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Steel Designers' Manual - 6th Edition (2003)
effective design
point using
n—factor method
(Pb' nXLT)
Fig. 16.5 Design modifications using m-factor or n-factor methods
an end moment such as horizontal wind load acting on a façade, should be regarded
as an ordinary beam since it does not have the benefit of non-uniform moment
loading.
For more complex arrangements that cannot reasonably be approximated by one
of the standard cases covered by correction factors, codes normally permit the direct
use of the elastic critical moment ME. Values of ME may conveniently be obtained
from summaries of research data. 6 For example, BS 5950: Part 1 permits lLT to be
calculated from
2 lLT =÷( p E/ py)÷( Mp/ ME)
(16.3)
As an example of the use of this approach Fig. 16.6 shows how significantly higher
load-carrying capacities may be obtained for a cantilever with a tip load applied to
its bottom flange, a case not specifically covered by BS 5950: Part 1.
16.3.7 Fully restrained beams
Basic design 445
The design of beams is considerably simplified if lateral – torsional buckling effects
do not have to be considered explicitly – a situation which will occur if one or more
of the conditions of Table 16.6 are met.
In these cases the beam’s buckling resistance moment Mb may be taken as its
moment capacity Mc and, in the absence of any reductions in Mc due to local buck-
LI