Title: Thermomechanical Hysteresis of Reinforced Concrete Beams Retrofitted with CFRP and UHPC

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

Publication: Structural Journal

Volume:

Issue:

Appears on pages(s):

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

DOI: 10.14359/51740864

Date: 6/4/2024

Abstract:
This paper presents the behavior of reinforced concrete beams retrofitted with carbon fiber reinforced polymer (CFRP) sheets and ultra-high-performance concrete (UHPC) jackets in a multi-hazard environment. Following the procedural protocol of a published standard, the beams are cyclically loaded under thermomechanical distress at elevated temperatures, varying from 25°C (77°F) to 175°C (347°F), to examine their hysteretic responses alongside ancillary testing. The thermal conductivity of UHPC is higher than that of 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 stage of the beams.