Shear and Flexural Behavior of UHPFRC-NC Composite
Beams Reinforced With High-Strength Steel and Steel Fibers
Under Static and Cyclic Loading
Introduction
Steel-concrete composite beams form coordinated working member units by means of
the composite action1provided by connectors, which fully exploits the distinct
mechanical properties of steel and concrete. In the lower tensile zone of the composite
beam, the steel with high tensile strength undertakes the tensile force, while in the
upper compressive zone, the concrete with excellent compressive performance bears
the pressure2. Compared with traditional reinforced concrete structures3, steel-concrete
composite beams significantly reduce their self-weight, possess good seismic
performance4, feature rapid construction5and have relatively low costs. Meanwhile,
they enhance the ultimate bearing capacity and deformation ability, making the failure
show signs in advance. Consequently, the application rate of traditional steel-concrete
composite beams in high-rise and super high-rise buildings is increasing. The
composite action needs to be achieved through shear connectors, and the composite
effect directly influences the working performance of steel-concrete composite beams.
Compared with the common flexible shear connector-studs6,7,8, PBL shear
connectors9,10,11possess better strength, stiffness, and shear performance and are
widely used in bridge engineering12 and high-rise building structures.
To date, a substantial number of researchers have conducted research work on
composite materials and composite structures incorporated with steel fibers to meet the
high requirements of modern engineering for material and structural properties. Several
researchers(Ren13, Cao14) have investigated the influences of steel fiber types and
matrix strength on the mechanical properties of cement-based composite materials. The
results indicate that micro-straight steel fibers are more prominent in enhancing the
mechanical strength of cube specimens, and it has been found that the content of steel
fibers can interact with the matrix shear strength in a coupled manner, thereby
improving the shear capacity of composite materials. In actual engineering projects, due
to the influences of wall effect, fiber content, specimen shape, and manufacturing
processes, etc., steel fibers tend to be unevenly distributed within the matrix15.
Mu16,17studied the impact of steel fiber orientation on cement-based composite
materials, and the results revealed that oriented steel fibers enhance the shear and
bending properties of the materials, and the effect is positively correlated with the steel
fiber content. Monteiro18added different fiber types to self-compacting concrete to
explore their influences on the mechanical properties. Among them, the addition of steel
fibers can significantly increase the mechanical properties of composite materials.
Conventional concrete exhibits excellent bearing capacity; however, it performs poorly
in terms of tensile and crack resistance properties. Therefore, Nguyen19conducted a
flexural study on six composite beams with different thicknesses and positions of steel
fiber layers to determine the optimal layout of steel fibers. Several researchers (He20,
Yoo21) designed steel-concrete composite beams using ultra-high-performance steel
fiber-reinforced concrete. The results demonstrated that steel fibers can increase the
integrity and crack resistance of concrete slabs and improve the ductility of composite
beams. Moreover, the steel-concrete composite beams with added steel fibers can also
significantly increase the cracking load and reduce the crack width under negative
bending moment22. Zhang23designed 22 push-out test specimens to study the shear
performance of high-strength bolts in steel-steel fiber concrete composite beams and
verified the reliability of the results through finite element analysis. Several researchers
(Wu24, Xu25,26) considered the construction and binding problems of section steel and
reinforcing bars in actual engineering and proposed to replace reinforcing bars, studs,
and other components with steel fibers in composite beams to shorten the construction
period and simplify the construction. Furthermore, since the shear mechanism of steel
fiber reinforced concrete beams is rather complex, Negi27has established a
mathematical model that takes multiple shear mechanisms into account. The aim of this
model is to predict its shear strength, and he has also proposed replacing traditional
transverse reinforcement with steel fibers, thereby reducing costs28. Dinh29put forward
a model for predicting, through experiments, the shear strength of steel fiber reinforced
concrete beams without stirrup reinforcement. This model has relatively high accuracy
and is superior to some existing models. Hassanin30,31,32explored the cyclic loading
and fatigue behaviors of steel-concrete composite beams. He studied the performance
of externally post-tensioned prestressing tendon-strengthened composite beams under
cyclic loading, clarifying the influences of strengthening effect and shear connection.
Using the finite element model, he investigated the failure modes under fatigue loading
and revealed relevant influences. Moreover, he discussed the influence of shear stud
distribution, verified relevant models and evaluated the applicability of existing codes,
providing references for related work. El-Sisi33 developed a two-node beam element
model with eight degrees of freedom. It has been verified by experiments that this
model can accurately simulate the performance of composite beams. Moreover, through
parametric studies, the influences of relevant factors have been revealed.
The aim of this study is to improve the mechanical properties of concrete by adding
steel fibers to the concrete part of the steel-concrete composite beam (Fig. 1, created
using SOLIDWORKS 2023, https://www.solidworks.com/ and SOLIDWORKS Visualize
2023, https://www.solidworks.com/zh-hans/media/solidworks-2023-solidworks-
visualize/), delay its failure process and ensure that the PBL shear connectors can fully
play their performance in the shearing process. In the experiment, the influence of
different steel fiber contents on the performance of PBL shear connectors and the
failure mode of concrete cracks was discussed. Combined with the finite element
software ABAQUS 2021, a model of randomly distributed steel fibers was established to
verify the experimental results by comparative analysis. In the numerical analysis, the
fiber diameter and length as well as the design parameters of PBL shear connectors
(such as the diameter and length of the penetrating reinforcement, the thickness of PBL
plate, the diameter and number of openings) are the connector variables. The research
results aim to provide a new reference basis for the shear performance of steel-
concrete composite beams.
Considering the limitations of experimental conditions, the range of steel fiber content in
this study is rather limited. Only specific types of steel fibers and concrete mix
proportions have been tested. In addition, only the influence of static loads on the
performance of concrete and PBL shear connectors has been taken into account in this
study, while the long-term impacts of dynamic loads or environmental factors (such as
temperature and humidity) on the performance of steel fiber reinforced concrete have
not been explored in depth.
Fig. 1
This study numerically investigates the shear and flexural behavior of ultra-high-
performance fiber-reinforced concrete (UHPFRC) beams with high-strength steel (HSS)
reinforcement under both static and cyclic loading. A total of 24 three-dimensional finite
element models were developed in Abaqus to simulate the performance of composite
specimens made of UHPFRC and normal-strength concrete (NSC) with varying
interface conditions (dry and wet), overlay types, and fiber contents. The accuracy of
the numerical approach was validated against experimental data. The results
demonstrate that UHPFRC specimens, especially those with steel fibers and HSS
reinforcement, exhibit significantly higher energy absorption (up to 2.45 times), peak
load capacity (up to 153.98 KN in direct shear and 305.30 KN in slant shear), and
stiffness compared to conventional NSC specimens. The NUW configuration (NSC-
UHPFRC-Wet) showed the most efficient performance in both loading regimes.
Moreover, under cyclic loading, the UHPFRC specimens experienced reduced crack
propagation and better energy dissipation (1.27 times more than NSC). These findings
support the use of UHPFRC overlays and advanced reinforcement strategies for
enhancing the durability and resilience of structural elements in civil engineering
applications.
