Design Aids

# Fixing Selection Worked Example

Select a joist hanger to fix a 140×45 joist spanning 2700mm @ 450 crs to a timber beam. 1.5kPa domestic floor. Assume dry in service condition. Floor joist reaction:

G = 0.5 kPa x 0.45 x 2.7 / 2 = 0.30kN
Qu = 1.5 kPa x 0.45 x 2.7 / 2 = 0.91kN
Qc = 1.8 kN

From the LUMBERLOK Timber Characteristic Loadings Brochure, for a 47 x 90 joist hanger:
Characteristic strength Pchar = 9.0 kN (downward)

 1.35G 1.2G+1.5Qu 1.2G+1.5Qc Design force N* 1.35 x 0.30 = 0.40 1.2 x 0.3 + 1.5 x 0.91 = 1.73 1.2 x 0.3 + 1.5 x 1.8 = 3.06 Design strength ΦN 9.0 x 0.8 x 0.6 = 5.8 9.0 x 0.8 x 0.8 = 7.7

Design strength (kN) = Pchar x phi x K1 The serviceability load gives the designer some idea of how much the joint will slip because at this load there is a straight line relationship between the load and deflection. The serviceability load published in some LUMBERLOK documents is the load at a joint slip of 1mm. From this the actual slippage of the joint can be calculated.

At a load of 2.5kN there will be 1 mm slip, so at a load of G+0.7Q = 0.94kN there will be:
joint deflection = 0.94 x 1 / 2.5 = 0.4mm slip at each joist hanger.