In this paper, the concrete gravity dam built 40 years ago was partially damaged by the M=7.3 Chi-Chi Earthquake in central Taiwan in 1999. The elastic wave tomography method was applied to identify the safety conditions of the repaired dam in 2010. The resulting velocity profiles showed that the total structure conditions were accepted as a good to questionable condition. The filled materials and cracks existed in some dam components. Seven years later, the updating tracing investigation revealed that the pervious detrimental zones were spatially extended and associated with time. These testing results were also consistent with the findings from the ground penetrating radar inspection.

Developing an appropriate and efficient inspection pattern for an unknown bridge substructure is a critical issue for bridge engineers, contractors, and bridge agencies. This paper introduces a two-phase near-surface inspection strategy to determine the foundation depth of fully submerged pile bents of an existing bridge. Electrical resistivity tomography inspection provided the overall interface between bridge substructure and surrounding soft soils. Ultraseismic inspection provided more information to determine the depth of the substructure. Time-lapse waveform image analysis and frequency analysis of ultraseismic inspection results also displayed varying degrees of reliability for estimating the pile bent length, which was positively confirmed with the bridge design charts. The entire set of investigations demonstrated strong conclusiveness in determining the foundation depths when the results from these two testing methods were corroborated with appropriate analysis modes.

A flexural wave impulse response approach is particularly applicable in the nondestructive evaluation of foundations of overwater structures, such as bridge piers or wharves, that lack access to their tops. The experimental procedure of the flexural wave impulse response method is similar to that of the traditional (longitudinal wave) impulse response method. In order to pre-verify the possibility of integrity testing on a single newly constructed pile bent, the transient-state flexural waves are induced by lateral impact and recorded by three triaxial accelerometers equidistantly mounted to a model concrete pile side. The frequency-based analysis used in the conventional impulse response testing cannot cope with the flexural wave impulse response testing due to its dispersive characteristics at low frequencies. Using the resonance solutions and flexural mode guided wave prediction curve is a simple and efficient method of finding the resonant frequency and phase velocity when knowing pile diameter and flexural wave impulse response results. The vibration responses in the radial and axial direction are measured at the impact position (position 0°). The angular/tangential direction responses are also analyzed at position 90° away from the impact position. These phase velocities measured at resonant frequencies have good matches with the theoretical flexural mode wave predictions at frequencies below 4,000 Hz. The testing results also indicate that the resonance characteristics of flexural waves traveling in a pile are not dependent on measurement positions but the engineering properties and geometrical characterization in the concrete pile.

This paper presents an in-depth study of the stress wave behavior propagating in a Rayleigh–Love rod with sudden cross-sectional area variations. The analytical solutions of stress waves are derived for the reflection and transmission propagation behavior at the interface of the cross-sectional area change in the rod, considering inertia and Poisson’s effects on the rod material. Examples solved using the finite element method are provided to verify the correctness of the analytical results. Based on the forward analysis of Rayleigh–Love wave propagation in a rod impacted by a striker rod, an impact-echo-type nondestructive testing (NDT) method is proposed to conduct defect assessment in rod-type structural components with sudden cross-sectional area changes within a cover medium. This proposed NDT method can identify the location, extension, and cross-sectional area drop ratios of an irregular zone in the rod to be inspected.

A two-phase ultrasonic velocity tomography technique was introduced to inspect the concrete quality of bridge pylons in Taiwan. In phase I, the modified cross-hole sonic logging method was applied to rapidly identify the aberrant sections of pylon shafts and horizontal beams. Most of the concrete quality was classified as good (G), ie the apparent P-wave velocity ranged from 3600 m/s to 4300 m/s. In phase II, the cross-sectional velocity image method examined the sections with possible anomalies and, in contrast, the uniform sections of the pylon shafts. The cross-sectional velocity image approach effectively demonstrated the spatial position and range of anomalies in the pylon shaft cross-sections. It was suggested that the relatively low-velocity zones, confirmed with surface concrete spalling, be listed as future repair targets for the bridge agency.