Title: Thermomechanical Relaxation of Reinforced Concrete Beams Strengthened with Carbon Fiber-Reinforced Polymer

Author(s): Yail J. Kim and Abdulaziz Alqurashi

Publication: Structural Journal

Volume: 115

Issue: 1

Appears on pages(s): 259-268

Keywords: carbon fiber-reinforced polymer (CFRP); relaxation; retrofit; strengthening; thermal

DOI: 10.14359/51701091

Date: 1/1/2018

Abstract:
This paper presents the behavior of reinforced concrete beams strengthened with carbon fiber reinforced polymer (CFRP) sheets subjected to relaxation induced by thermal and mechanical loadings that are applied simultaneously (thermomechanical loading). The range of elevated temperatures varies from 75 to 150°C (167 to 302°F) and the mechanical load represents a typical service condition (60% of the strengthened beam’s capacity at 25°C [77°F]), both of which are sustained for 30- to 75-minute periods. The heat conduction of the beams is measured by an infrared imaging technique to understand their thermal responses. Upon completion of the thermomechanical relaxation test, all beams are loaded to failure for residual capacity investigations. The progression of thermal loading across the CFRP-concrete interface exhibits a so-called latent heat effect that takes place with thermal conduction along the interface. During residual testing, the degraded interface reveals partial debonding that accompanies the retraction of CFRP strains. Thermomechanical relaxation influences the residual capacity, load displacement, and interfacial cracking patterns of the strengthened beams. According to analytical modeling, the elastic modulus of CFRP and the magnitude of a mechanical load affect the degree of thermomechanical relaxation. A design factor is proposed based on multiple regression to quantify the implications of thermomechanical relaxation for CFRP-strengthened beams.