Shear strength evaluation of headed stud connectors in steel-concrete composite structures with hollow core slabs

Kataoka, Marcela Novischi

doi:10.1590/s1678-86212025000100880

Abstract

This paper investigates the shear strength of connectors in steel-concrete composite structures, with a specific focus on precast hollow core slabs. Push-out tests were conducted to assess the load-bearing capacity of headed shear studs, welded to the steel profile and embedded in cast-in-place concrete. The experimental analysis was complemented by a numerical study using the finite element method (FEM), allowing for a detailed evaluation of the behavior of the connectors under shear forces. A parametric study was performed to examine the effects of concrete compressive strength and stud yield strength on the shear resistance of the connection. The results demonstrated a good correlation between experimental tests and numerical predictions, though theoretical formulas based on standards tended to overestimate the connector capacity. This research emphasizes the importance of accurately characterizing shear connectors to ensure the proper performance of composite structures, particularly in applications involving hollow core slabs.

Keywords
Headed stud; Hollow core slab; Composite structures; Push-out test; Finite element method; Precast concrete

Resumo

Este artigo investiga a resistência de conectores de cisalhamento em estruturas mistas de aço e concreto, com foco específico em lajes alveolares pré-moldadas. Ensaios do tipo push-out foram realizados para avaliar a capacidade resistente de conectores tipo pino de cabeça (headed studs), soldados no perfil de aço e embutidos no concreto moldado in loco. A análise experimental foi complementada por um estudo numérico utilizando o método dos elementos finitos (MEF), permitindo uma avaliação detalhada do comportamento dos conectores sob cargas de cisalhamento. Estudo paramétrico foi conduzido para investigar o efeito da resistência à compressão do concreto e da resistência ao escoamento dos pinos na resistência ao cisalhamento da ligação. Os resultados mostraram uma boa correlação entre os testes experimentais e as previsões numéricas, embora as fórmulas teóricas baseadas em normas superestimassem a capacidade dos conectores. A pesquisa destaca a importância de uma caracterização precisa dos conectores para garantir o desempenho adequado de estruturas mistas, especialmente em aplicações com lajes alveolares.

Palavras-chave
Pino com cabeça; Laje alveolar; Estruturas compostas; Ensaio de push-out; Método dos elementos finites; Concreto pré-moldado

Introduction

Steel-concrete composite structures have become increasingly prevalent in offshore and civil infrastructure, such as bridge decks and high-rise buildings. Their success largely depends on mechanical shear connectors, which are crucial for transferring shear forces between steel beams and concrete slabs (Nie et al., 2019; Fang et al., 2022a, 2022b). Various shear connectors, including headed studs, bolts, perfobond, ribs, and angle shear connectors, are used to achieve effective composite action (Wei et al., 2018; Fang et al., 2022a, 2022b; Jiang et al., 2022).

The performance of these connectors is vital as it affects the transmission of shear forces, stress distribution in the steel beam, weld integrity, and the surrounding concrete. The design and form of shear connectors, such as aspect ratio and diameter, significantly influence the strength and overall performance of the composite structure (Fang et al., 2023; Wang et al., 2023). Connectors are categorized as rigid or flexible. Rigid connectors resist shear through direct shearing with minimal deformation, often causing localized stress in the concrete, which can lead to failure. Conversely, flexible connectors handle shear through bending, tension, or shearing, displaying more ductile and gradual failure modes that maintain strength under significant movement.

Several studies have investigated shear connectors in steel-concrete composite elements. Push-out tests conducted by Prakash et al. (2012) examined the shear strength and stiffness of high-strength steel (HSS) studs, which fell within the Eurocode 4 (ECS, 2004) range but not at the extremes. The study suggested enhancements by incorporating steel fiber concrete around HSS studs in reinforced slabs.

The American Institute of Steel Construction Specification has long been a crucial resource for calculating the strength of headed steel stud anchors (shear connectors) in composite steel- concrete structures in the United States, dating back to 1993. Pallarés and Hajjar (2010) analyzes monotonic and cyclic tests from the literature on experiments involving headed stud anchors. With a focus on designing composite elements in seismic regions, the paper examines proposals from various authors and offers recommended shear strength values for the seismic performance of headed studs. By assuming that the monotonic steel strength of headed studs falls within the resistance factor range proposed by research, the author suggests that a reduction factor of 0.75 is appropriate for designing headed stud anchors subjected to shear loads in seismic conditions.

Parametric analyses with different stud diameters and concrete strengths, as conducted by An and Cederwall (1996), show that concrete compressive strength significantly impacts shear resistance. Additionally, Nguyen and Kim (2009) conducted a numerical and theoretical investigation to predict stud resistance. Comparing the results, it was found that the specifications outlined in LRFD (AASHTO, 2004) and Eurocode 4 (ECS, 2004) often overestimated capacity, contrary to the findings of Pallarés and Hajjar (2010), which suggested that Eurocode 4 (ECS, 2004) is conservative. In contrast to standard approaches, alternative design equations have been proposed by some studies, such as Lam (2007) and Araújo et al. (2016), which developed procedures based on experimental findings for calculating the shear resistance of headed studs in these composite structures.

