Flexural Behaviour of Segmental Composite Skew Slabs with Truss Shear Connector

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239 International Journal of Scientific Research Engineering & Technology (IJSRET), ISSN 2278 – 0882

Volume 4, Issue 3, March 2015

Flexural Behaviour of Segmental Composite Skew Slabs with

Truss Shear Connector

S. Dhanush1, K. Balakrishna Rao

2

1 Post Graduate Student, Structural Engineering, Department of Civil Engineering,

Manipal Institute of Technology, Manipal 2 Professor, Department of Civil Engineering, Manipal Institute of Technology, Manipal

ABSTRACT

In the recent times, use of concrete-concrete composite

slabs as bridge decks has become a common practice,

mainly due to the ease of construction and considerable

reduction in use of form work and labour. Most of the

recent designs for bridge decks are often skew, skew

shape of the slab facilitates a large variety of options for

an engineer in terms of alignment opportunities in case

of obstructions. Composite action of two concrete

members is achieved by the interface shear transfer

between the two members, this mechanism is of great

significance. The interface shear carrying capacity is

dependent on the surface properties and shear connectors

provided. In the present study we try to determine the

influence of truss shaped shear connectors on the

flexural load carrying capacity of slabs having various

degrees of skew-ness. Four series of slabs are modelled,

each corresponding to a certain degree of skew-ness,

each series in turn is sub-classified into sub-series based

on the number of shear connectors, and their layout.

Results show that the load carrying capacity of the slab

decreases as the angle of skew-ness increases, and the

load carrying capacity of all slabs increases as the

number of shear connectors in the longitudinal direction

increases. Shear connectors when provided in transverse

direction does not seem the influence the behaviour of

the slab. However, when transverse shear connectors are

provided along with longitudinal connectors the

behaviour improves slightly.

Keywords - Truss shear connector, Composite slab,

ATENA, Slab flexure test, Interface shear capacity.

I. INTRODUCTION

In view of infrastructure requirements across the country and

the emphasis for accelerating construction of bridges with a

view to reduce total construction time and minimize traffic

disruption, the fast construction of bridges using precast

segmental concrete-concrete composite construction has

assumed significance. In such a scenario, precast stay-in-place

deck panels would eliminate the need for form work and

staging which are main causes for traffic disruptions. The

remaining portion of the deck slab can be cast in place. Precast

slab that acts initially as a formwork is connected compositely

with in-situ concrete segments using shear connectors in order

to develop the required bending and shear resistance resulting

in composite slab.

In order for the composite slabs to exhibit monolithic

behaviour, the composite interface bond must remain intact. If

the bond is strong, the composite member will behave as a

single member when loaded as shown in Figure 1. and deform

similar to a solid member. The fully bonded interface lets the

horizontal shear developed to be transferred along the

interface. The complete composite behaviour is shown in

strains varying almost completely linear across the depth of

the slab as shown in Figure. 2(a).

Figure 1. Composite slab

(a) (b) (c)

Figure 2. Elastic behaviour of composite slabs,

(a) Fully composite, (b) Non-composite, (c) Partially

composite.

Most of the recent designs for bridge decks are often skew,

skew shape of the slab facilitates a large variety of options for

an engineer in terms of alignment opportunities in case of

obstructions, the behaviour of a skew slab is different from

that of a rectangular slab in a lot of ways, in the present study

skew slabs are analysed and compared to a square slab.

Benoyane et al [1]

(2008) studied the flexural behaviour of pre-

cast concrete sandwich composite panel having truss type

shear connector. The flexural test results showed that the

precast specimens had a load deflection profile similar to that

of one way and two way slab. The difference in load is less

than 4 %, when finite element result is compared to

experimental result of one way specimen. The difference in

deflection during elastic stage is less than 1.5 %. Therefore,

Finite element studies of the flexure test correlated with the

experimental values. Finite element studies were carried out

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by varying number of shear connectors for the one way slab

specimen. It was observed that increasing the number of shear

connector increases the ultimate load of the specimen.

Thanoon et al [2]

(2010) studied the structural behaviour of

ferrocement and brick composite slab panel. The slab is made

of two layers (precast ferrocement and brick mortar) joined

together using truss connectors. The slab was simply

supported and two line loads were created by applying load

through hydraulic jack. The peak load is about 30% of the

ultimate load. The concrete rib enhances the ductility of the

slab. The specimen with triple shear connector showed higher

experimental load. The increase in the number of shear

connector increased the compositeness, thereby increased the

load carrying capacity of the member.

