1,721,124 research outputs found
Wind action on the london eye cables. Part 2: damping device design and field measurements
Full text linkThis paper is part two in the description of the London Eye panoramic wheel damping system design. The system is meant to protect the structure against the wind action, mainly the aeolian vibrations and ice galloping. A particular accent on the experimental techniques and their critical review is put in this second section
Modal parameter changes of lowly damped civil structures due to people-structure interaction
No full textThe interaction between civil structures and people has been a widely studied topic in the last years and the comprehension of the whole system dynamics is considered a valuable tool to the purpose of structural health monitoring. This paper is intended to give evidence of people effects on the modal behaviour of very lowly damped civil structures, the considered is case is a steel stair walkway, placed at the ground floor of a new skyscraper in a Spanish city. The modal analysis of such a walkway has been carried out in different conditions, by forcing the structure by means of a hydraulic actuator and exploiting ambient vibrations. This allowed to achieve full knowledge of the stair dynamic behaviour alone. Furthermore a comparison between the two identification methods has been made possible. Then tests with 22 and 44 people walking on the stair have been performed to assess the structure vibration levels under operational condition and therefore consider all serviceability issues according to the international standards. In the meantime vibration data were used to compute the modal parameters of the complete system (stair + people). The results show that there is a significant damping ratio increase for the first modes at low frequency, once increasing the number of people. This limits the overall vibration levels, although the excitement is increased with the number of people. The damping ratio increase due to people is about 400 % for the first eigenmode when 44 people are walking together
Monitoring and qualification of a new track: long-time data acquisition campaign and data saving strategies
No full textMicrophone array measurements for the identification of mobile noise sources
No full textA modern parameter in the global quality assessment of high speed trains is the noise emission. An
innovative method for the identification and comparison of mobile acoustic sources was implemented: the
microphone array. Basis of the method is the “beamforming algorithm” that from a measure of the
acoustic pressure in several points allows to investigate the position and the characteristics of the sound
source. This source can be either fixed or moving respect to the array making the method capable of
separating different sources among a general noise signal perceived during a vehicle pass-by.
The method was developed using numerical models and proved to be effective testing it on site with
different known sound sources both fixed and moving.
After these tests an application of the pass-by noise measurements generated by a rail convoy was
investigated. The occasion was given by an experimental campaign settled for the evaluation of noise and
vibration emission of a standard ballast superstructure, within an European research
program(“HIPERTRACK”). Results showed the capability of the method to distinguish multiple sound
sources. The method showed the possibility to identify the noise emitted by a single wheelset. In this
paper an analysis of the noise emitted by the wheel-track interaction of different convoy typologies on the
same ballast superstructure has been performed and results will be discussed. A comparison between
noise and vibration recorded on the rail showed a good agreement. Time/frequency analysis was finally
implemented to identify the spectrum of the emission associated with every single bogie
L’INTERAZIONE UOMO-STRUTTURA E LA SUA MODELLAZIONE PER UNA PROGETTAZIONE STRUTTURALE AFFIDABILE
No full textTecniche per l’identificazione di sorgenti sonore: confronto tra beamforming e olografia acustica
No full textComparison 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
Two-Stage Automated Defect Recognition Algorithm for the Analysis of Infrared Images
No full textIn this article an algorithm for the analysis of raw thermal infrared images is proposed. The images are obtained by using the nondestructive evaluation method of the laser-spot thermography and aim at detecting the presence of surface defects. A laser is used to scan a test specimen through the generation of single pulses. The temperature distribution produced by this thermoelastic source is measured by an infrared camera and processed with a two-stage algorithm. In the first stage, simple mathematical and statistical parameters are used to flag the presence of damage. Then, once damage is detected, the thermal image's first and second spatial derivative and two spatial filters are computed to enhance contrast, and to locate and size the defect. Some of the advantages of the proposed method with respect to existing approaches include automation in the defect detection process and better defective area isolation through increased contrast.
The algorithm is first proven by analyzing simulated thermal images, and then it is experimentally validated by scanning the surface of a CFRP composite plate with induced defects
Long term operational modal analysis of a stadium grandstand to structural health monitoring purposes
No full textIn the last years an increasing interest has been devoted to all the topics related to security and safety of people. Particular attention has been paid to health monitoring of large civil structures hosting lot of people, like high-rise buildings and stadia. The vast scientific literature confirms the possibility to relate structural health to the evolution of modal parameters, often reaching the aim of localizing any eventual damage, a task otherwise impossible with different techniques. This paper shows a part of the long lasting project involving Politecnico di Milano in the setting up of a permanent health monitoring system at the G. Meazza stadium in Milan. As damage identification is related to changes of the modal parameters, the evaluation of their normal spread is fundamental to fix a threshold in order to identify possible worrying situations. This paper deals with the identification of the spread in the modal parameter estimation of one of the grandstands of the so-called 3° ring of the G. Meazza stadium in Milan, setting up an automated Operational Modal Analysis algorithm and analyzing a first set of data. Some ideas are gathered in order to identify the minimum number of identifications needed to have a robust estimation of the modal parameters. ©2009 IEEE
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