F. K. Kong MA, MSc, PhD, CEng, FICE, FIStructE, R. H. Evans CBE, DSc, D ès Sc, DTech, PhD, CEng, FICE, FIMechE, FIStructE (auth.)-Reinforced and Prestressed Concrete-Springer US (1987)

Analysis of framed structure (BS 8110) 411
Table 11.4-2 One-way slabs-ultimate bending moments and shear forces
(BS 8110: Clause 3.5.2.4)
First
End End interior Interior Interior
support span support spans supports
Moment" 0 0.086Fl" -0.086Fl 0.063Fl -0.063Fl
Shear 0.4F 0.6F 0.5F
" No further moment redistribution is allowed if the moment values of this table are used.
h F is the design ultimate load ( 1.46Gk + 1.6Qk) and I is the span of the slab.
If the structure is unbraced, the frame will have to resist both vertical
and lateral forces. BS 8110: Clause 3.2.1.3.2 then states that the unbraced
frame design may be based on the moments, loads and shears resulting
from either a braced-frame vertical load analysis as described above (see
Fig. 11.4-1) or, if more severe, the sum of the effects from (a) and (b)
below:
(a)
(b)
An elastic analysis of the type of sub-frame shown in Fig. 11.4-1(b)
loaded only vertically, with a uniform 1.2( Gk + Qk) throughout.
An elastic analysis of the complete frame under lateral load only, of
magnitude 1.2 times the characteristic wind load Wk, and assuming
points of contraflexure at the centres of all beams and columns, as
shown in Fig. 11.4-2.
This is readily justified if the column feet are 'fixed' and if the beams and
columns are of similar stiffness, but the assumption will be incorrect if
either of these conditions does not apply. For instance, if a column were
pin-footed then the point of zero moment would be at the bottom of the
column, and the mid-point assumption would underestimate the moment
at the top of the column.
The final loading pattern to be considered concerns the overall stability
of the building. Even though instability due to soil failure, e.g. by sliding or
n'rl nrr n. r ll.'T
Fig. 11.4-2 Assumed points of contraflexure for lateral-loading analysis (BS 8110:
Clause 3.2.1.3.2)