Effects of Partial Shear Connection of Curved in Plan Composite Steel-concrete Beams Under Combined Flexure and Torsion-libre

8/12/2019 Effects of Partial Shear Connection of Curved in Plan Composite Steel-concrete Beams Under Combined Flexure a

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Australasian Structural Engineering Conference (ASEC),

26 27 June 2008, Melbourne Australia

ISBN 978 1 877040 70 2

Paper No. 090

Effects of Partial Shear Connection of Curved in Plan CompositeSteel-Concrete Beams under Combined Flexure and Torsion

E.L. Tan, B. Uy

University of Western Sydney, Penrith South DC, NSW, Australia

Abstracts

Methods for the ultimate load analysis and design of straight composite steel-concrete beams

in flexure are well-established, and solutions can be obtained with relative ease. However,there are situations in which a composite beam is subjected to torsion, such as members that

are curved in-plan and edge beams. The concrete slab and the steel beam contribute to the

torsional strength and stiffness of a composite beam, but this composite action is usually

ignored in design codes of practice, which leads to conservative designs. Partial shear

connection is commonly used in the design of floor systems, and this is also ignored in the

design of composite beams for combined flexure and torsional actions. This paper

investigates the ultimate strength of composite steel-concrete beams which are curved in-plan.

Eight composite beams with realistic dimensions comprising of a universal steel beam and a

concrete slab were tested to failure. Four beams had full shear connection, with the other four

having partial shear connection, and the beams were subjected to a concentrated load applied

at the mid-span of the simply supported beams, whose ends were restrained against twistrotation. Based on the experimental results, the behaviour of the beams was assessed in terms

of member strength, stiffness and ductility. The increase in the torsional moment capacity in

the presence of flexure was also demonstrated and quantified. Beams with partial shear

connection were shown not to experience a reduction in their torsional strength in comparison

with beams with full shear connection.


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Australasian Structural Engineering Conference (ASEC), 2008, Melbourne, Australia

ISBN 978 1 877040 70 2

Paper No 090 Page 2

Effects of Partial Shear Connection of Curved in Plan Composite

Steel-Concrete Beams under Combined Flexure and Torsion

E.L. Tan, B. Uy

University of Western Sydney, Penrith South DC, NSW, Australia

1. Introduction

Composite steel-concrete construction is used extensively in modern buildings and highway

bridges. Their advantages include a higher span/depth ratio, reduced deflections and higher

stiffness ratio than traditional steel or concrete beam structures. Structures such as highway

bridges as shown in Figure 1, interchanges, balconies and edge beams are subjected to combined

flexure and torsion. Currently, there is no rational method to predict the strength capacity of

these forms of composite steel-concrete beams in the Australian Standard (AS 2327.1, 2003) or

other international standards on composite steel-concrete construction such as Euro-Code 4

(British Standard Institute, 1992), British Standard 5950 (BS 5950, 2000) or American Institute

of Steel Construction (AISC, 2006). Moreover, the problem becomes more complex when partial

shear connection (PSC) is used in the design, as it is commonly used to reduce the construction

cost and improve ductility without a great reduction in strength.

Figure 1 Highway bridge (Western Distributor at Darling Harbour, Sydney)

Few studies have been published on the behaviour of composite steel-concrete beams;

additionally partial shear connection has not been addressed in each set of the experimental test

programs as yet. A simplified method for the design of headed shear studs for curved in plan

composite steel-concrete beams has been suggested by Colville (1973). Other papers (Singh and

Mallick, 1977), (Ghosh and Mallick, 1979) and (Ray and Mallick, 1980) indicated that for

composite steel-concrete beams, there could be an increase in the torsional moment capacity in

the presence of flexure and an increase in flexural moment capacity in the presence of torsion.

Nie et al. (2000) later proposed a formula to predict the resistance of composite steel-concrete

beams under flexure and torsion. Thevendran et al. (1999) and (2000) presented both non-linear

analysis and experimental studies on curved in plan composite steel-concrete beams respectively.

