Shear Studs Distribution on Continuous Composite Beams

1 Introduction

Composite construction is a common theme in buildings and bridges. Composite members can be formed by connecting different materials together to create a single member benefiting from the good properties of these materials [1,2,3,4]. There are two methods in creating a composite section. The first is by mixing different materials having suitable properties. The second is the arrangement of different sections with different materials to obtain the best properties. Shear connectors are widely used between steel and concrete to produce composite steel–concrete beams to reduce or prevent the relative displacement between concrete and steel [5,6].

Figure 1(a) shows the obvious slip between concrete and steel due to the lack of interaction between concrete and steel, while (b) shows the composite action due to the bond created by the shear connector which causes a reduction in both deflection and strain between the sections (concrete and steel). Shear connectors cannot achieve a perfect rigid connection between materials, but it widely eliminates the interface slip. Using a proper connection leads the two components to work as one unit, and this connection is known as full or complete interaction [8,9,10,11,12,13,14].

Figure 1

(a) Non-composite and (b) composite beam [7].

However, all shear connectors are flexible to a certain degree and allow a certain amount of slip in the interface. As a result, this problem may occur when less connectors than the required number is used.

The key to composite work is the force transfer in the interface. This mechanism occurs by using shear connectors with different sections. Shear connectors should resist the horizontal forces developed between the composite materials [15,16].

To investigate the behavior of the composite concrete–steel beam joined by headed stud shear connectors, a finite element model is created [17,18]. The software program ABAQUS was utilized. The model's results were compared with experimental data and Practice Codes. The differences in concrete strength and the diameter of the shear connectors were investigated in parametric tests. The results reveal that the shear capacity of the headed studs could be overestimated when using finite element analysis.

To determine the shear and flexural strengths of composite simply supported beams, the finite element method is used [19,20,21,22]. These composite beams are made of steel and concrete and are subjected to a combination of shear and bending loads. A finite element model was built to compensate for the geometric nonlinearity of the beams, and the results were compared with the experimental results. The concrete slab's contributions to the composite beam's shear and moment capacity are calculated using a finite element model. For composite beams that are simply supported, the proposed design models offer a dependable and cost-effective method of design. The finite element results showed that the shear strength increase with the increase in the shear connection contribution.

Using multiple push-out tests, Rambo-Roddenberry et al. [22] studied the influence of steel plate thickness and shear connector location. According to their research, the thickness of the steel plate has an effect on the strength of shear studs in unfavorable locations. The strength difference between favorable and unfavorable positions is approximately 30%. Furthermore, the shear connector's tensile strength has a larger effect on the shear stud strength than the concrete's compressive strength.

Qureshi et al. [23] used 3D finite element models to investigate the spacing and layout of shear connectors in composite beams. The results showed that when the transverse spacing between the studs is 200 mm or more, shear resistance of shear connector pairs positioned in favorable positions is 94% of the strength of a single shear stud on average. A staggered pair of studs only has 86% of the strength of a single stud with the same spacing. Staggered pairs of shear connections have less strength than double shear studs in a favorable position.

Hosseini et al. [24] investigated the behavior of composite beams with trapezoidal profiled sheeting laid transverse to the beam axis. Four parameters were investigated using experimental findings from 24 full-scaled push test specimens, one of which was the shear stud arrangement. When compared to a layout with studs in the first four ribs, using studs just in the middle three ribs improved strength by 23%. Eurocode 4 and Johnson and Yuan [25] equations accurately predicted the stud strength for single stud/rib tests without normal load, with estimations within 10% of the characteristic test load. These equations underestimated the stud capacity by 40–50% when tested under normal load. AISC 360-16 generally overestimated the stud capacity, with the exception of single stud/rib push tests under normal load [26].

In this research, due to the importance of the shear connectors in reducing or preventing the relative displacement between concrete and steel, non-linear finite element analysis until failure is conducted on 24 continuous 2-span composite beams to investigate the effect of the arrangement and the number of shear connectors on the overall behavior of composite beams.

