Posttensioned FRP Composite Shells for Concrete Confinement

Experiments have shown that externally bonded fiber-reinforced polymer (FRP) jackets for square and rectangular columns are not as effective as they are for circular columns. The results of experiments on shape-modified concrete columns using posttensioned FRP shells are presented. Posttensioning was achieved by radially straining the precured FRP shell outwards to a substantial strain level, using expansive cement concrete, over a period of 60days. The prefabricated FRP shell was also used as a stay-in-place formwork. The effectiveness of shape modification using posttensioned FRP shells is compared to FRP-confined original square and rectangular columns, as well as shape-modified columns with nonshrink grout and externally bonded FRP jackets. It is shown that shape modification with posttensioning of FRP shells, using expansive cement concrete, can change the confinement from passive to active and improve significantly the axial strength and ultimate compressive axial strain capacity of square and rectangular columns.