The procedure for limiting deflections by use of span/effective depth ratios is set out in EC2 Section 4.4.3.
For the example considered
1650 x 390
Therefore the concrete is lightly stressed, p < 0.5%
The NAD(1) introduces a category of nominally reinforced concrete corresponding to p = 0.15%
Basic span/effective depth ratio for a simply supported beam, interpolating for p = 0.37%
NAD Table 7
For flanged beams where M>w > 3.0 the basic span/effective depth ratio should be multiplied by a factor of 0.8
The span/effective depth ratios given in NAD Table 7 are based on a maximum service stress in the reinforcement in a cracked section of 250 N/mm2. The tabulated values should be multiplied by the factor of 250/<rs for other stress levels, where a is the service stress at the cracked section under the frequent load combination. As a conservative assumption the Code states that the factor may be taken as
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