Advisory Desk
AD 437: Curtailment of transverse bar
reinforcement in composite beams with
steel decking designed using Eurocodes
The purpose of this Advisory Desk Note is to
provide guidance on the curtailment of transverse
bar reinforcement in slabs on composite beams
with steel decking, designed to EN 1994-1-1. Such
information was previously presented in AD 325,
for design to BS 5950-3.1, but the provisions
in EN 1994-1-1, and the clauses in EN 1992-1-1
to which it refers, give more explicit coverage
of this topic than the BS rules. The approach to
transverse bar curtailment is therefore different.
The transverse reinforcement is provided
to transfer longitudinal shear force from the
steel beam, via the shear connectors, out into
the effective breadth of the slab. Transverse bar
reinforcement may be needed to supplement the
resistance of the mesh in the slab, and these bars
must extend a sufficient distance from the beam
centreline.
Internal beams
A fundamental difference between EN 1994 and
BS 5950 is that the former adopts a so-called ‘strut
and tie’ model, through which shear resistance is
determined from consideration of concrete struts
in compression and reinforcement ties in tension.
A component of the force in the struts resists
longitudinal force in the slab, and the component
transverse to the beam axis is resisted by the
reinforcement.
For composite beams with decking spanning
perpendicular to the longitudinal axis of the
beam, the critical transverse shear plane is
adjacent to the steel flange. However, for decking
running parallel to the beam the critical plane is
normally in the nearest crest in the decking to the
shear connectors (see Figures 1 and 2).
When considering the need for bar anchorage
beyond these critical planes, for design to
BS 5950, AD 325 made certain assumptions (with
both a simplified and rigorous model) about how
the force in the slab decreases across the effective
width. The Eurocodes remove the need for such
assumptions by providing explicit guidance:
1. EN 1994-1-1, 6.6.6.2 makes reference to
2. EN 1992-1-1, 6.2.4 (7) states that the
3. EN 1992-1-1, 8.4.4 defines how to
With reference to Point 2, determining the
location that corresponds to ‘beyond the strut
requirement’ is not obvious, particularly given
that different angles can be chosen for the
28 NSC
EN 1992-1-1, 6.2.4
reinforcement should be anchored beyond
the strut requirement (see EN 1992-1-1,
Figure 6.7)
determine anchorage length
Feb 20
12 d
struts in what can be an iterative procedure.
As a (slightly) conservative simplification, the
point beyond which anchorage is needed may
be assumed to be the critical planes, as defined
above. This also results in an approach that is
common to that used in design to BS 5950.
Point 3 refers to clauses that consider the
tensile strength of the concrete, the strength
of the reinforcing bars, and a number of other
parameters. For typical bars in typical concrete
the result will be a need for an anchorage length
similar to the familiar value of 40 d (where d is
the bar diameter). When lightweight concrete
is used greater anchorage lengths are required,
as a function of the concrete oven-dry density
(see EN 1992-1-1, 11.3.1). Should larger bars be
chosen than are necessary, such that they are
stressed below yield, shorter anchorage lengths
will suffice.
Although the Eurocode methodology makes
no reference to the effective breadth of slab in
the context of transverse shear resistance, this
nevertheless remains an area of concrete subject
to significant in-plane stresses. In the absence of a
more rigorous analysis where a number of planes
are considered rather than just the critical plane
(which would most likely show that mesh alone
is sufficient in the outer reaches of the effective
breadth), we therefore recommend that the bars
extend at least 12 d beyond the effective breadth.
This is also in keeping with BS 5950 practice
(AD 325 Simplified Method)
It is important to note that when the decking
is perpendicular it may contribute to the
transverse reinforcement needed, but when the
decking is parallel it cannot be taken into account
(it has no ‘in-plane’ tensile resistance so cannot
contribute in a strut and tie model).
Edge beams
Notwithstanding differences in the definition of
anchorage length, EN 1994-1-1, 6.6.5.3 contains
detailing guidance for edge beams that aligns
with that given in BS 5950-3.1:
• If the edge of slab from the centreline of the
nearest shear connectors is less than 300 mm
then place U-bars around the shear connectors
• Where headed studs are used, the U-bars must
have a diameter not less than half that of the
studs, and the distance from the edge of the
slab to the centreline of the nearest studs
should not be less than 6 ds (where ds is the
stud diameter)
Contact: Eleftherios Aggelopoulos
Tel: 01344 636555
Email: advisory@steel-sci.com
Critical plane
adjacent to ange
of steel beam
Eective breadth of slab
40 d (NWC)
12 d
40 d (NWC)
Eective
concrete ange
Decking spanning
perpendicular to beam
Reinforcing bars,
diameter d
(bars spaced
ideally at multiples of
stud spacing)
Applied
longitudinal
shear
Figure1: Assumed pattern of transverse shear stresses and anchorage lengths, beam with transverse decking
Critical plane
for deck spanning
parallel to beam
Figure2: Critical plane for deck spanning parallel to beam
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/Welding#Drawn_arc_stud_welding.2C_process_783
/Composite_construction#Types_of_composite_beam
/Design_codes_and_standards#Introduction_to_Eurocodes
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