Strength and Ductility of Concrete Confined by Fiber Metal Laminate Composites

Abstract

This paper presents an experimental study on the compressive behavior of concrete cylinders confined with fiber metal laminate (FML) composites. This research was motivated by the need to address limitations of traditional fiber-reinforced polymer (FRP) composites used for civil infrastructure applications, which demonstrate linear elastic and brittle behavior in tension. FMLs are composed of thin metal sheets bonded to E-glass fiber-epoxy composites, resulting in a pseudoductile stress-strain response characterized by strain hardening after yielding of the metal layers. A total of 38 cylindrical concrete specimens were prepared, of which 10 were unconfined, eight were confined by three FRP layups, and 20 were confined by six FML layups. The FML layups comprised of thin 2024-T3 aluminum layers bonded to 400 g/m2 E-glass fiber fabrics, with variations in the number of metal layers, fiber orientation, and fabric architecture. The specimens were tested under uniaxial cyclic compression to investigate the strength and deformation capacity as a function of the degree of pseudoductility exhibited by the FML jackets. The results showed that the strength and ductility enhancement provided by the FML jackets was dependent on the stress-strain characteristics of the jacket material. Jackets characterized by strain-hardening tensile behavior, such as those with unidirectional fabric layers, showed substantial increases in confined strength but reduced ductility and energy dissipation. Conversely, jackets with pseudoductile tensile response, such as those using bidirectional off-axis fabric, were the most ductile, exhibiting stable strain softening behavior. Further, for the same level of confining pressure, FML-confined concrete demonstrated improved postpeak response and gradual strength degradation compared with FRP jacketed concrete. This suggests redistribution of hoop stresses within the FML jacket after initial yielding.