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Title: Flexural Behavior of Post-Tensioned Normal- and High- Strength Concrete-Filled Fiber-Reinforced Polymer Tubes

Author(s): Asmaa Abdeldaim Ahmed, Mohamed Hassan, and Radhouane Masmoudi

Publication: Structural Journal

Volume: 118

Issue: 2

Appears on pages(s): 73-88

Keywords: beams; concrete-filled FRP tubes (CFFT); confinement; fiber-reinforced polymer (FRP); high-strength concrete (HSC); post-tensioning; steel tendons

Date: 3/1/2021

Abstract:
This paper investigates the effect of using the post-tensioning (PT) on the flexural strength and ductility of rectangular concrete-filled fiber-reinforced polymer (FRP) tube (CFFT) beams. A total of eight PT CFFTs and two PT concrete beams, serving as control specimens, were tested up to failure under four-point static monotonic and cyclic loading. The effects of prestressed reinforcement, FRP tube versus steel stirrups, tube thickness, concrete type (normal- and high-strength concrete [NSC and HSC]), number of strands, and loading schemes were investigated. The test results revealed that the CFFTs post-tensioned with steel tendons could successfully improve serviceability and ultimate flexural capacity with good ductility behavior and energy absorption capacity compared to nonprestressed CFFT and PT concrete beams. PT CFFT beam achieved approximately 25% and 143% (on average) higher strength than those of CFFT and PT concrete specimens, respectively. Flexural capacities of PT CFFTs can be enhanced by increasing the concrete compressive strength without affecting their overall ductility. Increasing the number of strands had a slight effect on ultimate capacity and total energy absorption, but it did affect the cracking and deflection behavior. Furthermore, insignificant strength reduction occurred due to the cyclic loading of the PT CFFT beam compared to the monotonic loading specimen. Finally, a simple model was proposed to predict the flexural moment capacity of the tested PT CFFT beams as well as nonprestressed rectangular CFFT beams from the literature. The model yielded good yet conservative predictions with an average ratio (Mu(exp)/M(pred.)) of 1.06 ± 0.16 and a COV of 14.7%.


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