Engineering Structures 293 (2023) 116649

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Engineering Structures
journal homepage: www.elsevier.com/locate/engstruct

Review article

Flexural and shear behavior of steel-UHPC composite beams: a review

Carlos Alberto Benedetty a, Vinicius Brother dos Santos b, Pablo Augusto Krahl a, c,
Alexandre Rossi d, Flávio de Andrade Silva e, Daniel Carlos Taissum Cardoso e, Carlos
Humberto Martins a, *
a
Department of Civil Engineering, State University of Maringá, CEP 87020-900 Maringá, PR, Brazil
b
Department of Civil Engineering, Federal University of São Carlos, CEP 13565-905 São Carlos, SP, Brazil
c
Department of Civil Engineering, Mackenzie Presbyterian University, CEP 13073-148 Campinas, SP, Brazil
d
Faculty of Civil Engineering, Federal University of Uberlândia, CEP 38400-902 Uberlândia, MG, Brazil
e
Department of Civil and Environmental Engineering, Pontifical Catholic University of Rio de Janeiro, CEP 22451-040 Rio de Janeiro, RJ, Brazil

A R T I C L E I N F O A B S T R A C T

Keywords: Steel-Ultra-High Performance Concrete (UHPC) composite structures are a recent and innovative system with
Composite beams several applications. Steel-UHPC composite beams, for example, enable Accelerated Bridge Construction (ABC)
Steel due to the speed with which their components can be precast in the factory and practically installed on-site.
Concrete
Likewise, the improved properties of UHPC in terms of high compressive strength, ductility, toughness, and
UHPC
Headed stud
durability compared to Normal-Strength Concrete (NSC) allow for designing optimized slender cross-sections
Shear connectors and, consequently, lower weight. Despite all the advantages offered by steel-UHPC composite beams, the
study of their structural behavior began a few years ago, so there still need to be recommendations in the
principal construction codes that regulate their use. In addition, review studies need to discuss the current state-
of-the-art topic. This paper reviews the flexural behavior of steel-UHPC composite beams and the interaction of
shear connectors at the interface through push-out tests. Two databases of push-out and flexural tests were built
and discussed to address the main aspects that influence the behavior and performance of the composite system.

1. Introduction self-weight reduction promoted by the steel beam, it is possible to cover

greater spans [4,5], such as long-span bridge structures and parking
Steel-concrete composite structures cover structural elements such as buildings [6]. Likewise, steel–concrete composite beams are also used to
beams, slabs, and columns in which the best structural properties of each speed up the construction processes [7–9].
material are combined. Composite steel–concrete beams, for example, On the other hand, the advances in construction materials have
are composed of the union of a steel beam subjected predominantly to enabled the use of fiber-reinforced cementitious composites in steel­
flexural tensile stresses and a concrete slab supported on the upper –concrete composite structures. These materials offer improved tough­
flange subjected to flexural compressive stresses. For the two elements ness, ductility, and durability. An example is Ultra-High Performance
(steel beam and concrete slab) to behave as a single element, shear Concrete (UHPC), which has been increasingly used in constructing
connectors are used to prevent relative slippage at the steel–concrete steel–concrete composite beams due to its greater ability to control crack
interface. Several connectors have been analyzed in the literature. opening than ordinary concretes [5,10]. The compressive strength of the
However, in practice, headed stud shear connectors are mainly used due UHPC is usually over 150 MPa [11,12]; however, some standards, such
to their ease of installation during welding [1,2]. The method to eval­ as ASTM C1856 [13], consider it over 120 MPa. Furthermore, the total
uate the shear performance of this type of connection is through push- or partial replacement of Normal-Strength Concrete (NSC) slabs by
out tests, whose parameters obtained are the shear strength, slip ca­ UHPC slabs in composite beams leads to multiple advantages, for
pacity, stiffness, and failure mode [3]. Although the steel–concrete example, the reduction of the slab height, the decrease in the overall
composite beam system presents advantages in terms of flexural ca­ weight of the structure, improvement of serviceability, and prolongation
pacity compared to conventional reinforced concrete beams due to the of the structure service life [14–16].

* Corresponding author.
E-mail address: chmartins@uem.br (C.H. Martins).

https://doi.org/10.1016/j.engstruct.2023.116649
Received 24 April 2023; Received in revised form 23 June 2023; Accepted 19 July 2023
Available online 26 July 2023
0141-0296/© 2023 Elsevier Ltd. All rights reserved.
C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

The structural engineering field in which the steel-UHPC composite construction [31]. Likewise, manufacturing UHPC slabs under an
beams best fit is Accelerated Bridge Construction (ABC) [17–20]. The industrialized approach entails concrete with fewer defects since cli­
main reason is that all the structural components (steel beams, UHPC matic variables such as temperature and relative humidity do not
slabs, and connectors) are manufactured in the factory, significantly negatively impact concrete casting. Consequently, aspects such as the
reducing on-site construction time. The system also improves traffic durability and serviceability of the structure have better performance.
impact since the road closure time generated by the bridge construction According to Shao et al. [32], using this construction system can enable
is significantly reduced. Due to the UHPC being produced in an indus­ reductions in the structure’s weight by 10–30%. Furthermore, it is
trial plant when large volumes are required, two strategies can be used possible to eliminate formwork and scaffolding since only cranes are
to manufacture the UHPC slabs [21,22]. The first is to monolithically necessary to place the structural elements.
cast the slab directly on the top flange of the beam, embedding all the The steel-UHPC precast beam assembly can be done in two methods.
shear connectors [18]. On the other hand, the second option requires the The first one is through manufacturing UHPC panels installed one next
UHPC precast slab to be fabricated with shear pockets. Subsequently, the to the other until they completely cover the bridge span (Fig. 1a). This
slab is placed on the steel beam, where grouped shear connectors will be technique is more advantageous for large-span than medium and small-
located inside the shear pockets. Finally, the pockets are filled on the site span bridges because the slab is sectioned into several lightweight UHPC
with high-strength mortar or UHPC [23,24]. The steel-UHPC precast panels. The second coupling method involves manufacturing the slab
composite beams undoubtedly offer more construction practicality, in with a length covering the entire bridge span, an option more viable for
addition to an industrialized construction approach, because activities medium and small-span bridges (Fig. 1b). In both cases, shear pockets
such as assembling and disassembling formworks are eliminated [25]. are manufactured in the slab to establish a connection with the steel
Despite the advantages of the steel-UHPC precast composite beams beam by the shear connectors. The latter are welded or bolted to the
over conventional systems, there are no specific standard guidelines or beam flange, and the shear pockets are later cast with UHPC. In recent
design recommendations for using precast UHPC slabs [19]. It is a work, Yang et al. [33] compared the structural performance of beams
relatively new solution and the first experimental studies on this topic using these two slab-steel beam joining techniques through the four-
date from the end of the last decade. Therefore, there remain gaps and point bending test subjected to a positive moment. The researchers
aspects yet to explore regarding structural behavior [26]. For example, found that even though the division of the slab by segments (panels)
research in such a field focuses on studying the shear connector behavior facilitates transportation and installation activities, the flexural perfor­
in the interface by push-out tests due to the reduced thickness of slabs, mance of the composite beam can be negatively impacted. Due to gaps
shorter connectors with greater diameters are required [27], leading to a between adjacent slabs and the absence of connection between the faces,
connector with an aspect ratio out of the specified code limits that may relative slips arise at the interfaces near the gaps. These gaps cause the
affect ductility and failure modes [28]. On the other hand, several panels to work isolated until contact occurs. As a result, properties such
studies analyze the structural scale’s behavior by beam bending tests. as flexural stiffness and ductility of the composite beam can decrease by
The studies focused on the flexural behavior of supported beams subject 47.8% and 44.1%, respectively, compared to a monolithic slab [33].
to positive moments since it represents the most usual support condition Therefore, more studies are required to investigate panel lengths,
for medium and small-span bridges. Moreover, for this condition, the connector configurations in shear pockets, and plate connections.
maximum capacities of both components (steel beam and UHPC slab) is
leveraged. However, other studies have placed a particular interest in 2.2. Cross-section geometry
the behavior of steel-UHPC composite beams subject to hogging mo­
ments, which occur at internal supports of continuous beams. Hogging Steel-UHPC composite beam tests reported in the literature have
moments represent a critical aspect of steel-UHPC composite beams adopted cross-section geometries that differ significantly. Fig. 2 shows
since the component with the lowest ductility supports the tensile some cross-sections analyzed by several researchers; the different ge­
stresses. In that scenario, the UHPC slab is subject to flexural tensile ometries show the versatility of the composite beams to be applied in
stresses as the fibers and reinforcement bars are responsible for multiple situations. Generally, the most widely used system is coupling
restricting the crack opening [18,22,24,29,30]. Crack growth and type I (Fig. 2a) or H steel profiles to a low-height rectangular concrete
propagation in these critical regions can impair the strength capacity slab [34]. The interaction between these two elements is possible due to
and durability of the structure. A study on this topic and the definition of the union by commonly welded shear connectors on the top flange of the
the UHPC properties can mitigate such problems. profile. Yoo et al. [26] studied the flexural behavior of a UHPC slab
This review is intended to discuss the state of the art of steel-UHPC coupled to an inverted-T steel profile using welded connectors on the
composite beams and to elucidate research gaps and aspects of struc­ web (Fig. 2b). The researchers suggested that, due to the high stiffness of
tural behavior that still require attention. First, two databases on push- the concrete slab, the steel profile upper flange can be eliminated,
out and flexural tests in beams were compiled and analyzed. Addition­ allowing full utilization of UHPC’s potential. In addition, by adopting
ally, the accuracy of design standards prediction models of the headed this system, it is possible to reduce the amount of steel without impairing
stud shear capacity proposed by design codes and several authors were the mechanical performance of the composite beam. Another composite
investigated. Finally, it was carried on a review of the models that could beam was suggested by Zhao et al. [35] for applications such as long-
be implemented in future design standards of steel-UHPC composite span bridges. In this case, a UHPC T-beam can be connected to a hot
structures or to verify the shear stud capacity of existing structures. rolled steel beam, thus achieving a higher cross-section moment of
inertia with a composite web (Fig. 2c). This alternative allows a
2. Composite beams characteristics reduction of 47.0% in self-weight and 12.0% of its cost compared to the
conventional system (Fig. 2a) [36]. Using a steel box girder is commonly
2.1. Steel-UHPC precast system adopted when the structure’s self-weight must be reduced (Fig. 2d) [37].
Unlike the previous system, this type of solution presents advantages in
The construction system of steel-UHPC precast composite beams falls terms of stability due to high torsional stiffness, which is advantageous
within the approach of ABC and industrialized construction. Since the for applications such as bridges [38]. UHPC can also be a retrofit ma­
UHPC elements are manufactured in factories and then transported and terial in conventional steel–concrete composite beams. Placing a layer of
coupled to the steel beams on-site, the execution times of on-site activ­ UHPC on top of the concrete slab of a composite beam (Fig. 2e) protects
ities are considerably reduced. In addition, the high practicality and the structure due to its low permeability [39] and, consequently, pre­
speed with which the structural elements (steel beam, concrete slab, and vents the structure from ingressing aggressive agents. Due to the low
connectors) are assembled contribute to minimizing the impact of traffic porosity and high tensile strength of UHPC overlay, using this system in

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Fig. 1. Steel-UHPC composite beams with (a) precast panels and (b) continuous precast slab.

