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Steel Designers' Manual - 6th Edition (2003)
438 Beams
- 0 (I)
0
cc) C > Q_ —
',.
E2.
.LD
1.0
, 0.8
0.6
::
0 0.2 0.4 0.6 0.8 1.0
proportion of shear capacity present
F /P
shear
area A
plastic modulus for
whole section
plastic modulus for
shear area
Fig. 16.2 Moment – shear interaction for plastic or compact sections to BS 5950: Part I
of the structure. For beams, examples of potentially undesirable consequences of
excessive serviceability deflections include:
• cracking of plaster ceilings
• allowing crane rails to become misaligned
• causing difficulty in opening large doors.
Although earlier codes of practice specified limits for working load deflections, the
tendency with more recent documents 1 is to draw attention to the need for deflection
checks and to provide advisory limits to be used only when more specific guidance
is not available. Table 8 of BS 5950: Part 1 gives ‘recommended limitations’ for
certain types of beams and crane gantry girders and states that ‘Circumstances may
arise where greater or lesser values would be more appropriate.’ Not surprisingly
surveys of current practice 4 reveal large variations in what is considered appropriate
for different circumstances.
When checking deflections of steel structures under serviceability loading, the
central deflection Dmax of a uniformly-loaded simply-supported beam, assuming
linear–elastic behaviour, is given by