Gowthami [3]

(2014) studied the effects of different types of

shear connectors on one way and two way composite slabs

and found that two way slabs take much higher loads

compared to one way slabs for a given configuration of shear

connectors and that diameter of the bars does not have much

of a difference in the results of a one way slab, but shows

certain effects in the load carrying capacities of a two way

slab.

Sanjay Kumar [4]

(2013) performed numerical and

experimental analysis on skew RCC slabs with centre point

loading and compared the values. They concluded that slabs

with length of the shorter diagonal smaller than span are

favourable to the slabs in which length of the shorter diagonal

is greater than span, since the uplifts are lesser.

A Kabir et al [5]

(2002) studied the influence of reinforcement

pattern on the load carrying capacity simply supported skew

slabs and concluded that when reinforcement is provided

parallel to the edges is widely adopted due to ease in

fabrication and the ultimate load is not much lesser compared

to other patterns.

The authors in their previous study [6][8]

have studied the

effects of the size and shape of the truss connector on the

flexural load carrying capacity using beam models. It is found

that angles of inclination between 60o and 75

o show the best

results, it is also found that the influence of diameter of the

connector and depth of embedment is almost negligible.

II. NON LINEAR FINITE ELEMENT ANALYSIS

ATENA, a nonlinear finite element analysis software was

employed to analyse the flexural load carrying capacity of the

composite slabs. In ATENA, the interface parameters between

materials can be modelled to a great level of detail. Numerical

analysis would be very much helpful, to simulate the

experimental results. It helps to reduce the number of

experiments to be conducted.

In ATENA, steel plates are used as bearings where there is

a need to apply loads and supports, this is to eliminate the

influence of localization of stresses at immediate region under

the point of application. The mesh size adopted is 50mm and

brick elements are used for concrete modeling, whereas

tetrahedral elements are used for steel plates. The type of

solution adopted is modified Newton-Raphson method, to

optimize the node numbers Sloan iterations are used. The

stiffness used is the tangent stiffness and the values of the

stiffness is updated after each iteration. The number of

iterations under each load step is limited to 40.

The models are analysed under load controlled method,

the post peak behaviour is not studied. Displacement

controlled analysis is not performed.

Material modeling

The input properties for the different materials are as

described below:

Concrete

Concrete is modelled as 3D-Nonlinear cemetitious material,

with the following properties

Cube Strength (fcu) 30 MPa

Elastic modulus (E) 3.032 x 104 MPa

Poisson’s ratio(m) 0.2

Tensile strength 2.317 MPa

Compressive strength -25.5 MPa

Specific weight (ρ) 23 kN/m3

Coefficient of thermal expansion(α) 1.2 x 10-5

/K

Steel

Steel plates are used as bearings under supports and loads

only. It is modelled as a 3D-elastic-isotropic material, with

following properties

Elastic modulus (E) 2 x 105 MPa

Poisson’s ratio(m) 0.3

Specific weight (ρ) 78.5 kN/m3

Reinforcement

Reinforcement bars are modelled as reinforcement elements

with bilinear, elasto-plastic behaviour, with the following

properties

Elastic modulus E 2.1 x 105 MPa

Yield strength (fy) 415 MPa

Specific weight (ρ) 78.5 kN/m3

Coefficient of thermal expansion(α) 1.2 x 10-5

/K

Concrete-Concrete Interface

The interface region between the two concrete elements is

modelled using 3D-interface model with following properties

Normal stiffness 2 x 105 kN/m

3

Tangential stiffness 2 x 105 kN/m

3

Cohesion 0

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Geometric modeling

All the slabs have a constant width and span of 1m and

depth of 100 mm. The skew angle of the slab is varied as

shown in the Figure 6. The values assigned to θ are 0o (square

slab), 30o, 45

o, 60

o. The slab is simply supported on opposite

sides and is reinforced with 5 bars of 8mm at a spacing of 240

mm in both longitudinal and transverse directions. Same

reinforcement is provided at the top as well. In both cases

effective cover given is 15mm. In case of composite slab two

slabs of 50mm depth are modelled one above the other with an

interface layer. The depth of embedment of the shear

connector is between the top and the bottom reinforcement i.e.

70mm. The slab is loaded with line loads of 4kN per step for

all steps at the 1/3rd

span of the slabs in the transverse

direction.

(a)

(b)

Figure 3. (a) Solid slab (b) Composite slab

Figure 4. Square slab showing supports and loading

Figure 5. Typical slab showing supports, loading,

reinforcements and shear connector.

