Figure 5.21 shows the relationship between 9ef and Ml/Md for 9 = 3 and different values of p for the uncracked reinforced cross section.

Figure 5.21. Effective creep ratio as a function of the ratio Ml/Md for 9 = 3, uncracked rectangular cross section with symmetric reinforcement, edge distance t = 0,1h and a =Es/Ec = 6

The straight line for p = 0 is identical with expressions (4-4) and (5.19). With reinforcement, i.e. p > 0, expression (5.19) becomes more or less conservative. Cracked reinforced cross section

The cracked cross section can be treated analogously, although it is a little more complicated. As the simplest case, consider a rectangular cross section with bending moment only and tensile reinforcement only. The flexural stiffness in the cracked stage (ignoring any contributions from concrete in tension) can then be expressed as

where As = area of reinforcement d = effective depth £ = x/d x = depth of compression zone The relative depth of compression zone for a certain creep coefficient 9 can be obtained from

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