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Assessment of vibrations in museum's environment
Valach, Jaroslav ; Wolf, Benjamin ; Paulová, E. ; Urushadze, Shota
This paper deals with measurement of mechanical vibrations and accelerations threatening objects in museum collections. Two case studies are presented. The first case analyses situation in museum exhibitions strongly influenced by street traffic in its close proximity. It compares results obtained by sensitive professional measurement system to the custom-built user device for acceleration recording. The second case analyzes object’s accelerations during transport based on measurement by the custom-built device.
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Problems connected with the application of lamella flanges in steel bridge construction
Křístek, V. ; Kunrt, J. ; Škaloud, Miroslav ; Urushadze, Shota
Lamella flanges have lately grown very popular with the designers of steel bridges, because - in their belief - they provide us with the possibility of avoiding very thick flange plates in steel bridge structures. This belief is based on the assumption that the lamellas are perfectly plane and therefore, in perfect contact everywhere, so that the loading from one lamela is transmitted into other via pure compression, and that the perfect interaction of both lamellas is materialized by means of boundary fillet welds connecting both of the two lamellas. This simple assumption is, however, far from reality: it is not the means of steel fabricators, not even in the means of those which are very progressively equipped, to produce perfectly plane lamellas. Then both lamellass exhibit unavoidable initial curvatures, which in combination form a gap between the lamellas, and consequently the directly loaded lamela are pressed into this gap. As the loading acting on every bridge is many times repeated, the aforsaid phenomenon is also many times repeated, (we can say that the lamellas "breathe"), and then an unavoidable cumulative damage proces in the lamellas comes to being. The results of investigation will be described in the paper and thereby will demonstrate that the fatigue phenomenon accompanying the breathing of the lamellas can considerably limit the lifetime of the structure.
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Breathing-induced fatigue in thin-walled steel bridge construction
Škaloud, Miroslav ; Zörnerová, Marie ; Urushadze, Shota
Several years ago, the authors started an experimental investigation into the breathing phenomenon of the webs of thin-walled steel girders , which to date comprised more than two hundred tests. The cumulative damage behaviour generated by web breathing was analysed, the process of the initiation and propagation of fatigue cracks induced thereby was studied, and their impact on the failure mechanism and the fatigue limit state of the girders was determined. And, to conclude, a recommendation for design, taking account of the aforesaid, was established.
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Seismic performance of timber frames
Pospíšil, Stanislav ; Urushadze, Shota ; Koleš, Jan
A series of dynamic experiments was performed on one-story timber frame. In comparison with the previous frames [1, 2], improved connection between column and girder was used here. The tests included sinusoidal sweeps in two directions, arbitrary signals simulation earthquake loads in three directions, and snapback tests. Various parameters were measured, for example tension on columns and slabs, rotation between columns and beams, displacement of columns and acceleration of columns and beams. All these parameters lead to classification of the frame behavior with designed type of connection, for example the natural frequencies, eigenmodes and other dynamical properties of the structure. Parameter description will allow us to design and improve mathematical model of the timber frame.
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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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