Steel Designers Manual - TheBestFriend.org

This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007
To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/
Steel Designers' Manual - 6th Edition (2003)
a a
a
a
overlap
(a) (b)
cover width of decking
C b b_______
Fig. 21.16 Potential failure planes through slab in longitudinal shear
the decking is continuous over the beams, as in Fig. 21.3(a), or rigidly attached by
shear-connectors, there is no test evidence of the splitting mode of failure. It is
assumed, therefore, that the deck is able to provide an important role as transverse
reinforcement. The term Arfy may be enhanced to include the contribution of the
decking, although it is necessary to ensure that the ends of the deck (butt joints)
are properly welded by shear-connectors. In this case, the anchorage provided by
each weld may be taken as 4f tspy, where f is the stud diameter, ts is the sheet thickness,
and py is the strength of the sheet steel. Dividing by the stud spacing gives the
equivalent shear resistance per unit length provided by the decking.
Where the decking is laid parallel to the beams, longitudinal shear failure can
occur through the sheet-to-sheet overlap close to the line of studs. Failure is assessed
assuming the shear force transferred diminishes linearly across the slab to zero at
a distance of Bc/2. Therefore, the effective shear force that is transferred across the
longitudinal overlaps is (1 – cover width of decking/effective breadth) ¥ shear force.
The shear resistance at overlaps excludes the effect of the decking.
To prevent splitting of the slab at edge beams, the distance between the line of
shear-connectors and the edge of the slab should not be less than 100 mm. When
this distance is between 100 mm and 300 mm, additional reinforcement in the
form of U bars located below the head of the shear-connectors is to be provided. 12
No additional reinforcement (other than that for transverse reinforcement) need
be provided where the edge of the slab is more than 300 mm from the shearconnectors.
21.7.7 Interaction of shear and moment in composite beams
Basic design 623
Vertical shear can cause a reduction in the plastic moment resistance of a composite
beam where high moment and shear co-exist at the same position along the beam