Analysis & loading · Load take-down & combinations

Live load area reduction calculator

Reduction factor ψa = 0.3 + 3/√A for tributary areas over 20 m² (not for assembly, storage or Q > 5 kPa).

Standard: AS/NZS 1170.1 Cl 3.4.2

Inputs in the worked example

The live calculator starts with these values; change any of them and every result, check and diagram updates instantly.

Input	Value	Unit
Tributary area	60	m²
Uniform live load	3	kPa

Diagram for the worked example

ψa = 0.3 + 3/√A (≤ 1, ≥ 0.5) = IF(60<=20,1,MIN(1,MAX(0.5,0.3+3/SQRT(60)))) = 0.6873
Reduced live load = 0.6873*3 = 2.0619 kPa
Total on area = 2.0619*60 = 123.71 kN

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For preliminary design and education. Check every result against the current standard and your own engineering judgement before use.