Sdr Tir"e A Deformation

Figure 5.20. Illustration of load history and deformations

Tir"e A Deformation

Figure 5.20. Illustration of load history and deformations

The total deformation under long-term load can also be calculated directly using an equivalent E-modulus3 for the concrete, Ee = E</(1+y). This corresponds to line AC in figure 5.20.4 The total deformation under design load can be calculated in a similar way if an effective creep ratio 9ef is used, line AD in figure 5.20. The "effective equivalent concrete modulus" would then be Eef = Ec/(1+ 9ef) where yef is the effective creep ratio.

5.8.4.2 Effect of creep in cross sections

In the following, three examples are used to derive and illustrate the effective creep ratio ^ef. The examples deal with bending moment and curvature in the following cases, assuming linear elastic material behaviour:

a) uncracked unreinforced cross section (5.8.4.2.1)

b) uncracked reinforced section (5.8.4.2.2)

c) cracked reinforced section (5.8.4.2.3)

5.8.4.2.1 Uncracked unreinforced cross section

This is the simplest case for demonstrating the idea behind the effective creep ratio. The total curvature under a long-term bending moment Ml is (cf. line AC in figure 5.20):

The part caused by creep can be separated:

0 0