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Investigation of composite material degradation indicators using acoustic measurement: comparison with laser vibrometry
Fíla, Tomáš ; Urushadze, Shota ; Kytýř, Daniel ; Valach, Jaroslav ; Šperl, Martin
This paper deals with investigation of acoustic material degradation indicator (attenuation decrement drop of selected natural frequency) measured by a custom-built experimental device. Samples of C/PPS fibre composite material were analyzed. Acoustic signals were recorded and processed using spectral analysis and sound signal regression. Data measured by this method were verified by comparative experiment. Specimens were simultaneously measured using both acoustic experimental device and laser vibrometer. Modal analysis of the specimen were carried out prior to the experiment. This enabled assessment of specimens natural modes and therefore the best impact zone. In total, 10 measurements were performed for each specimen at the same level of degradation. Measured data were then processed and compared. The specimens were repetitively measured after designated number of loading cycles.
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Cyclic loading of masonry walls and its anti seismic reinforcing
Wünsche, Martin ; Hračov, Stanislav ; Pospíšil, Stanislav ; Urushadze, Shota
The damage of structural masonry walls is one of the most widespread harming injuries and cause of loss of serviceability and seismic capacity for a building. Therefore a research into possibilities which would improve these characteristics have been carried out within the 7th EC Framework programme project NIKER. The retrofitting approach is constrained by conservation requirements of minimum interventions which should not severely change the structural behavior and the structural appearance, and should prefer solutions without a necessity of total structural disassembling. This artikle provides an overview about the research that led to applications of the steel wire ropes and geo-nets ontoadobe brick walls.
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Experimental and numerical verification of vortex-induced vibration of hangers on the footbridge
Urushadze, Shota ; Pirner, Miroš ; Pospíšil, Stanislav ; Král, Radomil
The paper deals with vortex-induced oscillations of footbridge hangers at a very low wind speed. The two-spans (2x50m) reinforced concrete structure with the central pylon (25m height) is designed as the harp system of hangers with circular cross-section. The oscillations were observed at the low wind speed and the high double amplitudes has been measured. The wind-excited deformation shape corresponded to the 6th, 7th and 8th natural modes of a hanger. The individual hanger as well as thein group were analysed to estimate the dynamic response, possible aeroelastic vibration and special interference or coupling effects. It also includes proposal for the elimination of the extensive vibration. The analysis is complemented by numerical investigation using Computational Fluid Dynamics methods.
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Comparison of composite material degradation assesment methods using acoustic analysis and laser vibrometry
Urushadze, Shota ; Šperl, Martin ; Kytýř, D. ; Valach, J. ; Fíla, T.
Assessment of degradation rate of material can be carried out by many experimental techniques differing in complexity and sophistication. A relatively simple method based on acoustic analysis is described in this contribution. Degradation of material’s properties due to fatigue loading is detectable in decrease of their modulus of elasticity that can be derived from natural frequencies of specimens. These measurements utilize self-designed device capable of specimen excitation and acquisition of its vibration. The recorded signal is then processed by spectral analysis enabling determination of natural frequencies. Usefulness of the above mentioned acoustic method can be seen in the fact that the measured changes of material’s parameters are comparable to those obtained by laser vibrometry, which is by several orders more expensive technique.
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Investigations of orthotropic decks
Urushadze, Shota ; Frýba, Ladislav ; Pirner, Miroš
The investgations of orthotropic decks carried out in the Institute of Theoretivcal and Applied Mechanics,v.v.i., Academy of Sciensces of the Czech Republic, for the project of the European Union „BRIFAG“ are described. The response of orthotropic decks is studie under dynamic loads including the crack propagation, estimation of fatigue life of the bridge elements, e.t.c. It was found that the most vulenrable detail appeared at the spatial connection of the deck with cross and longitudinal beams. The most important results are shown in a a figure of stress ranges as a function of the number of stress cycles.
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