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)

144 Reinforced concrete beams-the ultimate limit state
Slenderness limits (BS 8110: Clause 3.4.1.6)
To guard against lateral buckling, the slenderness limits in Table 4.10-1
should not be exceeded. In the table, the term slenderness limit is defined
as the clear distance between lateral restraints, d is the effective depth and
be the breadth of the compression face of the beam midway between
restraints.
Table 4.10-1 Slenderness limits
Type of beam
Simply supported
Continuous
Cantilever
Slenderness limit
60bc or 250b~/ d whichever is the lesser
Same as above
25bc or lOOb~/ d whichever is the lesser
Comments
The slenderness limits in Table 4.10-1 are intended for ordinary beams;
design guidance on deep beams, in which the depth h is comparable to the
span/, is given in the CIRIA deep-beam guide [21]. See also the recent
References 22 and 23.
Minimum distance between bars (BS 8110: Clause 3.12.11.1)
(a)
The horizontal clear distance between bars should not normally be
less than hagg + 5 mm, or less than f/J, whichever is greater, where hagg
is the nominal maximum size of the coarse aggregate and ifJ is the bar
size (or the size of the larger bars if they are unequal).
(b) Where the bars are arranged in two or more rows, the gaps between
the corresponding bars in each row should be vertically in line and the
vertical clear distance between the bars should not be less than jhagg
or ifJ, whichever is greater.
(c)
Where an internal vibrator is intended to be used, sufficient space
should be left between bars to enable the vibrator to be inserted.
Maximum distance between bars (BS 8110: Clause 3.12.11.2)
The restrictions on maximum distance are intended for controlling crack
widths. They therefore apply to tension bars only and are summarized in
Fig. 5.4-1. Detailed explanations are given in Section 5.4.
Minimum lap length (BS 8110: Clause 3.12.8)
The minimum lap should not in any case be less than 15 times the bar size
or 300 mm whichever is the greater; for fabric reinforcement it should not
be less than 250 mm. BS 8110's further requirements are as follows.
Tension laps
The lap length should be at least equal to the anchorage length (See eqns
6.6-3(a), (b)) required to develop the stress in the smaller of the two bars
lapped.