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)

450 Practical design and detailing
Total axial loads (see Table 11.5-4)
3rd floor to roof
2nd to 3rd floor
1st to 2nd floor
Foundation to 1st floor
N3r 168 + 461 629 kN
N23 = 382 + 948 = 1330 kN
N 12 = 547 + 1435 = 1982 kN
Nn = 659 + 1922 = 2581 kN
N3r = 629 kN N23 = 1330 kN N12 = 1982 kN: Nn = 2581 kN
Step 6 Design bending moments
BS 8110's design minimum eccentricity (see Comments at the end) =
0.05h.
Minimum design moment = 0.05hN
Foundation to lst floor level:
0.05h Nn = 0.05 X 380 X 10-3 X 2581 (see Step 5)
= 49 kNm
Elsewhere, N < Nn and hence 0.05hN < 49 kNm.
Therefore the column design is governed by the column moments in
Step 3 as these are larger than 0.05hN.
Step7
M (roof junction) = 109 kNm
Reinforcement
Jcu -r = 40 N/mm 2 ·' Jy
-r = 460 N/mm 2
4 _ 380- 40- (bar ifJ)/2 _
h - 380 - 0
. 85
approx.
M (floor junction) = 107 kNm
Hence the design chart in Fig. 7.3-1 applies, and the results are as
shown in Table 11.5-5.
Step 8 Reinforcement details (see Fig. 11.5-15)
Comments on Step 1
Note BS 8110's definition of the term 'nominal cover', as explained under
Table 2.5-7 in Section 2.5(e).
Table 11.5-S Column reinforcement
N M
bh w Asc required 3 Asc provided
Location (N/mm 2 ) (N/mm 2 ) (Fig. 7.3-1) (Fig. 11.5-15)
3rd ft. to roof 4.4 2.0 0.4% bh = 578 mm 2 41'25 (1960 mm 2 )
2nd to 3rd fl. 9.2 2.0 0.4% bh = 578 mm 2 41'25 (1960 mm 2 )
1st to 2nd ft. 13.8 2.0 0.4% bh = 578 mm 2 41'25 (1960 mm 2 )
Fndn to 1st fl. 17.9 2.0 1.4% bh = 2021 mm 2 41'25 (3216 mm 2 )
• From Section 3.5, the minimum steel ratio is 0.4%.