Using Lamb Waves to Evaluate Debonding of Steel Plate Strengthened Concrete

Abstract

This is a preliminary study on using the dispersive characteristics of the Lamb wave modes traveling within the steel layer to assess the bonding condition. The dispersive curves are obtained by a multichannel analysis of surface waves. The frequency-phase velocity images obtained from finite-element analyses were constructed based on the phase velocity analysis scheme. These images were compared with the theoretical dispersion curves. The numerical models include pure steel, steel-concrete bi-layered and steel-epoxy-concrete composite plates. The results show the deviation of phase velocity for composite plate can be used to evaluate the bond condition.

Interfacial Debonding Detection for Rectangular CFST Using the MASW Method and Its Physical Mechanism Analysis at the Meso-Level

“…In the practical MASW test, the drop hammer is commonly adopted for excitation and the signal can be simplified as a half-period sine pulse signal as presented in Figure 2 [71]. Generally, the sensors are linearly arranged in the MASW test [74], and the dispersion curve can be derived through forwarding analysis on the output signal collected from each sensor using F-K transformation [74,75].…”

“…In general, if the material properties between the monitored specimen and its subbase are quite different, the guided wave can be simplified as a Lamb wave. Hence, the bonding condition monitoring of the cohesive layer, the material property prediction and even the damage level evaluation can be carried out by comparing the variation of the dispersion characteristics [67,71,83]. However, for CFSTs, this kind of simplification is not rigorous enough since the elastic material strength between concrete and steel is relatively close, compared with the idealized waveguide for Lamb wave.…”

“…The ideal waveguide for the Lamb wave is an infinitely thin plate. In addition to the typical dispersion characteristics, the Lamb wave is usually multi-mode, which can also lead to complex mode transitions near the defects or boundaries [54,67,71,83,84,85,86]. The Rayleigh wave in a half-infinite homogeneous medium is dispersion-free.…”

“…As discussed above, the excitation signal of the drop hammer can be simplified as a half-period sine pulse signal [71] in the practical MASW tests. In order to investigate the wave propagation excited by drop hammer, the signal amplitude of impulse force excitation is set to 1.0 × 10 −6 N and the time duration takes the value of 2.0 × 10 −6 s.…”

“…The horizontal resolution of the MASW method on the variation of the propagation medium has also been numerically and experimentally validated by Mi et al [70]. While changing the material properties of the bonding layer [71], the dispersion curves of the steel plate were investigated using the MASW method. The evaluation of the interfacial bonding status was achieved by observing the difference of the phase velocity between the dispersion curves obtained from the forward analysis on the time-history signals observed from each sensor and the theoretical dispersion curve of the Lamb wave.…”