Fig. 2. Some types of composite beams: (a) conventional steel-UHPC composite beam, (b) UHPC slab coupled to inverted-T steel profile [42], (c) UHPC T-beam
coupled to H-steel profile [35,36], (d) composite box girder [37,43–49], and (e) composite beam strengthened with UHPC overlay [40,41].

hogging moment regions can improve structural performance and base, making it possible to set specific inclination angles to the vertical.
durability [40,41] compared to conventional steel–concrete composite The push-out tests of this type of connector embedded in UHPC showed
solutions. that the inclined connectors improve the ductility of the connection
since they minimize the stud fracture.
2.3. Connector type On the other hand, demountable shear connectors appear to be a
competitive alternative to welded connectors since they can be used in
Coupling with shear connectors is the most frequently used method scenarios requiring disassembling structural components. This feature
to join the steel beam and the UHPC slab. In recent years, several con­ also benefits the owners since maintenance intervention time is drasti­
nectors’ geometries and material mechanical properties have been cally reduced when the replacement of a damaged part is needed.
analyzed by many authors to guarantee the full connection between the Furthermore, steel–concrete composite structures coupled with
composite beam elements. Some of the connectors found in the litera­ demountable shear connectors fit sustainable development and circular
ture are headed studs (Fig. 3a) [50,51], demountable bolts (Fig. 3b) economy concepts since the structural elements can be quickly dis­
[52–54], channel connectors (Fig. 3c) [55–57], U-type connectors [58], assembled and reused for other purposes [66]. A performance compar­
V-type connectors [59–61], and puzzle connectors [62–64]. Fig. 3 pre­ ison of welded and demountable connectors was conducted by Fang
sents some of the connectors studied in the literature. The headed stud is et al. [67]. The demountable connectors were manufactured of high-
the most used due to its practicality and welding speed since it is done strength steel, while the welded connector had normal-strength steel.
automatically with a stud-welding gun. In contrast, the welding pro­ The load per stud versus vertical slip relationships of the push-out tests
cedure for U and V-type connectors takes more time for execution since carried out with these connectors in the grouped configuration are
the entire connector base perimeter in contact with the flange must be shown in Fig. 4. It can be observed that the demountable connectors
welded using the manual electrode technique. Fig. 3d shows a novel stud presented better shear connection performance than the welded con­
developed by Xu et al. [65] called steel wedge block-crossed inclined nectors. The better performance is attributed to the high friction
stud. It consists of two-headed studs inclined and welded to a trapezoidal developed at the steel–concrete interface due to the pretension in the

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Fig. 3. Some types of shear connectors: (a) headed stud [51], (b) demountable shear connector [54], (c) channel connector [55], and (d) steel wedge block–crossed
inclined stud [65].

international technical standards have recommended models for pre­

dicting the shear stud connector’s capacity embedded in concrete with
at least 100 MPa of compressive strength. However, recent research has
explored using advanced cement-based composites such as UHPC in
steel–concrete composite structures, which allows for section demate­
rialization, more sustainable and durable construction, and diminishing
costs with transportation, lifting, and assembly operations on the con­
struction site. However, codes still do not contemplate recommenda­
tions for steel-UHPC composite connections. Therefore, it is necessary to
investigate the behavior of stud shear connectors embedded in this type
of concrete [27].

3.1. Push-out test

The push-out test is the most usual test to investigate the stud shear
connector behavior [68]. The dimensions and test procedure are
described in EN 1994–1-1:2004 [3] (Eurocode 4) and AS/NZS
2327:2017 [69] (Australian/New Zealand standard) consisting of shear
studs welded on the flanges to a HE 260B steel profile beam. The con­
nectors are spaced longitudinally and transversally 250 and 100 mm,
Fig. 4. Comparison between the load per stud versus slip behavior of welded respectively. The connectors are embedded in 600x650x150 mm slabs
and demountable connectors [67].
and a concrete cover of 15 mm, as shown in Fig. 5.
Some of the limits established by the standards concerning the height
connector. Additionally, the looseness of the hole where the connector is (h) to diameter (d) ratio h/d, cover thickness, and longitudinal and
inserted and the subsequent widening contribute to increased slippage transversal spacing between connectors are presented in Table 1. UHPC
at the interface. slabs have smaller thicknesses than NSC due to their high compressive
strength. Short studs are required when thin slabs are used on steel-
3. Shear connector behavior UHPC composite beams. Using this type of connector means that, in
many cases, the minimum aspect ratio requirements of Table 1 are not
Applying shear connectors ensures the steel–concrete connection in reached. Although there are no specific limits on design standards for
composite structures, allowing to transfer of forces between these ma­ UHPC embedded connectors, several studies have concluded that aspect
terials. This connection can be classified based on the interaction degree, ratios lower than those presented in Table 1 can be adopted for UHPC.
which impacts the analysis and design of steel-UHPC composite struc­ Kim et al. [27] suggest that the aspect ratio of studs embedded in UHPC
tures. Headed stud shear connectors are widely used in conventional slabs with a thickness of up to 75 mm can be reduced from 4.0 to 3.1
steel–concrete composite structures to transfer forces between structural without diminishing the shear capacity. Additionally, Wang et al. [70]
elements such as slabs, beams, and columns. As a result, numerous found that the reduction can reach up to 2.3. The aspect ratio reduction
studies have been conducted since the 1950 s to investigate the is possible because UHPC provides high confinement reducing the sus­
connector behavior in composite structures made with NSC. These ceptibility to cracking that can induce anchorage loss.
studies have focused on several parameters, such as the height h, In order to evaluate the main parameters that can influence the
diameter d, group effect, and strength of the steel stud, to analyze the behavior of headed studs in steel-UHPC composite structures, a push-out
connection’s shear strength, ductility, and failure modes. Consequently, database (Table 2) was built with 246 models presented in the literature.

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Fig. 5. Push-out test setup according to EN 1994-1-1:2004 [3] (dimensions in mm).

efficiency of the construction process by eliminating the additional

Table 1
formwork. In most steel-UHPC precast composite beam studies, the
Minimum requirements in international technical standards.
geometry adopted for the shear pockets is rectangular, and the di­
Standard Aspect Cover Longitudinal Transversal mensions remain constant along the height. The main reason is the
ratio h/d thickness c spacing sl (mm) spacing st (mm)
practicality of its construction due to its simple geometry. Only a single
(mm)
study by Fang et al. [73] was dedicated to the topic of shear pocket
AASHTO 4.0 50 6d 4d
geometries. The study considered three types of pockets: square shear
LRFD 2020
[71]
pockets with uniform cross-sections (Type I) or non-uniform cross-sec­
EN 1994-1- 3.0 50 5d 2.5d tions in the form of inverted cone-shaped pockets (Type II and III), as
1:2004 [3] shown in Fig. 6. The authors found that the specimen with Type II shear
GB 50917- 4.0 15 6d 4d pocket, compared to Type I specimens, exhibited increases of 1.8%,
2013 [72]
26.4%, and 12.8% associated with ultimate shear capacity, initial shear
AS/NZS 4.0 20 5d 1.5d*
2327:2017 stiffness, and ductility, respectively. However, a slight reduction in
[69] strength and stiffness was observed when using Type III shear pockets. In
addition, an inverted cone-shaped shear pocket with an appropriate
*Clear distance between the heads.
inclination (about 15◦ for Type II) decreases susceptibility to loss of
contact at the pocket-slab interface and improves the initial shear stiff­
These models adopted the push-out tests according to EN 1994-1-1:2004
ness. In contrast, when inverted conical shear pockets with excessive
[3] and AS/NZS 2327:2017 [69] standards or similar test setups
inclination are used (up to about 30◦ for Type III), the confinement
regarding specimen dimensions and precast slabs with similar material
action of the surrounding concrete is significantly reduced. Therefore,
in the shear pockets. However, due to its excellent mechanical proper­
using inverted cone-shaped shear pockets with an appropriate inclina­
ties, the UHPC slab thickness is less than that of NSC slabs, ranging
tion offers optimal strength, stiffness, and ductility in full-depth precast
between 35 and 100 mm. Hence, some studies shown in Table 2 have
concrete slabs.
modified the dimensions recommended in the standards.
The structural elements of UHPC, such as the slabs for composite
structures, are more promising to be precast due to the better casting 3.2. Failure modes
control, the elimination of formworks, and curing on site. After
analyzing the push-out database, it was found that most of the works are In NSC slabs, the failure modes presented in the literature were
related to UHPC slabs and that only 19.5% of the studies evaluated the concrete breakout (CB) or concrete pryout (CP). The most likely con­
connector’s shear capacity in precast slabs, that is, with the presence of crete failure mode is pryout failure rather than breakout failure. The CB
shear pockets. A shear pocket is an intentionally void or recessed area in occurs when free edge conditions govern the failure. Under such cir­
precast concrete slabs to accommodate the shear connectors used to cumstances, the failure planes form a volume of concrete around the
connect the slab and the supporting beam. These pockets are frequently anchor, separating this concrete from the connector (Fig. 7a). The CB
used in precast concrete construction to enhance the speed and failure manifests itself when the concrete surrounding the base of the

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Fig. 6. Shear pocket geometries analyzed by Fang et al. [73] (dimensions in mm).

Fig. 7. Failure modes of headed studs embedded in concrete [75].

headed stud is exposed to high tensile stresses, inducing the concrete to in the direction perpendicular to the applied shear force. The pryout
fail in a cone-shaped pattern around the base of the stud. The typical failure occurs when the concrete around the headed stud is exposed to
causes of breakout failure are inadequate concrete strength and insuf­ high shear stresses, inducing the concrete to fail in a wedge-shaped
ficient edge distance or spacing. In contrast, CP failure occurs in a local pattern. Inadequate embedment depth is the typical cause of pryout
area surrounding the anchor, corresponding to forming a concrete spall failure (Fig. 7b) [74,75].

Fig. 8. Failure modes of push-out specimens tested by Lin et al. [77].

