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Marquees and Wind
Whenever you put up a marquee or tent you must take into consideration the weather. Not only the weather at the time of erection but the worst weather that your site may receive.
You must make a reasonable guess at this by using both common sense and experience. If a site is exposed, near the coast and in the middle of winter then expect high winds! A sheltered site, inland in Summer will (on average) receive less wind. You must erect the marquee to withstand these winds. It takes many years of experience before you can be competent to make these decisions however the following will give you an insight into what you should be considering every time you put up your marquee.
News - Marquee blows awayThis is one of the cheaper far east made marquees. If this marquee was correctly pegged down, despite the marquee being much weaker construction than a proper commercial marquee it would not have blown away. Marquees have killed people, both as they were put up or when they blow away. You don't really want the adverse publicity this will cause and the increase in insurance. I would suggest the following:-
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Location
You must consider the location of your event as this has one of the greatest effects on the stability of your marquee.
Windspeed
Windspeed
The chart opposite shows the basic wind speed for the UK. This illustrates that the wind generally increases the nearer the coast and the further north you are. Wind speed also increases with height. It should come as no surprise that it will be windier on top of a hill then in a valley. It is also true that in winter we will have higher winds than in summer. These are generalisations and certain sites for example near tall buildings or during a summer thunder storms, can produce high winds at any time of year. A good tool for predicting the wind speed at your site is to use the website xcweather.co.uk which gives you an interactive map of the UK and a forecast of wind speeds for 7 days ahead. If high winds are forecast it may be prudent to have extra staff available on site for both maintenance of structures and help with evacuation of marquees if needed. It has proven in the past to be almost impossible to get the public out of marquees when it's raining or windy. It may be better to cancel or postpone the event rather than risk a life. The duration the marquee is constructed for is also a consideration for example it is quite easy to predict the weather on the morning of a summers day. However it is more difficult to predict the worst weather a marquee may receive for the next month. The safest solution is to erect all marquees so they will withstand the worst weather that could reasonably be expected. |  Basic windspeed Vb (m/s) (BS 6399: Part 28.3). From BRE Digest 346 Part 38 |
Ground Conditions
Assuming that you don't want your marquee to blow away you will need to anchor it to the ground. The most common way of doing this is to use steel pegs (some times called stakes or pins these are normally steel rods, for most small marquees around 25mm x 1000mm).
These will only resist pull out if they are used correctly. For example if the pegs are used on sand they will be almost useless.
These marquees will need special consideration as the pegs form part of the marquees integral structure. Depending on the site / time of year and ground conditions it is normal to "double up" on corners and seams. This means that each corner of the marquee has two or more guy ropes and pegs. This both improves pre tension (the force applied to the roof before wind or snow loading). You can almost not have enough pre tension on a marquee as this will reduce the amount of flapping that occurs. Less flapping will reduce the shock loading a peg will receive, reducing the chance of exceeding the pegs capacity.
The pegs should be angled away from the marquee when driven into the ground and the guy attached as low to the ground as possible (this increases resistance to pull out). Careful consideration should be given to the exact location of the pegs. If they are too far away from the marquee there will not be enough down force to keep the side poles from lifting causing the structure to fail. Too near and the roof will not be tensioned enough to resist the wind. A compromise is to have two sets of pegs one closer in than the other. The correct distance is normally just less then half the height of the side pole away from the marquee.
Another consideration is the amount of water contained within the ground. If the ground is saturated this will dramatically reduce the holding capacity of the ground. As the rain will run off the marquee at the edges this concentrates the water logging around the edge of the marquees.
Framed or Clear-span are not immune from blowing away! The wind has two effects. Firstly the wind tries to push the marquee horizontally which does not normally cause a problem. However the second effect is lift on the lea side of the marquee roof. This will lift the marquee. Although a marquee may only be lifted with a few kg of lift, the repeated lifting and falling of the marquee over many hours will knock the pegs out 1mm at a time. Resistance to this can be improved by angling the pegs so as they are not in line with the lift. If the pegs do fail then the marquee will be lifted up then crashed down. This will cause the marquee to fail. If high winds are forecast you can guy a framed marquee down. Rather than putting the guy ropes at a right angle to the marquee walls. You can put them parallel in line with the walls which provides excellent resistance to prevent the marquee from lifting. Your customers have an almost lemming like ability to do the wrong thing! You must stress both in your contract / T's and C's and face to face that if you open up the marquee on anything other than a calm day then a opening on a upwind wall must be matched with an equal size opening in the lea side wall. At the same time impress on them the importance of not removing the guy ropes / pegs or cross bracing! For more information please see the following:-
Safe use and operation of temporary demountable fabric tructures
HSE Event Saftey Guide (Second Edition) Codes of Practice For Marquee HireTraditional Marquees
Framed Marquees
Customers!
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