2 Description of samples

In this research, to study the effect of shear connectors, 3D nonlinear finite element analysis is conducted on 24 continuous 2-span composite beams with 2-point loads (one point load in each span). All beams have the same span details, length of 1 m for each span and the concrete slab was of width 250 mm and depth 8 mm. The steel I-section (IPE-140) had a depth of 140 mm, flange width of 72 mm, and thickness of 6 mm, while the web depth was 128 mm, thickness was 5 mm, and the total depth of the test samples was 220 mm as demonstrated in Figure 2.

Figure 2

Details of section specimens.

The strengthening of the concrete slab followed the criteria of the ACI construction code. Steel reinforcement in the longitudinal and transverse directions were based on shrinkage and temperature requirements [27,28]. Figure 2 demonstrates the negative and positive cross section of the beam.

The concrete slab was connected to a steel beam using the stud method. The shear connectors were assumed to be fully bonded to the I-steel beam's top flange and embedded in the concrete slab. The length and diameter of all studs were the same, but the number of studs varied depending on the study parameters from one sample to another. The variable parameters of the current study were divided into four categories:

2.1 Group A

The first group consisted of 6 steel–concrete beams (BC1, BC2, BC3, BC4, BC5, and BC6) with shear connectors divided into 2 rows with different distances 65, 85, 105, 150, 200, and 250 mm, respectively, as shown in Figure 3.

Figure 3

Shear connectors distribution for Group A.

2.2 Group B

The second group consisted of 6 steel–concrete beams (BC7, BC8, BC9, BC10, BC11 and BC12) with 1 of row shear connectors distributed along the longitudinal axis with distances of 65, 85, 105, 150, 200, and 250 mm, respectively, as shown in Figure 4.

Figure 4

Shear connectors distribution for Group B.

2.3 Group C

The third group included 6 steel–concrete beams (BC13, BC14, BC15, BC16, BC17 and BC18) single- and double-shear connectors distributed along the longitudinal axis with different distances 65, 85, 105, 150, 200, and 250 mm, respectively, as shown in Figure 5.

Figure 5

Shear connectors distribution for Group C.

2.4 Group D

The fourth group included 6 steel–concrete beams (BC19, BC20, BC21, BC22, BC23 and BC24) with one row shear connectors arranged staggered along the longitudinal axis with different distances 65, 85, 105, 150, 200, and 250 mm, respectively, as shown in Figure 6. The properties of materials used is shown in Table 1.

Figure 6

Shear connectors distribution for Group D.

Table 1

Properties of materials

Steel reinforcement		Reactive powder concrete
Modulus of elasticity (MPa)	2 × 105	Compressive strength (MPa)	100.29
Yield strength (MPa)	520	Modulus of elasticity (MPa)	44.5 × 103
Element type	T3D2	Dilation angle	40
Element size (mm)	20	Eccentricity	0.1
I-section steel		fbo/fco	1.16
Modulus of elasticity (MPa)	2 × 105	K	0.667
Yield strength (MPa)	300	Viscosity	0
Element type	C3D8R	Element type	C3D8R
Element size (mm)	20	Element size (mm)	20

3 Numerical model validation

To ensure that the current model in the ABAQUS software is appropriate, two samples are chosen and compared to Aggar's experimental results [29]. As demonstrated in Figure 7, the results of the experimental and the numerical model are in good agreement. Figure 8 shows the stress distribution in the experimental and numerical models of the sample (BC2).

Figure 7

Load–deflection curve of the experimental and numerical sample (BC2).

Figure 8

Comparison between the experimental and numerical stress distribution at failure for the sample (BC2) [31].

4 Discussion and results

The results of analyzing the specimens with ABAQUS software demonstrate that the number of shear connections and their arrangement have an effect on the ultimate load failure for composite beams.

4.1 Group A

The results of the analysis indicate that changing the shear connection spacing from 65 to 85 mm and 105 mm increased the ultimate load capacity; however, increasing the spacing from 105 to 150, 200, and 250 mm decreased the ultimate load capacity, as shown in Table 2. Figure 9 shows the load and deflection for the specimens of group A.

Table 2

Ultimate strength and deflection of midspan of group A

Group no.	Specimen	Ultimate strength (kN)	Deflection (mm)	Percentage
A	BC65	505.52	3.96	—
	BC85	582.33	4.77	15.19
	BC105	609.37	6.41	20.54
	BC150	508.78	5.18	0.64
	BC200	501.47	5.85	−0.80
	BC250	483.95	6.42	−4.27

Figure 9

Load–deflection for the specimens of Group A.

