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)

78 Axially /oaded reinforced concrete co/umns
as column links; smalIer-size links of ten faiI to hold the main longitudinal
bars securely, and may themselves be pushed out of shape in the concreting
process.
Links also provide lateral restraint to the concrete, resulting in an
enhanced axial-Ioad capacity (see 'Failure criteria for concrete' in Section
2.5 (f».
Concrete cover for durability (BS 8110: Clause 3.3)
Table 2.5-7 in Section 2.5(e) gives the concrete covers to meet the
durability requirements for the columns and other structural members.
Note that in Table 2.5-7 the meaning of nominal cover is as defined in
BS 8110: Clause 3.3.1.1, namely: the nominal cover is the design depth of
concrete to alI steel reinforcement, including links. It is the dimension used
in design and indicated on the drawings.
Fire resistance (BS 8110: Clause 3.3.6)
The fire resistance of a column depends on its minimum dimension and the
concrete cover, as shown in Table 3.5-1. Note that the fire resistance
requirements may in practice dictate the size of the column and the
concrete cover.
Table 3.5-1 Fire resistance requirements for columns
(BS 8110: Part 2: Clause 4.3.1)
Fire
rating
(hours)
Minimum dimension
(mm)
Fully exposed 50% exposed
Concrete cover to
MAIN reinforcement
(mm)
1
2
3
4
200
300
400
450
160
200
300
350
25
35
35
35
3.6 Design and detailing-illustrative examples
Example 3.6-1
Calculate the ultimate axialload of a 300 mm square column section having
six size 20 bars, if feu = 40 N/mm 2 and fy = 460 N/mm 2 •
SOLUTION
From eqn (3.4-2):
N = O.4fc..Ae + 0.75fyA sc
= (0.4) (40) (30OZ - 1885J + (0.75) (460) (1885) N
(where Ase = 1885 mm from Table A2-1)
= 2060 kN