Transmission Tower - Leg Rust 3

[speedyse86]

I work for a utility and a few of our towers, that sit in low areas, are rusting at the groundline of the legs. These are direct bury towers meaning that they dont have a cassion foundation but instead the steel legs have been driven or buried deep in the ground. A couple of the towers were so bad that we had to replace them but there are a few that are not as bad but still need attention. I am trying to generate options as to how to mitigate the rusting problem and to shore up the structural stability of the really bad towers. For the towers that dont have too much deterioration I think we will just clean the legs and repaint them or seal them with galv. For the really bad towers I think we need to do something structrually. Any ideas? I have attached a picture of the really bad leg. As you can see it is a three pronged leg and two of the prongs are rusted all the way through.

 

[msquared48]

Nothing comes up for the link.

Mike McCann
MMC Engineering

 

[speedyse86]

Thanks for the heads up. Hopfully this next one will work.

 

[Ron]

Speedyse86...bad idea to embed thin steel elements in the ground. You might consider repair and concrete encasement to a point above the ground level. Slope the top of the concrete.

 

[dik]

Further to Ron's comment, you might excavate around the corroded area and determine the extent of the corrosion. Often this is limited to the area of the soil subject to wetting and drying.

This portion can be excavated out and the leg reinforced as required, a new coating of a zinc rich primer and then encased in concrete.

If corrosion is caused by the soil or contents, then the entire support is suspect and you have a major reno job on hand.

Dik

 

[JAE]

Would it be possible to do the following for all three legs together?

1. Clean away all organics and topsoil in the top 8 to 12" of the area under the tower, extending beyond the legs perhaps min. 2 feet.
2. Design a solid mat foundation to be placed from this excavation, up 24" or more to encase the tower legs. The mat foundation would be designed to resist all vertical and overturning loads.
3. Weld onto the tower legs numerous headed studs. Or add cross members between legs. Anything to help bond the legs to the concrete mat.
4. Place a reinforced concrete mat.
5. Slope the top of the mat such that any standing water will drain off, and away from the tower legs.

Perhaps repaint the legs prior to this, near and above the top surface of the mat. Seal the joint interface between steel and concrete.

Just an idea.

 

[hokie66]

And a good idea, JAE. When there is a corrosion problem because steel is too close to the ground, pour a new concrete footing above ground.

 

[JedClampett]

Let's see, metal transmission towers, corroded to some uncertain capacity, carrying a valuable and dangerous commodity.
If you don't have enough technical firepower on staff, you need to hire some to perform a study, run calculations and recommend repairs on a tower by tower basis.
You don't want to partially patch over a problem, just to move the weak point.

 

[dik]

Thanks, Jed...

Dik

 

[speedyse86]

Thanks for all the help. The mat foundation was the way I was headed in the first place. Just wanted to see if others thought the same. Thanks.