Strengthening of Rcc Columns with Frpc Confinement
MECHANICS OF CONFINEMENT
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1. Preliminary Remarks Confinement of columns by means of FRP jackets is done by retraining the dilation of concrete by wrapping the fibers in the hoop direction of concrete columns. Confinement of columns by FRP wraps is termed as a passive strengthening technique since the fibers do not play any role in the elastic response of the axially loaded column. The tendency of concrete to dilate after cracking and the radial stiffness of the confining jacket to restrain the concrete dilation, are considered to be two important factors affecting the concrete confinement. By wrapping the concrete with an external continuous FRP jacket, the fibers in the hoop direction resist the transverse expansion of the concrete providing a confining pressure. At low levels of longitudinal stress; however, the transverse strains are so low that the FRP jacket induces little confinement, if any. At higher longitudinal stress levels, the dramatic increase in transverse tensile strains activates the FRP jacket and the confining pressure becomes more significant. The general confining pressure induces a tri-axial state of stress in the concrete. It is well understood that concrete under tri-axial compressive stress exhibits superior behavior, in both strength and ductility, as compared to concrete in uniaxial compression.
2. Parameters affecting confined compressive strength of concrete: The confined compressive strength of concrete columns is influenced by several factors apart from the material properties of FRP composites. Parameters such as size and shape of the cross section of the columns, grade of concrete, material properties of FRPC, nature of loading collectively affect the confined compressive strength. These parameters are discussed briefly in the following paragraphs.
1) Tri axial state of stress: Experimental evidence shows that the
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1. Preliminary Remarks Confinement of columns by means of FRP jackets is done by retraining the dilation of concrete by wrapping the fibers in the hoop direction of concrete columns. Confinement of columns by FRP wraps is termed as a passive strengthening technique since the fibers do not play any role in the elastic response of the axially loaded column. The tendency of concrete to dilate after cracking and the radial stiffness of the confining jacket to restrain the concrete dilation, are considered to be two important factors affecting the concrete confinement. By wrapping the concrete with an external continuous FRP jacket, the fibers in the hoop direction resist the transverse expansion of the concrete providing a confining pressure. At low levels of longitudinal stress; however, the transverse strains are so low that the FRP jacket induces little confinement, if any. At higher longitudinal stress levels, the dramatic increase in transverse tensile strains activates the FRP jacket and the confining pressure becomes more significant. The general confining pressure induces a tri-axial state of stress in the concrete. It is well understood that concrete under tri-axial compressive stress exhibits superior behavior, in both strength and ductility, as compared to concrete in uniaxial compression.
2. Parameters affecting confined compressive strength of concrete: The confined compressive strength of concrete columns is influenced by several factors apart from the material properties of FRP composites. Parameters such as size and shape of the cross section of the columns, grade of concrete, material properties of FRPC, nature of loading collectively affect the confined compressive strength. These parameters are discussed briefly in the following paragraphs.
1) Tri axial state of stress: Experimental evidence shows that the