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 443
Check lap length (see Section 4.10, under the heading 'Tension laps
(b)'):
cover to lapped bars = 20 + link fjJ = 36 mm
< 2(/J (64 mm)
spacing between adjacent laps * 100 mm
< 6f/J (192 mm)
Hence apply a factor of 1.4 to Table 4.10-2, so that:
full tension lap length = (1.4)(32f/J) = 45f/J
required lap length = [ ~s(z;;~)] ( 45f/J)
= n~~](45)(32) = 939 mm
Extend the tie bars 1500 mm from the column face at the support B.
External column tie (BS 8110: Clause 3.12.3.6.1).
(a) 2Ft = 2(36) = 72 kN.
[Floo~-~eight](Ft) = [ 4 -2 ~/80](36 ) = 55 kN
Hence 72 kN force need not be considered further.
(b) 3% of total design ultimate vertical load carried by column
* 3% of 1500 kN (calculations not shown)
= 45 kN < 55 kN in (a)
Hence, tie force = 55 kN. Minimum continuity external tie
(55)(10 3 ) 2 ( . •
= (0.87)(460) = 137 mm See remark on Ym for mternal tie)
The 25 mm U-bars at the external supports provide ample area.
Step 10 Reinforcement details
Figure 11.5-12 shows the reinforcement details.
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).
Comments on Step 2
The unit weight of reinforced concrete is taken as 24 kN/m 3 • As explained
in the beginning of Section 2.5, this value includes an allowance for the
weight of the reinforcement.
Comments on Step 3
In practice, the entire building frame can be readily analysed as a threedimensional
structure, using a computer package (BS 8110: Clause 2.5-1).