Accuracy

The calculation of deflection in Eurocode 2 using the rigorous method presented here is more advanced than that in BS 8110™ It can be used to take account of early-age construction loading by considering reduced early concrete tensile strengths.

However, the following influences on deflections cannot be accurately assessed:

■ Tensile strength, which determines the cracking moment.

■ Construction loading.

■ Elastic modulus.

Therefore any calculation of deflection is only an estimate, and even the most sophisticated analysis can still result in +15% to -30% error. It is advisable to give a suitable caveat with any estimate of deflection that others are relying on.

Figure 9

Recommended acceptance criteria for flat slabs

Deflection affecting partitions

Notes

If maximum permitted d = L/n and X is the position of maximum D where L = Span n = Limiting span-to-depth ratio, e.g. 250

then the deflection at X should not be greater than 2a/n. (Maximum deflection on gridlines may be more critical.)

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