Examination of strength reduction factor in CFRP-confined columns under axial compression

Abstract

In the strength design method, the safety level is tried to be reached by using strength reduction factors phi applied to the nominal strengths. In the current ACI 318-19, the safety factors phi are suggested as 0.65 for tie-reinforced concrete columns and 0.60 for plain columns, respectively. The aim of the present study is to evaluate the strength reduction factors of the confined columns with Carbon Fiber Reinforced Polymer (CFRP) subjected to axial compression load according to ACI 318-19. For this purpose, a total of 298 column test specimens with circular and rectangular cross-sections confined with CFRP collected from 18 different experimental studies in the literature were examined to determine the strength reduction factors. The first-order second-moment approach was used to determine these factors by reliability analysis, and the correlation effects between random variables were not taken into account. The target reliability index and the corresponding probability of failure were taken as beta =3.5 and p(F) = 2.33x10(-4) for different coefficients of variation of random variables, respectively. Then, these factors were been separately compared to those of recommended in the ACI 318-19. At the end of the study, the upper limits of the coefficients of variation that should not be exceeded were determined to ensure the target reliability of the columns.