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)

Elastic theory: cracked, uncracked and partially cracked sections 161
0·06 0.1 0·12 014 0·16
lc/tx:J3
Fig. 5.2-4 Second moment of area of cracked section [6] (d' !d = 0.1)
qk of 31.5 kN/m. The characteristic concrete and steel strengths are feu =
40 N/mm 2 and fy = 460 N/mm 2 respectively; Es = 200 kN/mm 2 and Ee is
given in Table 2.5-6.
(a) Determine the midspan service-load concrete strains at the level of
the tension reinforcement, at the tension face (i.e. the soffit) of the
beam, and at 250 mm below the neutral axis.
(b) If, because of creep, the value of Ee becomes half that in Table 2.5-6,
repeat the calculations for the long-term service-load strains in (a)
above.
SOLUTION
(a) Short-term strains due to service loading. For serviceability calculations,
BS 8110: Part 2: Clauses 3.3.2 and 3.3.3 recommend that the
partial safety factor Yr = 1 for both gk and qk. Therefore
· I d (1.0 X 24 + 1.0 X 31.5) X 10 2
service oa moment = 8
From Table 2.5-6,
= 694 kNm
Ee = 28 kN/mm 2 for feu = 40 N/mm 2
therefore