摘要(英) |
In generally, when
carrying out NDT field tests for piles, the influence of superstructures
can not be effectively isolated, the signals obtained in the tests thus
show certain complexity. Nevertheless, when boundary conditions or
geometries are complicated, one would be able to recognize such spatial
restraints on the test results, if one can induce the characteristics of
the corresponding axial and lateral responses of piles and to summarize
their generalizations. To obtain reliable test signals to correctly
determine the boundary conditions or geometries of piles, one can
usually use various kinds of hammer tips with different materials to
produce different durations for the impact forces. Since the significant
wavelengths of the stress waves are related to the durations of the
impact forces, the selection of hammer tips would affect the assessment
of the type and the size of defects. In this study, three slender
concrete rods were erected and tested with seven different contacting
tips of the impact hammer. To investigate the sensibility of impact
durations to the detectibility of the defects, various numerical
simulations and experiments were conducted. Four numerical models were
used in this research; one-dimension line element, two-dimensional
axialsymmetric element ,and ANSYS LS-DYNA SOLID 162 and ANSYS LS-DYNA
SOLID 164 elements, to simulate the axial and lateral vibrations and
wave propagations in an intact rod, a defective rod, and a rod with a
weak layer. By comparing with results from numerical models and those of
experiments, this study briefly generalizes the signal characteristics
generated by various impact hammers on these three different rods. |