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)

Flanged beantS 127
d' 60
x = (0.45)(700)
= 0.19 < (1 -lro)
Therefore the compression steel reaches 0.87/y and A~
calculated in Step (3a) above is acceptable.
(3 ) A Mu A'
c " = 0.87/yz + "
z/d was found in Step (3b) to be 0.80.
as
(705.6)(10 6 ) 2
As = (0.87)(460)(0.80)(700) + 759 = 3907 mm
Provide three 20 mm top bars (942 mm 2 )
Provide five 32 mm bottom bars ( 4021 mm 2 )
4.8 Flanged beams
The T -beam and the L-beam in Fig. 4.8-1 are examples of Ranged beams.
In practice the flange is often the floor slab and the question arises of what
width of the slab is to be taken as the effective width; that is, the width bin
Fig. 4.8-1. BS 8110 gives the following recommendations:
(a)
for aT-beam the effective width b should be taken as (1) bw + 0.2/z or
(2) the actual flange width, whichever is less;
(b) for an L-beam the effective width b should be taken as (1) bw + 0.1/z
or (2) the actual flange width, whichever is less, where bw is the web
width (Fig. 4.8-1) and lz is the distance between points of zero
moment along the span of the beam. For a continuous beam, lz may
of course be determined from the bending moment diagram, but BS
8110 states that lz may be taken as 0.7 times the effective span (as
defined at the end of Section 4.5).
I· b ----l_j_ r----b----1_1_
l
hr ~ hr
d
t d T
l •• As
_L •• As
-1 bwr- -Jbw~
Fig. 4.8-l
(a)
(b)