Neither the stage, nor the supporting structure will move. The Crab is not even that forward thinking in terms of engineering.
Knowing Mark Fisher's M.O. like I know the back of my hand this is going to be a very simple steel structure - basically two arches in two directions. Picture the Popmart arch in two directions.
The whole idea is tension and compression for anyone who has sat through a structural engineering class. The big squares at the Crab's 'feet' are actually ballast (basically giant weights) that will prevent the crab from moving. They will either be concrete slabs, or more likely giant tanks to be filled with water. Fisher has used this method on every tour he has designed. It is a cheap and easy way to keep stages in place. Giant plastic tanks are toured (and usually kept under the stage) - the steel structure is connected to them like giant heavy feet and that creates the foundation. This prevents the structure from swaying in high winds and rain. The brilliance behind it is that all they have to do when they get to a city is fill them with water. When enough are used they achieve the necesary weight to keep the steel structure in place.
The tricky part about the crab is its geometry. All the lights and sound and stuff will be pulling the body of the crab down directly over the stage in compression, thus pushing the legs out in tension. That is wny the ballast has to be heavy enough to push it back so C=T.
Here, however, if they are only utilizing four locations, I would guess they will tour four multi-ton concrete slabs. These are usually precast and are very commonly used to keep hoists attached to the sides of buildings when they are under construction. Since they usually tour at least one crane (ore rent locally) it is just about picking them up and dropping them on a flatbed trailer.
If the 170-ton gossip number is accurate (and it just may be with lights, sound, spiky thing, etc.) than divided by four it would only be 42.5 tons or 85,000 pounds being transferred to the crab's feet (plus the weight of the structure.) Not such a big deal.
As they seem to be utilizing arches (one of the strongest structural systems going back to the Romans) this really should not be all that difficult to tour.
Yes, they typically take three sets of structural steel with them when touring outside, but not all the electronics, lights, sound, and scenic elements (ie the really expensive stuff like LED screens.) Those items are packed up first after the gig, loaded-out and then trucked to the next location where one of the other two sets of steel has already been erected. It makes for a very efficient leap-frog logistics plan. All they have to do is set up the steel in three consecutive cities, then move the expensive assets and the band to the next city.
So thus, there will be three crabs.
As for the fabric tensile stuff on top, I have to imagine what we have seen is only very sketchy. It is obviously there to hide the guts of the production, but I do not think (hope) it is going to look like the basic renderings we have seen.
My current concern is the height of the crab. I actually hope the thing is extremely high. If the footprint shows something approximately 50 yards by 50 yards as can be seen on the US football stadium diagrams, I am hoping the lights are trimmed at a very high level, otherwise this thing is going to look very squat.
In any case, I am amped up by this idea because I truly think the endzone stadium show has run its course. Between U2, The Rolling Stones, Genesis, and I hate to say it, Bon Jovi, I really do not think there is much more you can do with a stage and a giant screen to be impressive.
Lets see what transpires, but I hope the team continues to release nuggets for geeks like me to chew on.
It's the support structure for the entire PA system and 360 degree screen which together weigh hundreds (thousands?) of pounds!
hmm