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

However, the UHPC stud shank (SS) failure mode (Fig. 7c) was observed, which do not meet the required ductility demand of 6 mm by
observed in 77.2% of the database results due to the higher compressive EN 1994–1-1:2004 [3]. Similarly, Cao et al. [78] studied a model with a
and tensile strength of the UHPC. In an experimental/numerical study stud height and diameter of 35 mm and 13 mm, respectively, with an h/
conducted by Ding, Zhu, and Shi [76], three aspect ratios (3.2, 4.0, and d of 2.7. The authors found that the studs could develop full strength
4.2) and two connector diameters (19 and 25 mm) were considered. All with this aspect ratio when embedded in UHPC due to their higher
test specimens exhibited SS failure at the interface between the steel and compressive and tensile strength than NSC. In a recent study, Qi et al.
UHPC slab, which was attributed to the excellent anchoring force of [50] performed a numerical analysis of several aspect ratios ranging
UHPC on studs. Only local spalling was observed in the compression from 2.0 to 6.0 using 16–30 mm diameter studs. The authors found that
zone below the stud root in the UHPC slabs. Other failure modes, such as the shear strength was not reduced when the aspect ratio was changed
concrete crushing (CC), stud pullout (SP), and concrete spalling (CS), from 6.0 to 2.0. This behavior showed no obvious influence on the shear
were less observed in the literature. behavior of studs and needs clarification. As a result, it was concluded
Lin et al. [77] studied the influence of three steel fiber volume that even studs with a short head and an aspect ratio as low as 2 could
fractions (1.0%, 2.0%, and 4.0%) on failure patterns, whose addition achieve full strength when used in UHPC slabs.
produced increases of 15.4%, 36.0%, and 21.6% in compressive strength Connectors with low aspect ratios are more common in UHPC slabs
concerning UHPC matrix without fibers. The shear strength in push-out since, due to their high compressive strength, the slabs can reach a lower
specimens increased by 10.7%, 33.5%, and 21.0%, respectively. Cracks thickness than NSC slabs. In compensation for the connector aspect ratio
form around the shear studs when the load reaches the peak value, and reduction, the increase of the connector diameter becomes necessary.
the shear studs exhibit certain deformation, with ductility observed until Wang et al. [70] were the first to investigate a large stud diameter by
the shear studs fracture. The detailed failure modes of push-out speci­ analyzing three aspects ratio (4.5, 4.0, and 2.3) with 22 mm and 30 mm
mens are presented in Fig. 8, where cracks appear around the headed diameters. The authors concluded that the shear strength, stiffness, and
shear stud, bar, and root when H-shaped steel is connected to UHPC ductility of the 30 mm diameter connectors were 15.0%, 45.0%, and
without steel fibers. In addition, cracks form around the shear stud root 60.0% higher than the 22 mm diameter connectors, respectively. Tong
when 4.0% of steel fibers are added to the UHPC. Therefore, adding steel et al. [79] studied two aspects ratio (4.2 and 6.1) with 13 and 19 mm of
fibers delays the development of cracks near the shear studs. However, stud diameter, respectively, and concluded that increasing the stud
the reasons for the appearance of cracks in different locations with diameter can significantly increase their shear capacity. The shear ca­
varying fiber volumes were unclear. pacity and elastic shear stiffness of studs with a diameter of 19 mm was
82.4% and 46.0% greater than that of 13 mm due to its higher cross-
3.3. Connector aspect-ratio influence section area, which allows a higher load for the same tension.
Additionally, Xu et al. [80], based on numerical analysis of studs
The diameter d, height h, and stud aspect ratio h/d are parameters with an aspect ratio between 2.0 and 5.4 and diameters of 22 and 30
that must be taken into account when analyzing the strength capacity of mm, found that the forces that act perpendicular to the stud are
the steel beam-UHPC slab interface. A low aspect ratio can lead to high- distributed from the stud root only between 18.0% and 25.0% of its
stress concentration and brittle failure around the stud, reducing the height when the h/d is 4.0. However, for studs with an aspect ratio equal
load capacity and connection ductility. In contrast, an adequate aspect to 2.0, the forces are distributed over a greater length, specifically be­
ratio results in even stress distribution across the concrete and steel tween 40.0% and 50.0% of the height. This distribution suggests that
studs, resulting in a more ductile connection with higher load capacity. using low aspect ratio studs promotes better efficiency in using low
The specimen information compiled in the database (Table 2) allows us aspect ratio studs, which promotes better efficiency in load distribution
to identify the ranges of these parameters adopted in the literature. For and can promote total strength shear capacity [81].
example, the ranges for h, d, and h/d were 20.0–150.0 mm (120 mm), Several researchers have developed parametric studies of push-out
10.0–40.0 mm (22 mm), and 1.0–9.3 (4.0), respectively. The most tests using nonlinear finite element analysis. These studies evaluated a
frequently used value in the studies is indicated in parentheses, and an broader range of aspect ratios. For example, Cao et al. [82] investigated
aspect ratio histogram of connectors used in UHPC is shown in Fig. 9. It the headed stud behavior in thin UHPC slabs (less than 100 mm) with
is possible to verify that connectors with an aspect ratio of 2.0 and 3.0 aspect ratios between 1.5 and 6.1 and stud diameters between 13 and 22
also predominate, less than the 4.0 recommended by most standards. mm. It was found that the stud diameter significantly impacts its shear
The initial study performed by Kim et al. [27] evaluated the head capacity and influences the improvement of other parameters, such as
stud behavior in UHPC slabs. The parameters studied were stud height the load-slip curve and the shear stiffness. In contrast, the influence of
(50, 65, and 100 mm) and diameter (16 and 22 mm), with aspect ratios the stud height is negligible, which can be explained because the stresses
h/d of 4.5, 4.1, and 3.1. According to the authors’ findings, reducing the concentrate in the stud root, and consequently, the failure occurs in this
aspect ratio from 4.1 to 3.1 for 16 mm diameter studs did not signifi­ region. A similar trend was observed in a recent experimental study
cantly impact the structural behavior. The shear strength and stiffness conducted by Fang et al. [83] on push-out tests with grouped studs
values remained similar. However, relative slips of 3.8–5.3 mm were embedded in precast UHPC slabs. For aspect ratios of 1.8–4.4, 19 mm of
stud diameter, and the same slab thickness, the increase in shear ca­
pacity and stiffness was slight as the stud height increased. However, a
higher stud corresponded to a larger slip deformability due to its flexural
flexibility. In contrast to that finding, Zhao et al. [84] concluded through
a numerical analysis that the increase in stud height from 25 to 45 mm
for 13 mm diameter studs positively impacted the shear capacity,
reaching increases of up to 40.0%. Furthermore, it was observed that
when the stud height was less than 25 mm, the flexural effect of the stud
decreased significantly, resulting in a pull-out failure without shear
fracture. This phenomenon indicates that the flexibility of the stud plays
an essential role in that behavior.
In another study, Hu et al. [85] evaluated studs with aspect ratios
between 3.0 and 7.5 and diameters between 16 and 40 mm. The studs
were embedded in both NSC and UHPC slabs to study the influence of
Fig. 9. Aspect ratio distribution of headed studs embedded in UHPC. concrete compressive strength. The authors concluded that the increase

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

in compressive strength of UHPC had a negligible influence on the shear the range of 4.0 and 5.0, as shown in Fig. 10.
capacity when the stud diameter was smaller than 30 mm. However, The study of the group effect of the studs embedded in UHPC began a
when large diameter studs are used (>30 mm), the concrete compressive few years ago. Wang et al. [70] studied grouped studs of 30 mm diam­
strength of UHPC is more significant. This influence is explained by the eter with longitudinal and transversal spacings of 5.0 and 3.0 times the
formation of a compressed concrete triangular region at the stud base, stud diameter, respectively. The results evidenced reductions in the ul­
contributing to the increase in the shear capacity of studs embedded in timate strength of 2.0–6.0% compared to a single stud. This behavior
UHPC. Regarding studs embedded in NSC, where the predominant suggests that the group effect slightly influenced the ultimate shear
failure modes are concrete breakout and concrete pryout, the concrete strength for the diameter and spacings evaluated due to the UHPC me­
compressed region fails prematurely due to a higher susceptibility to chanical properties, which presented no visible cracks. Whereas obser­
cracking due to low concrete strength. The concrete compressed region vations of the UHPC slabs allow verification of fewer visible cracks than
at the connector base is the wedge block. Increases in the connector those observed in NSC specimens, a better cracking control is beneficial
diameter lead to a larger wedge block size. In addition, its susceptibility for durability. Furthermore, the interfacial slips for this last material
to rupture decreases as the compressive strength of UHPC increases. For were higher since the cracks promoted reduced shear stiffness. In
example, Fang et al. [83] found that large-diameter connectors exhibi­ another study developed by Tong et al. [79], a percentage reduction in
ted improved shear behavior, with the initial shear stiffness, ultimate the shear capacity of 3.0% was found, within the range observed by
shear strength, and ductility increasing by up to approximately 39.0%, Wang et al. [70]. The study used 19 mm diameter connectors with
36.0%, and 56.7%, respectively, as the stud diameter was increased longitudinal and transversal minimum spacings of 65 mm and 50 mm,
from 16 mm to 22 mm. Large-diameter connectors are compatible with respectively. From the load-slip curves of the push-out tests, a secant line
UHPC slabs since the strength capacity of both elements can be fully was drawn at 0.2 mm of slip, and the elastic shear stiffness was calcu­
reached at the moment of failure [28,86]. Furthermore, Hu et al. [87] lated from its slope. In addition, the group effect promoted reductions of
found that the increase in shear stud capacity with increasing stud up to 19.6% in the elastic stiffness of studs. Longitudinal spacing ratios
diameter had an approximately linear trend. A similar behavior was up to 2.0 were evaluated by Hu et al. [85] on 30 mm diameter studs. The
observed by Duan et al. [88], but the authors highlighted that the stud authors found that when the longitudinal spacing is less than 3d in the
strain capacity decreases significantly with the increase in the stud arrangement of grouped large-headed studs, stress overlap occurs due to
diameter. the interaction between the studs, resulting in reduced shear capacity.
Therefore, it is recommended that the stud spacing in the direction of the
shear force should be>3d for the grouped studs embedded in steel-UHPC
3.4. Group effect composite structures. Additionally, the authors highlight that the
spacing specification in EN 1994–1-1:2004 [3] for the transversal di­
The grouped stud arrangement can promote a decrease in the ulti­ rection to the shear force is appropriate for steel-UHPC composite
mate strength and ductility of the connection, depending on the spacing structures [85].
between adjacent studs due to the non-uniform stress distribution and Ding et al. [81] are more conservative regarding the spacing of
the overlapping effect, making the studs within a group unable to ach­ grouped studs, suggesting a value of at least 4.0 times the stud diameter
ieve their ultimate tensile strength simultaneously [89–91]. The in both directions. This experimental study on grouped studs embedded
grouped stud arrangement is more common in precast slabs with shear in UHPC precast slabs with shear pockets showed that a reduction in
pockets than in monolithic slabs. The longitudinal (sl) and transversal spacing from 4.0 to 2.5 times the diameter implied a 13.4% decrease in
(st) spacings are the parameters the standards restrict to avoid the group shear strength. Additionally, the ductility of the connection was
effect. In addition, the stud spacing is a function of the stud diameter, as impaired. Fang et al. [73] recently developed an experimental study on
presented in Table 1. On the other hand, design standards make no the group effect. The results revealed that the shear strength could
recommendations regarding the spacing of studs embedded in UHPC. decrease around 15.0% when spacings equal to or less than 2.7 times the
Therefore, the most common group effect study method is varying the sl stud diameter are adopted. As well as Hu et al. [85] highlighted that the
and st spacings in the push-out specimens. Since stud diameters vary for spacings recommended by the EN 1994–1-1:2004 standard could be
each study, the ratio between spacing and diameter (s/d) can be estab­ applied to steel-UHPC composite structures since they are conservative.
lished to compare studies in the literature. The specimens in the data­ Also, it was analyzed by Fang et al. [73] if embedding the grouped
base presented sl/d and st/d ratios of up to 24.0. For the longitudinal connectors in shear pockets of precast slabs and not in monolithic slabs
spacing, the more frequent sl/d ratios were in the range of 4.0 and 6.0. could influence the connection behavior. It was found that connections
While for the transversal spacing, the more frequent st/d ratios were in

Fig. 10. (a) Longitudinal and (b) transversal spacing ratios of headed studs embedded in UHPC.

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

fabricated using shear pocket slabs exhibited 4.0–9.0% and 3.0–21.0% samples can be observed for loads less than 200 kN, which is associated
reductions in shear capacity and stiffness, respectively, compared to with conventional diameter connectors failure capacity. In contrast,
monolithic slabs. In monolithic specimens, the shear force is transmitted most models have low accuracy in predicting the capacity of large-
directly to the surrounding concrete of the studs, leading to vertical and diameter connectors. This trend may be because complex mechanisms
diagonal splitting cracks around the connectors. In precast specimens such as crushing and crack bridging of the UHPC contribute to the shear-
with shear pockets, the load is transferred to the precast slab by the strength capacity since high contact pressures are generated between the
shear pockets, resulting in cracks propagating downwards along the concrete and studs due to large diameters. This loading promotes the
interface between the precast slab and the shear pocket. The monolithic growth and propagation of cracks over a broader region. The models of
casting method is more efficient, utilizing both the studs and the slab, the standards developed from experimental data on NSC do not account
while the properties of the pocket-to-slab interface often constrain for these mechanisms. The Japanese standard JSCE-2007 [94] and
precast casting. American standard AASHTO LRFD 2020 [71] presented the best accu­
racy among the models analyzed. On the other hand, the model of the
3.5. Shear capacity prediction models of stud connectors ANSI/AISC 360–22 [92] and GB 50017–2017 [93] standard was less
accurate but highly conservative.
Several models can be used to predict the shear capacity of con­ Due to the current standards do not have specific calculation models
nectors embedded in cementitious matrices. However, many of these for connectors embedded in UHPC, in recent years, several researchers
calculation models are based on data from composite push-out tests with have proposed formulations to predict the shear capacity of connectors
slabs and connectors with NSC. Such is the case of the principal design embedded in UHPC. Wang et al. [96] proposed an empirical equation to
standards EN 1994–1-1:2004 [3], AASHTO-LRFD 2020 [71], ANSI/AISC calculate the shear capacity of demountable connectors embedded in
360–22 [92], GB 50017–2017 [93], and JSCE-2007 [94]. The equations UHPC with an aspect ratio greater than or equal to 1.5. According to the
of these models are summarized in Table 3, and it can be observed that authors, connector fracture is the dominant failure mode in connectors
the connector shear capacity corresponds to the lower value between the with these characteristics. The formula for determining the shear ca­
concrete crushing force and the force associated with the connector pacity is a function of the product of the cross-sectional connector area,
failure. In addition, models such as the EN 1994–1-1:2004 [3] standard the ultimate tensile strength, and an empirical reduction constant. The
and the JSCE-2007 [94] consider the connector aspect ratio, whereas value of the constant less than 1 in Equation 7 indicates that the trans­
ANSI/AISC 360–22 [92] accounts for the group effect and the stud versal force necessary to fracture the connector is less than if it acted
arrangement on the flange. axially, confirming the existence of the tension force that arises in the
The models in Table 3 were used to predict the shear capacity of the connector due to the presence of the head. On the other hand, Krus­
headed stud connectors of each specimen from the Appendix A database. zewski et al. [51] improved the Hegger et al. [97] model to be applied to
It was possible to verify their accuracy through the experimental and a wider range of UHPC strengths. In addition, it allowed the model to
calculated values. In the cases in which the concrete elastic modulus was account for imperfections in the weld collar. An interesting aspect of this
not reported in the paper, Equation (6), proposed by Graybeal [95] for model is that it allows taking into account possible dimensional varia­
predicting the elastic modulus of the UHPC, was applied. tions in the weld collar, which may influence the connector shear ca­
√̅̅̅̅ pacity. Recently, Xu et al. [28] developed a formulation for the shear
E = 3840 fc′ (6) capacity of headed connectors for more common situations. In other
words, cases where low-height connectors are embedded in reduced-
When fc′ is the concrete compressive strength in MPa. thickness slabs when using high compressive strength concrete. Addi­
In equations such as those of the EN 1994–1-1:2004 [3] and JSCE- tionally, Wang et al. [98] proposed a more generalized equation
2007 [94] standards, safety factors equal to 1.0 were adopted. Like­ regarding concrete compressive strength since it can be applied to both
wise, the mechanical parameters of the materials were those measured NSC and UHPC. The equations of each model are in Table 4.
experimentally without being penalized by reduction factors since the Some calculation models in Table 4 were used to predict the shear
intention is to evaluate the ability of the models to predict the actual capacity of headed stud connectors embedded in UHPC precast slabs.
shear capacity of headed stud connectors. The experimental values of push-out tests with this slab type were
In general, it can be seen in Fig. 11 that the models show acceptable extracted from the database in Appendix A and contrasted with the
precision when used to predict the shear resistance capacity of con­ calculation values. Models such as that of Hu et al. [99], Huang et al.
nectors embedded in UHPC. Furthermore, the capacity accuracy in most [100], and Fang et al. [83] were not considered in the analysis since not