Figure 6. Typical slab showing supports

(all dimension in mm)

Figure 7. Truss type shear connector with 60o inclination,

70mm depth of embedment and 8mm diameter

III. RESULTS AND DISCUSSION Table1: Nomenclature for slab models

Solid Full depth solid slab

Non-

Composite

Two-half slabs, without any shear

connector

2L Two connectors in longitudinal

direction

3L Three connectors in longitudinal

direction

2T Two connectors in transverse direction

3T Three connectors in transverse

direction

2L-2T Two connectors in both direction

3L-3T Three connectors in both direction

Results and discussions for 0o slab

Figure 8. Load v/s Deflection graph for solid and non-

composite slab for θ = 0o

Figure 8. shows the load v/s deflection behavior of the solid

slab when compared with a non composite slab for a sqaure

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slab. From the figure it is seen that the load carrying capacity

of non- composite slab is much lower than solid slab. This is

due to the absence of monolithic action between the two

composite members in the non-composite slab.

Figure 9. and Figure 10. show the load v/s deflection for 0

degree slab with shear connectors in transverse and

longitudinal directions respectively. It is evident that shear

connectors when provided in transverse directions does not

improve the behaviour in anyway, whereas in longitudinal

direction they increase the load carry capacity to a great

extent, when two connectors are provided in longitudinal

direction, it is as good as a solid slab, when three connectors

are provided the load carrying capacity is much higher than

the solid slab itself.

Figure 9. Load v/s Deflection graph for slabs with connectors

in transverse direction only for θ = 0o

Figure 10. Load v/s Deflection graph for slabs with

connectors in longitudinal direction only for θ = 0o

Figure 11. shows the load v/s deflection comparison of

composite slabs, when shear connectors are provided in both

longitudinal and transverse directions. When compared to

Figure 9. It can be seem that transverse connectors when

provided independently do not affect the load carrying

capacity, however when provide along with longitudinal

connectors it does improve the behaviour slightly.

Figure 14. and Figure 15. show the load v/s deflection for 30

degree slab with shear connectors in transverse and

longitudinal directions respectively. When compared to the 0

degree slab, it can be seen that the load carrying capacity has

decreased. However, the rest of the behaviour is similar.

Transverse connectors have no much influence; longitudinal

connectors improve the load carrying capacity.


connectors in both the directions for θ = 0o

Figure 12. Load v/s Deflection graph for all the slabs for θ =

0o


Transverse connectors when provided with longitudinal

connectors improve the behaviour slightly, Figure 16. It must

also be noted that the window between the solid and non-

composite slab is reduced when compared to 0 degree slab as

seen in Figure 13.

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composite slab for θ = 30o


connectors in transverse direction only for θ = 30o


connectors in longitudinal direction only for θ = 30o


connectors in both the directions for θ = 30o

.

Figure 17. Load v/s Deflection graph for all the slabs for θ =

30o

Figure 12, Figure 17, Figure 22 and Figure 27. shows the load

v/s deflection comparison of all the slabs for 0 degree, 30

degrees, 45 degrees and 60 degrees respectively. By

compassion it can be seen that, irrespective of the degree of

skew-ness of the slab, the general trend is the same. Solid

slabs performs much better than a Non-Composite slabs. It has

a much higher failure load. Transverse connectors do not alter

the load carrying behaviour; longitudinal connectors improve

the behaviour significantly. Transverse connectors when

provided along with longitudinal connectors does improve the

load carrying capacity, although not significantly


Figure 18. shows the load v/s deflection for solid and

non-composite slab for 45 degrees slab. Figure 19, Figure 20,

and Figure 21. shows the load v/s deflection comparison for

45 degree slab when connectors are provided in transverse

direction, longitudinal direction and both transverse and

longitudinal directions respectively. Here again, the behaviour

is similar, as for 0 degree slab and 45 degree slab, however the

load carrying capacity has further reduced

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composite slab for θ =45o


connectors in transverse direction only for θ =45o

.


connectors in longitudinal direction only for θ =45o


Behaviour of 60 degree slab is very similar to that of all

the other slabs, except the load carrying capacity has reduced

to a great extent; the window between the solid and the non-

composite slab has reduced. Figure 23. shows the load v/s

deflection for

solid and non-composite slab for 45 degrees slab. Figure 24,

Figure 25, and Figure 26. shows the load v/s deflection

comparison for 60 degree slab when connectors are provided

in transverse direction, longitudinal direction and both

transverse and longitudinal directions respectively.


