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Steel Designers' Manual - 6th Edition (2003)
Corus
Construction
Centre
www.corusconstruction.com
Subject Chapter ref.
MULTI-STOREY DESIGN
EXAMPLE
Design code Made by PEP Sheet no.
BS 5950: Part 1: 2000 Checked by TRM
The smallest value of l cr is 5.45, which is < 10. Therefore the frame 2.4.2.7
is sway sensitive, and as lcr is not less than 4.0, the amplified sway
method may be used.
This gives an amplification factor for NHFs in the Y direction of:
= / ( 115 . -15
. ) = 114 .
kamp lcr lcr
(for clad structures, provided that the stiffening effect of masonry
infill wall panels or diaphragms of profiled steel sheeting is not
explicitly taken into account.)
Cautionary notes to analysis approach
1. Results are for sway only in the Y direction using NHF in the
Y direction from the gravity combination. This analysis must
normally be repeated for sway in the X direction using NHF in
the X direction. The choice is then to either:
(a) use the smallest value of lcr to determine one value of k amp
applied to loads in both directions, or
(b) calculate a lcr and hence k amp for each direction.
Similarly a k amp could be calculated for each load combination
and applied to each appropriate combination.
2. The results from a simple tower constrained out-of-plane at all
levels take no account of out-of-plane deflections and their
influence on P–d effects. An analysis of the whole building is
required to spot this effect and determine whether it is significant.
In this example the tower constrained out of plane is only
a reasonable assumption owing to the very symmetric nature of
the building as a whole. If the whole building is considered then
there could be other columns (even simple ones not in braced
bays) that lean over more. These will have a detrimental effect
on the braced areas. That is, whilst not affected themselves
(being simple columns), they will increase the P–d effect on the
braced towers. Taking the worst sway index for all columns also
helps to compensate for any out-of-plane deflections.
Worked example 89
2
12