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.


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

Any help is much much appreciated.


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