Monitoring Damage in Concrete Columns Using Ultrasonic Tomography

Full-scale reinforced concrete (RC) and ultra-high-performance fiber-reinforced concrete (UHP-FRC) columns subjected to reversed cyclic loads are imaged using ultrasonic tomography before, during, and after loads are applied. Concrete columns with varying geometries and detailing, loading protocols, and material types are considered. The columns contain internally embedded concrete strain gauges, the data from which are used to establish extent of accumulated damage caused by the applied loads at certain locations within the columns. A newly developed hybrid air-coupled ultrasonic system is used to collect a large volume of through-thickness ultrasonic data across the cross section at the plastic hinge region of the column. Ultrasonic monitoring was carried out at increasing load levels up to a drift ratio of 1%. The ultrasonic data are used to back-calculate wave velocity tomo-graphic images (tomograms) across the cross section. A comparison of ultrasonic and strain gauge data shows that ultrasonic tomograms indicate damage progression within the columns, considering both global and local spatial scales. The results also confirm that the UHP-FRC column exhibited much less internal damage at a given load level compared to conventional reinforced concrete columns. Keywords: air-coupled ultrasonics; collapse; earthquake; imaging; seismic loading; strain gauges; ultra-high-performance fiber-reinforced concrete.