Revision to ASCE 113 Substation Structural Design Guide

[CivilStructEngr]

I understand that there is supposed to be a revision to ASCE 113 Substation Structural Design Guide to bring it in line with the latest ASCE 7 loading trends.

What is the status of that? Can we have a sneak peek at it? Or at least an idea of the direction it is heading?

 

[transmissiontowers]

As you may have read around here, I Chair the committee that is doing the revision. The ASCE 7 is a sticky subject and seems to be changing to larger loads for our structures. We hear that the wind maps that we use from ASCE 7-2005 which were based on a 50 year MRI changed a lot in ASCE 7-2010 and are changing even more in ASCE 7-2016 or whatever the next version will be. They seem to be going to seismic style return periods. I am no wind expert but our structures behave much differently than a building.

Our problem is the younger committee members want to just adopt the ASCE 7 maps because they are the latest and greatest while the older members (like me) do not see much advantage to arbitrarily raising the loads we design for. The problem is our industry has an exemption from the ASCE 7 wind maps and associated factors because our structures an not buildings and bridges that human life would be in jeopardy if our stuff failed. I can understand the building guys overdesigning their structures to protect human life because they don't know the dead loads and live loads that well. We know with a much greater certainty our loads. The other problem is that historically, we have not had many structural failures using the old wind maps and the older members don't see the need to increase the loads just because the building guys say so.

That being said, we are a consensus committee and the result will be some compromise where we adopt ASCE 7 maps but strip out the big overload factors. We don't have enough funds to have our own wind maps produced. The other problem is the center of the country uses weather station data to make the maps while the hurricane regions use a computer Monte Carlo simulation to draw the wind speeds and the combined map uses different methods.

The old 113 version used a simpler seismic method that worked fine. The revision is heading toward the ASCE 7 seismic method, but I'm in Texas and we don't allow earthquakes down here so I have a very vague understanding of the complexities. Again, the older members don't see many substation structures that failed during an earthquake using the old method so changing to a more strict building type seismic seems like we are changing just because the building guys say so.

We are adding a chapter on foundation design but will not tell you how to design them. It should be just a high level overview of the types of foundations that we use in the industry and what to look for when you design them. There will also be an appendix for comment they is a rough proposal what a Standard would look like if our Guide were to be advanced to a Standard like ASCE 10, ASCE 48, etc.

Whenever people contact me to get a "ruling" on what is in ASCE 113 and how it should be interpreted, I tell them it is just a guide and they are free to ignore it and do what the substation owner wants. They can use whatever wind speed and earthquake they want to design their substation. We put the original guide together to do some knowledge transfer from the old timers that had to make our own rules for substation design to the younger college graduate who learned building design in school. With the volatility in the petro-chem industry, some of their engineers may try to branch out and start designing our structures and they may benefit by reading our Guide.

HTH

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I have been called "A storehouse of worthless information" many times.

 

[CivilStructEngr]

Thank you Transmissiontowers,
I'm a bit older (not necessarily wiser) too. I'm with a larger engineering firm active in the T&D realm with the initials "HDR" I agree with your assessment. I would like to join the 113 Committee if that is possible.

 

[transmissiontowers]

We are pretty far along on the committee and are not accepting new members at this time. If you can hang on for a few years, the committee may reform to make it into a Standard.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[TLinesKC]

Any idea on when the revised ASCE 113 will be published?

 

[transmissiontowers]

The publish date is a good question. We have just come from a meeting in August in St Louis where we went over 300 technical committee comments on the new content. We did not get to another 550 editorial comments. Hopefully late 2017 or early 2018, we will get the document to ASCE for publication.

_____________________________________
I have been called "A storehouse of worthless information" many times.