Civil Engineering Reference
In-Depth Information
Almost the whole of Chapter 3, on simply-supported beams and slabs,
applies equally to the sagging moment regions of continuous members.
The properties of hogging moment regions of beams are treated in Section
4.2, which applies also to cantilevers. Then follows the global analysis of
continuous beams and the calculations of stresses and deflections.
Both rolled steel I- or H-sections and small plate or box girders are con-
sidered, with or without web encasement and composite slabs. It is always
assumed that the concrete slab is above the steel member, because the use
of slabs below steel beams with which they are composite is rare in build-
ings, though it occurs in bridges. The depth of a beam can be reduced by
partial embedment of the steel section within the concrete slab [37].
The use of precast or prestressed concrete floor slabs in composite
frames provides an alternative to composite slabs [38]. It is outside the
scope of this topic.
4.2
Hogging moment regions of continuous
composite beams
4.2.1
Classification of sections, and resistance to bending
4.2.1.1
General
Section 3.5.1, on effective cross-sections of beams, is applicable, except
that the effective width of the concrete flange is usually less at an internal
support than at mid-span. This width defines the region of the slab where
longitudinal reinforcement may be assumed to contribute to the hogging
moment of resistance of the beam. The plastic neutral axis always lies
below the slab, so the only contribution from concrete in compression is
from the web encasement, if any.
In EN 1994-1-1, the effective width in hogging bending is as explained
in Section 3.5.1, except that the effective span
L
e
is
the approximate
length of the hogging moment region, which can be taken as one-quarter
of each span. So at a support between spans of length
L
1
and
L
2
, Equation
3.55 for effective width of a T-beam with pairs of stud connectors at
lateral spacing
b
0
becomes
b
eff
=
[(
L
1
+
L
2
)/4]/4
+
b
0
=
(
L
1
+
L
2
)/16
+
b
0
(4.1)
provided that at least
b
eff
/2 is present on each side of the web. There is a
different rule for cantilevers.
The rules for the classification of steel elements in compression
(Section 3.5.2) strongly influence the design of hogging moment regions.
