How many rawlbolts to hold down a windy tarpaulin sun shade?

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How many rawlbolts to hold down a windy tarpaulin sun shade?

Postby aoline » Sat May 10, 2008 4:47 pm

Regards, I had a search but could not find other relevant posts.

I've built a simple 25mm galvanised tube construction on my flat roof with the idea to add green 60% sun shade over it to create a more pleasant relaxing area.

However, trying to do the calculations in case a strong wind arrives I want to be sure this structure is tied down securely. I understand that wind pressure on a structure like this is mostly upwards so it is the foot anchors that matter most.

I am using rawlbolts into the top of a concrete like stone wall. Each bolt takes a kN load of between 2.3kN and 4.7kN or about 500lbs to 1,000lbs. I think the 1,000lbs is a bit of a perfect estimate so I am happy to proceed at 500lbs.

I have 21 of these anchors with the potential to add a few more. This suggests a strength of 10,500lbs add the weight of the metalwork another 400lbs so let's call this 11,000lbs.

The shade area is 64m2 or 688ft2.

P = 0.00256 x V2 , where: P = wind pressure and V = wind speed.

This wind pressure code suggests that my typical fastest gust wind of 35mph to produce a force of 3.135lbs per ft2 which multiplied by my surface area is 2,157lbs of total pressure which is well below my structure strength.

Question:

Does this all seem about right or have I messed up my approximate calculations?

Any help is much much appreciated.

Thanks,
Matthew
aoline
 

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