| Popis: |
This paper deals with the development of a discrete numerical 2D and 3D solid pile model with a discontinuity and defects to simulate non-destructive testing using the pile integrity test (PIT). The pile discontinuity and defects were modelled by reducing the specific finite elements and the elastic modulus of concrete. The wave-propagation response of the pile was analyzed based on a step-by-step numerical integration using the Hilber-Hughes-Taylor (HHT) method in the time domain. The concept of a system-response analysis was originally formulated based on the integration of individual reflectograms into a reflectogram surface, which is generated in a 3D cylindrical coordinate system. The use of reflectogram surfaces enables an understanding of wave propagation based on their velocity to a higher level than is usually the case with standard, one-dimensional reflectograms. Changes in the velocity responses on the reflectogram, shifting from a positive to a negative value, point to the locations of discontinuities and defects in the discrete 3D pile model, and there is a clear difference in the reflectograms, depending on the position of the measuring point. The study defines the typological models of the reflectogram: without discontinuities and defects, pile-head defect, defect in the middle of the pile length or a reduced modulus of elasticity in the middle of the pile length, pile-base defect or reduced modulus of elasticity in the pile-base zone and reduced modulus of elasticity in the pile-head zone. V prispevku je prikazan in razvit diskretni numerični 2D in 3D trdninski model pilotov s prekinitvami in napakami, namenjen simulaciji ne-destruktivnega testiranja z uporabo PIT (pile integrity test). Modeliranje prekinitev in napak v pilotih je bilo izvedeno z redukcijo posebnih končnih elementov in modula elastičnosti betona. Analiza odgovora širjenja valov v pilotih je bila izvedena na podlagi postopne numerične integracije z uporabo metode Hilber-Hughes-Taylor v časovni domeni. Originalno je opredeljen koncept analize odgovora sistema z integracijo posameznih reflektogramov v ploskev reflektograma, ki je generirana v 3D cilindričnem koordinatnem sistemu. Z uporabo ploskev reflektograma je mogoče razumeti širjenje valov s pomočjo hitrosti, ki je na višjem nivoju kot je običajno za standardne, eno-dimenzionalne reflektograme. Spremembe odzivov hitrosti na reflektogramu, ki se spreminjajo iz pozitivne v negativno vrednosti, kažejo na lokacijo prekinitev in napak diskretnega 3D modela pilotov. Pri tem obstaja jasna razlika v reflektogramih v odvisnosti od položaja merilnega mesta. Študija definira tipološke modele reflektograma: pilot brez prekinitev in napak, napaka glave pilota, napaka v sredini dolžine pilota oziroma zmanjšani modul elastičnosti v sredini dolžine pilota, napaka noge pilota oziroma zmanjšani modul elastičnosti v območju noge pilota ter zmanjšani modul elastičnosti v območju glave pilota. |
