Acoustic emission monitoring of hybrid FRP-concrete columns

Fiber-reinforced plastic tubes can be used as permanent formwork and extern al reinforcement for concrete columns. Failure of such columns is often acc ompanied by audible noise from cracking of concrete and shifting and settli ng of aggregates, snapping of the inner layers of the jacket, and ultimatel y fiber fracture. Since the state of the concrete core is not readily visib le from the outside, nondestructive evaluation tools such as acoustic emiss ion (AE) can help assess its structural integrity. The objective of this re search was to investigate the applicability of AE technique to hybrid colum ns, and to correlate the AE parameters to the state of stress in concrete. The AE signature of hybrid columns was studied on over 40 specimens with di fferent lengths, cross sections, jacket types, and jacket thicknesses. The study showed that (1) rate of change of cumulative AE counts with respect t o the applied load correlates well with the degree of damage sustained by t he concrete core; (2) longer specimens, thicker jackets, and unbonded tubes display higher AE activities; and (3) the Kaiser effect is not present in hybrid columns.