Simplified Design of FRP-Confined Square RC Columns under Bi-Axial Bending

Available guidelines do not provide design procedures for the general case of retrofitting reinforced concrete (RC) columns using fiber reinforced polymer (FRP) sheets subjected to simultaneous bi-axial flexural and axial loads. In many practical cases, columns essentially undergo simultaneous axial force and bi-axial bending moments, especially in in-situ construction. This paper suggests a simplified design method based on the equivalent uni-axial moment concept to calculate the required number of layers FRP sheets for retrofitting RC square columns. The proposed procedure is then verified against available bi-axial moment and axial force test data found in the literature. Results demonstrate that the proposed procedure is appropriate for practical applications with acceptable accuracy. It also appears that retrofitting RC square columns by longitudinal fiber arrangement is only effective for columns with tension-controlled behavior, while transverse and combined longitudinal-transverse arrangements are more effective in enhancing the load bearing capacity of both the compression- and tension-controlled columns. A design example will also be presented.