Reliability-Based Evaluation of the Stiffness Reduction Factor for Slender GFRP Reinforced Concrete Columns

Abstract

The stiffness of concrete columns is adjusted by a factor referred to as the stiffness reduction factor or the stability resistance factor when utilizing the simplified second-order moment magnification method for designing slender reinforced concrete (RC) columns. The stiffness reduction factor of 0.75 in ACI 318, CSA A23.3, and CSA S6 was calibrated for steel-RC columns using reliability analysis to account for the variability in concrete strength, steel strength, and applied loads. The upcoming ACI 440 code adopts the same stiffness reduction factor for the design of slender glass fiber-reinforced polymer (GFRP) RC columns when using the moment magnification method. The structural reliability of slender GFRP-RC columns designed using a stiffness reduction factor of 0.75 was not evaluated despite the difference in the GFRP statistical parameters and stiffness characteristics as compared with conventional steel. The objective of this research is to conduct a reliability analysis of slender GFRP-RC columns to evaluate the reliability index associated with the use of the stiffness reduction factor and provide recommendations regarding the optimum value of the factor to meet code target safety limits. Monte Carlo simulation is used to conduct the reliability analysis. Statistical input parameters (distribution type, bias ratio, and coefficient of variation) of GFRP based on an extensive experimental database are utilized in the study. The proposed research presents a necessary step toward quantifying the safety associated with the design provisions proposed in upcoming ACI 440 code.