Frame Marquee collapse during pull down...

[Junior8]

https://www.bbc.co.uk/news/uk-england-hampshire-65970802

[ImagineerTom]

I'm not seeing anything like the number of diagonal / X-bracing beams I would expect to see on a structure that size. I'm also wondering why they're using a crane to install....

Clearly the weekend for it - a stage in Strasbourg had to be held up with emergency telehandlers as it would appear someone only put half the bolts in and a bigtop with stage in it in Vitry-sur-seine came down in a storm because the lighting truss inside were installed so close to the rough they acted like a knife when the winds hit. 

[Junior8]

Glad you thought that Tom I counted them too. But something else happened too I fear.

[ImagineerTom]

If there's not enough X's then that style of structure is just a series of (top heavy) basic A-frame shapes that are only held upright by the strength of a few dozen pop rivets being pulled in their weakest orientation - only a slight knock (enough to pop a couple of rivets) would be enough to set of a cascade of failures that would end up looking remarkably like the "after" picture.

In 't olden days the original install method for that style of structure was to install a series of proper guy ropes to several of the frames so that there's a pyramid shaped "solid" structure from which everything is built and it's only when every cross brace and re-enforcement was installed would you remove the guys; reversing the process for the take down.

[alistermorton]

Presumably doing it "the olden way" isn't considered cost effective these days so some way is sought to "streamline" the process i.e. take less tie and cost less in labour?

 

[ImagineerTom]

Exactly - just like the world of submersible building key safety processes were dropped by people who didn’t actually understand why they were created in the first place.  

[Andrew C]

Local news said that it was being dismantled.  I wonder if someone decided to take out too many longitudinal / cross members too early?

[kerry davies]

Following Brexit, the pandemic and a shortage of experienced crews the only surprise is that there are not a lot more of these incidents in a lot more branches of the events industry. This looks like the result of a combination of causes boiling down to people taking shortcuts.