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)

218 Shear, bond and tors ion
(b)
(c)
hogging one; therefore, from Fig. 6.4-1, As = 4 top bars.
Within 2665 mm of support A, the moment is always a sagging one;
therefore As = 3 bottom bars.
In between these regions, the moment is sometimes a hogging one
and sometimes a sagging one, and it will be conservative to take As =
two size 32 bars. In practical design, however, the procedure as
explained here is considered too tedious; the simplified procedure as
used in Step 4 is usually adopted.
Comments on Step 5
It has been pointed out that when the support reaction imposes a compression
on the member, shear failure rarely initiates within a distance d
of the support, where dis the effective depth [1]. Therefore, in a situat ion
like this, the designer is justified in providing shear reinforcement on the
basis of the shear force Vat 800 mm from the support B, if he so wishes.
Indeed, BS 8110: Clause 3.4.5.10 specifically gives the designer this
freedom of choiee. (Note that at the time when the authors called for the
recognition of the enhanced shear resistance near supports, the then Code
of Practice CP 114 did not recognize such enhanced resistance [1].)
Example 6.4-3
Ii the beam in Example 6.4-2 had been a ftanged beam, having the CroSSsection
in Fig. 6.4-3, how should the solution be modified?
SOLUTION
Since the solution to Example 6.4-2 is based on the dimensions of the rib,
it applies equally to ftanged beams. This is not to say that there is no
difference in behaviour between rectangular beams and ftanged beams [1,
25], but in current design practice such a difference is ignored.
I~ ,
2000
L
2bo
Fig. 6.4-3
"1
I
d-d'.740
1
~ 350 l-
t
60
J
d
6.5 Shear strength of deep beams
A beam having a depth comparable to the span length is called a deep
beam. The design of deep beams is a topie whieh recurs in practice but
whieh is not yet covered by BS 8110. Recently, the research at the Uni-