Effects of CFRP composites on strength and ductility of slender concrete columns

  ABSTRACT

In recent years, retrofitting of concrete structures is the major problem of existing civil structures. Concrete columns are essential structural components in concrete structures. Most researches have mainly concentrated on the stress-strain model, the compressive strength, and the shape of cross section of short columns. The fact is commonly accepted that FRP composites increase the strength and ductility of short columns. But, with increasing slenderness, slenderness effects can prohibit the column from attaining its maximum performance and the column may become susceptible to instability. Because the FRP composites have a higher strength and lower stiffness than steel, the FRP wrapped columns tend to be more susceptible to slenderness effects. This paper presents the results of experimental studies about mechanical properties of retrofitted slender concrete columns with CFRP composites. In this study, 30unreinforced

concrete cylinders 100 mm diameter with variable height of 200, 400, 600, 800, and

1000 mm were prepared and retrofitted. In every group, a plain specimen (unwrapped) and five wrapped specimens with different fiber orientations (0, 0/0, 90/0, 45, and 45/0) were tested under pure compressive axial force up to failure. The results of testing the columns have shown that the CFRP composites are most effective in increasing the strength and ductility of slender columns.