Swiss Federal Gymnastics Festival

[kerry davies]

Paul, as Tom states there were no walls on the clearspan and I think we need to put tents and marquees in perspective for a moment.

 

Chris has pointed out the lack of organised response, absence of stewards and complete absence of the Skewen War Cry (runawayrunaway) which seems common to many of these incidents. Plan for disaster or it will become a tragedy. Have "controllers" briefed on what to do with the crowd. That is nothing to do with tents, stages and marquees, just poor management.

 

In 1987 we lost 15 million mature trees including giant oaks and 22 people died in winds that gusted at 81 mph for four hours with isolated gusts of 120 mph in the flatlands where Paul lives. In Scotland winds with gusts of up to 100 mph, meaning mostly 80 mph, took down stone walls, chimneys off tenements and dozens of roofs. What's the point of a tent then? The punters should all be indoors with a cocoa long before that.

 

I have been outdoors in 80 mph winds, few BR members will have. Breathing is almost impossible and sheep get blown over. (REALLY!) At 35-40 mph walking is difficult, at 45-50 slates start to fly and chimneys fall, at 50-60 large trees are uprooted and walls get blown over. Over about 60 is a rare occurrence with widespread damage and above 70 serious structural damage occurs. 80 mph is fit for loonies and Welshmen on mountains only. That is what these people were faced with.

 

You may be ignorant of tents and the ways of the strange breed that are tentmasters, Paul but you would need to be seriously bonkers to even think of holding a tented event at half the wind speeds forecast for this one. Marquees may be able to take it, if they are reputable makes and well erected, punters don't fare so well.

 

ETA for Paul. To understand what the lack of walls does, think "umbrella" and think "paragliding". Rob has it right. Mainly walls prevent this though it is amazing how much stability the roof panels and walls add to a frame.

[ImagineerTom]

Paulears

 

Firstly all the structural calculations (and designs assumptions) are based on them being fully assembled (ie with the walls on) so if the walls are off you're working in uncharted territory. More importantly, think of the cross-section of a marquee with the walls off - you've got a chunk of air trapped under the apex of the roof (not to mention the turbulence that all the framework on the inside creates) which means that the roof effectively becomes a solid aerofoil. The air passing "through" the tent passes straight thru, the air that passes over the tent takes longer creating a pressure difference which tries to "lift" the roof upwards (or in the case of turbulence inside flip this the other way) since a 40m square airplane wing produces enough lift to get a few hundred tones of airplane in to the sky can you imagine the forces a 1000m2 marquee roof produces?

 

It's slightly more complicated with bigtops as they are generally circular and the height of the roof is considerably more than the walls (whereas a clearspan has a 1:1 ratio of wall height to roof height) so the air movement is different and you actually end up with them acting as a funnel causing them to bellow in & out; hence why the good manufacturers put blow-out sections on the cupola's to stop the differential occurring. The strongest bigtop design is the "high dome" style (see http://www.letsdothe.../mama_class.jpg) because the structure itself (put up properly with all the walls on) is effectively "invisible" to wind due to the perfect symmetry - failure of this design comes from turbulence of wind passing the king-poles and other obstructions, or from ground failure due to sudden saturation (ie stakes pulling out of the ground so that the structure looses its perfect shape thus loosing its invisibility) and also being hit by debris that damages the membrane and thus changes the shape. It's quite remarkable when putting them up/down how a loose floppy structure that's shaking in the wind suddenly becomes an incredibly stable and still structure as it jacks up to full height and thus shape.

 

here endeth the lesson

[Gerry]

I have never been, or likely to be, involved with supplying or erecting tens/ marquees.

But a question as an ordinary member of the public.

If I was there and I was told to evacuate the site, where would/ should I go?

My natural instinct would be to find shelter to get out of the rain but what sort of shelter, if any, should I seek?

Cheers

Gerry

[cfmonk]

Hi Gerry,

 

That's sort of my point. Here and at Pukkelpop the public sheltered from the horrific conditions in a marquee, it's perfectly logical to the normal mind. If I was there I would be as far away from the 10 tonnes of metal attached to a sail as I could be. In fact, as far away from anything as I could be. Anything travelling at 50mph is lethal be that banner, pop up, deck chair, umbrella or bicycle.

 

My advice if you are ever unfortunate to be in this situation is get into the middle of open space and lie down!! Be careful of lightning though...

[kerry davies]

You shouldn't even have to think about it, Gerry. An evacuation plan to a relatively safe area should be in place as part of the event manual. Go where you are guided.

 

Most BR members already have a mental plan from fire alarm evacs and practice. Avoid hazards, find a safe place and get everyone there in a calm and efficient manner.

 

For me? I just love a nice quiet lie down in a ditch somewhere upwind and away from large trees. In all my years of drinking and ditch dwelling I never came to any harm in a nice dry ditch.