Civil Engineering Reference
In-Depth Information
Figure 3.14
Class boundaries for webs, for f
y
=
355 N/mm
2
shear connection (Section 3.5.3.1) is used. Even then,
is sufficiently
small for the web to be in Class 1 or 2. (This may not be so for the much
deeper plate or box girders used in bridges.)
During construction of a composite beam, the steel beam alone may be
in a lower slenderness class than the completed composite beam, and may
be susceptible to lateral buckling. Design for this situation is governed by
EN 1993-1-1 for steel structures.
α
3.5.3
Resistance to sagging bending
3.5.3.1
Cross-sections in Class 1 or 2
The methods of calculation for sections in Class 1 or 2 are in principle the
same as those for composite slabs, explained in Section 3.3.1, to which
reference should be made. The main assumptions are as follows:
•
the tensile strength of concrete is neglected;
•
plane cross-sections of the structural steel and reinforced concrete
parts of a composite section each remain plane;
and, for plastic analysis of sections only:
•
the effective area of the structural steel member is stressed to its
design yield strength
f
yd
(
=
f
y
/
γ
A
) in tension or compression;
•
the effective area of concrete in compression resists a stress of 0.85
f
cd
(where
f
cd
γ
C
), which is constant over the whole depth between
the plastic neutral axis and the most compressed fibre of the concrete.
=
f
ck
/
