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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.

www.ijsret.org

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

www.ijsret.org

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

Volume 4, Issue 3, March 2015

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

Poissons ratio(m) 0.2

Tensile strength 2.317 MPa

Compressive strength -25.5 MPa

Specific weight () 23 kN/m3

Coefficient of thermal expansion() 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

Poissons ratio(m) 0.