thermal and mechanical (bending and traction) loads. It has a great sensibility indeed it allows evaluating μm displacements and bending angle of the order of one hundredth of degree, operating in a temperature range between −190°C and 750°C. The paper concludes with the description of the mathematical model of the proposed sensor and with the correspondent numerical characterization in order to estimate sensor capabilities. Numerical simulation points out the potentials of the new proposed sensor.
Authors: Daniele Tosi, Massimo Olivero, Guido Perrone
Abstract: In the present work we report on the development of a low cost interrogation system of fiber Bragg grating sensors for structural health monitoring. The developed scheme uses two gratings and a directional coupler as sensing point, and it includes self-compensation of temperature effects. The reading equipment consists of a standard photodiode for telecom applications with custom signal-conditioning electronics. The characterization of multiplexed sensors, carried out in real framework conditions, shows that the system can work in a temperature range of -20÷+40°C, making strain measurements up to at least 320με with an accuracy of ~3% and an acquisition rate of 12 samples/min. Further, a budget evaluation is drawn to asses the feasibility of our interrogation system as a low cost solution to increase the extent of structural health monitoring in funds-limited applications.
Authors: Daniel J. Inman, Justin Farmer, Benjamin L. Grisso
Abstract: Autonomous, wireless structural health monitoring is one of the key goals of the damage monitoring industry. One of the main roadblocks to achieving autonomous sensing is removing all wiring to and from the sensor. Removing external connections requires that the sensor have its own power source in order to be able to broadcast/telemetry information. Furthermore if the sensor is to be autonomous in any way, it must contain some sort of computing and requires additional power to run computational algorithms. The obvious choice for wireless power is a battery. However, batteries often need periodical replacement. The work presented here focuses on using ambient energy to power an autonomous sensor system and recharge batteries and capacitors used to run an active sensing system. In particular, we examine methods of harvesting energy to run sensor systems from ambient vibration energy using piezoelectric elements.
Authors: A.P. Bovsunovsky, O. Bovsunovsky
Abstract: A closing crack causes the dynamic behavior of a vibrating system to be significantly non-linear and, consequently, the appearance of non-linear resonances (that is super- and subharmonic one). The main idea of the proposed procedure of crack location and size estimation is based on the determination of the vibration response non-linearity around the superharmonic resonance of order 2/1 and subharmonic resonance of order 1/2 at different parameters of driving force. First parameter of driving force under investigation is its point of application. It is shown both numerically, with the use of the finite element model of a cracked beam, and experimentally that the level of non-linearity of vibration response at non-linear resonances is strongly dependent not only on the crack size but also on the driving force application point along the cracked beam. Moreover, the abrupt change of the non-linearity of vibration response when driving force is applied close to the crack clearly indicates its location. In such a way the procedure of damage detection is proposed to estimate both the crack size and location in beams. Second parameter is the level of driving force asymmetry. Addition of the static component to the harmonic driving force varies the state of crack making crack more or fully open or closed. As a result the level of non-linearity of vibration response at any non-linear resonance varies from maximal value (in absence of static component) to practically zero value (when the static component of driving force is so large that crack becomes permanently open or closed at vibration). In such a way the presence of crack can be detected without preliminary information on the vibration response of a structure in the intact state.
Authors: Andreas Kyprianou, Cristinel Mares, Charalambos D. Charalambous, John E. Mottershead
Abstract: Relative entropy has been employed, as an alternative to other regularization methods, in solving ill-conditioned linear inverse problems. Damage detection when treated as structural modification imparted by the damage leads to a linear inverse problem involving frequency response functions. This problem is amenable to ill-conditioning issues that could arise from the low frequency response values and noisy experiments. This article formulates and solves using the minimum relative entropy method the damage detection and localization problem on a simulated cantilever beam.

Showing 51 to 60 of 103 Paper Titles