EFFECT OF CONFINEMENT ON THE INTERACTION DIAGRAMS FOR RC SECTIONS WITH CFRP GRIDS AND WRAPS

Application of CFRP composite materials is a popular method of strengthening reinforced concrete members. Wrapping columns with these materials is used in seismic retrofi ts because of the increase in the strength and ductility of concrete, and therefore, of the column itself. This is particularly ben-efi cial for compression-controlled columns that fail by concrete crushing due to the fact that ductility and strength of the member is signifi cantly improved. For the design of columns, interaction diagrams are used which defi ne the maximum capacity of compression members that are subjected to axial force and bending moments. This work includes the development of interaction diagrams for circular compression members confi ned with CFRP composites. The concrete confi nement can be light (low confi nement pressure) or heavy (high confi nement pressure). In this paper, three levels of confi nement are evaluated: (a) zero confi nement, (b) light confi nement with the use of a CFRP composite grid, and (c) heavy confi nement with the use of CFRP composite wraps with two different thicknesses of the wrap. A comparison of the unconfi ned section to the light and heavily confi ned sections shows a considerable difference primarily in the compression-controlled region where the axial compression and bending moment are signifi cantly enhanced. The balance point for both light and heavy confi nement has moved higher up on the interaction diagram, which changes the range of the compression and tension zones. This is evident for both light and heavy confi nement. Also, the failure mode of compression-controlled columns is more ductile because of the change in the behavior of concrete due to confi nement