Table 3
Models of the main standards to predict the shear capacity of headed stud connectors.
Standard Calculation model Equation
⎡ ( ) ⎤
EN 1994–1-1:2004 [3] πd2 (1)
⎢0.8fu 4 √̅̅̅̅̅̅̅̅̅̅̅̅̅ ⎥
⎢ 0.29αd2 fck Ecm ⎥
PRd = min⎢
⎢ ; ⎥
⎥
⎣ γV γV ⎦

( √̅̅̅̅̅̅̅̅̅̅ )
AASHTO LRFD 2020 [71] Qn = min 0.5Asc f′c Ec ; Asc Fu (2)
( √̅̅̅̅̅̅̅̅̅̅ )
ANSI/AISC 360–22 [92] Qn = min 0.5Asa f′c Ec ; Rg Rp Asa Fu (3)
( √̅̅̅̅̅̅̅̅ )
GB 50017–2017 [93] c
NV = min 0.43As Ec fc ; 0.7As fu (4)
⎡ √̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅ ⎤
JSCE-2007 [94] ( )
hss (5)
⎢31Ass f′cd + 10000 ⎥
⎢ dss Ass fsud ⎥
Vsud = min⎢⎢ ; ⎥
⎥
⎣ γ b γ b ⎦

[Note] fu, Fu, fsud = stud ultimate tensile strength; fck, f’c, f’cd, fc = characteristic cylinder concrete compressive strength; Ecm, Ec =
elastic modulus; Asc, Asa, As, Ass = stud cross-section area; hss = stud height; d, dss = stud diameter; γv = partial factor (1.25); γb =
member factor (1.3); α = 0.2(hsc/d + 1) for 3 ≤ hsc/d ≤ 4 or α = 1 for hsc/d > 4; Rg = group effect coefficient (1.0; 0.85; 0.7); Rp =
position coefficient (0.75; 0.6).

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Fig. 11. Comparison between the experimental and analytical shear stud capacity through the standard models: (a) EN 1994-1-1:2004 [3], (b) AASHTO LRFD 2020
[71], (c) ANSI/AISC 360-22 [92], (d) GB 50017-2017 [93] and (e) JSCE-2007 [94].

all the studies provide the necessary parameters for their application, 4. Flexural behavior of steel-UHPC composite beams
such as the dimensions of the weld collar. The predicted results are
shown in Fig. 12, where the mean value of the ratio between Pu-cal/Pu-exp, 4.1. Monotonic three and four point bending tests
and the standard deviation for each model is also indicated in Table 5. It
is observed that the equations proposed by Fang et al. [73] and Xu et al. Several authors have studied the flexural behavior of steel-UHPC
[28] present the highest accuracy of the set of models evaluated. composite beams through three and four-point bending tests. Fig. 13
Therefore, the equations proposed by these authors could be considered shows the test setups adopted in the works of Zhu et al. [22] and Tong
an option for future implementation in design standards for steel-UHPC et al. [102]. Fig. 13a shows a composite beam in which the concrete slab
composite structures. is predominantly subjected to flexural compressive stresses and the steel

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Table 4
Calculations models to predict the shear capacity of headed stud connectors embedded in UHPC.
Study Calculation model Equation

Wang et al. [96] Pu = 0.644Asce fu (7)

( )
Kruszewski et al. [51] Pu = Asc Fu + 0.16 βf′c − 0.983 f′c db 2 (8)
⎡ ⎛ ⎞ ⎤
Hu et al. [99] √̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅ (9)
2
⎢ πd ⎜ S(d + Stanθ) H2 + S2 ⎟ ⎥
Pu = β⎣fsu + ⎝SH + √̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅ ⎠τ ⎦
4
cosθ H2 + (S/cosθ)2
Huang et al. [100] Pu = 0.8Asc fsu + 2fcu dwc lwc (10)
Wang et al. [98] 0.7nπd2 √̅̅̅̅̅̅̅̅ (11)
Pu = fu + 0.4nπd2 fc fu
4
Fang et al. [73] Pu = 1.1ka kt Asc fu (12)
{ [ ( ) )]}
Xu et al. [28] 1
(
1 c − 28.5 2 (13)
Pu = fu As 1.04 − 197exp − 50(α − 1)2 −
2 2 6.7
[( ) ]/
Wu et al. [101] Pu = 0.85 + 0.5ηfc /fu As fu λ (14)
( )
Fang et al. [83] Pu = ka kt 0.95Asc fu +650f′c dwc lwc /d2 (15)

[Note] Asce, Asc, As = stud effective cross-sectional; fu, fsu, Fu = stud ultimate tensile strength; f’c, fcu, fc = compressive strength of UHPC; db, d = stud
diameter; β = dimensionless factor (0.0119) [51]; β = strength reduction factor due to the group effect [99]; S = length of the wedge block; H =
height of the wedge block; θ = radial angle; τ = characteristic shear strength of UHPC; dwc = weld collar diameter; lwc = weld collar height; n = the
number of stud connectors; ka = stud arrangement factor (0.80; 0.85; 1.15) [73]; kt = slab thickness reduction factor (0.85) [73]; kt = slab
thickness reduction factor (0.88; 0.93) [83]; α = connector aspect ratio (1.0 ≤ α = hs/ds ≤ 4.0); c = cover thickness over the headed stud; η =
increase coefficient due to the stud weld collar (2.5); λ = Partial strength factor (1.24).

practicality and comparative purposes. The database is presented in

Table 6. Additionally, Fig. 14 shows which studies evaluated three or
four points bending tests and the type of moment the composite beam
was subjected. It is observed that the type of test setup commonly
adopted to evaluate flexural behavior is the four-point bending test
(4PBT). The 3PBT has been predominantly focused on studying the
contribution of the UHPC in the negative moment regions since applying
a single concentrated force simulates the action of a support reaction in a
continuous composite beam. The higher tensile strength of UHPC,
associated with the fibers’ bridging action, can limit the opening and
propagation of cracks in these regions, which is advantageous over
conventional concrete and can extend the structure’s service life [67].
Table 7 summarizes the minimum, maximum, and most frequently
adopted dimensions in the flexural tests of steel-UHPC composite beams
reported in the studies of Table 6. The data in Table 7 may be useful
when defining the limit dimensions of steel-UHPC composite beams
analyzed by parametric analysis. In general, it can be observed that the
Fig. 12. Shear capacity prediction of headed studs embedded in UHPC precast most tested UHPC slab thickness and steel beam depth are 100 mm and
slabs through calculation models of several authors.
250 mm, respectively.
Additionally, the concrete compressive strength and yield strength of
the steel beam and the connector are presented in the histograms of
Table 5
Comparison of shear capacity between experimental and calculated results. Fig. 15. This way, verifying the strength ranges adopted in the studies is
possible. Regarding the concrete compressive strength (Fig. 15a), it is
Study Average (Pu-cal/Pu-exp) S.D.
observed that different classes of UHPC have been evaluated in the
Wang et al. [96] 0.74 0.28 studies. The highest compressive strength has a value of 183 MPa. An
Kruszewski et al. [51] 1.23 0.48
interesting aspect in Fig. 15b is that few studies have evaluated the
Wang et al. [98] 1.91 0.78
Fang et al. [73] 1.05 0.37 behavior of high-strength steel-UHPC precast composite beams. The
Xu et al. [28] 1.20 0.46 reason may be that normal-strength steel beams are more commercially
Wu et al. [101] 1.50 0.62 available than high-strength steel beams. The latter is frequently used in
special projects that require a higher mechanical performance of the
structural element. A similar situation occurs with the connectors
beam to tensile stresses. The cross sections of the beam in this setup are
(Fig. 15c).
subject to positive moments, so it is possible to evaluate the maximum
potential of each material. However, fewer studies have analyzed beams
4.1.1. Negative moment region
where the slab is predominantly subjected to flexural tensile stress and
The first study that reported the analysis of steel-UHPC precast
the steel beam to flexural compressive stress (Fig. 13b). In this case, the
composite beams subjected to the negative moment was that of Wang
studies are focused on evaluating the potential of the UHPC to restrict
et al. [29]. In addition to confirming the speed and practicality advan­
crack openings due to the tensile stresses generated in the slab. This
tages of ABC, this work investigated the torque influence of the bolts that
situation is more usual in semi-continuous or continuous beams in the
connect the UHPC panels to the steel beam flange. The structural per­
support regions.
formance of the composite beams was evaluated in terms of load ca­
A review of experimental studies focused on the flexural behavior of
pacity, crack opening, strain distribution, and slippage at the steel beam-
steel-UHPC composite beams was carried out. Only studies with cross-
UHPC panel interface. The bolting torque was found to influence the
sectional geometry similar to that of Fig. 2a were considered for
composite beam stiffness and the slip at the interface. If the torque

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Fig. 13. Test setups to evaluate the flexural behavior of steel-UHPC composite beams: (a) 4PBT with UHPC under positive moment [22] and (b) 3PBT with UHPC
under negative moment [102].

