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Transverse reinforcement for composite beams
Posted on in Composite design

In composite beams, the longitudinal shear connection between the steel and the concrete parts is provided by shear connectors. But how can we prevent the transferred longitudinal force from the shear connectors from splitting the concrete flange?

The longitudinal shear resistance of the concrete flange must be checked to ensure that the force from the shear connectors can be transferred into the slab. It might require transverse reinforcement.

To determine the longitudinal shear resistance, Eurocode 4 states that the rules of Eurocode 2 for reinforced concrete slabs should be used. The relevant shear failure surfaces determined by the Eurocode 4 are shown below for concrete slabs with sheeting.

Calculating transverse reinforcement in composite beam to Eurocode 4

The practical solution is to make the studs high enough for type ‘a’ or ‘d’ to govern.
The effective transverse reinforcement for the shear failer surfaces above is the following:

Effective transverse reinforcement area in composite beams

Both top and bottom reinforcement play an essential role in preventing splitting of the concrete.

The decking may also be part of the transverse reinforcement, but needs to be adequately anchored and the ribs of the decking must run perpendicular to the beam.

Using the model given in the Eurocode 2 in which the flange is considered to act as a system of compressive struts combined with a system of ties from the transverse reinforcement, the design shear strength of the concrete flange can be determined with the following expression:

where

Asf is the area of effective reinforcement for the failure surfaces

sf is the spacing of the reinforcement bars

vEd is the design value of the transverse shear force

hf is the depth of the flange

θf is the angle of dispersion of the force from the shear connector

Position of the mesh

However, the transverse reinforcement may affect the resistance of the shear studs as well.

As reported in NCCI PN001a-GB test results, the resistance for shear studs in transverse trapezoidal sheeting is not only depended on the number of the studs but on the position of the mesh as well.

Effect of the reinforcement on the resistance of the shear studs

They have introduced a reduction factor (kmod) additional to the solid slab reduction factor (kt).


Click HERE to read more about calculating the design resistance of a headed shear stud in our previous blog post.

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