Member Sizing

Having settled on the structural design, I then did a quick calculation to determine what member sizes we required. I assumed that a 100kg person would grab hold of the edge of rim, and with a downward velocity a conservative maximum would be to design for a 2kN load there. The calcs are shown below, and show just how efficient this structure is with 20mm diameter, 2mm thick aluminium circular hollow sections working fine. One point to note however, is that these probably wouldn't be large enough for someone to hang directly off them (the bars would start at approximately 2.5m above the ground, and so are within jumping reach), but they still wouldn't be too large.

Taking this one stage further, I have put together a bill of materials and included on this a weight calculation. Amazingly, the total mass of the whole structure is predicted at under 20kg, with the timber board accounting for most of it! Due to the above consideration about bottom bars, it would be more realistic to say under 25kg. However, the construction would be done in stages with the heavy 12kg board attached near the end, so this design is definitely lightweight enough to be easily lifted into place.

Materials	Specification	Material	Mass (kg)
Wooden Board	1.4 x 0.8m, 15mm thick	Treated Timber	12.60
Board Frame	30 x 3mm RHS	Aluminium	2.27
Support Structure	Ø20, 2mm thick CHS	Aluminium	1.07
Clamps	6mm thick plate	Aluminium	1.82
Clamp inserts	Various shapes	Rubber	1.64
		Total	19.40 kg
	Density of Timber	750 kg/m^3
	Density of Aluminium	2810 kg/m^3
	Density of Rubber	1522 kg/m^3