Strange Tower Base Connection 1

[msquared48]

This is the connection for a 60 foot tall guyed steel lattice tower in Eastern Oregon. So much for the easy part...

What I do not understand is the base configuration with the triangular steel beams and the tower legs sitting at one point of the triangle. There should be no moment at the base since this is a guyed tower, but I am reading otherwise due to the structural configuration, and the tower is technically set off center of the concrete footing. I have not seen it yet, but I wonder if this tower base was designed to develop the moment capacity of the steel lattice tower. At first I thought that the steel beams were an after thought to plumb the tower, but the shims look about the same thickness.

Anyone seen a base like this one? I note that the smaller tower in the background is also guyed and mounted off center of its concrete footing. Perhaps this is common?

Mike McCann, PE, SE (WA)

 

[Archie264]

Actually I didn't mean eccentricity in the footing but, rather, an unsymmetrical frame. It seems they would need that for stability if they were to raise the system into place using it's final position as a hinge point, akin to how a dump truck is configured. The two base plates away from the tower would then be designed to resist uplift. But, surely someone who works with towers would know immediately.

 

[dhengr]

Mike:
I’ll be darned, you may have proved, or be proving what I was suggesting in my first post. You’re saying essentially what I was trying to say, maybe inelegantly. But, without the benefit of any loads, dimensions, etc., or the software to run an analysis on that tower, I had no idea of real numbers.

 

[rb1957]

certainly is an odd looking arrangement. bracing is continuous and welded to the columns ... suggests on-ground construction and pivoting into place. mined you the base plates on the two obvious legs don't look to be aligned ?

the 2nd tower in the background ... base looks different, as though the single leg is inside the triangle (as oppoesed to this one where the single leg is nested into the corner.

lord knows what the triangle of steel is doing, other than complicating things !?

base moment ... why not say zero moment ? whatever moment develops there is small compared to the moment reacted by the guys and maybe local yielding would make it less ?

is the tower built in segments ? or one piece ?

another day in paradise, or is paradise one day closer ?

 

[msquared48]

rb1957:

The tower is built in three 20 foot segments that are bolted together. As for the moment, to say it is zero is not what is there. It affects the verticals and the webbing. If this were a tapered base, yes, but that is not the case.

Webbing is a very strange arrangement, too, as it is a staggered "Z" shape on each side, with the height of each "Z" at 1.8 feet, overlapped 50%, netting 0.9 feet between the horizontals. Never seen that before, and apparently, neither has TnxTower. May have to model this in RISA and import it.

Fun and games, right.

Mike McCann, PE, SE (WA)

 

[msquared48]

I guess the webbing pattern is documented after all in TnxTower - called Z Rohn65. Sweet...

Mike McCann, PE, SE (WA)