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The present numerical study focuses on the problem of dynamic interaction of piled foundations under harmonic excitation at high frequencies relevant for the vibration protection practice. The finite-element programs Plaxis (2D & 3D) and Abaqus are employed for time- and frequency-domain analyses, respectively.
As a first step, dynamic impedances...
Citations
... The model set-up can accommodate up to a 5×5 layout; when smaller configurations are examined, the "redundant" piles are replaced by soil. For further details see Efthymiou [23]. ...
... Surprisingly, this is true even at low frequencies, at which the interference of body waves has a more substantial effect on the response. The good agreement is confirmed for all configurations considered herein (details are shown in Efthymiou [23]). ...
... Consequently, calculating the dynamic impedance of a pile group with the specific model would lead to inaccurate results due to the inconsistency between the location of the inertial loading in this case (direct loading of the pile group) and the length of the infinite elements following the previous implementation of the indirect loading with the point load. However, the direct-solution steady-state dynamic analysis tool in Abaqus has been already verified in the case of inertial loading of a pile group using different models in the work of Efthymiou [23]. In these cases, the pile group is placed in the center of each model, and the infinite element length is consistent with the inertial loading, as can be indicatively seen in Figure A4. ...
Using the finite-element method (FEM), this study presents results on piled foundations excited by a stationary or moving harmonic vertical point load acting on the soil surface at a given distance. For the stationary loading case, typical configurations of pile groups and corresponding piled rafts are examined in the frequency domain. The contribution of the raft alone in the overall response is also explored. The soil is modelled as a linear-elastic continuum with hysteretic damping. A wide range of frequencies from 8 to 64 Hz is considered. Of interest is the resulting vertical oscillation mode. The influence of the number of pile rows in the direction of wave propagation on the resulting vibration reduction is assessed by monitoring a reference pile at the furthest back pile row and an observation point at the free-field behind. The associated wave-passage effect is quantified through appropriate transfer functions for the piles. Subsequently, the case of a harmonic load travelling with a constant speed parallel to the pile group is investigated. Most importantly, it is revealed that a good approximation for this case is a stationary load located on the moving load path at the shortest distance from the pile group. This has important implications in the vibration protection practice, as detailed modelling of moving loads is then not required. The methodology presented can be extended to arbitrary foundation geometries and layered soil profiles.
Bei der Prognose von Bauwerksschwingungen infolge Erschütterungsquellen in der Nachbarschaft, z. B. aus Verkehr, Baumaßnahmen oder Maschinenschwingungen, stellt sich mitunter die Frage, welchen Einfluss die Gründung des Bauwerkes auf Amplitude und Frequenzgehalt der resultierenden Schwingungen hat. In diesem Beitrag werden die sogenannten induzierten Erschütterungen von Bauwerken auf Pfahl‐ und auf Flachgründungen auf der Basis von numerischen Berechnungen systematisch miteinander verglichen. Nach einer Beschreibung der Berechnungsmethode mit der „Thin Layer Method“ (TLM) im Frequenzbereich werden zunächst Einzelpfähle im homogenen Halbraum sowie solche in einer Bodenschicht auf steiferem Untergrund betrachtet. Angeregt durch horizontale und vertikale Kräfte an der Bodenoberfläche in einigem Abstand werden die Amplituden der Schwinggeschwindigkeit (Schwingschnellen) in Höhe des Pfahlkopfes vor und nach Einbau des Pfahles ermittelt und verglichen. Es werden dabei Frequenzen zwischen 1 Hz und 40 Hz betrachtet. Der Einfluss der Bodenschichtung wird diskutiert. Im zweiten Teil der Arbeit werden die Schwingschnellen von Flach‐ und Pfahlgründungen unter gleicher Anregung berechnet und miteinander verglichen. Es werden charakteristische Unterschiede aufgezeigt. Zur Berücksichtigung der aufgehenden Bauwerke werden diese stark vereinfacht als starre Massen modelliert. Die Berechnungsergebnisse leisten einen Beitrag zur einleitenden Fragestellung.
