Steel lattice towers angles fabrication

[RobertBuc]

We are in process of replacing some rusted members of lattice tower. The members are structural angle shapes with one of the legs at the ends bent out to create a wider, flat surface to accommodate bolting for the end connections. The bending process would seem to induce stresses in the angle. Also with the corner bent out would need to grind the old corner to get a flat surface. I have looked but haven't come across any fabrication specifications to make sure the integrity of the angle is not compromised. Anyone have any experience with this? Thanks

 

[jayrod12]

Pictures? Or at least a sketch would result in much more tailored responses.

 

[RobertBuc]

Here's part of a detail drawing showing some of the pieces. Hope that helps.

 

[XR250]

Never seen anything like it.
Can you just weld or bolt flat plates to the angle?

 

[msquared48]

Who was the original tower Designer/Manufacturer?

Mike McCann, PE, SE (WA)

 

[Lomarandil]

Took me a while to remember where I saw this recently -- it was for some Caltrans highway signs.

Presumably, if the axial demand is low enough, the residual stresses aren't an issue. If it's bracing governed by buckling, that seems plausible -- but I imagine that most lattice towers are made up with tension bracing...

If it can be made to calc out, I can see how it'd be incredibly appealing on the fabrication side.

 

[thaidavid40]

Must take a relatively heavy shop press to effectively and efficiently flatten even a modest sized angle like this. Is it practical in the average shop these days?

Thaidavid

 

[dhengr]

RobertBuc:
That’s not a common detail, that I’ve seen used before, but it does seem doable. The reshaping is probably done with some heating of the end of the angles and then the use of a die or several progressive dies and a heavy press. This would allow the transition btwn. the vert. leg to the flat to be reformed in a controlled and nice clean manner, and it would likely help flatten the material at the radius btwn. the two angle legs also. And, to a good extent, the heating would eliminate much of the high yielding, cracking/ripping and residual stresses which would take place if done cold. The fact is that this shape allows for more bolting space, and actually sorta takes a shape in keeping with the shear flow and shear lag transition which would normally take place in the unformed shape. That is, the connection forces/stresses moving from the horiz. leg, up and out into the entire section in some distance similar to the formed shape.

 

[RobertBuc]

The original towers were fabricated in Italy. It would not be economical to go overseas to get a relatively small number of pieces. Would prefer sourcing from US.
I agree with responders that it's a nice looking detail and shaped to go with the flow of stress in the members, which are tension only bracing members.
As responders note they must use some heavy press and heat to fabricate. I'm looking for way to specify process that would not damage the ends, other that just saying don't damage the ends. Perhaps a method to test/verify after fabrication?
Thanks
RobertBuc

 

[racookpe1978]

CAD/CAM plasma cut the two flat side shapes, then fillet weld the two flat plates in a simple jig.

Or, accept the higher weight of the replacement angles, and plasma cut the centers. A press can flatten the two ends if you push into a form made at the correct final angle (plus the 3% strain bend relief.)

How many need replacement of each different size? Or are there many different size pieces to be made?

 

[RobertBuc]

As for quantities, we are just getting into the job and don't have a handle on it yet.