Deflection limits

Deflection in beams is a major issue in structural design. Engineers adopt deflection limits which suit the nature of the building. For example, according to AS 1170.1 Minimum design loads on structures (known as the SAA Loading Code):

maximum allowable deflection = span ÷ 300

This means that to calculate the deflection in a beam which spans 6,000 mm, divide 6,000 by 300.

6,000 ÷ 300 = 20

So a span of 6,000 mm has a maximum allowable deflection of 20 mm.