External FRP confinement of concrete columns using shape modification technology

ABSTRACT

Fiber Reinforced Polymer (FRP) composites are effective for strengthening circular concrete columns. However, the effectiveness of FRP confinement for square and rectangular columns is greatly reduced due to loss of the membrane effect. Shape modification is a possible approach for eliminating the effects of column corners and flat sides, thereby restoring the membrane effect and improving the compressive behavior of FRP-confined square and rectangular concrete columns. A shape modification technology using chemical posttentioning achieved by using expansive cement concrete is studied. Shape modification by using expansive cement concrete and prefabricated FRP composite shells can change the FRP confinement from “passive” to “active”, and thus increase the axial strength as well as the ductility of square and rectangular columns compared to the original columns with the same number of FRP composite layers. Parametric studies regarding the optimal geometry of the shape-modified cross-section are presented utilizing the analytical model.