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Dynamics of beam pair coupled by visco-elastic interlayer
Náprstek, Jiří ; Hračov, Stanislav
Two parallel slender beams with visco-elastic interlayer can serve as a relevant mathematical model of a number of engineering systems. A typical example is a double skin facade of tall buildings. The outer skin can be considered as a dynamic damper and thus contribute to comfort inside the building. Many applications emerge in power piping when using two coaxial pipes with an interlayer in order to suppress vibration due to flow and structure interaction. Similar inconvenient behavior can exhibit panels which fall into the flutter post-critical state. Further applications can be expected at industrial chimneys, towers, etc. In principle the idea of vibration damping using such a formation is inspired by very well known tuned mass damper. However its internal structure, function, limitations and singular states are incomparably more complicated and therefore adequate applications should be cautious.
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Dynamic analysis of tall slender structure equipped with passive absorber and founded on various subsoils using simplified model
Hračov, Stanislav
The paper is focused on the investigation of dynamic behavior of tall slender structures taking into account the soil-structure interaction effect (SSI) and a presence of a tuned mass damper (absorber). The main aim is to qualitatively and quantitatively assess effects of both phenomena on changes in basic dynamic properties and response of the structure. The real tower equipped with absorber is chosen and analyzed. Analytical and numerical analysis of modal properties and of the response of a simple discrete model are performed. The structure and absorber are represented by one degree of freedom, the interaction interface by spring-dashpot system. This simplified model together with multi degree of freedom discrete model is analyzed parametrically for different dynamic properties of subsoil to cover all possible dynamic effects. The influence of neglecting of both phenomena is quantified and suggestions for assessments of such a type of structures are proposed.
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Modal analysis of tall slender structures using software GMAST
Hračov, Stanislav ; Pospíšil, Stanislav ; Brůna, Tomáš
The paper is concerned with a verification of modal properties of tall slender structures computed by recently developed software GMAST. Software GMAST determines eigen-frequencies, eigen-modes and corresponding modal quantities of stacks, towers, guyed masts and similar civil engineering structures using slope-deflection method. A numerical model is based on an idealization of the structure as a continuous 2D beam with continuously distributed parameters on elastic supports. Shaft of structure is divided into sections which could be considered as prismatic i.e. with constant unit mass, bending stiffness and static axial force. The effect of guy ropes is introduced in a form of elastic supports with a frequency dependent stiffness. The applicability of the software in praxis is presented on an example of existing structures, for which the numerically and experimentally identified modal properties are compared.
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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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Applicability of existing indexes of non-proportionality of damping in case of theoretical model of slender structure with installed TMD
Hračov, Stanislav ; Pospíšil, Stanislav ; Náprstek, Jiří
The paper analyzes an applicability of to date published indexes of non-proportionality in the case of a linear viscously damped numerical model of slender structure equipped with tuned mass damper (TMD). The installation of TMD into the structure not only reduces the level of undesired vibration, but it can also cause due to damping element of TMD a significant increase of damping nonproportionality. The paper recommends the most suitable indexes for such a type of structure and points out to impropriety of the others. The point of view of is also focus on the validity of the existing criterions for neglecting of non-diagonal terms of a modal damping matrix. Only indexes and criterions based on the properties of the modal damping matrix were taking into account.
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Analýza vlastních čísel viskózně tlumené soustavy se dvěma stupni volnosti z hlediska změny parametrů sekundárního subsystému
Hračov, Stanislav ; Náprstek, Jiří ; Pospíšil, Stanislav
Příspěvek se zabývá analýzou neklasicky tlumené soustavy se dvěma stupni volnosti z hlediska jejích vlastních čísel. V příspěvku byly odvozeny vztahy mezi parametry soustavy, která má násobná komplexní vlastní čísla. Parametrický problém byl řešen analyticky i graficky. Byl také zkoumán vliv vzájemného frekvenčního naladění na přetlumení jednotlivých vlastních čísel s nárůstem sekundárního útlumu. Byly definovány režimy a jejich subintervaly přetlumení s ohledem na zvolenou poměrnou hmotnost a vzájemné frekvenční naladění. Hranice mezi subintervaly představují mj. vzájemná frekvenční naladění subsystémů pro případ soustavy s násobnými komplexními vlastními čísly. V příspěvku byla také zkoumána fáze mezi složkami komplexních vlastních tvarů a jejich vztah k jednotlivým vlastním číslem jako funkcí sekundárního útlumu.
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