Flexural Behaviour of Segmental Composite Skew Slabs with Truss Shear Connector

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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.

Text of Flexural Behaviour of Segmental Composite Skew Slabs with Truss Shear Connector

  • 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.