substation bus structure using STAAD 2

[oengineer]

I am working on a single-phase bus support for a substation. I am trying to model the insulator in STAAD. The insulator is made of porcelain material and rest on top of a HSS column. What is the best the best way to model the insulator in STAAD so that the loads for the bus items sitting on top of the insulator are transferred to the HSS column. What type of member should be used for the insulator? Should the insulator be treated as a dummy member? Any suggestions/comments are appreciated.

 

[transmissiontowers]

ASCE 113 is the right place to go for the methods. I chair the committee that is revising the guide and we are adding some verbiage about foundations and anchor bolt design. AFA the shear in the bolts, we are assuming the top nut is tightened by the turn of the nut method to make sure the shear transferred to all bolts. The OP has posted the same question in the forum I pointed to above and I have a more extensive answer on how I design bus support base plates there. Lomarandil, you are correct about the FE analysis of plates in bending. You can probably spend several days doing a FEA of a plate worthy of a doctoral dissertation, but structures have been installed and working for many years that were done in the days before computers.

Our industry is somewhat unique in that we are willing to accept some structural failures in the quest for lighter structures. The building and bridge guys OTOH, are not allowed the same latitude. A building collapse or bridge failure is not acceptable under anything other than a 5000 year extreme event. If one of my towers or substation bus structures falls down, you can't charge your smartphone for a few hours or days.

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

 

[Lomarandil]

Exactly. No need to complicate the base plate design -- you'll end up saving the client more by using a quick hand check and a little extra steel than you would by spending hours on an FEA model and getting everything down to a gnat's tooth.

 

[oengineer]

Thank you all for your input. It has been really helpful with my task.

@transmissiontowers
I appreciate your information regarding the design of the base plate. Especially the information you posted at thread181-27567 (

http://www.eng-tips.com/viewthread.cfm?qid=402289

). Do you h--ave any knowledge of designing stiffener plates for base plates? I do not see any info regarding the addition of stiffener plates to the column to help reduce the thickness of the base plate in ASCE 113 and ASCE 48-11. Would you happen to have a design example? Please let me know if you have any recommendations for stiffener added to base plate design.

 

[transmissiontowers]

Stiffener plates can certainly be added but they complicate the simple bending analysis that we use in the hand calculation method. The reduction in thickness (and structure cost) when using them will probably be offset by the increased cost of welding them to the column. You also have to take into account the stiffener punching into your column. The hand method works well enough and is easy to visualize the base plate bending where it welds to the HSS tube. When the complication of the stiffened plate is introduced, you can make some assumptions on the new bending planes but you may be back coding up the base as a FEA to see where the stiffened plate is bending. We have a reference in ASCE 113 to an old book from the Lincoln Arc welding foundation called Design of Welded Structures by Omer W. Blodgett that is very good in explaining base plate and stiffener design. My 1966 edition has a price on the inside cover of $7.00 and you might find it somewhere for a little more but it is a very good reference.

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

 

[oengineer]

@transmissiontowers
Thank you for your response regarding the stiffener plates. In regards to your method of calculating the bend line for the base plate design, what is your method for determining the tangential bend line length & the distance of the anchor bolt center to the tangential bend line (in ASCE 113 this dimension is designated as c_i). I understand the method you used for the parallel bend line. I am trying to determine which bend line (the parallel or the tangential) provides the best base plate design for my hand calculation. Do you subtract subtract the width of the HSS from tangential bend line to account for the galvanizing drain. Please see link for my sketch

http://files.engineering.com/getfile.aspx?folder=4f762d98-2da6-4fa3-b140-cca6e541c7e4&file=Doc2.pdf

. Here is another document which mentions the tangential bend line

http://files.engineering.com/getfil...ile=PLS-POLE_Base_Plate_bend_line_tangent.pdf

,you can see the information much better on this figure when you zoom in (I initially had issues see the words). Here is a copy of ASCE 113

http://files.engineering.com/getfil...f64-9674e56342ff&file=ASCE_113_base_plate.pdf

. Any recommendations are greatly appreciated.

 

[transmissiontowers]

You will need to check the bending planes that produce the thickest plate so you will check at least 2 in your example sketch and more if you want. The one you call tangential should probably be at 45° to the plate edge to give the shortest bend line. If the tube is square and the 4 bolts are square and the plate is square, the 45° line will be correct. Even if the tube is rectangular and the bolt pattern is also rectangular, the 45° line is the one I check.

Your PLS-POLE reference is more for 8, 12, or 16 sided T-Line poles where they consider bending only along a flat and not tangent to a vertex. Their equations come from ASCE 48-2011.

From ASCE 113 section 6.8 (I wrote some of it about numbers of bolts and the plate thickness, but was talking about big dead end poles with 20 to 48 bolts). Look at Figure 6-1a and check the bend lines 1-1, 2-2, and 3-3. If the hole in the plate is the same size as the HSS tube, you have to subtract the tube width from the effective bend lines 1-1 and 2-2. Choose the maximum bolt load for 3-3 and do the thickness calculation for all bend lines and pick the thickest plate.

There is a paper by a guy named Horn about pole baseplate design that is around 100 pages. Do a search for Daniel Horn and a paper called Technical Manual monopole bases. I found a copy at

http://www.towernx.com

that you can download. I believe he was in the telecom world and did large monopole base plates but the concept is the same.

Good luck.

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