Spline-shape modification for FRP-confined concrete columns: theory and evaluation

The confinement efficiency for FRP-confined square concrete columns is relatively low

compared to circular columns due to a large area of ineffectively-confined concrete and stress

concentration at sharp corners. Shape modification of square concrete columns has been proposed but

modifying the shape of cross-section from a square to a circle results in a significant increase in crosssectional

area and self-weight of the columns, which raises new issues and is not practical when the

space in the structure is limited. To address the abovementioned issues, a spline-shaped cross-section is

proposed in this study as a target shape for shape modification. A finite element model was first built and

validated with results from a previous experimental program. Specimens with square, circular shapemodified

and spline-shaped modified cross-section and confined with FRP were modelled and compared.

A number of spline-shaped cross-sections with different aspect ratios (defined as the ratio of minor axis to

the major axis) were incorporated in this study. Results from the analysis showed that the confinement

efficiency of FRP-confined spline-shaped concrete columns was higher than square or circular columns.

Among the spline-shaped columns, those with a small aspect ratio achieved higher confinement

efficiency than those with a large aspect ratio.