1,720,973 research outputs found
Comparison of different serviceability assessment measures for different events held in the G. Meazza Stadium in Milano
No full textStadia structures, like the G. Meazza in Milano, nowadays host many events that they were not originally designed for. Apart from the traditional football matches many live rock concerts and other public happenings are hosted. In this paper a comparison is made in order to classify the different kind of events in terms of vibration serviceability assessment measurements. The reached vibration levels must be evaluated against the serviceability levels given in existing guidance in order to prevent dangerous situations, such as panic or other uncontrollable phenomena in the crowd. Standards exist to evaluate vibration levels, among them the most widely used are ISO2631-1, ISO2631-2 and BS6841, which differ in the frequency weighting used and in the quantities used to identify the vibration, even though the starting point is the same measured acceleration time histories. More than a comparison of the two standards, already discussed in other papers, this paper investigates the level reached during different events and the influence of all choices left free to the technician performing measurements. Standards are applied to a set of vibration measurements taken on different events on different parts of the G. Meazza stadium. Results are then compared to the reference values suggested in the standards and to the limits found in literature. The effect of the dynamic response of the different sub-structures of the stadium on the reached vibration levels is analyzed and a set of results are given in order to asses the validity of limits given both in the standards and in literature. © 2009 Society for Experimental Mechanics Inc
Rail inspection in track maintenance: A benchmark between the wavelet approach and the more conventional Fourier analysis
No full textNowadays the power of data analysis tools like the wavelet decomposition of signals is well known and spread. On the other hand the theoretical advantages of such methods often fight with reality, when real field signals are collected and analysed: it sometimes comes out that this time–frequency approach somehow fails, demanding for a deeper insight into the kind of physical problem to be considered, and requiring a sort of “benchmark” between the traditional Fourier approach and the more recent time–frequency one. In this paper, sharply application-oriented, the possibilities offered by the wavelet techniques have been analysed: both the DSP specialist and the field engineer points of view have been joined to exploit the new approach of its best. A real problem has been considered, in which acceleration signals from a train bogie are collected and real-time analysed, to get a diagnostic tool to know the track condition of a subway line. This paper would like to look for a compromise point between complex mathematics based techniques, such as wavelet packet, sometimes hard to comprehend to the application engineer, and the physical meaning of these tools helping in fixing the real method limits.
Therefore the aim is not just trying this analysis on an almost random process, like the accelerations measured on a running bogie, to locate defects, but rather a discussion on the development of the continuous and discrete wavelet transform, in comparison with the classical Fourier analysis or filter banks. Only the minimum mathematical background is provided in the text, with the needed references, to give tools fit for comprehending the physical meaning of the new tools, capable of sparing computing effort, while preserving or even improving the system effectiveness
Evaluation of serviceability assessment measures for different stadia structures and different live concert events
No full textNowadays large civil structures such as stadia and basketball fields host many events that they were not originally designed for. In particular, live rock concerts are the ones raising problems linked to the higher level of vibrations reached and sometimes maintained for a significant duration. These vibration levels must be evaluated against the serviceability levels given in existing guidance in order to prevent dangerous situations, such as panic or other uncontrollable phenomena in the crowd. Standards exist to evaluate vibration levels, among them the most widely used are ISO2631 and BS6841, which differ in the frequency weighting used and in the quantities used to identify the vibration, even though the starting point is the same measured time histories. In this paper the two standards are compared in different situations to evaluate their efficiency in detecting anomalous vibration levels. The comparison is performed considering different events in the same structure (G. Meazza Stadium in Milano) and comparing the same event in two different structures (Red Hot Chili Peppers in the Milano and Manchester Stadium). The obtained results are a good starting base for the evaluation of the performance of the standards and also to evaluate the performance in terms of vibration serviceability of the different structures
Influence of the measurement mesh on the spread of the modal parameters of a stadium grandstand, identified via Operational Modal Analysis techniques
