Kwang-Yeun Park

The bearings or the seismic isolation bearings that play a critical role in bridge structures are fixed to the substructure by anchor bolts. However, the embedment depth of the constructed anchor bolts does often not reach the designed one and may lead to safety issues. The present study proposes an ultrasonic non-destructive testing (NDT) method to verify the embedment depth of the anchor bolts installed on bridges in-service. The P-wave of 50–100 kHz that is usually used in the NDT of concrete was transmitted from the head of the anchor bolt and its arrival time on the concrete cover was measured. The shortest arrival time of the ultrasonic pulse and the corresponding path were then analyzed to formulate their relationship and obtain the distance traveled by the ultrasonic pulse along the anchor by inverse analysis using the equation error estimation. The instability occurring in the inverse analysis is settled by regularization. Finally, the embedment depth of the anchor bolt can be estimated by the analysis of the graph plotting the position of the ultrasonic transmitter and the distance traveled by the pulse along the anchor. The proposed method is validated numerically and experimentally. The method is expected to contribute to the NDT of civil structures by making it possible to estimate the embedment depth of anchor bolts by the means of ultrasonic transducers using P-waves of 50–100 kHz.

The construction of prestressed concrete bridges has witnessed a steep increase for the past 50 years worldwide. The constructed bridges exposed to various environmental conditions deteriorate all along their service life. One such degradation is corrosion, which can cause significant damage if it occurs on the main structural components, such as prestressing tendons. In this study, a novel non-destructive evaluation method to incorporate a movable yoke system with denoising algorithm based on kernel principal component analysis is developed and applied to identify the loss of cross-sectional area in corroded external prestressing tendons. The proposed method using denoised output voltage signals obtained from the measuring device appears to be a reliable and precise monitoring system to detect corrosion with less than 3% sectional loss.

A non-destructive evaluation method is proposed to identify the sectional loss of the external tendon of prestressed concrete structures by detecting the change of the magnetic flux in the external tendon exposed to a magnetic field. The method uses a solenoid-shaped device with two coils: a primary coil for producing magnetic field and secondary coil for damage detection, wrapping the external tendon. A current applied to the primary coil in the device causes the magnetic field. Then, the change in the magnetic flux by the damage in the external tendon is detected by the variation of the voltage in the secondary coil in the device as the device moves along the tendon. An alternating current is applied to the primary coil to minimize the effect of the moving speed of the device. As a result, the damaged area can be detected with a low-level energy current. In addition, a wrapping solenoid-shaped device that is easy to disassemble and assemble was developed for in situ inspection. The measured signal from the secondary coil has a sinusoidal form with the same frequency as the applied current to the primary coil, and the peak curve of the measured signal provides enough information to detect the damage. It is shown that the proposed method can quantitatively identify one or multiple damaged-tendon locations as well as damages of at least 2 cm.