applied to the bolts does not guarantee the full shear connection be­ 4.2. Failure modes
tween the steel beam and the panels, the stiffness may decrease due to
increased slip at the interface. Additionally, higher compressive stresses Steel-UHPC composite beams can reach different failure modes
in the steel beam and larger crack openings in the concrete are devel­ depending on the load type, material mechanical properties, and geo­
oped, leading to higher compressive strains in the steel beam and larger metric characteristics of the elements. From a design approach, fully
concrete crack openings. Qi et al. [24] developed a similar study. connected composite beams subject to positive moments achieve
However, the slabs of the composite beams were continuously cast maximum flexural strength when the concrete slab crushing and steel
(Fig. 1b) instead of being composed of panels (Fig. 1a). Therefore, the beam yielding occur. However, in practice, the composite beam global
coupling stage of panels using bolts was eliminated due to the absence of failure can occur due to a single or several local failures. Fang et al. [67]
joints. In cases where the spans of the structure are not significantly tested steel-UHPC precast composite beams, and experimental results
large, such as small-span bridges, this alternative may be more practical showed that the mechanical properties of the precast slab and the shear
and faster than the technique evaluated by Wang et al. [29]. The shear pocket influence the failure mode. When the precast slab was made with
connection between the UHPC slab and the steel beam was made using NSC and the shear pockets with UHPC, slab failure occurred in the re­
shear pockets filled with high-strength mortar and, in other cases, with gion adjacent to the shear pocket (Fig. 16). This failure mode is attrib­
UHPC. The results indicate that the bridging effect of the steel fibers in uted to the difference between the NSC properties and the improved
the cracks caused by the negative moment presents a lower crack width properties of the UHPC. The results suggest that the slab mechanical
than the composite beams with a conventional concrete slab. Also, a properties and the shear pockets should be compatible with similar
more uniform stress and strain distribution was observed, suggesting a strengths to minimize this failure mode. Regarding crack patterns,
better flexural behavior. composite beams without shear pockets predominantly develop trans­
versal cracks. However, precast composite beams with shear pockets
4.1.2. Positive moment region may also develop longitudinal cracks due to the shear forces developed
Due to the high compressive strength of UHPC, more studies have on the front faces of the pocket.
been conducted to evaluate the slab contribution to the flexural per­ Another failure mode can occur is connector fracture associated with
formance of steel-UHPC composite beams under the action of the posi­ the connection degree at the interface [102]. For example, fracture
tive moment [23,33,67,102]. For example, Hu et al. [23] found that connector failure may occur if the shear force at the steel beam-UHPC
properties such as yield load, ultimate load, and stiffness in the elastic slab interface exceeds the total connector shear strength capacity.
regime can be improved up to 4.6%, 11.3%, and 10.8% when adopting a Furthermore, a low shear strength capacity can occur due to several
UHPC precast slab from four-point bending tests on steel-NSC and steel- factors, such as an insufficient number of connectors at the interface or
UHPC precast composite beams. On the other hand, in a recent study, poor connector weld quality. Composite beams with a partial connection
Tong et al. [102] found that the ultimate load improvement can be are more susceptible to this type of failure since insufficient connectors
slightly higher, precisely 18.0%. Such findings show that the thickness do not restrict the relative slip at the interface.
of the NSC slab can be optimized by replacing it with a thinner UHPC On the other hand, local instabilities can arise in steel-UHPC com­
layer. In addition to the experimental study, Hu et al. [23] developed a posite beams subjected to bending moment and contribute to structural
parametric analysis in which the authors concluded that increasing the element failure. For example, the compression flange and the web can
steel beam strength produces more significant increases in the ultimate suffer local buckling, as shown in Fig. 13. However, buckling does not
flexural capacity of the composite beam compared to the increases represent a risk in the first case (Fig. 13a) since the concrete slab resists
observed when improving the concrete compressive strength. In other most compressive stresses. In contrast, when the beam is subjected to a
words, high-strength steel beams can increase load capacity by up to negative moment, the flange can suffer significant distortions because it
95.9% over normal-strength steel beams. At the same time, the increase is the only element responsible for resisting compressive stresses. This
in concrete compressive strength produces not-so-pronounced im­ distortion is a more usual instability in slender web beams concerning
provements in ultimate flexural capacity. the local buckling. Fig. 13b shows the two types of buckling coinciding
in a beam subjected to a negative moment.

12
 C.A. Benedetty et al.
Table 6
Database of bending tests on steel-UHPC composite beams.
Author System Test setup Span Concrete slab Steel beam Shear connectors

bc hc fc Vf bf tw tf h fy fu dcs hcs fy fu Arr. Fix.

(m) (mm) (mm) (MPa) (%) (mm) (mm) (mm) (mm) (MPa) (MPa) (mm) (mm) (MPa) (MPa)

Yoo and Choo [26] M 4PBT 2 248 50 59 2 225 8 13 150 396 554 13 50 370 470 1CRa W
100 183
Choi et al. [103] M 4PBT 2 248 50 120 1.5 197 8 11.8 180.8 397 550 13 50 371 472 1CRa W
100 150 200 9 13 150 18.5
180 225 150.8
Wang et al. [29] P 4PBT 8.7 1000 200 163 2.5 320b – 14b 660 354.6 568.3 22 100 – – 2CR W+B
164.7 200c 20c
Wang et al. [104] M 3PBT/4PBT 1.5 600 50 119.3 2 280b 12 8b 278 346.5d 488.5d 13 35 – 528.3 2CR W + IT
4.5 60 600c 20c 353.2e 500.5e
Hu et al. [23] P 4PBT 4.2 900 130 49.5 2 255 14 14 250 387.1 542.3 30 120 390.4 435.6 4GC W
124.7
Qi et al. [24] P 4PBT 4.2 900 130 49 2 255 14 14 250 360 505 30 120 390.4 435.6 4GC W
124
125
Zhu et al. [15] M 4PBT 3.51 810 90 171 3 200 8 12 200 420 – 16 65 320 400 9GC / 2CR W
Zhu et al. [22] M 3PBT 1.84 500 55 52.6 3 – 8 10b 222 418.21 540.35 13 42 400 – 2CR W
170 12c
Zhu et al. [105] M 4PBT 1.56 550 90 171 3 200 8 12 200 387 556 16 65 540 571 2CR and 3CR W
1.82 810 120
2.34
Liu et al. [106] M 4PBT 5.0 600 90 60.5 2 175 7 11 350 224.2d 342.7d 16 70; 80 – 480 2CR W
13

100 133.3 282.4e 396.9e

125
Zhang et al. [18] M 3PBT 1.84 500 55 52.6 170 3 130 8 10b 225 418.21 540.35 13 42 400 – 2CR W
12c 14 80 640 – B
d d
Zhu et al. [17] M 4PBT 3.51 810 90 171 3 200 8 12 200 378 549 16 65 320 400 2CR W
396e 564e
b b
Liu et al. [30] M 3PBT 3.2 600 60 152.3 2.5 190 8 8 268 360.1d – 10 40 – – 2CR W
120c 10c 353.7e
Lu et al.[41] M 3PBT 4.0 700 54 112 2 250 10 16 260 460 550 22 70 263 410 2CR / W
3GC
Shi et al.[107] M 3PBT 3.0 1250 100 103 0 250 9 14 250 367 511 19 80 506 600 2CR W
Wan et al.[40] M 3PBT 4.2 1200 160 125 2 400 24 36 400 523 704 20 120 – – 3CR W
Zhu et al.[108] M 3PBT 2.12 615 90 137 3 175 – – 175 422.6d 587.1d 13 25 – – 2CR W
451.6e 583.6e 16 65 – –
Tong et al.[102] M/P 4PBT 3 580 100 140.1 2.2 175b 10 20 350 794d 889d 13 80 373 455 9GC / W
3.2 230c 777e 870e 19 80 375 458 2CR
He et al.[37] M 4PBT 2.3 450 80 124 2 80 8 8 140 523 704 8 – – – PSC W
100

Engineering Structures 293 (2023) 116649

He et al.[109] M 4PBT 2.3 450 80 124 2 80 8 8 140 523 704 8 – – – PSC W
550 100
110
Fang et al.[67] P 4PBT 2.4 600 75 45.19 2 255 14 14 250 256.66 440.62 22 60 371.23 491.21 4GC W
145.45 22 – 670.54 891.68 B

[Note] M = monolithic slab, P = precast slab, bc = slab width, hc = slab depth, fc = concrete compressive strength, Vf = fiber volume fraction, bf = flange width, tw = web thickness, tf = flange thickness, h = steel beam
depth, fy = yield stress, fu = ultimate strength, dcs = connector diameter, hcs = connector height, 3PBT = three-point bending test, 4PBT = four point bending test, #CR= # connector row, #GC= # grouped connectors, PSC
= perfobond strip connectors, Arr. = Arrangement, Fix. = Fixation, W = welded, IT = interface treatment, and B = bolted.
a
Welded on each side of the web, b upper flange, c lower flange, d flange, and e web.
C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

5. Current challenges and future research needs

Numerous studies have discussed the flexural behavior of steel-

UHPC composite beams and the shear connection performance be­
tween both components. In the present paper, a comprehensive review
of these aspects was presented. However, several gaps were observed,
and more research needs to be conducted for their understanding. Thus,
future research is necessary since:

• Most of the steel-UHPC composite beams evaluated in the flexural

studies incorporate steel fibers in the matrix. However, attention has
yet to be paid to the influence of the fiber volume fraction, orienta­
tion, and distribution on parameters such as flexural capacity, crack
patterns, and failure modes of steel-UHPC composite beams.
• The geometric shape adopted for the shear pockets of precast UHPC
slabs is usually square or rectangular. However, the effects on the
Fig. 14. Relationship between the number of studies and test setup type. connection behavior when other geometric shapes and pocket sizes
are adopted are unknown.
• The design standards for composite structures establish the mini­
Table 7 mum dimensional requirements for headed studs embedded in con­
Minimum, maximum, and most common dimensions of the steel-UHPC com­
ventional concretes. However, no consensus exists on the
posite beams.
requirements for headed studs embedded in UHPC.
Dimension Nomenclature Min. Max. Most common • Few studies on the flexural behavior of steel-UHPC composite beams
dimension
have evaluated the structural performance achieved using high-
Span (m) L 1.5 8.7 2.0 strength steel beams and high-strength studs. Using components
UHPC slab width (mm) bc 248 1000 600
with these characteristics can increase the shear strength capacity of
UHPC slab thickness hc 50 200 100
(mm)
the structural element. However, the effects on ductility and failure
Steel beam depth (mm) h 140 660 250 modes still need to be understood.
Flange width (mm) bf 80 600 200 • The shear strength capacity analysis of headed studs made it possible
Web thickness (mm) tw 7 14 8 to identify that the models found in the literature have low accuracy,
Flange thickness (mm) tf 8 20 12
mainly when it is required to predict the shear capacity of large-
diameter headed studs embedded in UHPC. More research is
required to develop accurate models since the number of connectors

Concrete slab

Steel beam Stud

Fig. 15. Distribution of the (a) concrete compressive strength, (b) yield strength of the steel beam, and (c) yield strength of the stud.

14
C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Fig. 16. Failure mode of steel-NSC precast composite beam with UHPC in shear pockets [67].

necessary to resist the longitudinal shear in steel–concrete composite (longitudinal and transversal) is at least 4d, the group stud’s shear
beams depends on the capacity calculated through said models. strength reduction will be negligible compared to the monolithic
connection system of non-grouped studs.
6. Conclusions • Steel-UHPC precast composite beams develop better structural per­
formance in terms of load capacity, stiffness in the linear regime, and
This paper has extensively reviewed the behavior of studs embedded control cracking than those made with steel-NSC. In this sense,
in UHPC and the flexural performance of steel-UHPC precast composite achieving the same load level with cross sections of lower height and
beams. After collecting, compiling, and analyzing two databases on consequently smaller self-weight is possible. Additionally, studies
experimental tests, it was possible to conclude that: show that high-strength steel beams can significantly increase the
element’s performance, reaching flexural capacities up to 95.0%
• The steel-UHPC precast composite beam system is promising for greater than normal-strength steel beams.
ABC. The low weight of the components and their assembly practi­ • The mechanical properties of the material used to cast the shear
cality allows for reducing the construction time and costs concerning pocket should be similar to that of the precast slab to prevent pre­
conventional systems, as demands for lower capacity cranes and mature crushing failure in the region adjacent to the shear pocket.
transport vehicles. In addition, if demountable connectors are used Using materials with significantly different strengths can lead to
to connect the slab to the steel beam, the activities of maintenance, premature failure in the regions close to the slab’s shear pockets,
repair, and even disassembly of the structure can be carried out more limiting the beam’s maximum flexural capacity.
quickly. These advantages make steel-UHPC precast composite
beams an industrialized solution compatible with the circular econ­ CRediT authorship contribution statement
omy approach focused on structural dematerialization.
• The increase in the stud diameter has a more significant impact on Carlos Alberto Benedetty Torres: Conceptualization, Methodol­
the increase in shear strength than parameters such as the stud height ogy, Validation, Formal analysis, Investigation, Writing – original draft.
or the concrete compressive strength. This increase is because the Vinicius Brother dos Santos: Conceptualization, Methodology, Vali­
shear studs embedded in the UHPC matrix are subject to better dation, Formal analysis, Investigation, Writing – original draft, Writing –
confinement than the NSC matrix. Additionally, the perpendicular review & editing. Pablo Augusto Krahl: Conceptualization, Supervi­
forces to the stud that generate the shear stress tend to concentrate in sion, Writing – review & editing. Alexandre Rossi: Conceptualization,
a region close to the stud base, favoring its fracture. For this failure Writing – review & editing. Flávio de Andrade Silva: Conceptualiza­
mode, the stud diameter, which also impacts its cross-sectional area, tion, Writing – review & editing. Daniel Carlos Taissum Cardoso:
is the parameter that contributes the most to the shear stud capacity. Conceptualization, Writing – review & editing. Carlos Humberto
Therefore, using a short stud with a large diameter is more appro­ Martins: Conceptualization, Supervision, Writing – review & editing,
priate to guarantee better performance and efficiency in the steel- Project administration, Funding acquisition.
UHPC connection.
• In general, the models present in the design standards have low
Declaration of Competing Interest
precision to predict the shear capacity of large-diameter headed
studs. Because these have better compatibility with steel-UHPC
The authors declare that they have no known competing financial
composite beams, the standards must adopt new models to safely
interests or personal relationships that could have appeared to influence
predict the shear capacity of headed studs.
the work reported in this paper.
• The shear capacity of studs embedded in UHPC precast slabs was
predicted with good agreement by the model proposed by Fang et al.
Data availability
[73]. Given that the current standards do not have specific steel-
UHPC connection models, the mentioned model is a viable option
Data will be made available on request.
for designing or verifying the shear capacity connection of steel-
UHPC composite structures.
• The grouping stud arrangement caused by the shear pocket in the Acknowledgments
precast slab represents a critical aspect of the connection perfor­
mance. The reduced spacing between connectors can increase the This study was financed by the Conselho Nacional de Desenvolvi­
susceptibility to decreases in shear strength (group effect). However, mento Científico e Tecnológico (CNPq) provided under Project No.
the experimental results show that if the spacing in both directions 408498/2022-6, and the Coordenação de Aperfeiçoamento de Pessoal
de Nível Superior - Brasil (CAPES) - Finance Code 001.