The growing demand for sustainable construction practices led Pavlović et al. (2013) to investigate a range of alternatives for shear connectors, including bolts and headed studs. This investigation aimed to deepen understanding of failure modes of shear connectors and enhance the competitiveness of prefabricated composite structures. Casting high-strength bolted shear connectors into prefabricated concrete slabs offers a higher degree of prefabrication compared to the standard method of grouting welded headed studs into designated pockets of concrete slabs. Furthermore, bolted shear connectors can be easily disassembled along with the concrete slab, thus facilitating improved sustainability of construction, simplified maintenance, and the evolution of modular structural systems. Tests by Ernst, Bridge and Wheeler (2009) addressed concrete crushing near connectors, using innovative push-out rigs and reinforcement techniques to enhance performance.

Experimental studies in Kruszewski and Zaghi (2021) examined traditional and novel shear connectors, including UHPC dowel connectors, highlighting different failure modes and the impact of connector design on capacity. Xu and Sugiura (2013) emphasized the critical role of concrete strength and stud dimensions on failure modes, with parametric FEM analysis revealing the effects of varying concrete strength and stud size on shear stiffness and strength. Finally, Hou and D’Mello (2013) provided insights into shear transfer mechanisms in shallow floor systems with asymmetric steel sections with circular web openings and concrete slab. Push-out tests indicated increased shear resistance with larger web openings and higher concrete strength.

This study focuses on evaluating the shear connection between steel profiles and hollow core slabs using headed studs and cast-in-place concrete. Shear strength was assessed through push-out tests, complemented by numerical simulations to deepen the understanding of composite action behavior Steel-concrete composite structures have become increasingly prevalent in offshore and civil infrastructure, such as bridge decks and high-rise buildings. Their success largely depends on mechanical shear connectors, which are crucial for transferring shear forces between steel beams and concrete slabs (Nie et al., 2019; Fang et al., 2022a, 2022b). Various shear connectors, including headed studs, bolts, perfobond, ribs, and angle shear connectors, are used to achieve effective composite action (Wei et al., 2018; Fang et al., 2022a, 2022b); Jiang et al., 2022).

The performance of these connectors is vital as it affects the transmission of shear forces, stress distribution in the steel beam, weld integrity, and the surrounding concrete. The design and form of shear connectors, such as aspect ratio and diameter, significantly influence the strength and overall performance of the composite structure (Fang et al., 2023; Wang et al., 2023). Connectors are categorized as rigid or flexible. Rigid connectors resist shear through direct shearing with minimal deformation, often causing localized stress in the concrete, which can lead to failure. Conversely, flexible connectors handle shear through bending, tension, or shearing, displaying more ductile and gradual failure modes that maintain strength under significant movement.

Several studies have investigated shear connectors in steel-concrete composite elements. Push-out tests conducted by Prakash et al. (2012) examined the shear strength and stiffness of high-strength steel (HSS) studs, which fell within the Eurocode 4 (ECS, 2004) range but not at the extremes. The study suggested enhancements by incorporating steel fiber concrete around HSS studs in reinforced slabs.

The American Institute of Steel Construction Specification has long been a crucial resource for calculating the strength of headed steel stud anchors (shear connectors) in composite steel- concrete structures in the United States, dating back to 1993. Pallarés and Hajjar (2010) analyzes monotonic and cyclic tests from the literature on experiments involving headed stud anchors. With a focus on designing composite elements in seismic regions, the paper examines proposals from various authors and offers recommended shear strength values for the seismic performance of headed studs. By assuming that the monotonic steel strength of headed studs falls within the resistance factor range proposed by research, the author suggests that a reduction factor of 0.75 is appropriate for designing headed stud anchors subjected to shear loads in seismic conditions.

Parametric analyses with different stud diameters and concrete strengths, as conducted by An and Cederwall (1996), show that concrete compressive strength significantly impacts shear resistance. Additionally, Nguyen and Kim (2009) conducted a numerical and theoretical investigation to predict stud resistance. Comparing the results, it was found that the specifications outlined in LRFD (AASHTO, 2004) and Eurocode 4 (ECS, 2004) often overestimated capacity, contrary to the findings of Pallarés and Hajjar (2010), which suggested that Eurocode 4 (ECS, 2004) is conservative. In contrast to standard approaches, alternative design equations have been proposed by some studies, such as Lam (2007) and Araújo et al. (2016), which developed procedures based on experimental findings for calculating the shear resistance of headed studs in these composite structures.

The growing demand for sustainable construction practices led Pavlović et al. (2013) to investigate a range of alternatives for shear connectors, including bolts and headed studs. This investigation aimed to deepen understanding of failure modes of shear connectors and enhance the competitiveness of prefabricated composite structures. Casting high-strength bolted shear connectors into prefabricated concrete slabs offers a higher degree of prefabrication compared to the standard method of grouting welded headed studs into designated pockets of concrete slabs. Furthermore, bolted shear connectors can be easily disassembled along with the concrete slab, thus facilitating improved sustainability of construction, simplified maintenance, and the evolution of modular structural systems. Tests by Ernst, Bridge and Wheeler (2009) addressed concrete crushing near connectors, using innovative push-out rigs and reinforcement techniques to enhance performance.

