An improved wrapping scheme of axially loaded fiber-reinforced polymer confined concrete columns

Abstract Columns failed near the mid-zone were commonly found in practical engineering when subjected to an increasing compression load caused by the vertical ground motion during an earthquake, indicating that more confinement may be necessary at the mid-zone. Fiber-reinforced polymer (FRP) materials have been widely used to strengthen the columns. Different wrapping schemes, including full, partial, and nonuniform wrap, have been proposed. Generally, FRP-confined concrete stub columns using the existing wrapping schemes failed by the rupture of FRP at the middle zone, indicating the middle zone of the columns were not well confined by using the existing wrapping schemes. A new wrapping scheme with more FRP sheets applied in the middle zone is proposed. Experimental tests with a total of 28 specimens were conducted to evaluate the performance of different wrapping schemes, based on which an arrangement way that the applied FRP materials decrease from the middle zone to the end is recommended. The results suggest FRP materials along the height of a column can be more efficiently utilized by using the recommended wrapping scheme. Additionally, compared with the specimens using the existing wrapping schemes with the same amount of FRP materials, the recommended wrapping scheme significantly improves the strength and ductile behavior of columns.