(3) The values in Table 3.2 are based on the following equation: Ecm = 9.5 (fck + 8)1/3 (Ecm in kN/mm2; fck in N/mm2)

They relate to concrete cured under normal conditions and made with aggregates predominantly consisting of quarzite gravel. When deflections are of great importance, tests should be carried out on concrete made with the aggregate to be used in the structure. In other cases experience with a particular aggregate, backed by general test data, will often provide a reliable value for Ecm, but with unknown aggregates, it would be advisable to consider a range of values.

(4) As a rule, since the strength classes of concrete fck correspond to a strength at an age of 28 days, the values for Ecm in Table 3.2 also relate to that same age. Where great accuracy is not required, Ecm can also be determined from Table 3.2 for a concrete age t other than 28 days. In this case, fck is replaced by the actual concrete strength at the time t. Poisson's ratio

P(1) For design purposes Poisson's ratio for elastic strains may be taken equal to 0.2.

P(2) If cracking is permitted for concrete in tension, Poisson's ratio may be assumed as zero. Coefficient of thermal expansion

P(1) For design purposes, where thermal expansion is not of great influence, it may be taken equal to 10 x 10-6/°C. Creep and shrinkage

(1) Creep and shrinkage of the concrete depend mainly on the ambient humidity, the dimensions of the element and the composition of the concrete. Creep is also influenced by the maturity of the concrete when the load is first applied and on the duration and magnitude of the loading. Any estimation of the creep coefficient $(t,to), and of the shrinkage strain, ecs, should take these parameters into account.

(2) In cases where great accuracy is not required, the values given in Table 3.3 and Table 3.4 respectively can be considered as final creep coefficient to) and the final shrinkage strain ecs Z of a normal weight concrete subjected to a compressive stress not exceeding | 0.45 I fck at the time to at first loading. In Table 3.3, the creep coefficient to) is related to Ecm, according to Table 3.2 and Equation 3.5. Where greater accuracy is required, reference should be made to Appendix 1.

(3) The data given in Table 3.3 and Table 3.4 apply for a range of the average temperature of the concrete between 10 °C and 20 °C. Therefore, seasonal variations of temperature between - 20 °C and + 40 °C can be accepted. In the same way, variations in relative humidity around the average values given in Table 3.3 and Table 3.4 between RH = 20 % and RH = 100 % are acceptable.

Table 3.3 — Final creep coefficient 0(z,to) of normal weight concrete
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