15
C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Appendix A. Database of push-out tests

Table 2

Table 2
Database of push-out tests for headed connectors embedded in UHPC slabs.
Ref. Nom. Concrete slab Shear pocket Stud shear connector Structural response

b h t c Vf fc bsp hsp nst dst hst hst /dst sl st fy fu Pu δu FM

(mm) (mm) (mm) (mm) (%) (MPa) (mm) (mm) (-) (mm) (mm) (-) (mm) (mm) (MPa) (MPa) (kN) (mm)

[27] 1 600 650 150 50 2 200.0 – – 4 22 100 4.5 250 100 372.0 466.0 201.00 6.86 SS
2 600 650 100 35 2 200.0 – – 4 16 65 4.1 250 100 384.0 484.0 119.00 4.40 SS
3 600 650 100 50 2 200.0 – – 4 16 50 3.1 250 100 384.0 484.0 106.33 5.47 SS
4 600 650 75 25 2 200.0 – – 4 16 50 3.1 250 100 384.0 484.0 111.67 5.21 SS

[78] STA-1–3 320 500 50 15 3.5 135.9 – – 4 13 35 2.7 200 110 – 400.0 60.10 0.75 SS

[91] PSUHPC1 660 1150 250 100 2 124.0 – – 2 30 150 5.0 – 120 390.4 435.6 221.30 3.90 SS
PGUHPC1 660 1150 250 100 2 124.0 – – 6 30 150 5.0 150 120 390.4 435.6 387.00 6.62 SS
PGUHPC2 660 1150 250 100 2 124.0 320a 440a 6 30 150 5.0 150 120 390.4 435.6 393.80 5.60 SS
260b 380b
PGUHPC3 660 1150 250 100 2 124.0 320a 440a 6 30 150 5.0 150 120 390.4 435.6 392.50 6.30 SS
260b 380b

[70] UHPC22 400 500 150 50 2 124.0 – – 2 22 100 4.5 – 120 400.9 482.6 375.20 5.12 SS
UHPC30 400 500 150 30 2 124.0 – – 2 30 120 4.0 150 120 390.4 435.6 354.10 5.80 SS
UHPC30-I 400 500 150 80 2 124.0 – – 2 30 70 2.3 150 120 390.4 435.6 338.30 5.50 SS
UHPC30-II 400 500 100 30 2 124.0 – – 2 30 70 2.3 150 120 390.4 435.6 333.80 6.10 SS

[82] D13H80 320 500 95 15 2 135.9 – – 4 13 80 6.2 200 110 375.0 450.0 57.25 0.51 SS
D16H80 320 500 95 15 2 135.9 – – 4 16 80 5.0 200 110 375.0 450.0 84.13 0.62 SS
D19H80 320 500 95 15 2 135.9 – – 4 19 80 4.2 200 110 375.0 450.0 114.88 1.06 SS
D22H80 320 500 95 15 2 135.9 – – 4 22 80 3.6 200 110 375.0 450.0 157.50 0.96 SS
D13H20 320 500 35 15 2 135.9 – – 4 13 20 1.5 200 110 375.0 450.0 45.58 0.38 SS
D13H35 320 500 50 15 2 135.9 – – 4 13 35 2.7 200 110 375.0 450.0 52.71 0.44 SS
D13H50 320 500 65 15 2 135.9 – – 4 13 50 3.8 200 110 375.0 450.0 54.34 0.54 SS
D13H65 320 500 80 15 2 135.9 – – 4 13 65 5.0 200 110 375.0 450.0 54.00 0.50 SS
D13H80U110 320 500 95 15 2 110.0 – – 4 13 80 6.2 200 110 375.0 450.0 53.74 0.40 SS
D13H80U140 320 500 95 15 2 140.0 – – 4 13 80 6.2 200 110 375.0 450.0 52.85 0.44 SS
D13H80U170 320 500 95 15 2 170.0 – – 4 13 80 6.2 200 110 375.0 450.0 58.94 0.43 SS

[50] TC 600 650 150 50 2 146.7 – – 4 22 100 4.5 250 100 400.0 500.0 203.80 – SS
TX 600 650 150 50 2 165.7 – – 4 22 100 4.5 250 100 400.0 500.0 212.50 – SS
P-100 600 650 150 50 2 100.0 – – 4 22 100 4.5 250 100 400.0 500.0 194.70 – SS
P-120 600 650 150 50 2 120.0 – – 4 22 100 4.5 250 100 400.0 500.0 202.50 – SS
P-140 600 650 150 50 2 140.0 – – 4 22 100 4.5 250 100 400.0 500.0 208.20 – SS
P-200 600 650 150 50 2 200.0 – – 4 22 100 4.5 250 100 400.0 500.0 220.30 – SS
P-16 600 650 150 50 2 160.0 – – 4 16 100 6.3 250 100 400.0 500.0 120.90 – SS
P-20 600 650 150 50 2 160.0 – – 4 20 100 5.0 250 100 400.0 500.0 177.40 – SS
P-24 600 650 150 50 2 160.0 – – 4 24 100 4.2 250 100 400.0 500.0 240.80 – SS
P-27 600 650 150 50 2 160.0 – – 4 27 100 3.7 250 100 400.0 500.0 287.60 – SS
P-30 600 650 150 50 2 160.0 – – 4 30 100 3.3 250 100 400.0 500.0 313.90 – SS
P-2 600 650 150 106 2 160.0 – – 4 22 44 2.0 250 100 400.0 500.0 207.80 – SS
P-3 600 650 150 84 2 160.0 – – 4 22 66 3.0 250 100 400.0 500.0 207.80 – SS
P-4 600 650 150 62 2 160.0 – – 4 22 88 4.0 250 100 400.0 500.0 207.80 – SS
P-5 600 650 150 40 2 160.0 – – 4 22 110 5.0 250 100 400.0 500.0 207.80 – SS
P-6 600 650 150 18 2 160.0 – – 4 22 132 6.0 250 100 400.0 500.0 207.80 – SS

[79] PS13 600 650 150 70 2.2 140.1 – – 4 13 80 6.2 250 80 373.4 455.1 83.10 1.97 SS
PS19 600 650 150 70 2.2 140.1 – – 4 19 80 4.2 250 80 374.9 457.8 151.50 3.32 SS
PG19 600 650 150 70 2.2 140.1 140 220 9 19 80 4.2 65 50 374.9 457.8 147.60 3.44 SS

[85] U30S 400 500 150 30 2 124.0 – – 2 30 120 4.0 – 120 400.4 520.2 363.20 6.62 SS
U30G 400 500 150 30 2 124.0 – – 6 30 120 4.0 150 120 400.4 520.2 354.10 5.80 SS
U16S-C100 400 500 150 30 2 100.0 – – 2 16 120 7.5 – 120 400.0 – 136.50 – SS
U16S-C120 400 500 150 30 2 120.0 – – 2 16 120 7.5 – 120 400.0 – 136.50 – SS
U16S-C140 400 500 150 30 2 140.0 – – 2 16 120 7.5 – 120 400.0 – 137.00 – SS

[85] U16S-C160 400 500 150 30 2 160.0 – – 2 16 120 7.5 – 120 400.0 – 137.10 – SS
U16S-C180 400 500 150 30 2 180.0 – – 2 16 120 7.5 – 120 400.0 – 137.20 – SS
U16S-C200 400 500 150 30 2 200.0 – – 2 16 120 7.5 – 120 400.0 – 137.30 – SS
U22S-C100 400 500 150 30 2 100.0 – – 2 22 120 5.5 – 120 400.0 – 214.20 – SS
U22S-C120 400 500 150 30 2 120.0 – – 2 22 120 5.5 – 120 400.0 – 216.00 – SS
U22S-C140 400 500 150 30 2 140.0 – – 2 22 120 5.5 – 120 400.0 – 217.40 – SS
U22S-C160 400 500 150 30 2 160.0 – – 2 22 120 5.5 – 120 400.0 – 218.60 – SS
U22S-C180 400 500 150 30 2 180.0 – – 2 22 120 5.5 – 120 400.0 – 219.80 – SS
U22S-C200 400 500 150 30 2 200.0 – – 2 22 120 5.5 – 120 400.0 – 221.00 – SS
U30S-C100 400 500 150 30 2 100.0 – – 2 30 120 4.0 – 120 400.0 – 375.10 – SS
U30S-C120 400 500 150 30 2 120.0 – – 2 30 120 4.0 – 120 400.0 – 378.60 – SS
U30S-C140 400 500 150 30 2 140.0 – – 2 30 120 4.0 – 120 400.0 – 382.90 – SS
U30S-C160 400 500 150 30 2 160.0 – – 2 30 120 4.0 – 120 400.0 – 388.30 – SS
(continued on next page)

16
C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Table 2 (continued )
Ref. Nom. Concrete slab Shear pocket Stud shear connector Structural response

b h t c Vf fc bsp hsp nst dst hst hst /dst sl st fy fu Pu δu FM

(mm) (mm) (mm) (mm) (%) (MPa) (mm) (mm) (-) (mm) (mm) (-) (mm) (mm) (MPa) (MPa) (kN) (mm)

U30S-C180 400 500 150 30 2 180.0 – – 2 30 120 4.0 – 120 400.0 – 396.40 – SS
U30S-C200 400 500 150 30 2 200.0 – – 2 30 120 4.0 – 120 400.0 – 403.70 – SS
U35S-C100 400 500 150 30 2 100.0 – – 2 35 120 3.4 – 120 400.0 – 546.90 – SS
U35S-C120 400 500 150 30 2 120.0 – – 2 35 120 3.4 – 120 400.0 – 568.50 – SS
U35S-C140 400 500 150 30 2 140.0 – – 2 35 120 3.4 – 120 400.0 – 583.20 – SS
U35S-C160 400 500 150 30 2 160.0 – – 2 35 120 3.4 – 120 400.0 – 593.60 – SS
U35S-C180 400 500 150 30 2 180.0 – – 2 35 120 3.4 – 120 400.0 – 601.40 – SS
U35S-C200 400 500 150 30 2 200.0 – – 2 35 120 3.4 – 120 400.0 – 608.50 – SS
U40S-C100 400 500 150 30 2 100.0 – – 2 40 120 3.0 – 120 400.0 – 647.40 – SS
U40S-C120 400 500 150 30 2 120.0 – – 2 40 120 3.0 – 120 400.0 – 691.20 – SS
U40S-C140 400 500 150 30 2 140.0 – – 2 40 120 3.0 – 120 400.0 – 720.50 – SS

[85] U40S-C160 400 500 150 30 2 160.0 – – 2 40 120 3.0 – 120 400.0 – 741.10 – SS
U40S-C180 400 500 150 30 2 180.0 – – 2 40 120 3.0 – 120 400.0 – 755.30 – SS
U40S-C200 400 500 150 30 2 200.0 – – 2 40 120 3.0 – 120 400.0 – 765.60 – SS

