Existing longitudinal chassis member
Gross weight of trailer = GA = 800 Kg (based on the original estimated weight)
draw bar length = L = 0.95 m
R = 0.36 x GA for braked trailers = 288 Kg
Bending moment = M = 9.81 x R x L = 2684.016 Nm
Z required = M / 160 = 16.7751 cm3
Box section properties
breadth = b = 5 cm
depth = d = 5 cm
thickness = t = 0.3 cm
I = (b.d^3 / 12) - ((b-2t).(d-2t)^3)/12 =20.84 cm4
Z = I/(d/2) = 8.33968 cm3
50% of required
Suggested longitudinal chassis member
Gross weight of trailer = GA = 1000 Kg (based on my worst guess)
draw bar length = L = 0.95 m
R = 0.36 x GA for braked trailers = 360 Kg
Bending moment = M = 9.81 x R x L = 3355.02 Nm
Z required = M / 160 = 20.968875 cm3
Box section properties
breadth = b = 7 cm
depth = d = 7 cm
thickness = t = 0.4 cm
I = (b.d^3 / 12) - ((b-2t).(d-2t)^3)/12 =76.94 cm4
Z = I/(d/2) =21.98 cm3
105% of required