Pole Bending & Shear

[sumwonlost]

I am building a structure for my caravan and require assistance with calculation for force.

In essence it is a telescopic pole structure holding up an awning.

I am using aluminium 6061-T6 with the outer pole being 32mmOD x 2.5mm wall thickness and inner pole 27mm x 2.5 wall thickness. Both poles are 1.5m long.

The outer pole has a 6mm hole 20mm from the top and the inner pole has a 6mm hole 100mm from the bottom and at intervals of 100mm. Therefore the outer pole overlaps the inner pole by 120mm (100mm below hole and 20mm above hole) when fully extended and holes aligned.

The holes are used for me to put in a 6mm stainless steel bolt through the outer pole at the required height of the inner pole, thereby holding up my structure.

I realise that the stainless steel bolt will not shear before the aluminium pole either shearing through at the hole or bending.

Logic also tells me that that the poles are likely to bend before the bolt shears through poles, elongating the holes.

Therefore I need to know how much force can be applied on top of poles when fully extended before they bend? I assume the bending won't occur at the overlapped section (centre) nor on outer bigger pole and also ask at what point on the inner point?

Your assistance would be very much appreciated - as this then helps me determine how many poles I require to hold up the awning weight safely.

 

[paddingtongreen]

reading through, the first thing I see is that the OD of the inner pole and the ID of the outer pool are the same. I've never seen that work, I don't think it can.

The bend, when it happens will be the smaller tube, at the top of the outer tube. It seems to me that it would be better to drill the holes in the larger tube, you are further weakening the weaker member.

How is this to be supported and how connected to the awning?

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin