The failure of the columns occurred by the crushing of the concrete
on the compression face. Considerable deflection was observed near
the failure (15 to 20 mm). In Fig.9, the right side depicts a typical
relationship between the horizontal force and its corresponding
deflection in LVDT1 (at the top of the columns). The strengthening
technique does not provide a significant concrete confinement for
the second series of columns. The increase on the dissipated energy
was marginal.
The strengthening techniques for the columns loaded by a vertical
load of 250 kN provided an average increase in the load carrying
capacity:
• 10% of the columns confined with a CFRP sheet
• 26% of the columns strengthened with CFRP laminate strips
• 32% of the columns strengthened with CFRP laminate strips and
a sheet .
For columns loaded by a vertical load of 650 kN an average increase
on the load carrying capacity was provided:
• 9% of the columns strengthened with CFRP laminate strips
• 18% of the columns strengthened with CFRP laminate strips and
a sheet .
The ultimate load of all the columns obtained from the experiment
was compared with the result from the analytical modeling and is
presented in Table 2.
In a comparison of the load carrying capacity:
• the results obtained from the numerical analysis (FEM – ATENA
program) were approximately 20% higher than the theoretical
analysis results (interaction curves) for all the tested column
specimens
• the results obtained from the experiment were approximately
25 – 35 % higher than the theoretical analysis results and about
6 – 14 % higher than the numerical non – linear analysis.
By testing the ultimate strain of the CFRP strips during failure, the
actual strain in the strip was verified. The value decreased with the
increased axial load.
The values of the ultimate strain in the failure for columns
strengthened by the CFRP strips in the slits and confined by the
sheets were relatively higher than for other strengthened columns
under an equal axial compression load.