Experimental studies in Kruszewski and Zaghi (2021) examined traditional and novel shear connectors, including UHPC dowel connectors, highlighting different failure modes and the impact of connector design on capacity. Xu and Sugiura (2013) emphasized the critical role of concrete strength and stud dimensions on failure modes, with parametric FEM analysis revealing the effects of varying concrete strength and stud size on shear stiffness and strength. Finally, Hou and D’Mello (2013) provided insights into shear transfer mechanisms in shallow floor systems with asymmetric steel sections with circular web openings and concrete slab. Push-out tests indicated increased shear resistance with larger web openings and higher concrete strength.

This study focuses on evaluating the shear connection between steel profiles and hollow core slabs using headed studs and cast-in-place concrete. Shear strength was assessed through push-out tests, complemented by numerical simulations to deepen the understanding of composite action behavior.

Experimental program

The push-out test described below was conducted as part of the experimental program outlined in Sales (2014) to ascertain the resistance of the headed studs. The specimen consisted of headed shear studs welded to a steel profile and encased in concrete, representing the prevalent method for transferring forces between steel and concrete materials in composite structures. The push-out specimen underwent monotonic loading under load control. Figure 1 illustrates details of the test specimen, highlighting the positions of the shear studs, the slab, and the cast- in-place concrete surrounding the connectors.

Figure 1
Test specimen layout (unit: millimeter)

The precast concrete hollow core slabs had a total depth of 160 mm and a length of 1250 mm, featuring three headed stud shear connectors. A concrete topping, 40 mm thick, was cast in place simultaneously with the concrete surrounding the studs. All studs were 19 mm in diameter, with a specified overall height of 112 mm, welded in the middle of each flange with cast-in-place concrete surrounding them. Figure 2 illustrates the dimensions of the elements comprising the push-out specimen.

Figure 2
Dimensions of the elements that comprise the specimen (unit: millimeter)

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Table 1
Mechanical properties of the materials

The mechanical properties of the steel profile, shear connectors, and hollow core slab were provided by the manufacturers. Additionally, the properties of the cast-in-place concrete used in the topping of the slab and surrounding the shear studs were determined through standard tests, including compressive and tensile tests. Table 1 outlines the mechanical properties of the materials.

The push-out specimen was equipped with displacement transducers, denoted as A, B, C, D, G, H, I, and J in Figure 3, to measure the slip between the slab and the steel profile. Additionally, strain gauges were affixed to the shank of the studs to determine the strain of the connectors. The tests were conducted under force control, with the load applied measured by a load cell. The test setup and instrumentation of the specimen are depicted in Figure 3.

Regarding the analysis, the studies were conducted based on the total applied load divided by six studs, assuming that the shear connectors are flexible, thereby implying that the loading is evenly distributed. Table 2 presents the maximum load per shear stud obtained theoretically and experimentally for the push-out specimen. The theoretical values were calculated according to the prescriptions of the Brazilian code NBR 8800 (ABNT, 2008) (Equation 1) and Eurocode 4 (ECS, 2004) (Equation 2). The safety factor was omitted for a more realistic comparison, and the concrete compressive strength used in the calculations was the average value where fck is indicated in the equation.

Based on the results presented in Table 2, the design rules specified in Eurocode 4 (ECS, 2004) were more conservative than those in NBR 8800 (ABNT, 2008), but both standards overestimated the stud capacity. The predicted stud resistance according to Eurocode 4 (ECS, 2004) was 9.6% higher than the experimental results, while that of NBR 8800 (ABNT, 2008) was 48.7% higher. Therefore, in this case, the European standard was more suitable.

Nonlinear FE analysis

Numerical simulation offers a cost-effective alternative to traditional structural analysis by replacing expensive and time-consuming physical models. To validate the simulation results, the numerical data were compared with experimental findings.

A three-dimensional finite element model was developed to predict the capacity of shear stud connectors, specifically replicating one of the push-out specimens from Sales (2014). This model included shear connectors (headed studs) with a square cross-section, omitting the head, as noted by Hejazi and Azadbakht (2015). Since the focus of the paper was on analyzing the strength of the shear connectors, the studs served solely as the connection between the steel profile and the concrete slab, without considering the adhesion between steel and concrete. Details of the model, including the concrete topping of the slab and the shear connectors, are illustrated in Figure 4.

Figure 3
Tests setup and instrumentation

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Table 2
Theoretical and experimental results

Figure 4
Push-out numerical model

The geometry was constructed using Midas FX+, which also facilitated the visualization of results during pre- and post-processing. The software DIANA was employed to process the numerical model using the finite element method (FEM).

Unlike the procedures adopted in the experimental test, in the numerical simulation, the loading was applied with displacement control. This method was chosen for its ease of convergence, which ensures smoother and more stable simulations.

Materials

Properties

The mechanical properties inputted into the numerical model for the cast-in-place concrete, such as compressive strength, tensile strength, Young Modulus, and yielding stress, were based on the values determined in the experimental program. Since a fracture test of the concrete was not conducted, the tensile fracture energy was determined using the guidelines outlined in the CEB-FIP Model Code 1990 (CEB, 1993), as per Equation 3.

G_{f} = G_{f 0} {(\frac{f_{c m}}{10})}^{0.7}

Eq. 3

Where:

fcm = Average compressive strength; and

Gf0 = 0.03 for maximum aggregate diameter equal to 16 mm.

