Concrete column shape modification with FRP shells and expansive cement concrete

Fiber Reinforced Polymer (FRP) composites are an effective material for strengthening circular concrete columns. Confinement of square and rectangular columns is not as effective as confinement of circular columns. The flat sides of square and rectangular columns remain largely unconfined and the FRP jacket is effective only along the two diagonals of the cross-section. Shape modification of square and rectangular columns to circular and elliptical columns is implemented. Two methods are used to achieve shape modification: (a) modifying the cross-section with non-shrink grout and applying an FRP jacket using wet layup, and (b) filling the annular gap between the original section and a prefabricated FRP shell with expansive cement concrete. Several mix designs of expansive cement and Portland cement were used for obtaining the desired level of expansion. An analytical model and a finite element model are used to predict the stress–strain behavior of the test specimens. Parametric studies regarding the optimal geometry of shape-modified cross-sections are presented utilizing the analytical model.