Concrete haunch width (Composite beams: EC4 Eurocode)
The concrete haunch (i.e. the concrete within the trough adjacent to the stud) plays a major role in the interaction with the shear connectors. It's shape will depend on whether the decking is trapezoidal or re-entrant.
In Tekla Structural Designer, when decking ribs are parallel to the beam, by default it is assumed that the decking is continuous and the studs are site welded. As a result the haunch width b0 is automatically calculated from the re-entrant or trapezoidal decking profile per EN 1994-1-1:2004 Figure 9.2 as shown below:
If the studs are shop welded, so the decking has to stop and start, you are allowed to increase the haunch width as per EN 1994-1-1:2004 clause 6.6.4.1.
For parallel decks this increased b0 dimension gives a significantly increased shear stud capacity, which is beneficial for achieving the required minimum shear interaction.
-
Under 'Floor construction', set the 'Welding condition' to 'Shop welded'.
The effect of this is to set the decking to be discontinuous over the supporting beam.
-
Under 'Metal deck', set the 'Haunch width above beam for parallel decking, b0' to the width required.
The default b0 is the deck trough width as defined in the program's metal decking database.
- Minimum value of 1 * stud diameter
- Maximum value of MIN[2 * bf , bf + b2] for re-entrant decking
- Maximum value of MIN[2 * bf , bf + b1] for trapezoidal decking
Where, bf is the composite beam flange breadth, and b1 and b2 are the maximum width of rib values given in the decking properties.