The test results indicated that the load-carrying capacity decreased with an increase in thespan/radius of curvature ratio of the curved composite steel-concrete beams. The non-linear


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finite element analysis using the ABAQUS programme in the paper (Thevendran et al., 2000)

was in good agreement with the experimental results in the paper (Thevendran et al., 1999).

Nevertheless, more experimental tests are needed to be carried out to look into other parameters

such as the degree of shear stud connection and span/radius of curvature ratio. This paper has

considered the bending-torsion interaction curve of the composite steel-concrete beams which is

of great practical interest for structural designers.

2. Experimental programme

2.1 Details of test specimens

Eight composite steel-concrete beams CCBF-1, 2, 3, 4 and CCBP-1, 2, 3, 4 were tested as

summarised in Table 1. Each of the specimens was 6.2 m in length and simply supported at a

span of 6 m. The steel beams adopted were universal beam sections of a 200UB29.8 cross-

section. The concrete slab thickness was 120 mm with a width of 500 mm. 19 mm nominal

diameter headed shear studs were used.

Table 1 Details of test specimens

Specimen Beam

Span/

Radius

Radius

(m)

Lever arm

(mm)

Degree of

shear

connection

(%)

Stud section

(19 mm

Studs)

Stud

spacing

(mm)

CCBP-1 Composite 0.275 21.8 220 50 1 460

CCBP-2 Composite 0.294 20.4 235 50 1 460

CCBP-3 Composite 0.455 13.2 362 50 1 460

CCBP-4 Composite 0.634 9.47 502 50 1 460

CCBF-1 Composite 0.291 20.65 232 100 2 460

CCBF-2 Composite 0.303 19.79 242 100 2 460

CCBF-3 Composite 0.424 14.14 338 100 2 460

CCBF-4 Composite 0.632 9.49 501 100 2 460

2.2 Test set-up and loading procedure

A 1000 kN hydraulic jack was used to apply a point load at the mid-span of the test specimens to

induce both flexure and torque to the composite beams as shown in Figure 2. Displacementcontrol was used with a loading rate of 1/80 mm/sec for the first hour. The loading ratio was then

increased progressively until the peak load capacity of the test specimens was reached. The

loading was terminated when either the maximum stroke of the hydraulic jack was attained or

the load reading dropped drastically during the testing.

The test specimens were supported by a roller system at one end and a pinned system at the other

end. An end support arrangement has been set-up at both ends to induce a counter resistance to

the twisting of the composite steel-concrete beams as shown in Figure 2. This prevents the

composite steel-concrete beams from falling off their supports during the testing.


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Figure 2 Photographs of the composite steel-concrete beams

2.3 Material properties

Material tests were conducted to obtain the true strength and mechanical properties of the

components of the test specimens. Concrete cylinders were prepared during the casting for

compressive strength and tensile splitting tests. The average concrete compressive strength at

twenty-eight days of curing was 39 N/mm2, whilst the flexural tensile strength at the beginning

of the testing was 3.3 N/mm2.

Eight steel coupons were cut out from the flange and the web of the steel beams. Five 12 mm

reinforcing bars, five 10 mm round stirrup bars and five shear studs were also tested using a 500

kN INSTRON universal testing machine for tensile tests. The average tensile strength results are

summarised in Table 2 below.

Table 2 Structural steel tensile test results

Steel

flange

Steel

web

Shear

stud

Reinforcing bar

N12

Round stirrup bar

R10

Yield stress (N/mm2) 350 375 400 584 380

Ultimate stress (N/mm2) 493 510 498 684 503

2.3 Push-out tests

Push-out tests provide the load-slip characteristics of the shear studs that were used in the

composite steel-concrete beams. Push-out test specimens CCBPT-F1 and CCBPT-F2 were

designed to represent the full shear connection of the composite steel-concrete beams, whilst

CCBPT-P1 and CCBPT-P2 represented the partial shear connection of the composite steel-

concrete beams. Based on the tests, the ultimate shear strength was averaged to be 138 kN per

shear stud. The average slip capacity was 13 mm. From the tests, we can conclude that there

was no significant difference in the behaviour of the shear studs for full shear or partial shear

arrangement.