The compressive fracture energy was assumed to be 50 times the tensile fracture energy, as recommended by Feenstra and Borst (1993). For the manufactured elements (hollow core slab, studs, and steel profile), catalog information was utilized. Table 3 provides a summary of the mechanical properties incorporated into the numerical model. The compression and tensile strength values are average values.

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Table 3
Materials properties of the numerical model

Constitutive models

Concrete: The constitutive model used for the concrete was suitable for brittle or quasi-brittle materials. To characterize crack distribution, the Total Strain Model was employed, offering a straightforward concept. The Total Strain Model can be represented by either the Rotating Crack Model or the Fixed Crack Model. In the numerical model created for this study, the Fixed Crack Model was utilized. Tensile concrete behavior was assumed to be brittle, while an ideal elastic-plastic model was employed for compression, as depicted in Figure 5a.

Steel: Tresca and Von Mises plasticity models are applicable to steel elements as they are ductile materials. The Von Mises model of maximum energy distortion was chosen for the steel elements in this model, under the assumption that the maximum energy accumulated in material distortion should not exceed the maximum distortion energy of the same material in a uniaxial tensile test. In summary, a steel model was adopted with Von Mises plasticity criteria and ideal plasticity without considering hardening or strain hardening. In the ideal plasticity model, also known as the perfectly plastic model, the material does not support efforts after reaching the yield stress, as shown in Figure 5b. The main distinction between the perfectly plastic model and one that incorporates work hardening and softening is the level of accuracy in representing the behavior of steel under large deformations.

Finite elements

Only one type of finite element, the solid element HX24L, a plane state element, was utilized to construct the finite element mesh. This finite element was selected based on the capabilities of the DIANA software and was used to represent both the concrete and steel components. The HX24L element features eight nodes and three degrees of freedom per node. An illustration of the finite element can be found in DIANA FEA BV (2024) and is depicted in Figure 6.

FE mesh and boundary conditions

Various mesh densities were tested to balance result quality with processing time. Ultimately, a mesh with elements measuring 20 mm in size was chosen due to its favorable compromise between element size and numerical solution stability.

For the numerical model, boundary conditions included constraints on displacements in the x, y, and z directions at the base, simulating conditions identical to those in the experimental test. Loading was applied at the top of the steel profile. The schematic representation of the boundary conditions and loading application is depicted in Figure 7.

Figure 5
Stress-strain law for (a) concrete; (b) steel elements (profile and studs)

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Table 4
Parameters for materials constitutive models

Figure 6
Finite elements used in the numerical model

Figure 7
FE mesh and boundary conditions

Validation of the numerical model

To ensure the accuracy of the numerical model, the simulation results were validated against experimental data. The analysis focused on parameters such as load per stud, slip, and strain. The ultimate shear resistance of the shear connection was determined by dividing the ultimate load of the test specimen by the number of shear connectors.

The experimental curves depicted in Figure 8 illustrate that the slip of each shear stud varies according to its vertical position. Studs closer to the support base exhibit less slip, while those nearer to the load application point experience higher slip. In the numerical results, slip values exhibited minimal variation; however, an average curve was presented to simplify the comparison.

Figure 8
Experimental and numerical results of load per shear stud vs slip curves

The ultimate shear resistance of the models showed satisfactory agreement, despite discrepancies in initial stiffness. Nevertheless, the numerical model was deemed valid, as observed in similar studies such as Shim, Lee and Yoon (2004) and Souza, Kataoka and El Debs (2017), where the curve behavior during tests conducted with displacement control resembled the numerical curve obtained in this study. Additionally, both the point of cracking initiation and the maximum force applied were found to be equivalent.

The slip distribution across the entire push-out numerical model is depicted in Figure 9. As anticipated, the highest slip occurred at the top of the steel profile, where the loading was applied, gradually decreasing towards the base due to the contribution of the shear connectors.

Notably, the slip along the shank of the shear studs revealed that the highest stress was concentrated approximately one-third of the distance from the extremity welded to the profile.

Figure 9
Vertical displacements in numerical model (unit: millimeter)

The same conclusion can be drawn from the strain distribution along the studs, as depicted in Figure 10. Stress concentration was not observed in the middle of the stud length, but rather closer to the base where it was welded to the steel profile. Near the end of the stud, which would correspond to the head, tensile stresses were practically negligible.

The comparison of stud strain between the numerical and experimental results revealed certain discrepancies, attributable to several factors. A primary factor is the difference in loading modes: the experimental test employed force control, while the numerical simulation utilized displacement control. Displacement control often results in a more stable analysis as it enables the structure to accommodate stress redistribution during loading, leading to more accurate depictions of structural behavior. Additionally, other sources of variance may include differences in boundary conditions, material properties, and inherent simplifications in the numerical model. For instance, the numerical model may incorporate idealized boundary conditions, perfect bond assumptions, and material behaviors that do not fully capture the complexities of the experimental setup, such as specimen imperfections. Figure 11 illustrates the comparison of stud strain, emphasizing these differences between the numerical and experimental results.

The final configuration of the headed studs in the numerical results closely resembled that of the experimental model, as depicted in Figure 12. A pronounced curvature near the steel profile was observed at the base of the connector, indicating stress concentration. Additionally, the rotation of the connector head suggested that it was not anchored into the concrete. This behavior is indicative of a typical failure mode of shear connectors, as mentioned in Lam (2007).

