Title:
Fiber-Reinforced Polymer Reinforcing Bar-Reinforced Ultra-High-Performance Concrete Flexural Members with Compression-Controlled Design
Author(s):
Shih-Ho Chao and Venkatesh Babu Kaka
Publication:
Structural Journal
Volume:
122
Issue:
4
Appears on pages(s):
67-83
Keywords:
compression-controlled; compressive ductility; durability; fiber-reinforced polymer (FRP); resilience; restoring force; stiffness; ultra-high-performance concrete (UHPC); ultra-high-performance fiberreinforced concrete (UHP-FRC)
DOI:
10.14359/51745468
Date:
7/1/2025
Abstract:
Noncorrosive fiber-reinforced polymer (FRP) reinforcement presents
an attractive alternative to conventional steel reinforcement,
which is prone to corrosion, especially in harsh environments
exposed to deicing salt or seawater. However, FRP reinforcing bars’
lower axial stiffness leads to greater crack widths when FRP reinforcing bars elongate, resulting in significantly lower flexural stiffness for FRP bar-reinforced concrete members. The deeper cracks and larger crack widths also reduce the depth of the compression zone. Consequently, both the aggregate interlock and the compression zone for shear resistance are significantly reduced. Additionally, due to their limited tensile ductility, FRP reinforcing bars can rupture before the concrete crushes, potentially resulting in sudden and catastrophic member failure. Therefore, ACI Committee
440 states that through a compression-controlled design, FRP reinforced concrete members can be intentionally designed to fail
by allowing the concrete to crush before the FRP reinforcing bars
rupture. However, this design approach does not yield an equivalent
ductile behavior when compared to steel-reinforced concrete
members, resulting in a lower strength reduction, ϕ, value of 0.65.
In this regard, using FRP-reinforced ultra-high-performance
concrete (UHPC) members offer a novel solution, providing high
strength, stiffness, ductility, and corrosion-resistant characteristics.
UHPC has a very low water-cementitious materials ratio (0.18
to 0.25), which results in dense particle packing. This very dense
microstructure and low water ratio not only improves compressive
strength but delays liquid ingress. UHPC can be tailored to achieve
exceptional compressive ductility, with a maximum usable compressive strain greater than 0.015. Unlike conventional designs where ductility is provided by steel reinforcing bars, UHPC can be used to achieve the required ductility for a flexural member, allowing FRP reinforcing bars to be designed to stay elastic. The high member
ductility also justifies the use of a higher strength reduction factor,
ϕ, of 0.9. This research, validated through large-scale experiments,
explores this design concept by leveraging UHPC’s high compressive
ductility, cracking resistance, and shear strength, along with a
high quantity of noncorrosive FRP reinforcing bars. The increased
amount of longitudinal reinforcement helps maintain the flexural
stiffness (controlling deflection under service loads), bond strength,
and shear strength of the members. Furthermore, the damage resistant capability of UHPC and the elasticity of FRP reinforcing
bars provide a structural member with a restoring force, leading to
reduced residual deflection and enhanced resilience.