×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Base Plate Design for Bus/Equipment Stands in HV Substation

Base Plate Design for Bus/Equipment Stands in HV Substation

Base Plate Design for Bus/Equipment Stands in HV Substation

(OP)
For three years I worked with a large utility that has a complete library of standard structures. Everything is overdesigned so as to provide fool-proof reproduction of substation structures. There are no managers or supervisors with enough gumption to question the use of costly designs which ultimately come out of the rate payers' pockets.

Now I'm with a company where my design will be implemented in the construction of brand new substations supporting renewable energy. By nature, I am meticulous and not wasteful of money or resources. I have no problem sizing the steel members to support bus work and equipment. But I could use a little feedback on base plate design. At the utility, 1" base plates were used on all structures. So far, I have done some fundamental calcs evaluating the yield strength of plate under a resolved moment. I found that 1/2" plate can be used for most structures and 3/4" plate used for the worst-case (i.e. tall, single-phase bus support). Any thoughts?  

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

Check your designs with the many AISC base plate examples out there. The much maligned Design Guide 2 covers this.
For standard wide flange columns or posts with axial loads, the design is pretty straight forward.
Having said that, there is some savings in standardizing equipment & connections. No point in reinventing the wheel on a job-to-job basis.   

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

Question, are you grouting the baseplates or are they supported by nuts on the anchor bolts?, it makes a difference.

With galvanized structures, we, and many others in the business, kept an air gap under the baseplate.

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

Without going into detail, consider that components of the electrical generation / transmission system (such as the  substations you are working on) are essential services and are expected (by the public) to survive predictable catastrophic events (e.g. hurricanes, earthquakes, heavy snow loads, etc.) with minimal damage.  Having electrical power available is a primary requirement to begin recovery from a disaster.  The bottom line, IMHO, be conservative in your designs - no one will care how much money was saved during construction if power cannot be delivered (by the utility) for weeks / months.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

(OP)
I appreciate the responses so far. First, the base plate will be off the top of concrete with two nuts for each anchor bolt (galvanized steel structure). Second, I am aware of the critical nature of such facilities. Our substations are all within the same region where 90 mph wind and short circuit forces will govern. Seismicity is not a consideration (Seismic Zone 0). And lastly, our scope of work is such that I will be able to create a standard, efficient design for each type structure to be confidently installed as, again, all of the work is within the same region. Safety factors (LRFD and ASCE No.113) are built into the design from the top, down. I don't want to arbitrarily call out 1" base plates across the board to incorporate additional safety. From a preliminary drawing I have, we will need 283 base plates for equipment and bus stands. Consider this, if 199~ 1/2" and 84~ 3/4" plates are required for one large substation and 1" plates were instead ordered, how much unnecessary steel has been purchased? I estimate 5,410 pounds! Can anyone provide a dollar estimate for this excess steel?

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

very rough estimates, about $2750, or about ~30 engineering hrs.
 

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

MasterSnake - Here is a thread from 2 years ago with estimates for fabricated steel from about $1.50 to $3.00 per pound:
thread507-219493: Fabricated Structural Steel Cost
To make a fair comparison consider that the engineering time and fabrication process are very similar whether the thickness is 1/2", 3/4" or 1". I would say that an estimate of $1.00 to $1.50 per pound is reasonable, based on that thread. Say $8000 for 5410 pounds.

Please don't misinterpret my suggestion to be conservative as meaning to make a "mindless" decision to go with 1" thick material for all baseplates.

My idea of conservative for this application could be to use 3/4" thickness where 1/2" is calculated and 1" thickness for the 3/4" situations. By proportioning out your numbers this would appear to be about 3200 pounds of "unnecessary" steel that is "worth" about $4800.

To make a fair comparison, be sure to consider this cost (whatever you decide it to be) against the total value (not just the structural aspects) of the substation project.

www.SlideRuleEra.net idea
www.VacuumTubeEra.net r2d2

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

(OP)
Thanks again for the feedback, fellas! SlideRuleEra, the link to the thread regarding steel pricing was informative. I should of done a little more homework before posting the question. But hey, we all learn as go along. Specifically, for substation design, I referred back to ASCE No. 113 and found formalae to determine required base plate thickness. I ran some calcs and it looks like, indeed, base plates will come in around 1". Maybe I was a little harsh on the big utility... at least my intentions are good in not trying to be wasteful in design.

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

I asked about the grout because those with airspace under them see bigger bending moments.

One of the things I quickly realized when I was a young, gung ho, designer was that the old guys were no slouches, If I found something I thought was over designed I learned to ask why; if I saw a short cut, I took a good look because if it really was shorter, it would be the well worn path, the people who came before would have checked it out.

Michael.
Timing has a lot to do with the outcome of a rain dance.

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

Along the lines of what Pad is saying....
The first place I worked had some good "old guys". One in particular I remember was a very practical engineer. He had very basic approaches to his designs and was very good at explaining himself. This, even though there was a bit of a language barrier with his being from India.
I can recall him having me design base plates for a large industrial project. When I came back with 8 or so different thicknesses, he patiently sat me down and explained how my calc's were correct but my engineering was all wrong and how much more simple I could make our schedules and fabrications if I grouped those plates into one or two thicknesses.
He also used to explain that "engineering is not an exact science. We have to make guided decisions based on the best research available. If we get a member size that we  think is on the edge of that research and science, there is nothing wrong with going to the next biggest size."
I've tried to carry his practical advice as it came from real number crunching, not an FEA program that spit out a stress ratio of 0.95.  

RE: Base Plate Design for Bus/Equipment Stands in HV Substation

Even though you are in Seismic Zone 0, according to the IEEE 693, your equipment (and structures) is expected to have acceptable performance at 0.1g and less.

Refer to Section 8.5.2.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources