ABSTRACT
For design purpose, BS 8110 idealizes the stress/strain curves for reinforcement to that shown in Fig. 3 .2 - l(b ) , which applies to both tension and compression. The partial safety factor ym for the ultimate limit state is taken as 1.15 (see Table 1 .5-2). Therefore the design strengths, in tension and compression, are
1 ^ 5 = 0.87f y (3 .2 -1 )
The design yield strains are the strains at 0.87/y and are hence calculated as 0.87f y/E s = 0.002 for f y = 460 N/m m 2 and 0.0011 f o r / y = 250 N/m m 2. (Note: Es = 200 kN/mm 2 from Fig. 3 .2 - l(b ) .)
The stress/strain characteristics of concrete were briefly referred to in Section 2.5(d). The exact shape of the stress/strain curve is much dependent on the concrete strength. Figure 3 .2 -2 (a) shows typical curves
Fig. 3.2-1 Stress/strain curves for reinforcement
for short-term loading. Within the range of concrete mixes used in prac tical design, the following general statements may be made:
(a) Up to about 50% of the maximum stress, the stress/strain curve may be approximated by a strainght line.
