Velocity tomography-based condition inspection on concrete pylons of a pedestrian suspension bridge

The velocity tomography inspection, including modified cross-hole sonic logging and ultrasonic velocity tomography methods, was introduced to detect the reinforced concrete pylons of a pedestrian suspension bridge in northern Taiwan. At the first stage, the modified cross-hole sonic logging method was employed to rapidly identify the positions of gross anomalies on the shafts and horizontal beams of the bridge pylons. The possible anomaly sections, usually with a relatively low velocity, were chosen for the ultrasonic velocity tomography testing in order to finely determine the velocity spatial distribution image and localize the anomaly positions. The on-site inspection results indicate that the lower horizontal beams and connection zones with concrete shafts on the pylon were significantly attributed to a questionable level (i.e., velocity of 3,000∼3,600 m/s). These structural detrimental positions have been provided for the bridge agency for the further improvement plan on the bridge pylons.