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)

Design and detailing-illustrative examples 445
The correction due to the continuity bending moment at support B is
(520 kNm)/(9 m) ± 58 kN, where 520 kNm is the redistributed moment
taken from Fig. 11.5-6. Therefore, the final end shears are 338 ± 58 =
396 kN (at B) and 280 kN (at A).
Comments on Step 5
Internal support B. The design procedure, using Tables 4.7-1 and 4.7-2,
is that of the I.Struct.E. Manual [20]. All the design tables and design
equations were derived in Section 4. 7.
Span AB. The reinforcement for the flanged section is designed using the
'I.Struct.E. Manual's design procedure (Case II: 0-30% moment redistribution)',
as explained in Section 4.8.
End supports A and C. The bending moments are in each case taken as
40% of the initial fixed-end moment, in accordance with a common
practice in design-see the final paragraph in the solution to Example
11.4-1(a). (If the reader wishes, he might of course obtain these support
moments by analysing the building as a complete structure or else analyse
the appropriate subframes.) What is important is the understanding that
the bending moments as shown in Fig. 11.5-6 are already in equilibrium
with the design ultimate loads. The safety of the beam is not in question;
the 40% fixed-end moments assumed for the end supports A and B are
really to ensure serviceability.
Curtailment diagram (Fig. 11.5-10). See under the heading 'Curtailment
and anchorage of bars' in Section 4.10.
The resistance moments as shown in Fig. 11.5-10 have been obtained as
follows. Consider, for example, the internal support B:
Mu = K'fcubd 2
= (0.139)( 40)(350)( 475 2 ) Nmm
= 440 kNm
As = 4021 mm 2 (5T32)
A~ = 1608 mm 2 (2T32)
A, 3327 2 0f<
bd = (350)(475) =
0
A~ _ 1608 _ Of<
bd - (350)( 475) - 1 0
From Fig. 4.5-2 (BS 8110 design chart),
M = (6.8)(350)(475 2 ) Nmm = 535 kNm
Of course, in the calculations for the spans AB and BC, b should be taken
as the effective flange width.
Comments on Step 6
Shear design to BS 8110 is explained in Section 6.4. With reference to Step
6(d), the shear forces have been taken, not at the respective support face,