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savva
17th November 2010, 01:33 PM
What is the max height of a free standing external birdcage ie height to smallest base dimension ratio. and other factors is it the same as an external tower?

ChrisEng
17th November 2010, 07:40 PM
TG 20:08 does not give any height to base ratios or maximum heights for external birdcages.

It states that there should be a factor of safety against overturning of at least 1.2.

It would therefore involve working out the wind and instablilty loads on the tubes, boarded lifts, etc against the self weight of the scaffold. Even then the vertical joints will need to be spliced/ lots of ledger, sway and plan bracing would be required.

A tower only has generally four standards and is limited to 8.0m high and should only have a ratio of 3.5 to 1 in lower wind conditions.

Not sure I would want to see a 35m high free standing birdcage only 10.0m wide without additional kentledge, but all depends on wind pressures, location, etc.

Sorry no simple answer as cannot just extrapolate a tower to a birdcage.

savva
18th November 2010, 08:02 PM
exactly what I thought. I thought there would of been a more definite calc or ratio for this.

aom
18th November 2010, 08:16 PM
Run it through cads or similar, they work out the safe maximum height.

johnnyd
8th December 2010, 07:53 AM
If you put a birdcage through CAD or CASE it says it is a scaffold out of the "norm" so therefore it requires a design, so it will show no safe height!!!
All birdcage scaffolds should have a design, even a 1 lift birdcage and the design will show it at 2 lifts as it has to have a kicker !!

Ryan_Berry
18th January 2011, 08:58 PM
Hi Savva,

If you are interested I have uploaded an album which is similar to what was asked previously:

http://www.scaffoldersforum.com/members/ryan_berry-albums-37m-high-completely-free-standing-scaffold-13m-wide-min.html

I hope you enjoy the pics.

Ryan