Figure 10
Strain in the shear studs in numerical model (unit: mm/mm)

Figure 11
Loading per shear stud vs stud strain curves

Figure 12
Final configuration of the studs of the experimental model (Sales, 2014)

Parametric study

Assuming that the proposed finite element model accurately represents the behavior of the push-out specimen tested, a parametric analysis was conducted to further study the behavior of headed shear studs. This analysis focused on the effects of cast-in-place concrete compressive strength and stud strength on the behavior of the push-out specimen.

Concretes with compressive strengths of 25, 30, 40, 50, 60, 70, 80, and 90 MPa were simulated, along with stud yielding strengths of 540, 450, and 380 MPa. Twenty-four numerical models were simulated in the parametric study, with each yield strength of the stud associated with eight compressive strengths of concrete.

The properties such as tensile strength (fctm) and Young Modulus (Eci) were calculated according to NBR 6118 (ABNT, 2023), using Equations 4 and 5 for concretes with compressive strengths between 20 and 50 MPa, and Equations 6 and 7 for concretes with compressive strengths between 55 and 90 MPa. The fracture energies (tensile and compressive) were calculated as indicated in Table 4. Table 5 presents the properties adopted for each cast-in-place concrete used in the parametric analysis. The characteristic compression strength values were used in the numerical models.

E_{c l} = α_{E} .5600 . \sqrt{f_{c k}}

Eq. 4

f_{c t m} = 0.3 \cdot f_{c k}^{2 / 3}

Eq. 5

E_{c i} = 21 \cdot 5 \cdot 10^{3} \cdot α_{E} \cdot {(\frac{f_{c k}}{10} + 1, 25)}^{1 / 3}

Eq. 6

f_{c t m} = 2.12 \cdot \ln (1 + 0.11 . f_{c k})

Eq. 7

Where:

f_ck = characteristic concrete compressive strength; and

G_f0 = 0.03 for maximum aggregate diameter equal to 16 mm.

According to the parametric analysis, both the compressive strength of the concrete and the strength of the studs have a significant influence on the resistance of the shear connections formed by headed studs, as illustrated in Figure 13. This figure depicts the slip of the second stud, reflecting its intermediary position within the push-out specimen.

Analyzing each type of shear connector separately, it is evident that the initial stiffness was not affected by the change in concrete compressive strength. However, the resistance and the load level at which cracking began showed substantial increases, particularly for the studs with a yield strength of 540 MPa.

Figure 14a illustrates the load per stud versus concrete compressive strength curves for three yield strengths of shear studs (380 MPa, 450 MPa, and 540 MPa). The behavior of the curves indicates that concrete compressive strength had a greater influence on the resistance of the studs for models with shear connectors with a yield strength of 450 MPa. For instance, considering the variation of concrete strength from 25 to 90 MPa, the increase in load per stud was 67.94%. In contrast, the model with weaker studs exhibited lesser influence from the concrete strength, with a percentage increase in load per stud of 52.4%. Meanwhile, the models with studs with a yield strength of 540 MPa demonstrated an intermediate behavior, showing an increase of 58.74%. Table 6 provides further details on the influence of concrete compressive strength on the load per shear stud.

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Table 5
Properties of the cast in place concrete used in the parametric analysis

Figure 13
Load per shear stud vs slip curves

Figure 14
(a) Load per shear stud vs concrete strength curves; (b) Load per shear stud vs concrete strength

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Table 6
Percentage of the increase in load per shear stud by increasing the concrete strength

The most pronounced increase in load per stud was observed for concrete compressive strength of 60 MPa, with each shear connector resistance increased by 30.87% when stud strength varied from 380 to 540 MPa. Table 7 illustrates the percentage variation in load per stud corresponding to changes in the yield stress of the shear connectors.

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Table 7
Percentage of the increase in load per shear stud by increasing the stud strength

For theoretical analysis, the shear strength of the shear stud was determined using the predictions from NBR 8800 (ABNT, 2008) and Eurocode 4 (ECS, 2004) across 24 models. These predictions were then compared to numerical results obtained through the equations outlined in Table 2. The comparison revealed that Eurocode 4 (ECS, 2004) is more adept at predicting the resistance of such push-out specimens in terms of stud strength in shear. Conversely, NBR 8800 (ABNT, 2008), which considers three levels of stud strength, consistently overestimated the shear connector strength, as depicted in Figure 15.

Figure 15
Load per shear stud vs concrete strength

The disparity between the stud capacity provided by NBR 8800 (ABNT, 2008) and Eurocode 4 (ECS, 2004) amounted to approximately 48% in most cases. Tables 8, 9, and 10 present the load per stud values calculated according to the codes provisions and compare them with the numerical results. The Brazilian code consistently overestimated the stud capacity across all scenarios, sometimes predicting a resistance twice as high as the values obtained from numerical simulations. In contrast, the European standard yielded values closer to the numerical results, particularly for models with concrete compressive strength exceeding 50 MPa.

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Table 8
Results of the standards provisions for the parametric analysis of 380 MPa shear stud

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Table 9
Results of the standards provisions for the parametric analysis of 450 MPa shear stud

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Table 10
Results of the standards provisions for the parametric analysis of 540 MPa shear stud.