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3. Experimental results and discussion

3.1 Moment-curvature response

The moment-curvature curves for all eight composite steel-concrete beams are illustrated in

Figure 3 below. All measurements have been taken from the mid-span of the test specimens.

Moment-Curvature Diagram at Mid-span

0

50

100

150

200

250

0 10 20 30 40 50 60 70

Curvature x 106(mm

-1)

Moment(kNm)

CCBF-1

CCBF-2

CCBF-3

CCBF-4

CCBP-1

CCBP-2

CCBP-3

CCBP-4

Figure 3 Moment-curvature diagram for composite steel-concrete beams

From the moment-curvature curves, composite steel-concrete beams with lower span/radius ofcurvature ratio had higher flexural moment capacities than those with a higher ratio. For

example, CCBF-4 achieved 46 % of the flexural moment capacity of the CBPF-1; CCBP-4

achieved 45 % of the flexural moment capacity of CCBP-1. These results show that ultimate

flexural moment capacity decreases with an increase in the span/radius of curvature ratio.

Moreover, with the increase of the span/radius of curvature ratio, the failure mode changes from

flexure to the combined action of flexure and torsion.

From Figure 3, the flexural moment capacity of the composite steel-concrete beams with partial

shear connection had a similar or slightly higher value than those with full shear connection

when the span/radius of curvature ratio is lower. For example, CCBP-3 achieved 108 % of theflexural moment capacity of the CBPF-3; CCBP-4 achieved 114 % of the flexural moment

capacity of CCBF-4. A possible reason could be that the degree of shear connection has less

influence on the flexural moment capacity when the main failure mode is due to the combined

action of flexure and torsion.


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3.2 Torque-twist response

Torque-Twist Diagram

0

5

10

15

20

25

30

35

40

0 20 40 60 80 100 120 140 160 180

Twist (mRad)

Torque(kNm)

CCBF-1

CCBF-2

CCBF-3

CCBF-4

CCBP-1

CCBP-2

CCBP-3

CCBP-4

Figure 4 Torque-twist diagram for composite beams

The torque-twist diagram for all eight composite steel-concrete beams has been illustrated in

Figure 4. The torque capacities for all composite steel-concrete beams seemed to hover around

the 34-40 kNm mark. Since the readings were similar, we can conclude that all composite steel-

concrete beams could have reached their maximum torque capacities at failure. However, every

composite steel-concrete beam had a different level of twist in the diagram.

All composite steel-concrete beams with full shear connection except for CCBF-2 had achieved

a similar torque capacity of 24 kNm. CCBF-2 had obtained the highest torque capacity of 33

kNm. For composite steel-concrete beams with partial shear connection, their torque capacities

were similar from a range of 25-29 kNm. Their twist angle varied from 15-100 mRad.

Composite steel-concrete beams with a higher span/radius of curvature ratio tend to have a

higher twist angle than those with a lower ratio. This is normal, since the composite steel-

concrete beams with higher ratio were subjected to torque earlier than those with a lower ratio.

3.3 Interface slip

Using linear variable differential transducers (LVDTs), the interface slip between the concrete

slab and the top steel flange was measured during the tests. These measurements were taken at

the support ends of the composite steel-concrete beams where the interface slip was the highest.

Relative slip was recorded when the maximum applied load was reached during the tests. All

these measurements are summarised in Table 3.