connectors in both the directions for θ =45o

Figure 22. Load v/s Deflection graph for all the slabs for θ

=45o


composite slab for θ =60o

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connectors in transverse direction only for θ =60o


connectors in longitudinal direction only for θ =60o


connectors in both the directions for θ =60o

Figure 27. Load v/s Deflection graph for all the slabs for θ

=60o

Ansuman [7]

(2012) studied the influence of angle of skew

ness on the performance of skew bridges. It was found that

when the length of the shorter diagonal was less than the span

of the slab it behaved like a one-way slab and when length of

shorter diagonal was larger than the span it behaved like a

two-way slab and Gowthami [3]

(2014) studied the effects of

different types of shear connectors on one way and two way

composite slabs and found that two way slabs take much

higher loads compared to one way slabs for a given

configuration of shear connectors.

Figure 28. Load v/s Deflection graph for all the solid slabs for

different values of θ

In our present study all the slabs except the 0 degree

slab have length of shorter diagonal less than span of the slab,

the reduction in the load carry capacity can be explained due

to this. For better understanding and for comparison the load

v/s deflection results for solid slab, slabs with 2 longitudinal

shear connectors and 3 longitudinal shear connectors are

plotted in Figure 28, Figure 29 and Figure 30 respectively. It

can be seen that irrespective of the configuration or the

presence of shear connectors for a given type of slab the load

carrying capacity decreases as the angle of skew-ness of the

slab increases.

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Figure 29. Load v/s Deflection graph for all slabs with 2L

connectors for different values of θ

Figure 30. Load v/s Deflection graph for all slabs with 3L

connectors for different values of θ

IV. CONCLUSIONS

a) The load carrying capacity of the slabs decreases as the

angle of skew-ness of the slab increases.

b) The load gap between the solid and the non-composite

slab decreases as the angle of skew-ness of the slab

increases.

c) In a slab, shear connectors provided in the transverse

direction does not improve the behaviour in any

significant way.

d) As the number of connectors in the longitudinal direction

is increased, the load carrying capacity of the slab also

increases.

e) Transverse connectors when provided with longitudinal

connectors influence the load carrying behavior,

increasing it slightly.

V. ACKNOWLEDGMENTS

The authors would like to express their sincere thanks to The

Director, and H.O.D, Civil engineering, Manipal Institute of

Technology, Manipal, for providing necessary facilities

required for the present study and also express their deepest

gratitude towards the Department of civil engineering, BMS

College of Engineering, Bangalore, for letting us avail the

facilities of the software ATENA.

REFERENCES

[1] Benoyane, A.A. Abdul Samad, D.N. Trikha, A.A. Abang

Ali, S.H.M. Ellinna, “Flexural Behavior of pre-cast

concrete sandwich composite panel – Experimental and

theoretical investigations”, Construction and Building

Materials, 2008, 22, PP 580-592.

[2] Waleed A. Thanoon, Yavuz Yardim, M.S. Jaafar, J.

Noorzaei, “Development of interlocking mechanism for

shear transfer in composite floor ”, Construction and

Building Materials, 2010, 24, PP 2604-2611.

[3] N. R. Gowthami, K. Ramanjaneyulu “Segmental

Composite Bridge Decks”, MTech Thesis, JNTU

Ananthapur, 2014.

[4] Sanjay Kumar, “Finite Element Modelling of Skew Slab

With Edge Supports”, MTech Thesis, Thapar University,

Patiala, July-2013

[5] A Kabir, S M Nizamud-Doulah, M Kamruzzaman,

“Effective Reinforcement Layout For Skew Slabs”, 27th

Conference on our World in Concrete & Structures: 29 -

30 August 2002, Singapore, PP. 271-276

[6] S. Dhanush , K. Balakrishna Rao, “Truss Type Shear

Connectors Used in Segmental Composite Slab”,

Proceedings of The International Conference on

Advances in Civil Engineering Materials and Processes,

Coimbatore, Jan-2015

[7] Ansuman kar, Vikash Khatri, P. R. Maiti, P. K. Singh,

“Study on Effect of Skew Angle in Skew Bridges”,

International Journal of Engineering Research and

Development, Volume 2, Issue 12 (August 2012), PP. 13-

18

[8] S. Dhanush , K. Balakrishna Rao, “Behaviour of

Segmental Composite Skew Slabs Subjected to Flexure

Loading”, Proceedings of The National Conference on

Technological Innovations for Sustainable Infrastructure,

National Institute of Technology, Calicut, March-2015

Documents

Flexural Behaviour of Segmental Composite Skew Slabs with Truss Shear Connector