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)

406 Practical design and detailing
of size 16 mm and above, and smaller sizes commanding a higher unit
price. The normally available sizes, their mass/metre length and their
normal maximum lengths are given in Table 11.3-1. The basic price
usually applies to bars up to standard lengths of 12 m.
Lengths longer than those shown in Table 11.3-1 are usually provided
by lapping as explained in Section 4.10 or by proprietary connectors or
welding. It is good practice to use the maximum diameter consistent with
the design requirements concerning bond and crack widths. The number of
different diameters to be used on a particular job should be minimized to
simplify ordering, stocking and sorting. There is an oft-quoted 'natural'
law, with many variations, which states that if something can go wrong it
will-hence it is unwise to use small changes (e.g. 2 mm) in bar diameter
since they are not readily separately distinguishable on site.
Academic courses, in this subject, normally limit their attention to the
provision of the necessary reinforcement at a particular section and
thereby ignore the problems associated with detailing [7]. The Institution
of Structural Engineers [10] has pointed out that 'bad detailing can lead to
disaster just as surely as a defective overall scheme-in fact it is much the
more frequent cause of trouble'.
It is surprising that comparatively little attention has been paid to this
part of the design and construction process, and to the tests [11-15] which
have shown the shortcomings of some 'standard' reinforcement details.
The student must be aware of the difficulties involved in curtailment,
lapping beam-column joints, short cantilever brackets, deep beams, etc.
Concrete mixes can be designed depending upon the available basic
materials (see Section 2.7) to give a large variety of commercial
characteristic strengths up to a current practical limit of, say, 70 N/mm 2 . It
is obviously desirable to limit this variety on any particular job, and
preferable to have a limitation between jobs also. For this reason it is
recommended that for normal dense aggregate reinforced concrete, grades
of 30, 35 and 40 are used Ucu = 30, 35 and 40 N/mm 2 respectively). Having
decided on the grade of concrete to be used, Table 2.5-6 will give
estimates of the moduli of elasticity, if required.
Table 11.3-1 Steel Reinforcement data (see also Tables A2-1 and A2-2)
Size (mm) 8 10 12 16 20 25 32 40
Normal max.
length (m) 10 10 10 12 18 18 20 20
Mass/metre
(kg/m) 0.395 0.617 0.888 1.58 2.47 3.85 6.31 9.86