Conclusions

The study developed a three-dimensional nonlinear finite element model using the commercial software DIANA to simulate the load-slip behavior of headed shear studs in precast hollow core slabs. The integration of hollow core slabs into composite structures represents an innovative approach, enhancing the efficiency and performance of mixed steel-concrete systems by optimizing the interaction between shear connectors and concrete components. By conducting push-out tests and numerical simulations, the shear behavior of the studs was thoroughly analyzed, and the proposed model was validated against experimental data. The primary objectives were to determine the shear capacity of the studs, assess the influence of key parameters, and compare the results to theoretical values according to both Brazilian and European standards. A parametric study involving 24 push-out specimens with varying stud strengths and concrete compressive strengths was also carried out. Based on the findings, the following conclusions were drawn:

the push-out test results revealed that the NBR 8800 (ABNT, 2008) and Eurocode 4 (ECS, 2004)specifications overestimated the shear capacity of headed studs by up to 48.74% and 9.66%, respectively;
a satisfactory correlation was observed between experimental and numerical results, particularly in terms of ultimate shear resistance and the initiation of concrete cracking. However, initial stiffness did not align as well. Consistent with findings in the literature, displacement control was identified as a more suitable method for studying stud behavior, as it better accommodates structural deformations and stress distribution during loading compared to force control;
the parametric analysis demonstrated that concrete compressive strength influences both ultimate capacity and stud forces. This influence was most significant in models with shear connectors of 450 MPa yield strength. For weaker studs (380 MPa), concrete strength had less impact, while studs with 540 MPa yield strength showed an intermediate response. The analysis also revealed that stud yield strength affects stud resistance, but this effect varies depending on concrete compressive strength. Specimens with concrete compressive strengths exceeding 50 MPa exhibited a marked increase in load per stud as the shear connector strength increased; and
the capacities of headed stud shear connectors from the parametric analysis were compared with the design rules of Eurocode 4 (ECS, 2004) and NBR 8800 (ABNT, 2008). The Brazilian code overestimated stud capacity in all cases, in some instances predicting double the resistance values obtained from numerical simulations. The European standard provided values closer to the numerical results, particularly for models with concrete compressive strengths above 50 MPa. The predictions from both standards were calculated without safety factors.

Acknowledgments

The authors would like to express their gratitude for the financial support from CNPq (National Council for Scientific and Technological Development). They also appreciate Sales for providing the experimental data and the assistance from the Computer Lab of the Department of Structural Engineering at the School of Engineering of São Carlos – USP for providing the software.

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KRUSZEWSKI, D.; ZAGHI, A. E. Load transfer between thin steel plates and ultra-high performance concrete through different types of shear connectors. Engineering Structures, v. 227, 111450, 2021.
LAM, D. Capacities of headed stud shear connectors in composite steel beams with precast hollow core slabs. Journal of Constructional Steel Research, v.63, p.1160–1174, 2007.
NGUYEN, H. T.; KIM, S.E. Finite element modeling of push-out tests for large stud shear connectors. Journal of Constructional Steel Research, v. 65, p.1909-1920, 2009.
NIE, J. et al. Technological development and engineering applications of novel steel-concrete composite structures. Frontiers of Structural and Civil Engineering, v. 13, n. 1, p. 1–14, 2019.
PALLARÉS, L.; HAJJAR, J. F. Headed steel stud anchors in composite structures: part I: shear. Journal of Constructional Steel Research, v. 66, p. 198-212, 2010.
PAVLOVIĆ, M. et al. Bolted shear connectors vs. headed studsbehaviour in push-out tests. Journal of Constructional Steel Research, v. 88, p. 134–149, 2013.
PRAKASH, A. et al. Modified push-out tests for determining shear strength and stiffness of HSS stud connector-experimental study. International Journal of Composite Materials, v. 2, n. 3, p. 22-31, 2012.
SALES, M. W. R. Conector de cisalhamento tipo pino com cabeça para viga mista aço–concreto com laje alveolar Goiânia, 2014. Master (Dissertation) – Federal University of Goiás, Goiânia, 2014.
SHIM, C.S.; LEE, P. G.; YOON, T. Y. Static behavior of large stud shear connectors. Engineering Structures, v. 26, n. 12, p. 1853–1860, 2004.
SOUZA, P. T.; KATAOKA, M. N.; El DEBS, A. L. H. C. Experimental and numerical analysis of the push-out test on shear studs in hollow core slabs. Engineering Structures, v. 147, p. 398–409, 2017.
WANG, S. et al. Experimental and numerical study on shear behavior of ultrahigh-performance concrete rubber-sleeved stud connectors in composite structures. Engineering Structures, v. 293, 116582, 2023.
WEI, X. et al. Distribution of shear force in perforated shear connectors. Steel & Composite Structures, v. 27, n. 3, p. 389–399, 2018.
XU, C.; SUGIURA, K. FEM analysis on failure development of group studs shear connector under effects of concrete strength and stud dimension. Engineering Failure Analysis, v. 35, p.343–354, 2013.

Edited by

Editor:
Marcelo Henrique Farias de Medeiros

Publication Dates

Publication in this collection
11 Apr 2025
Date of issue
Jan-Dec 2025

History

Received
19 Sept 2024
Accepted
01 Dec 2024

This is an Open Access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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» https://dianafea.com/diana-manuals/

[8] ERNST, S.; BRIDGE, R. Q.; WHEELER, A. Push-out tests and a new approach for the design of secondary composite beam shear connections. Journal of Constructional Steel Research, v. 65, p.44-53,2009.

