Title:
Torsion and Shear Flow of Hollow Reinforced Concrete Beams Retrofitted with Carbon Fiber-Reinforced Polymer Sheets
Author(s):
Yail J. Kim and Abdulaziz Alqurashi
Publication:
Structural Journal
Volume:
122
Issue:
4
Appears on pages(s):
35-49
Keywords:
carbon fiber-reinforced polymer (CFRP); hollow sections; rehabilitation; strengthening; torsion.
DOI:
10.14359/51743305
Date:
7/1/2025
Abstract:
This paper presents the torsional behavior of hollow reinforced
concrete beams strengthened with carbon fiber-reinforced polymer
(CFRP) U-wraps. Test parameters involve variable wall thickness
in the section and the width and spacing of the externally
bonded CFRP sheets. An experimental program is conducted with
27 beams (three unstrengthened and 24 strengthened) to examine
their capacities, shear flows, and force distributions when incorporating
a ratio of 0.27 to 0.46 between the areas of the hollow
and gross cross sections. The stiffness and capacity of the test
beams are dominated by the wall thickness, and the effectiveness
of CFRP strengthening becomes pronounced as the void of the
beams decreases. The presence of CFRP redistributes internal
shear forces in the cross section, which is facilitated by narrowing
the spacing of the U-wraps. The effective zone of CFRP retrofit
is positioned near the outer boundary of the strengthened section.
Regarding crack control, multiple discrete U-wraps with narrow
spacings outperform wide U-wraps with enlarged spacings. While
the location of a shear-flow path is dependent upon the wall thickness,
the width of the U-wraps controls the effective shear-flow
area of the beams. The size of the void is related to the stress levels
of internal reinforcing components, including yield characteristics.
Transverse stirrups are the principal load-bearing element for
the unstrengthened beams; however, the reliance of the stirrups is
reduced for the strengthened beams because the U-wraps take over
portions of the torsional resistance. Through a machine learning
approach combined with stochastic simulations, design recommendations are proposed.