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Tents and marquees


Roderick

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There is a growing discussion here about whether the walls of marquees and tents should be opened or closed when the wind starts picking up.

I have always been of the believe that walls should be closed in high wind. This forces the wind over the roof and creates a downforce.

Opening walls could create an upforce and destabilise the structure. Most engineers' reports I have seen support that concept.

 

But recently there has been a push to open the walls in windy conditions, supported by other engineers' reports.

 

Before this blows out of proportion (pun intended) I'd be interested what my learned friends have to say in this matter.

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closed and down, otherwise the "trapped" air in the roof apex makes it act like an aeroplane wing and lift. Also significant secondary damage from the stuff inside the marquee blowing around. That said, conventional A-frame marquee's only have a wind rating of slightly over a sneeze so it's largely academic.

 

Big-Tops the policy is to close all the walls and keep an eye on everything - proper brand-name big-tops have blow-out panels in the cupola (the big metal shape on the top) so that if the wind pressure does build up inside to the extent it could be a problem they will pop open giving you a warning that the wind is too strong. I think the lowest-rated bigtop we have is rated for 80mph winds; a combination of the shape and significant over-engineering (compared to conventional marquees) which mean they can take a real pounding.

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In the UK the generally accepted norm is that when winds of 40 mph are expected, not when they happen but are forecast imminently, the walls should be closed and secured and the marquee evacuated. In some cases where unexpected gusts hit a marquee with an open side, such as a stage cover, I would temporarily open walls as blow throughs but if so would shut the stage and evacuate the immediate area. That would normally be around 25-30 mph as I saw fit.

 

The point being that opening walls is one of the last things and the management system should have taken account of site choice, weather forecast, tent management and evacuation plans before the necessity occurs.

 

As far as big tent engineered load ratings of 80 mph are concerned they may well be true but two things to bear in mind are that the US stages that fell down in 60-70 mph winds were rated at 90 mph and that I, for one, can't even stand up in a hurricane or cyclone force wind which is what 80 mph is.

 

Check out the MUTA guidance and marquee calculations in the IStructE Guide.

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http://www.stareventsgroup.com/downloads.php

 

Provides some useful information - although you will have to register...no big deal as I have yet to receive any junk mail from SH.

Down near the bottom of the page is the "High Wind Speed Actions".

 

I can't speak for Oz, but in the UK the marquee supplier/erector should be able to provide the documentation that advises on loadings/wind/correct usage.

 

If you don't want to register then I can send you the .PDF.

 

KC

 

 

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  • 2 weeks later...

while not commercially, I too have put up more than my fair share of marquees, especially for being only 17! But in windy conditions we always have walls on when its windy, because if the wind gets inside then it pushes the roof up and off. I have also heard of roof sections being damaged due to this, but that was partly due to poor workmanship.

 

HTH :D

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