Analysis-Oriented Stress-Strain Model for Concrete Confined with Fiber-Reinforced Polymer Spirals

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Title: Analysis-Oriented Stress-Strain Model for Concrete Confined with Fiber-Reinforced Polymer Spirals

Author(s): Thomas A. Hales, Chris P. Pantelides, Priyank Sankholkar, and Lawrence D. Reaveley

Publication: Structural Journal

Volume: 114

Issue: 05

Appears on pages(s): 1263-1272

Keywords: axial loads; concrete columns; confinement model; fiber-reinforced polymer; glass fibers; spiral; stress-strain

Date: 9/1/2017

Abstract:
Considerable research has been conducted for confinement of reinforced concrete (RC) columns with external fiber-reinforced polymer (FRP) jackets. Research is limited with respect to concrete confinement using internal FRP spirals. Concrete columns internally reinforced with FRP spirals and longitudinal bars have advantages because FRP composite materials are not susceptible to corrosion. This is a desirable alternative for coastal structures and structures subjected to severe environmental conditions, which deteriorate with time due to corrosion of steel reinforcement. Existing models for concrete confined with steel spirals cannot represent the behavior of FRP-confined concrete adequately because they are based on a constant confining stress. FRP composites behave in a linear elastic manner with confining stress increasing continuously until failure. An analytical confinement model has been developed and is proposed for describing the axial strength and stress-strain relationship of FRP-spiral-confined circular columns based on plasticity and the Popovics’ concrete model. FRP spirals have a lower modulus of elasticity compared to steel spirals and, hence, a larger bar diameter and smaller pitch is required for satisfactory performance. The proposed model, developed based on triaxial behavior of concrete, provides an accurate representation of FRP-spiral-confined concrete in axial compression experiments for a wide range of confining stress and could be used in analysis and design.