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)

Table 6.4-2 Values of A.vl Sv (mm)for
various tink-bar sizes cp and tink spacings Sv
Shear resistance in design calculations (BS 8110) 213
Sy 8 10 12 16
100 1.00 1.57 2.26 4.02
150 0.67 1.05 1.51 2.68
200 0.50 0.79 1.13 2.01
250 0.40 0.63 0.90 1.61
300 0.33 0.52 0.75 1.34
discussed on paragraph (f) immediately preceding Example 6.3-1.
BS 8110: Clause 3.4.5.6 gives the following equation for the shear
resistance V b of a system of bent-up bars:
. d - d'
V b = A sb (0.87fyy) (cos a + SIO a cot (J) -- (6.4-4)
Sb
where A sb is the cross-sectional area of the bent-up bar(s), fyy the
characteristic strength, a and {J are the angles defined in Figs 6.3-4
and 6.3-5, d the effective depth, d' the concrete cover to the centres
of the top reinforcement (see Fig. 6.3-4) and Sb is the spacing of the
bent-up bars (= Sy in Fig. 6.3-4). BS 8110 stipulates that bent-up bars
should be so arranged that:
(1) The angles a and {J are both greater than or equal to 45°;
(2) The spacing Sb should not exceed 1.5d.
In practice, the angle a is specified by the designer. {J and Sb are
related by the following equation (see Example 6.3-1 and Fig.
6.3-5):
Sb = (cot a + cot (J) (d - d') (6.4-5)
Having specified a value for a not less than 45°, a value not exceeding
1.5d is specified for Sb, and (J is then calculated from eqn (6.4-5).
Equation (6.4-4) can then be used to calculate V b • Equation (6.4-4)
was derived in Section 6.3 as eqn (6.3-6).
Comments on Step 6
For further information on the subject of bond and anchorage, see Section
6.6.
The use of BS 8110's shear design procedure is illustrated in Example
6.4-1. As will be seen, Table 6.4-2 is a useful design aid.
Example 6.4-1
BS 8110's minimum links are defined by eqn (6.4-2).
(a)
(b)
Brietly explain the technical background to the equation.
Show that BS 8110's minimum link requirements are met by 'Grade
250 (mild steel) links equal to 0.18% of the horizontal section', as
recommended by the I.Struct.E. Manual [26].