[87] UHPCG 660 1150 250 100 2 124.0 – – 6 30 150 5.0 150 120 385.4 – 354.10 5.80 SS
U120 660 1150 250 100 2 120.0 – – 6 30 150 5.0 150 120 385.4 500.0 336.61 6.98 SS
U180 660 1150 250 100 2 180.0 – – 6 30 150 5.0 150 120 385.4 500.0 342.51 6.90 SS
U200 660 1150 250 100 2 200.0 – – 6 30 150 5.0 150 120 385.4 500.0 339.37 6.87 SS
U30 660 1150 250 100 2 124.0 – – 6 30 150 5.0 150 120 385.4 500.0 310.29 7.01 SS
U35 660 1150 250 100 2 124.0 – – 6 35 150 4.3 150 120 385.4 500.0 338.60 6.98 SS
U40 660 1150 250 100 2 124.0 – – 6 40 150 3.8 150 120 385.4 500.0 359.55 6.90 SS
U-2 660 1150 250 190 2 124.0 – – 6 30 60 2.0 150 120 385.4 500.0 353.98 6.98 SS
U-4 660 1150 250 130 2 124.0 – – 6 30 120 4.0 150 120 385.4 500.0 357.60 6.81 SS
U-5 660 1150 250 100 2 124.0 – – 6 30 150 5.0 150 120 385.4 500.0 355.79 6.91 SS
U-7 660 1150 250 40 2 124.0 – – 6 30 210 7.0 150 120 385.4 500.0 356.52 6.96 SS
Gu-2d 660 1150 250 100 2 124.0 – – 6 30 150 5.0 120 385.4 500.0 307.97 6.83 SS
Gu-3d 660 1150 250 100 2 124.0 – – 6 30 150 5.0 120 385.4 500.0 328.98 6.98 SS
Gu-4d 660 1150 250 100 2 124.0 – – 6 30 150 5.0 120 385.4 500.0 331.88 6.77 SS
Gu-5d 660 1150 250 100 2 124.0 – – 6 30 150 5.0 120 385.4 500.0 335.86 6.98 SS
Gu-7d 660 1150 250 100 2 124.0 – – 6 30 150 5.0 120 385.4 500.0 334.05 6.98 SS
Gu-10d 660 1150 250 100 2 124.0 – – 6 30 150 5.0 120 385.4 500.0 335.14 6.98 SS

[80] D22T150H120 600 650 150 30 2 125.0 – – 4 22 120 5.5 250 100 412.0 480.0 192.70 4.57 SS
D22T150H60 600 650 150 90 2 125.0 – – 4 22 60 2.7 250 100 412.0 480.0 208.80 5.62 SS
D30T150H120 600 650 150 30 2 125.0 – – 4 30 120 4.0 250 100 468.0 525.0 377.3 5.59 SS
D22T75H60 600 650 75 15 2 125.0 – – 4 22 60 2.7 250 100 412.0 480.0 192.70 3.93 SS
D30T75H60 600 650 75 15 2 125.0 – – 4 30 60 2.0 250 100 468.0 525.0 379.40 4.39 CP/SS

[81] S19-80–2.5 600 700 100 20 3 167.0 300 450 12 19 80 4.2 48 48 – 415.0 110.00 3.67 SS
S19-80–4 600 700 100 20 3 167.0 300 450 12 19 80 4.2 76 76 – 415.0 127.00 3.99 SS
S19-80–6 600 700 100 20 3 167.0 300 450 12 19 80 4.2 114 114 – 415.0 124.00 3.99 SS
S19-60–4 600 700 100 40 3 167.0 300 450 12 19 60 3.2 76 76 – 415.0 123.00 3.62 SS
S22-80–4 600 700 100 20 3 167.0 300 450 12 22 80 3.6 88 88 – 415.0 145.00 4.19 SS
S25-80–4 600 700 100 20 3 167.0 300 450 12 25 80 3.2 100 100 – 415.0 167.00 4.03 SS
S25-100–4 600 700 120 20 3 167.0 300 450 12 25 100 4.0 100 100 – 415.0 175.00 4.30 SS

[77] 1 100 100 150 70 0 97.0 – – 2 10 80 8.0 – 100 400.0 – 67.90 7.08 SS
2 100 100 150 70 1 112.0 – – 2 10 80 8.0 – 100 400.0 – 69.90 9.14 SS
3 100 100 150 90 2 132.0 – – 2 10 60 6.0 – 100 400.0 – 76.70 8.88 SS
4 100 100 150 70 4 118.0 – – 2 10 80 8.0 – 100 400.0 – 74.00 9.22 SS

[84] S-13–25-i 360 550 50 25 3 134.0 – – 4 13 25 1.9 200 170 265.0 392.0 46.90 2.04 SS
S-13–35-i 360 550 50 15 3 134.0 – – 4 13 35 2.7 200 170 265.0 392.0 63.20 2.59 SS
S-13–45-i 360 550 50 5 3 134.0 – – 4 13 45 3.5 200 170 265.0 392.0 74.70 2.07 SS
S-10–35-i 360 550 50 15 3 134.0 – – 4 10 35 3.5 200 170 265.0 392.0 88.80 2.71 SS
S-16–35-i 360 550 50 15 3 134.0 – – 4 16 35 2.2 200 170 265.0 392.0 103.20 2.27 SS
S-10–20 360 550 50 30 3 120.0 – – 4 10 20 2.0 200 170 345.0 490.0 36.6 – SP
S-10–25 360 550 50 25 3 120.0 – – 4 10 25 2.5 200 170 345.0 490.0 45.3 – SP
S-10–30 360 550 50 20 3 120.0 – – 4 10 30 3.0 200 170 345.0 490.0 49.8 – SS
S-10–35 360 550 50 15 3 120.0 – – 4 10 35 3.5 200 170 345.0 490.0 53.7 – SS
S-10–40 360 550 50 10 3 120.0 – – 4 10 40 4.0 200 170 345.0 490.0 56.4 – SS
S-10–45 360 550 50 5 3 120.0 – – 4 10 45 4.5 200 170 345.0 490.0 58.4 – SS
S-10–50 360 550 50 0 3 120.0 – – 4 10 50 5.0 200 170 345.0 490.0 60.8 – SS
S-13–20 360 550 50 30 3 120.0 – – 4 13 20 1.5 200 170 345.0 490.0 59.0 – SP

[84] S-13–25 360 550 50 25 3 120.0 – – 4 13 25 1.9 200 170 345.0 490.0 73.1 – SP
S-13–30 360 550 50 20 3 120.0 – – 4 13 30 2.3 200 170 345.0 490.0 78.2 – SS
S-13–35 360 550 50 15 3 120.0 – – 4 13 35 2.7 200 170 345.0 490.0 81.8 – SS
S-13–40 360 550 50 10 3 120.0 – – 4 13 40 3.1 200 170 345.0 490.0 84.8 – SS
S-13–45 360 550 50 5 3 120.0 – – 4 13 45 3.5 200 170 345.0 490.0 88.4 – SS
S-13–50 360 550 50 0 3 120.0 – – 4 13 50 3.8 200 170 345.0 490.0 91.6 – SS
S-16–20 360 550 50 30 3 120.0 – – 4 16 20 1.3 200 170 345.0 490.0 86.5 – SP
S-16–25 360 550 50 25 3 120.0 – – 4 16 25 1.6 200 170 345.0 490.0 104.3 – SP
S-16–30 360 550 50 20 3 120.0 – – 4 16 30 1.9 200 170 345.0 490.0 109.7 – SS
(continued on next page)

17
C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Table 2 (continued )
Ref. Nom. Concrete slab Shear pocket Stud shear connector Structural response

b h t c Vf fc bsp hsp nst dst hst hst /dst sl st fy fu Pu δu FM

(mm) (mm) (mm) (mm) (%) (MPa) (mm) (mm) (-) (mm) (mm) (-) (mm) (mm) (MPa) (MPa) (kN) (mm)

S-16–35 360 550 50 15 3 120.0 – – 4 16 35 2.2 200 170 345.0 490.0 113.2 – SS
S-16–40 360 550 50 10 3 120.0 – – 4 16 40 2.5 200 170 345.0 490.0 118.3 – SS
S-16–45 360 550 50 5 3 120.0 – – 4 16 45 2.8 200 170 345.0 490.0 123.7 – SS
S-16–50 360 550 50 0 3 120.0 – – 4 16 50 3.1 200 170 345.0 490.0 128.2 – SS
S-10–35-235 360 550 50 15 3 120.0 – – 4 10 35 3.5 200 170 235.0 – 44.80 – SS
S-10–35-345 360 550 50 15 3 120.0 – – 4 10 35 3.5 200 170 345.0 – 53.70 – SS
S-10–35-390 360 550 50 15 3 120.0 – – 4 10 35 3.5 200 170 390.0 – 56.70 – SS
S-10–35-420 360 550 50 15 3 120.0 – – 4 10 35 3.5 200 170 420.0 – 59.50 – SS
S-13–35-235 360 550 50 15 3 120.0 – – 4 13 35 2.7 200 170 235.0 – 67.30 – SS
S-13–35-345 360 550 50 15 3 120.0 – – 4 13 35 2.7 200 170 345.0 – 81.80 – SS
S-13–35-390 360 550 50 15 3 120.0 – – 4 13 35 2.7 200 170 390.0 – 87.80 – SS
S-13–35-420 360 550 50 15 3 120.0 – – 4 13 35 2.7 200 170 420.0 – 91.00 – SS
S-16–35-235 360 550 50 15 3 120.0 – – 4 16 35 2.2 200 170 235.0 – 93.60 – SS
S-16–35-345 360 550 50 15 3 120.0 – – 4 16 35 2.2 200 170 345.0 – 113.20 – SS
S-16–35-390 360 550 50 15 3 120.0 – – 4 16 35 2.2 200 170 390.0 – 122.10 – SS
S-16–35-420 360 550 50 15 3 120.0 – – 4 16 35 2.2 200 170 420.0 – 127.20 – SS

[73] M− 16− 50 400 450 50 15 2 130.0 – – 4 16 35 2.2 100 100 352.2 447.8 90.27 1.65 SS
M− 19− 50 400 450 50 15 2 130.0 – – 4 19 35 1.8 100 100 346.9 487.2 143.16 4.44 SS
M− 22− 50 400 450 50 15 2 130.0 – – 4 22 35 1.6 100 100 371.2 491.2 178.32 5.51 SS/SP/CS
M− 19− 75 400 450 75 15 2 130.0 – – 4 19 60 3.2 100 100 346.9 487.2 157.58 5.18 SS
M− 22− 75 400 450 75 15 2 130.0 – – 4 22 60 2.7 100 100 371.2 491.2 210.76 6.37 SS
M− 25− 75 400 450 75 15 2 130.0 – – 4 25 60 2.4 100 100 342.2 452.0 252.13 5.33 SS
P-16–50 400 450 50 15 2 130.0 215 215 4 16 35 2.2 100 100 352.2 447.8 86.01 1.42 SS
P-19–50 400 450 50 15 2 130.0 215 215 4 19 35 1.8 100 100 346.9 487.2 129.81 4.22 SS
P-22–50 400 450 50 15 2 130.0 215 215 4 22 35 1.6 100 100 371.2 491.2 169.19 4.46 SS/SP/CS
P-19–75 400 450 75 15 2 130.0 215 215 4 19 60 3.2 100 100 346.9 487.2 148.76 5.38 SS
P-22–75 400 450 75 15 2 130.0 215 215 4 22 60 2.7 100 100 371.2 491.2 201.20 6.65 SS
P-25–75 400 450 75 15 2 130.0 215 215 4 25 60 2.4 100 100 342.2 452.0 229.30 5.36 SS
P-22–75-A 400 450 75 15 2 130.0 255a 255a 4 22 60 2.7 100 100 371.2 491.2 205.00 7.50 SS
215b 215b
P-22–75-B 400 450 75 15 2 130.0 295a 215a 4 22 60 2.7 100 100 371.2 491.2 186.72 6.66 SS/CS
295b 215b
M60 400 450 75 15 2 130.0 – – 4 22 60 2.7 60 60 371.2 491.2 178.56 4.14 SS
P60 400 450 75 15 2 130.0 215 215 4 22 60 2.7 60 60 371.2 491.2 169.06 3.66 SS
GM60 400 450 75 15 2 130.0 – – 9 22 60 2.7 60 60 371.2 491.2 167.96 4.42 SS
PM60 400 450 75 15 2 130.0 215 215 9 22 60 2.7 60 60 371.2 491.2 152.59 6.09 SS

