Civil Engineering Reference
In-Depth Information
these bending moments from columns. One justification for using
e
c
0 is
that the bending moments in the beams are calculated using the span
between column centres, rather than the smaller span between the centres
of the 'pin' connections. Eurocodes 3 and 4 at present give no guidance
on this subject.
In the following example, it will be assumed that
L
e
=
L
and that the
load from a nominally pinned connection acts at 100 mm from the face of
the steel column section, so that
=
e
c
=
0.5
h
a
+
100 mm
The beam is assumed to be simply-supported at the pin, so its span is less
than that to the column centre-line.
5.4.4.3
Elastic global analysis
This method of analysis is generally applicable to braced composite frames
with rigid or nominally pinned joints. The flexural stiffness of hogging
moment regions of beams is treated as in Section 4.3.2. For columns,
concrete is assumed to be uncracked, and the stiffness of the longitudinal
reinforcement is usually included, as it may not be negligible.
Bending moments in beams may be redistributed as in Section 4.3.2,
but end moments found for composite columns may not be reduced,
because there is insufficient knowledge of the rotation capacity of
columns.
Where the beam-to-column joints are nominally pinned, as in the
external columns in the example in Section 5.7, the bending moments
in a column are easily found by moment distribution for that member
alone.
5.4.4.4
Rigid-plastic global analysis
The use of this method for a braced frame is not excluded by EN 1994-1-
1, but there are several conditions, which make it unattractive in practice.
In addition to the conditions that apply to beams (Section 4.3.3), these
include the following.
(1)
All connections must be shown to have sufficient rotation capacity, or
must be full-strength connections with
M
j,Rd
≥
1.2
M
pl,Rd
, as explained
in Section 5.3.2.
(2)
Unless verified otherwise, it should be assumed that composite
columns do not have rotation capacity.