Figure 10 shows stress distribution for specimens of Group A.

Figure 10

Stress distribution for specimens of Group A.

4.2 Group B

The results of analysis of the second group also showed that the change in the spacing of shear connection from 65 to 85 and 105 mm led to an increase in the ultimate load capacity, while increasing the spacing from 105 to 150, 200, and 250 mm led to a decrease in the ultimate load capacity as shown in Table 3. Figure 11 shows the load and deflection for the specimens of Group B.

Table 3

Ultimate strength and deflection of midspan of Group B

Group no.	Specimen	Ultimate strength (kN)	Deflection (mm)	Percentage
B	BC65	464.67	3.82	—
	BC85	505.21	4.99	8.85
	BC105	520.75	5	12.20
	BC150	473.13	5.3	1.94
	BC200	455.16	6.54	−1.93
	BC250	435.22	8.24	−6.23

Figure 11

Load–deflection for the specimens of Group B.

Figure 12 shows stress distribution for specimens of Group B.

Figure 12

Stress distribution for specimens of Group B.

4.3 Group C

The results of analysis of the third group showed that the shear connections with a spacing of 105 mm gave the highest ultimate load capacity than all the other spacings of the same group but with less difference percent than Group A and Group B, as shown in Table 4. Figure 13 shows the load and deflection curves of group C.

Table 4

Ultimate strength and deflection of midspan of Group C

Group no.	Specimen	Ultimate strength (kN)	Deflection (mm)	Percentage
C	BC65	440.53	4.25	—
	BC85	450.23	4.57	2.20
	BC105	460.67	4.38	4.57
	BC150	442.09	5.01	0.35
	BC200	440.4	6.4	−0.03
	BC250	420.19	6.81	−4.62

Figure 13

Load–deflection for the specimens of Group C.

Figure 14 shows stress distribution for specimens of Group C.

Figure 14

Stress distribution for specimens of Group C.

4.4 Group D

The results of analysis of the fourth group showed that the shear connections with a spacing of 150 mm gave the highest ultimate load capacity than all the other spacings of the same group and the arrangement of shear connection led to the buckling in the flange of the steel I-section, Table 5 shows deflection and ultimate load for Group D. Figure 15 shows the load and deflection curves of Group D.

Table 5

Ultimate strength and deflection of midspan of Group D

Group no.	Specimen	Ultimate strength (kN)	Deflection (mm)	Percentage
D	BC65	386.64	3.71	—
	BC85	392.97	4.74	1.64
	BC105	410.53	3.12	6.18
	BC150	415.2	16.65	7.39
	BC200	410.06	11.19	6.06
	BC250	365.2	13.75	−5.55

Figure 15

Load–deflection for the specimens of Group D.

Figure 16 shows stress distribution for Group D.

Figure 16

Stress distribution for Group D.

As shown in Figure 17, it can be noticed that the effect of changing the spacing of shear connectors for Group A is more effective than the other groups.

Figure 17

The curve of ultimate load–deflection for all groups.

5 Conclusion

This study presented a numerical investigation of composite steel–concrete members using ABAQUS software, and the outcomes of this study were as follows:

• The composite steel concrete beam with 2 symmetrical shear stud rows has higher bending strength capacity by 17, 32, and 48% compared with the groups B, C, and D, respectively.

• For the fourth group (D), the deflection was fluctuating up and down, which resulted from nonsymmetrical distribution of the shear connectors. And this case was considered the worst condition compared with the symmetrical distribution.

• The optimum spacing was 105 mm in all groups (A, B, C, and D) compared with all other spacings of 65, 85, 200, and 250 mm.

• When comparing the optimum spacing of shear connector (105 mm) with other spacings such as 150, 200, and 250 mm, the bending strength capacity of the composite beam was reduced by 20, 20, and 26%, respectively.

Acknowledgments

The authors express their gratitude to Al-Mustaqbal University college, Babylon, Iraq for their contribution in completing this work.

1. Funding information: The authors state no funding involved.

2. Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.

3. Conflict of interest: Authors state no conflict of interest.

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