[9] EUROPEAN COMMITTEE FOR STANDARDIZATION. EN 1994-1-1: Eurocode 4: design of composite steel and concrete structures: part 1-1: general rules and rules for buildings. Brussels, 2004.

[10] FANG, S. et al. Effects of stud aspect ratio and cover thickness on push-out performance of thin full-depth precast UHPC slabs with grouped short studs: experimental evaluation and design considerations. Journal of Building Engineering, v. 67, 105910, 2023.

[11] FANG, Z. et al. Static behavior of grouped stud shear connectors in steel–precast UHPC composite structures containing thin full-depth slabs. Engineering Structures, v. 252, 113484, 2022a.

[12] FANG, Z. et al. Interfacial shear and flexural performances of steel–precast UHPC composite beams: full-depth slabs with studs vs. demountable slabs with bolts. Engineering Structures, v. 260, 114230, 2022b.

[13] FEENSTRA, P. H.; BORST, R. Aspects of robust computational modeling for plain and reinforced concrete. Heron, Delft, v. 38, n. 4, p. 3-76, 1993.

[14] HEJAZI, M.; AZADBAKHT, J. Semi-rigid composite connection with a partial depth end-plate. Structures and Buildings, v. 168, p.387–401, 2015.

[15] HUO, B. Y.; D’MELLO, C. A. Push-out tests and analytical study of shear transfer mechanisms in composite shallow cellular floor beams. Journal of Constructional Steel Research, v. 88, p. 191–205, 2013.

[16] JIANG, H. et al. Push-out tests on demountable high-strength friction-grip bolt shear connectors in steel–precast UHPC composite beams for accelerated bridge construction. Steel & Composite Structures, v. 45, n. 6, 2022.

[17] KRUSZEWSKI, D.; ZAGHI, A. E. Load transfer between thin steel plates and ultra-high performance concrete through different types of shear connectors. Engineering Structures, v. 227, 111450, 2021.

[18] LAM, D. Capacities of headed stud shear connectors in composite steel beams with precast hollow core slabs. Journal of Constructional Steel Research, v.63, p.1160–1174, 2007.

[19] NGUYEN, H. T.; KIM, S.E. Finite element modeling of push-out tests for large stud shear connectors. Journal of Constructional Steel Research, v. 65, p.1909-1920, 2009.

[20] NIE, J. et al. Technological development and engineering applications of novel steel-concrete composite structures. Frontiers of Structural and Civil Engineering, v. 13, n. 1, p. 1–14, 2019.

[21] PALLARÉS, L.; HAJJAR, J. F. Headed steel stud anchors in composite structures: part I: shear. Journal of Constructional Steel Research, v. 66, p. 198-212, 2010.

[22] PAVLOVIĆ, M. et al. Bolted shear connectors vs. headed studsbehaviour in push-out tests. Journal of Constructional Steel Research, v. 88, p. 134–149, 2013.

[23] PRAKASH, A. et al. Modified push-out tests for determining shear strength and stiffness of HSS stud connector-experimental study. International Journal of Composite Materials, v. 2, n. 3, p. 22-31, 2012.

[24] SALES, M. W. R. Conector de cisalhamento tipo pino com cabeça para viga mista aço–concreto com laje alveolar Goiânia, 2014. Master (Dissertation) – Federal University of Goiás, Goiânia, 2014.

[25] SHIM, C.S.; LEE, P. G.; YOON, T. Y. Static behavior of large stud shear connectors. Engineering Structures, v. 26, n. 12, p. 1853–1860, 2004.

[26] SOUZA, P. T.; KATAOKA, M. N.; El DEBS, A. L. H. C. Experimental and numerical analysis of the push-out test on shear studs in hollow core slabs. Engineering Structures, v. 147, p. 398–409, 2017.

[27] WANG, S. et al. Experimental and numerical study on shear behavior of ultrahigh-performance concrete rubber-sleeved stud connectors in composite structures. Engineering Structures, v. 293, 116582, 2023.

[28] WEI, X. et al. Distribution of shear force in perforated shear connectors. Steel & Composite Structures, v. 27, n. 3, p. 389–399, 2018.

[29] XU, C.; SUGIURA, K. FEM analysis on failure development of group studs shear connector under effects of concrete strength and stud dimension. Engineering Failure Analysis, v. 35, p.343–354, 2013.

