Basic span/effective depth ratio (interpolating for p) = 39.2 Table 7

400 x 403

Modification factor for steel stress = —-— = 1.19

460 x 295

Since flange width > 3 x rib width, a 0.8 modification factor is required. Since span > 7 m, no further modification is required. Permitted span/effective depth ratio = 39.2 x 1.19 x 0.8 Cracking

For exposure class 1, crack width has no influence on durability and the limit of 0.3 mm could be relaxed. However, the limit of 0.3 mm is adopted for this example.

Satisfy the requirements for control of cracking without calculation. Check section at mid-span:

Minimum reinforcement, As =

Eqn 4.78


Aa can be conservatively taken as the area below the neutral axis for the plain concrete section, ignoring the tension reinforcement, as shown in Figure 4.10.

Figure 4.10 Tensile zone of plain concrete section Depth to neutral axis = 92 mm

Check limit on bar size.

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