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Title: Long-Term Behavior of Glass Fiber-Reinforced Polymer- Reinforced Columns under Multi-Axial Loading

Author(s): Yail J. Kim

Publication: Structural Journal

Volume: 119

Issue: 2

Appears on pages(s): 31-44

Keywords: fiber-reinforced polymer (FRP); long-term; modeling; sustained loading; time-dependent behavior

DOI: 10.14359/51732649

Date: 3/1/2022

This paper presents the time-dependent behavior of non-slender concrete columns reinforced with glass fiber-reinforced polymer (GFRP) bars under concentric, uniaxial, and biaxial loadings. A service-level load is applied at 28 days after concrete casting and sustained for up to 100 years. Conforming to force equilibrium and displacement compatibility, a sectional analysis model is developed in conjunction with a mathematical procedure, called Bayesian inference, to address potential uncertainty. The formulated model is validated against published experimental data and is employed to predict the columns’ response with variable eccentricities, loading angles, concrete strengths, and section losses. When the short-term loading is shifted from concentric to uniaxial-eccentric, abrupt changes are noticed in the concrete and GFRP strains. Biaxial loading brings about unfavorable distress compared with its uniaxial counterpart. Excessive biaxial loading angles between 30 and 40 degrees, measured from the horizontal axis, swiftly raise the short-term concrete strains. Regarding the characteristics of the constituent materials, early-age responses are remarkable during the 2 months after loading. Under the eccentric loadings, long-term concrete stresses are redistributed, and an irregular pattern is observed in the compression region for the first 10 years. Furthermore, creep and shrinkage relieve the concrete stresses over time. The elastic and shrinkage components in the long-term concrete strains are appreciable with the uniaxial and biaxial loadings, whereas the creep component accounts for less than 1% of the total strains for 100 years. With an increase in the concrete strength, GFRP strains decrease; however, the reinforcing bar strains rise as the concrete section spatially damages. When the column is biaxially loaded, the vulnerability of creep rupture is elevated in the GFRP reinforcement relative to the case of the uniaxial loading.