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Table 3 Average interface slips

Relative

interface

slip (mm)

Maximum

interface

slip (mm)

CCBF-1 1.3 2.7

CCBF-2 2.4 2.7

CCBF-3 0.8 1.1

CCBF-4 1.1 3.4

CCBP-1 6.9 7.3

CCBP-2 2.3 2.7

CCBP-3 0.9 1.0

CCBP-4 0.7 1.6

As expected, the overall slip measurements from the composite steel-concrete beams with full

shear connection were much lower than those with partial shear connection. The relativeinterface slip for composite steel-concrete beams with full shear connection and partial shear

connection registered an average 1.4 and 2.7 mm respectively. Higher interface slip is required

for the composite steel-concrete beams with partial shear connection where flexural moment

capacity is required. For example, CCBP-1 reached a relative interface slip of 6.9 mm compared

with that of 1.3 mm for CCBF-1.

3.4 Bending-torsion interaction

Interaction Diagram

Colville (1973)Concrete Slab

Nie (2000)

Ray and Mallick(1980)

Steel Beam

CCBF

CCBP

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0 0.2 0.4 0.6 0.8 1 1.2

M / Mu

T/Tu

Figure 5 Bending-torsion interaction diagram

Figure 5 shows the interaction curves of CCBF and CCBP test specimens compared with the

interaction curves suggested by Colville (1973) and other researchers. Colvilles (1973)

Equation (1) could be used to provide a lower bound interaction relationship for composite steel-

concrete beams as shown in Figure 5.


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1

22

=

+

UU T

T

M

M (1)

M = Flexural moments at failure in test

MU = Theoretical values of ultimate flexural momentsT = Torsional moments at failure in test

TU = Theoretical values of ultimate torsional moments

From Figure 5, both CCBF and CCBP curves have illustrated that there is no significant increase

in flexural moment capacity in the presence of torsion. However, there is a significant increase in

torsional moment capacity in the presence of flexure.

3.5 Modified bending-torsion interaction models

Based on the experimental test results, bending-torsion interaction models are suggested for

curved in plan composite steel-concrete beams with full and partial shear connections. The

interaction equations can be written as follows:

For full shear connection,

17.0 +

=

UU MM

TT when 10


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5. Acknowledgements

The authors would like to acknowledge the Australian Research Council Discovery Project for

the support of this project. The authors would also like to thank Messrs Bridge, Grant, Rowlan,Knust and Laird from the University of Wollongong for their assistance during the tests. Lastly,

the author would like to acknowledge Mr Kaewunruen for his support during the tests as well.

6. References

American Institute of Steel Construction. AISC steel construction manual. American Institute of

Steel Construction; 13 ed; 2006.

British Standards Institution, BS 5950-1-2000. Structural use of steelwork in building. Code of

practice for design. Rolled and welded sections. BSI Standards; 2000.

British Standards Institution. Euro-Code 4: design of composite steel and concrete structures,part 1.1 general rules and rules for buildings, DDENV 1994-1-1. European Committee for

Standardisation (CEN); 1992.

Colville J. Tests of curved steel-concrete composite beams. Journal of the Structural Division,

ASCE 1973;99:1555-1570.

Nie J, Luo L, Hu S. Experimental study on composite steel-concrete beams under combined

bending and torsion. Composite and Hybrid Structures 2000;2:631-638.

Ray MB, Mallick SK. Interaction of flexure and torsion in steel-concrete composite beams. The

Indian Concrete Journal 1980;54:80-83.

Standards Australia. Australian Standard AS 2327.1-2003 Composite structures, Part 1: Simply

supported beams. Standards Australia International Ltd; 2003.Thevendran V, Chen S, Shanmugam NE, Richard Liew JY. Experimental study on steel-concrete

composite beams curved in plan. Engineering Structures 2000;22:877-889.

Thevendran V, Chen S, Shanmugam NE, Richard Liew JY. Nonlinear analysis of steel-concrete

composite beams curved in plan. Finite Elements in Analysis and Design 1999;32:125-139.

Documents

Effects of Partial Shear Connection of Curved in Plan Composite Steel-concrete Beams Under Combined Flexure and Torsion-libre