Behaviour of Short and Slender CFRP Confined Concrete Columns with Innovative Laminate Systems Under Axial Loading

Abstract

The aim of this project was to develop a high-performance climate adaptation system for the rapid strengthening of existing bridge and building columns. As part of the project a series of tests were conducted to study the performance of circular concrete columns wrapped with innovative carbon fiber reinforced polymer (CFRP) laminate systems having varying fiber orientations and stacking sequences. The experimental testing program included tests on FRP retrofitted concrete columns under concentric axial loading. The studied parameters include the effects of FRP fiber orientation, FRP stacking sequence, number of FRP layers and column slenderness ratio.

The short, medium and tall columns had heights of 600 mm, 1200 mm and 1800 mm, with slenderness ratios: kl/r = 16, 32 and 48. Specimens were batched into five series, namely, Series 0 (control), and Series 1, 2, 3, 4 and 5 based on their fiber orientation and stacking sequences. Each sequence had varying combinations and orientations (0°, 90°, ±45°) of unidirectional (UD) and woven (W) ±45 CFRP, resulting in a total of twelve unique layups. Two replicates were considered for each layup and height combination. The results show that the stress-strain behavior of CFRP-confined concrete is strongly influenced by CFRP fiber orientation, layup sequence, number of layers and the slenderness.

As part of the analytical study, existing design-oriented models for predicting peak confined strength and strain are assessed for the tested columns, and improved strength and strain enhancement coefficients are proposed for columns having varying slenderness based on regression analysis. The study further examines the ability of various FRP confinement constitutive models in the literature to predict the full stress-strain response of the columns.

As part of the numerical study, finite element modelling (FEM) is used to predict the responses of the tested columns. Following the validation, a numerical parametric study investigating the effects of concrete strength, FRP type, section shape, column size and internal steel reinforcement is presented.