摘要(英) |
This dissertation is
a study for using the simulated transfer function obtained from the
impact-echo method to evaluate the material properties of substrate
layer for a laminate concrete structure. The peak amplitude in
impact-echo spectrum may be varied by the energy and the contact time
produced by the impact force. The experimental result needs to be
transformed into transfer function for quantitative evaluation. The
different acoustic impedance (Z) in substrate layer such as air, earth
or water may lead to different spectral amplitude corresponding to
concrete layer. Thus it is possible to non-destructively evaluate the
substrate geological state for tunnel, mining pit or dike which is unfit
for coring. The purpose of this study is as following. 1. Explore
the connection between the experimental spectral amplitude corresponding
to the interface of a composite concrete plate in transfer function and
acoustic impedances for different substrate layers such as epoxy, gypsum
and low-strength concrete. 2. Using numerical simulation to study the
relationship between ratio of acoustic impedance for substrate and
concrete layer (Z2/Z1) and the spectral amplitude corresponding to the
interface in transfer function. The thickness of substrate layer is also
concerned as a variable. The experimental results show, for
various tests applying on the same specimen, the spectral amplitude
corresponding to depth of the interface may differ greatly. After
transformation, the amplitudes in the transfer functions become stable.
Take the experimental parameters into the previously developed equation
for relating peak-amplitude to the thickness of a pure concrete plate
without substrate layer. The predicted amplitude for the 10 cm-thick
plate is 1.571, which has 11.5% error to the average experimental
amplitude, 1.39. The relation between Z2/Z1 ratio and spectral amplitude
corresponding to the interface in transfer function developed by
numerical model can be used for predicting the experimental results for
composite plates. Comparing the numerical and experimental results
of composite plates with epoxy, gypsum, low strength mortar substrates,
the order of spectral amplitudes values are epoxy >Gypsum > low
strength mortar. The correlation is high. |