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 procedure for rectangular beams 117
0·40Sfcubx
Fig. 4.6-7
(0.87)( 460)(2455) = (0.405)( 40)(250x) + 0.87( 460)(982)
x = 145.5 mm; xld = 0.22
It is necessary to check that the steel design strengths 0.87/y are in fact
attained. From Fig. 4.6-8,
E~ = 0~~:n(0.0035) = 0.003
Est = (1~~:~)(0.0035) = 0.012
These strains exceed the design yield strains (see Fig. 4.5-1) and
therefore the design strengths 0.87/. are reached. The ultimate
moment of resistance is conveniently determined by taking moments
about the centroid of the concrete compression block in Fig. 4.6-7:
0.87/yA~(Oix -
d')
= (0.87)(460)(982)(65.48 - 40)(10- 6 ) = 10.0 kNm
0.87/yAst( d, - Oix)
Fig. 4.6-8