-	Hollow core slab	Steel profile	Shear connector	Cast in place concrete
Compressive Strength (MPa)	50.0	-	-	28.0
Tensile Strength (MPa)	3.3	-	-	3.5
Young Modulus (GPa)	39.6	200.0	200.0	27.0
Yielding Stress (MPa)	-	345.0	540.0	-

Experimental Maximum Load per stud (kN)	83.00
ABNT NBR 8800 (2008) (kN)	$Q_{Rd} < \frac{A_{cs} \sqrt{f_{ck} E}}{2} = \frac{2.84 \sqrt{2.8 \cdot 2700}}{2} = 123.46 kN A_{c s} f_{u c s} 2.84 \cdot 54 = 153.36 kN$	Eq. 1
Eurocode 4 (2004) (kN)	$\begin{matrix} P_{Rd} < 0.29 \cdot α \cdot d^{2} \sqrt{f_{ck} E} = 0.29 \cdot 1 \cdot ({1.9}^{2}) \sqrt{2.8 \cdot 2700} = 91.02 kN \\ 0.8 A_{cs} f_{ucs} = 0.8 \cdot 2.84 \cdot 54 = 122.69 kN \end{matrix}$	Eq. 2
Note: Q_Rd, P_Rd = maximum load per shear stud;
	A_cs = cross section area of the connector;
	α = empirical parameter that represents a combination of factors influencing the mechanical behavior of connectors in steel-concrete composite structures;
	d = diameter of the connector;
	f_ucs = rupture stress of the connector steel;
	E = young modulus of the concrete; and
	f_ck = characteristic concrete compression strength.

-	Hollow core slab	Steel profile	Shear connector	Cast in place concrete
Young Modulus (GPa)	39.60	200.0	200.0	27.00
Compressive Strength (MPa)	50.00	-	-	28.00
Tensile Strength (MPa)	4.00	-	-	3.50
Tensile fracture energy (N.mm/mm²)	0.09	-	-	0.06
Compressive fracture energy (N.mm/mm²)	4.63	-	-	3.08
Yielding Stress (MPa)	-	350.00	540	-
Poison (ʋ)	0.20	0.30	0.30	0.20

Parameters	Value
Concrete
Total Strain model	Fixed
Tensile curve	Exponential
Compression curve	Parabolic
Tensile fracture energy (G_f)	CEB (CEB, 1993)
Compressive fracture energy (G_c	Feenstra and Borst (1993)
Shear retention (β)	0.1
Steel (profile and shear connector)
Von Mises	Ideal plasticity

Properties	C25	C30	C40	C50	C60	C70	C80	C90
Young Modulus (GPa)	28	31	35	40	42	43	45	47
Tensile strength (MPa)	2.56	2.90	3.51	4.07	4.30	4.59	4.84	5.06
Tensile fracture energy (N.mm/mm²)	0.057	0.065	0.079	0.093	0.105	0.117	0.129	0.140
Compressive strength (MPa)	25	30	40	50	60	70	80	90
Compressive fracture energy (N.mm/mm²)	2.849	3.237	3.959	4.628	5.258	5.857	6.431	6.983

Increase in concrete strength (MPa)	25-50	50-90	Total (25-90)
Stud Strength	25-50	50-90	Total (25-90)
540 MPa	27.49%	19.53%	52.40%
450 MPa	35.61%	23.83%	67.94%
380 MPa	32.21%	20.06%	58.74%

Increase in stud strength (MPa)	380 - 450	450 - 540	380 – 540
Concrete compressive strength	380 - 450	450 - 540	380 – 540
25 MPa	2.59%	17.06%	20.10%
30 MPa	11.06%	7.48%	19.37%
40 MPa	5.70%	13.43%	19.90%
50 MPa	9.13%	14.12%	24.54%
60 MPa	10.20%	18.75%	30.87%
70 MPa	12.50%	15.92%	30.41%
80 MPa	12.52%	14.16%	28.46%
90 MPa	13.05%	10.65%	25.10%

Concrete compressive strength	Stud 380 MPa
Concrete compressive strength	Numerical result (MPa)	NBR 8800 (MPa)	NBR8800/ Numerical result	EC4 (MPa)	EC4/ Numerical result
25 MPa	57.93	107.92	1.86	72.96	1.25
30 MPa	61.98	107.92	1.74	72.96	1.17
40 MPa	70.05	107.92	1.54	72.96	1.04
50 MPa	73.86	107.92	1.46	72.96	0.98
60 MPa	77.17	107.92	1.39	72.96	0.94
70 MPa	81.28	107.92	1.32	72.96	0.89
80 MPa	85.45	107.92	1.26	72.96	0.85
90 MPa	88.29	107.92	1.22	72.96	0.82

Concrete compressive strength	Stud 450 MPa
Concrete compressive strength	Numerical result (MPa)	NBR 8800 (MPa)	NBR 8800/ Numerical result	EC4 (MPa)	EC4/ Numerical result
25 MPa	59.44	127.80	2.15	86.40	1.45
30 MPa	68.84	127.80	1.85	86.40	1.25
40 MPa	74.05	127.80	1.72	86.40	1.16
50 MPa	80.61	127.80	1.58	86.40	1.07
60 MPa	85.04	127.80	1.50	86.40	1.01
70 MPa	91.44	127.80	1.39	86.40	0.94
80 MPa	96.15	127.80	1.32	86.40	0.89
90 MPa	99.82	127.80	1.28	86.40	0.86

Shear strength evaluation of headed stud connectors in steel-concrete composite structures with hollow core slabs

Avaliação da resistência ao cisalhamento de conectores tipo pino com cabeça em estruturas mistas de aço e concreto com lajes alveolares

Abstract

Resumo

Introduction

Experimental program

Nonlinear FE analysis

Materials

Properties

Constitutive models

Finite elements

FE mesh and boundary conditions

Validation of the numerical model

Parametric study

Conclusions

Acknowledgments

References

Edited by

Publication Dates

History