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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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Experimentální studie dynamiky chůze ve vertikálním a horizontálním směru
Pirner, Miroš ; Urushadze, Shota
The authors have noticed the newest observations and few analysis of excitation mechanism. They suppose that the import knowledge of the forces frequencies of step or strides for different walking velocities is the most important for the further analysis and analysis of the mechanisms. The authors received the vertical force dependence on the walking velocity, on stride length and on the weight of pedestrian. The new research step is focused onlateral horizontal forces.
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Basic information serving to developed qualitatively new codes corresponding to probabilistic assessment exposed to dynamic loaded structures
Pirner, Miroš ; Fischer, Ondřej ; Marek, Pavel ; Urushadze, Shota
The first condition for a reliable structure is a well-judged design, correctly and carefully calculated, and based on authentic input values. So fare we were used to take these values from the Codes and in the case that they can very accidentally, this variability can be respected by means of a coefficient. A more realistic approach is to take into account directly the random nature of the property in question, and to describe it in probabilistic terms (by a histogram). This can be done with the use of SBRA (Simulation Based Reliability Assessment) method. Here some considerations are shown, how the actual Czech Codes should be reorganized for probabilistic design, in the case of dynamic civil engineering problems. In this paper the problems of loading are treated; the problems of structural response and some special examples are shown in the full text on CD.
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