Transformer Foundation Design using Reinforced Concrete 2

[oengineer]

I am working on a foundation design for a transformer to be used in a substation. I am given a vertical load and told the height of the transformer. This transformer does not have an oil spilled containment, it is just a rectangular slab. I have been given initial dimensions for the transformer foundation slab. I have designed transformers in the past for refineries, but this is my first time doing it for a substation. I believe it should be designed the same way. Is that assumption correct?

When previously designing transformer foundations, the information I first obtained was: the erection & operating weight of the transformer, plan dimension of transformer base, height of transformer, center of gravity location when dealing with seismic, and anchor bolt size & location. The geotechnical information I used was the soil allowable bearing pressure, soil density, and ground water table location.

I computed my lateral shear load and moment caused by wind and/or seismic loads, then checked for the soil bearing pressure, sliding & overturning stability. After determining that the size of my foundation was adequate, I designed the the slab as a regular one-way slab based on the applied forces for strength. Then I designed/checked my anchor bolts.

I was asked about the considering 2/3 dimensions of the slab, dealing with eccentricity, and considering the center of gravity. Some of these other checks seem unfamiliar. The transformer is not in a seismic area, so I am not sure the need for center of gravity (I can assume the center of gravity based on the foot print of the transformer since I don't have vendor drawings).

Please let my know if you see something I am missing/overlooking. Any suggestions/comments are appreciated.

 

[SlideRuleEra]

Keep in mind that the Risk Category (Table 1.5-1 of ASCE 7-10) should be either Category III, "Buildings and other structures, not included in Risk Category IV, with potential to cause a substantial economic impact and/or mass disruption of day-to-day civilian life in the event of failure."

or Category IV, "Buildings and other structures required to maintain the functionality of other Risk Category IV structures."

This may (or may not) be different than transformers at refineries.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[Teguci]

Sounds like you are putting together a bid set that should have a big prelim stamp on it. They should give you the final size, weight and COG once they've selected the XFMR and performed the soils report. As a side note, the one time I did this, the Utility company told me not to provide anchor bolts. I pushed back and they put it in writing.

 

[DETstru]

Sounds like you have everything covered. Like Teguci said, if you don't have a final cut sheet on the transformer I would put the max load and transformer size you assumed directly on the drawings (I do this anyway, even if I have the final cut sheet). That way if they come back with a transformer that weighs 20% more you can show them exactly what was designed for.

 

[racookpe1978]

If this is a green field installation, you will need to anchor the fire separation walls as well: normally I see them integrated into the gravel oil retention pit around the foundation. Very surprised they believe you don't need one. Depends on separation distance between heat susceptible units.

In an existing yard, the walls are usually in place for the replacement transformer, and the foundations left in place. Gravel dug out and silt removed too.