No full textOperational modal analysis offers a powerful tool to the aim of structural health monitoring of civil structures. Vibration data gathered during the structure normal life can be used to identify a set of modal parameters and so to keep their evolution under control. Anyway this kind of modal analysis leads to results that are affected by a higher spread if compared to the ones given by the traditional experimental modal analysis performed using known forcing. This is mainly due to the forcing nature, which is assumed to be white noise but this is often a wide assumption, and to the external parameters values, such as temperature or structure loading which are changing from one identification to the others and are seldom measurable. The aim of this paper is to investigate the influence of the number of measurement points on the spread in the identification of the modal parameters of one of the Milano Stadium grandstands. At the moment only two accelerometers per stand are installed in the stadium as permanent monitoring transducers to provide an indication of the reached maximum vibration levels, the idea is to exploit the same system to the aim of monitoring the modal parameters evolution. In this work the advantages of increasing the number of sensors per stand is investigated studying its influence on the spread of the identified parameters. © 2009 Society for Experimental Mechanics In
Evaluation of performances and reliability of a wavelet based modal parameter estimation method applied on the modal identification of the Meazza stadium grandstands in Milan
No full text
Experimental investigation of the pre-tension effects on the modalparameters of a slender pre-tensioned concrete beam
No full textSlender pre-tensioned concrete structures are nowadays of common use, due to their unique features. Slender beam can be used to sustain large structures and important loads leaving the architects a lot possibilities in the structure design. The health of such structures is strictly related to the conditions of the tendon that, in many cases, are not accessible. Visual inspection is the most used technique to assess the tendon condition even if in many cases access to the inspection points is very difficult or impossible This paper investigates the possibility of detecting a pre-stress loss or a tendon failure by means of modal analysis. A pre-stressed concrete beam has been built and tested under laboratory conditions, varying the applied pre-stress and the number of active tendon. Modal analysis has been performed in each of the experimental condition and attention has been focussed on the variation of all identified modal parameters, frequency, damping and mode shapes. Furthermore a set of damage indexes have been computed to highlight the most sensible magnitude able to identify a change on the structure. Obtained results showed that an accurate analysis is needed in order to identify a change in modal parameters due to variations in the pre-stress, while tendon failure leads to more important changes in the identification results. The performed study are the starting point in order to properly tune a numerical model of the beam useful to accurately interpreter structural changes. ©2010 Society for Experimental Mechanics Inc
Comparison between different operational modal analysis techniques for the identification of large civil structure modal parameters
No full textA reliable modal analysis is fundamental in vibration-measurements-based monitoring of large civil structures, such as the grandstands of the Meazza stadium in Milan. In this paper different techniques to extract the modal parameters out of data gathered under normal operational conditions have been compared: these methods work both in time and frequency domain,. A large amount of data has been collected since summer '03 during different sort of events: concerts, football matches and windy days; in all events a lot of different measurement points have been acquired and this allowed to apply all the identification techniques with different kinds of excitation. The comparison also takes into account the capability to correctly identify the modal parameters while reducing the number of transducers put on the structure. This will allow for a reduction of the number of transducers being part of the permanent monitoring system that is going to equip the structure in a close future
A measurement system for quick rail inspection and effective track maintenance strategy
No full textSafety and environment impact of urban railway play a primary role in the management of Public Transportation Companies. One of the critical problem is trackmaintenance activity, requiring a reliable knowledge of the rail status (such as, for urban transport system, corrugation and localised damage) so that a proper intervention can be performed only when necessary. The public transportation company of Milan (ATM S.p.A.) has started a cooperation with Politecnico di Milano to develop new techniques for track condition inspection, through accelerometer measurements performed on standard operating bogies. This avoids the use of special cars that can operate only when traffic is stopped and permits the collection of a large amount of data improving reliability through measurement repetitions. A feasibility study of a foolproof diagnostic tool is developed in this paper. In particular, it shows the best measurement points, how the sub-structure on which the train is travelling, and the travelling conditions influence the recorded vibration levels. Signal processing techniques, at this stage, are still off-line. Anyway the system has already been designed in order to work under “real time” conditions (a prototype is already existing), also reducing the huge amount of collected data to keep only the essential ones. The attentions have been focused here on the measurement problem, postponing the theoretical aspects to a future paper
- …
