Hole in Center of Baseplate for Circular or Rectangular Columns

[RFreund]

Before getting into some sort of complicated stress analysis, does anyone know if there are guidelines for holes in the center of a baseplate for circular or rectangular HSS columns?

When thinking about this the center does not seem all that important as the design is normally based on an effective cantilever distance to the bolts. However if you were to say remove then entire center of the baseplate then the moment from that cantilever distance is applied to the face of the column. I suppose though that you could add radial stiffener plates that would help distribute this moment.

Anyone done something like this before? In this case the hole is for plumbing/conduit so I imagine this has been done before. For reference, the column is 24" diameter with a substantial moment at the base on the order of 100 kip-ft.

Thanks!

EIT

http://www.HowToEngineer.com

 

[racookpe1978]

What is the diameter OD of the vertical column? 24 inch?
If so, what is the diameter and wall thickness and material spec of the baseplate?
What is the proposed bolt circle dia of the baseplate? (or only 4x bolts at what spacing?)
What thickness baseplate?
What is the proposed diameter of the hole for the electrical conduit?
How do you propose attaching the baseplate to the vertical member? Any radial braces?
Will you have a access plate to connect up and route the electrical conduits?

 

[BAretired]

How large is the hole?

BA

 

[JStephen]

If you use a yield-line analysis through the base plate, you could figure moment at any section and see what effect the hole has.

The big polygonal utility poles have commonly have holes of varying sizes in the base plate- in some cases, just making them a circular ring.

 

[RFreund]

Sorry for the lack of info, but in my defense I was mainly looking for some type of design guide. I was thinking there might be something out there because I"m sure monopole type structures and utility poles use this detail. However, here is some additional info:

What is the diameter OD of the vertical column? 24 inch?

Yes, 3/4" thick

If so, what is the diameter and wall thickness and material spec of the baseplate?

Base plate is currently 36x36 w/ 10 bolts but I like the idea of a circular baseplate and circular bolt pattern (I can change to that). ASTM A36 material

What is the proposed diameter of the hole for the electrical conduit?

Currenlty 7" diameter

How do you propose attaching the baseplate to the vertical member? Any radial braces?

Fillet weld around the outside of the column. I can add radial braces at the base plate if necessary.

Will you have a access plate to connect up and route the electrical conduits?

Yes, probably.

Thanks again!

EIT

http://www.HowToEngineer.com

 

[paddingtongreen]

It is done all the time with tubular transmission towers. I can't tell you how to calculate this, we bought the towers from specialist with in-house programs, we designed the footings based on their provided reactions.

Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin

 

[BAretired]

You probably have seen this link:

http://www.towernx.com/downloads/Technical_Manual_MP_BasePL.pdf

BA

 

[transmissiontowers]

ASCE 48 is the standard for utility poles and base plates and has a section on base plate design. If you have PLS-POLE, there is a base plate check which uses the ASCE 48 method. The Daniel Horn paper referenced above is also excellent. On your HSS tube and base plate, you should have some way to drain the zinc if it is galvanized. Many manufacturers use key slots in the inside hole to drain the molten zinc. The shaft to base plate weld is also critical and difficult to do if the welder cannot get inside to do a seal weld. Unsealed backing bars can be a problem with trapping the pickling acid before galvanizing.

ASCE 113 also has the older ASCE 48-2005 method and is currently being revised.

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

 

[RFreund]

Ahh! Thanks BA, I've seen it many times and for some reason failed to realize that it addressed this situation. There seems to be some limits but it should serve as a good starting point.

Thanks for the other suggestions as well.

EIT

http://www.HowToEngineer.com

 

[frogit22]

Seems like a problem some sort of external stiffener between the column and base plate could resolve. Chamfering the top corners is usually a good idea.