Title: Thermomechanical Hysteresis of Reinforced Concrete Beams Retrofitted with Carbon Fiber-Reinforced Polymer and Ultra-High-Performance Concrete

Author(s): Yail J. Kim and Ibrahim Bumadian

Publication: Structural Journal

Volume: 121

Issue: 5

Appears on pages(s): 189-202

Keywords: carbon fiber-reinforced polymer (CFRP); hysteresis; retrofit; strengthening; thermomechanical loading

DOI: 10.14359/51740864

Date: 9/1/2024

Abstract:
This paper presents the behavior of reinforced concrete beamsretrofitted with carbon fiber-reinforced polymer (CFRP) sheets andultra-high-performance concrete (UHPC) jackets in a multi-hazardenvironment. Following the procedural protocol of a publishedstandard, the beams are cyclically loaded under thermomechanicaldistress at elevated temperatures, varying from 25 to 175°C (77to 347°F), to examine their hysteretic responses alongside ancillarytesting. The thermal conductivity of UHPC is higher than thatof ordinary concrete by more than 62% and, according to a theoretical inference, premature delamination would not occur within the foregoing temperature range. The difference in load-carrying capacities between the strengthened and unstrengthened beams declines with temperature. While the UHPC+CFRP retrofit scheme is beneficial, CFRP plays a major role in upgrading the flexural resistance. The thermomechanical loading deteriorates the hysteretic loops of the beams, thereby lowering the stiffness and capacity. Elevated temperatures are concerned with the pinching, plasticity, characteristic rigidity, stress redistributions, and energy-release patterns of the beams. Due to the retrofit, the configuration of plastic hinges alters, and the localized sectional deformations form a narrow damage zone. The adverse effects of the temperatures on rotational stiffness are pronounced during the early loading stageof the beams.