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 details (BS 81 10) 145
(a) Where a lap occurs at the top of a section as cast, and the minimum
cover is less than twice the bar size, the lap length should be
multiplied by a factor of 1.4.
(b) Where a lap occurs at the corner of a section and the minimum cover
to either face is less than twice the bar size, or where the clear
distance between adjacent laps is less than 75 mm or six times the bar
size, whichever is greater, the lap length should be increased by a
factor of 1.4.
(c) In cases where both conditions (a) and (b) apply, the lap length
should be increased by a factor of 2.
Compression laps
The lap length should be at least 25% greater than the compression
anchorage length (see eqns 6.6-3 (a), (b)). Table 4.10-2 gives values
of ultimate anchorage bond lengths and lap lengths for Type 2 deformed
bars (fy = 460 N/mm 2 ) and BS 4483 Fabrics, for feu = 40 N/mm 2 and over,
as calculated from eqn (6.6-3(b)).
Table 4.10-2 Ultimate anchorage lengths and lap lengths for feu ::::: 40 N/mm 2 ( </J =
bar size)
Reinforcement type
Tension anchorage and lap lengths
Compression anchorage length
Compression lap length
/y = 460 N/mm 2
32</J
26</J
32</J
Fabric
25</J
20</J
25</J
Curtailment and anchorage of bars (BS 8110: Clause 3.12.9)
(a) Except at an end support, every bar should extend beyond the
theoretical cut-off point for a distance not less than the effective
depth of the member or 12 bar sizes, whichever is greater. The
theoretical cut-off point is defined as the location where the resistance
moment of the section, considering only the continuing bars, is equal
to the required moment.
(b) A bar stopped in a tension zone should satisfy the additional
requirement that it extends a full anchorage length lu (eqn 6.6-3(b))
from the theoretical cut-off point, unless other conditions detailed in
Clause 3.12.9.1 of BS 8110 are satisfied.
(c) At a simple end support, each tension bar should have an effective
anchorage of 12 bar sizes beyond the centre line of the support unless
other conditions detailed in Clause 3.12.9.4 of BS 8110 are satisfied.
The effective anchorage lengths of hooks and bends are explained in
Fig. 6.6-1.
Comments
For anchorage of links, see Section 6.6.
Simplified rules for curtailment of bars (BS 8110: Clause 3.12.10.2)
The recommendations above relate the curtailment of bars to the theoretical
cut-off points. In practical design, bending moment diagrams are often