[28] D22T150-I 600 650 150 120 2 125.0 – – 4 22 30 1.4 250 100 412.0 480.0 190.20 3.02 SS
D22T150-II 600 650 150 105 2 125.0 – – 4 22 45 2.0 250 100 412.0 480.0 194.80 2.39 SS
D30T150 600 650 150 30 2 125.0 – – 4 30 120 4.0 250 100 468.0 525.0 377.30 5.59 SS
D22T55 600 650 55 10 2 125.0 – – 4 22 45 2.0 250 100 412.0 480.0 190.30 4.97 SS

[28] D30T55 600 650 55 10 2 125.0 – – 4 30 45 1.5 250 100 468.0 525.0 304.20 3.34 SS/CP
D22T35 600 650 35 5 2 125.0 – – 4 22 30 1.4 250 100 412.0 480.0 178.60 2.62 SS
D30T35 600 650 35 5 2 125.0 – – 4 30 30 1.0 250 100 468.0 525.0 226.30 1.22 CP

[86] D13H120T150 600 650 150 30 2 125.0 – – 4 13 120 9.2 250 100 – – 77.10 1.54 –
D13H120T150C200 600 650 150 30 2 200.0 – – 4 13 120 9.2 250 100 – – 86.20 1.53 –
D16H120T150 600 650 150 30 2 125.0 – – 4 16 120 7.5 250 100 – – 114.30 3.49 –
D16H120T150C200 600 650 150 30 2 200.0 – – 4 16 120 7.5 250 100 – – 117.30 2.54 –
D19H120T150 600 650 150 30 2 125.0 – – 4 19 120 6.3 250 100 – – 150.70 3.52 –
D19H120T150C200 600 650 150 30 2 200.0 – – 4 19 120 6.3 250 100 – – 155.40 2.94 –
D22H120T150 600 650 150 30 2 125.0 – – 4 22 120 5.5 250 100 412.0 480.0 188.00 4.57 –
D22H120T150C200 600 650 150 30 2 200.0 – – 4 22 120 5.5 250 100 412.0 480.0 204.10 2.21 –
D25H120T150 600 650 150 30 2 125.0 – – 4 25 120 4.8 250 100 – – 273.90 3.88 –
D25H120T150C200 600 650 150 30 2 200.0 – – 4 25 120 4.8 250 100 – – 310.30 2.62 –
D30H120T150 600 650 150 30 2 125.0 – – 4 30 120 4.0 250 100 468.0 525.0 409.10 5.97 –
D30H120T150C200 600 650 150 30 2 200.0 – – 4 30 120 4.0 250 100 468.0 525.0 452.20 5.64 –
D13H60T75 600 650 75 15 2 125.0 – – 4 13 60 4.6 250 100 – – 70.60 1.55 –
D16H60T75 600 650 75 15 2 125.0 – – 4 16 60 3.8 250 100 – – 95.60 1.25 –
D19H60T75 600 650 75 15 2 125.0 – – 4 19 60 3.2 250 100 – – 152.20 4.08 –
D22H60T75 600 650 75 15 2 125.0 – – 4 22 60 2.7 250 100 412.0 480.0 185.60 5.16 –
D25H60T75 600 650 75 15 2 125.0 – – 4 25 60 2.4 250 100 – – 260.10 5.90 –
D30H60T75 600 650 75 15 2 125.0 – – 4 30 60 2.0 250 100 468.0 525.0 376.30 4.67 –
D30H60T75C200 600 650 75 15 2 200.0 – – 4 30 60 2.0 250 100 468.0 525.0 394.10 4.29 –
D13H60T150 600 650 150 90 2 125.0 – – 4 13 60 4.6 250 100 – – 73.80 – –
D16H60T150 600 650 150 90 2 125.0 – – 4 16 60 3.8 250 100 – – 100.90 – –

[86] D19H60T150 600 650 150 90 2 125.0 – – 4 19 60 3.2 250 100 – – 160.40 – –
D22H60T150 600 650 150 90 2 125.0 – – 4 22 60 2.7 250 100 412.0 480.0 217.10 5.59 –
D25H60T150 600 650 150 90 2 125.0 – – 4 25 60 2.4 250 100 – – 270.60 – –
D30H60T150 600 650 150 90 2 125.0 – – 4 30 60 2.0 250 100 468.0 525.0 399.90 – –
D13H45T55 600 650 55 10 2 125.0 – – 4 13 45 3.5 250 100 – – 77.10 5.98 –
D16H45T55 600 650 55 10 2 125.0 – – 4 16 45 2.8 250 100 – – 108.30 4.14 –
(continued on next page)

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C.A. Benedetty et al. Engineering Structures 293 (2023) 116649

Table 2 (continued )
Ref. Nom. Concrete slab Shear pocket Stud shear connector Structural response

b h t c Vf fc bsp hsp nst dst hst hst /dst sl st fy fu Pu δu FM

(mm) (mm) (mm) (mm) (%) (MPa) (mm) (mm) (-) (mm) (mm) (-) (mm) (mm) (MPa) (MPa) (kN) (mm)

D19H45T55 600 650 55 10 2 125.0 – – 4 19 45 2.4 250 100 – – 124.40 4.66 –

D22H45T55 600 650 55 10 2 125.0 – – 4 22 45 2.0 250 100 412.0 480.0 164.00 4.85 –
D22H45T150 600 650 150 105 2 125.0 – – 4 22 45 2.0 250 100 412.0 480.0 182.90 3.03 –
D25H45T55 600 650 55 10 2 125.0 – – 4 25 45 1.8 250 100 – – 163.90 2.00 –
D30H45T55 600 650 55 10 2 125.0 – – 4 30 45 1.5 250 100 468.0 525.0 275.50 3.32 –
D30H45T55C200 600 650 55 10 2 200.0 – – 4 30 45 1.5 250 100 468.0 525.0 343.80 4.70 –
D30H45T150 600 650 150 105 2 125.0 – – 4 30 45 1.5 250 100 468.0 525.0 303.40 – –
D13H30T35 600 650 35 5 2 125.0 – – 4 13 30 2.3 250 100 – – 65.00 3.62 –
D16H30T35 600 650 35 5 2 125.0 – – 4 16 30 1.9 250 100 – – 89.00 3.18 –
D19H30T35 600 650 35 5 2 125.0 – – 4 19 30 1.6 250 100 – – 113.80 4.10 –
D22H30T35 600 650 35 5 2 125.0 – – 4 22 30 1.4 250 100 412.0 480.0 133.80 2.90 –
D25H30T35 600 650 35 5 2 125.0 – – 4 25 30 1.2 250 100 – – 161.80 1.88 –
D25H30T150 600 650 150 120 2 125.0 – – 4 25 30 1.2 250 100 – – 242.20 – –
D30H30T35 600 650 35 5 2 125.0 – – 4 30 30 1.0 250 100 468.0 525.0 227.60 3.65 –
D30H30T35C200 600 650 35 5 2 200.0 – – 4 30 30 1.0 250 100 468.0 525.0 279.90 5.39 –

[110] ST-1 600 650 70 20 2 120.3 – – 4 16 50 3.1 250 100 370.0 460.0 97.23 3.70 SS

[88] UHPC-16 550 550 200 50 1.5 152.5 – – 4 16 150 9.4 250 130 360.0 – 93.75 3.32 SS
UHPC-19 550 550 200 50 1.5 152.5 – – 4 19 150 7.9 250 130 360.0 – 130.84 2.55 SS
UHPC-22 550 550 200 50 1.5 152.5 – – 4 22 150 6.8 250 130 360.0 – 145.50 1.54 WF
UHPC-25 550 550 200 50 1.5 152.5 – – 4 25 150 6.0 250 130 360.0 – 150.63 1.53 WF

[76] S19-80 600 700 100 20 3 167.0 300 450 12 19 80 4.2 76 76 – 415.0 126.50 3.99 SS
S25-80 600 700 100 20 3 167.0 300 450 12 25 80 3.2 100 100 – 415.0 167.25 4.03 SS
S25-100 600 700 120 20 3 167.0 300 450 12 25 100 4.0 100 100 – 415.0 174.50 4.30 SS
ST19-80–0.17 600 750 100 20 3 167.0 300 450 12 19 80 4.2 76 76 – 415.0 122.92 3.75 SS
ST19-80–0.27 600 750 100 20 3 167.0 300 450 12 19 80 4.2 76 76 – 415.0 93.33 3.10 SS
ST19-80–0.47 600 750 100 20 3 167.0 300 450 12 19 80 4.2 76 76 – 415.0 67.92 2.72 SS
ST25-80–0.27 600 750 100 20 3 167.0 300 450 12 25 80 3.2 100 100 – 415.0 128.96 2.13 SS
ST25-100–0.27 600 750 120 20 3 167.0 300 450 12 25 100 4.0 100 100 – 415.0 155.21 3.20 SS
ST19-80–0.37* 600 750 100 20 3 167.0 300 450 12 25 80 3.2 100 100 – 415.0 79.88 – SS
ST19-80–0.57* 600 750 100 20 3 167.0 300 450 12 25 80 3.2 100 100 – 415.0 65.13 – SS
ST25-100–0.37* 600 750 120 20 3 167.0 300 450 12 25 100 4.0 100 100 – 415.0 151.42 – SS
ST25-100–0.47* 600 750 120 20 3 167.0 300 450 12 25 100 4.0 100 100 – 415.0 146.46 – SS
ST25-100–0.57* 600 750 120 20 3 167.0 300 450 12 25 100 4.0 100 100 – 415.0 138.50 – SS
ST25-100–0.70* 600 750 120 20 3 167.0 300 450 12 25 100 4.0 100 100 – 415.0 136.42 – SS
ST19-80–0.27–120* 600 750 100 20 3 120.0 300 450 12 19 80 4.2 76 76 – 415.0 78.00 – SS
ST19-80–0.27–140* 600 750 100 20 3 140.0 300 450 12 19 80 4.2 76 76 – 415.0 82.42 – SS
ST19-80–0.27–160* 600 750 100 20 3 160.0 300 450 12 19 80 4.2 76 76 – 415.0 85.04 – SS
ST19-80–0.27–180* 600 750 100 20 3 180.0 300 450 12 19 80 4.2 76 76 – 415.0 87.13 – SS

[83] H35D19C65 400 450 100 65 2 161.4 215 215 4 19 35 1.8 100 100 427.3 532.8 196.52 4.00 SS
H35D19C40 400 450 75 40 2 161.4 215 215 4 19 35 1.8 100 100 427.3 532.8 182.16 3.06 SS
H35D19C15 400 450 50 15 2 161.4 215 215 4 19 35 1.8 100 100 427.3 532.8 170.56 2.21 SS
H60D19C15 400 450 75 15 2 161.4 215 215 4 19 60 3.2 100 100 427.3 532.8 176.42 4.00 SS
H85D19C15 400 450 100 15 2 161.4 215 215 4 19 85 4.5 100 100 427.3 532.8 187.70 5.00 SS
H60D16C15 400 450 75 15 2 161.4 215 215 4 16 60 3.8 100 100 411.4 487.4 148.02 3.68 SS
H60D22C15 400 450 75 15 2 161.4 215 215 4 22 60 2.7 100 100 371.2 491.2 203.01 5.11 SS
H50D16C25 400 450 75 25 2 161.4 215 215 4 16 50 3.1 100 100 411.4 487.4 148.50 2.58 SS
H50D19C25 400 450 75 25 2 161.4 215 215 4 19 50 2.6 100 100 427.3 532.8 178.36 3.31 SS
H50D22C25 400 450 75 25 2 161.4 215 215 4 22 50 2.3 100 100 371.2 491.2 201.99 4.04 SS

[Note] b = slab width, h = slab height, t = slab thickness, c = concrete cover, Vf = fiber volume fraction, fc = compressive strength, bsp = shear pocket width, hsp = shear
pocket height, nst = stud number per slab, dst = stud diameter, hst = stud height, hst/dst = stud aspect ratio, sl = longitudinal spacing, st = transversal spacing, fy = yield
stress, fu = ultimate strength, Pu = ultimate load per stud, δu = slip at the peak load, FM = Failure Mode, SS = stud shank fracture, CP = concrete pryout, SP = stud
pullout, CS = concrete spalling, and WF = welding fracture.
a
Top dimension.
b
Bottom dimension.

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