Wide Flange Column Embedment Into Pier Footing

[samchrun]

Hello,

Need some help in figuring out the required embedment length of a wide flange column into a pier footing to fully develop axial and flexure load to the pier. Thanks

 

[hokie66]

This sounds like a trick question I was asked 45 years ago as a student. If you are a student, you are not allowed to post homework questions.

 

[cap4000]

Try to get the book by N.Subramanian, Design of Steel Structures on page 1092 it describes "Pocket Bases". It should help you with the elastic steel analysis he uses.

 

[samchrun]

I haven't been a student for six years...why would it be trick question? cap4000..i'll look into that book you recommended.

 

[hokie66]

My apologies, then. Socketing steel columns into pier footings is not a common solution...I've never seen it done. But I defer to the book mentioned by cap4000.

 

[samchrun]

no apologies needed,I work in the solar industry and it seems solar racking manufacturers prefers this method of construction.

 

[a2mfk]

If your configuration and design will allow it, I would avoid it for constructability and design issues. You are mixing trades, and it makes it hard to level the steel, among other things.... This is a fixed base column, so you are trying to develop moment into the footing via the pier?

 

[paddingtongreen]

Like Hokie, I never heard of this before. There are a couple of ways that come to mind:

To form a void in the footing drop the column in, level and plumb externally, and fill with grout.

To externally level and plumb the column with connectors, and then place the concrete.

I don't like either of them, all columns would have to be done simultaneously.

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

 

[a2mfk]

Can you provide a sketch? I imagined a pad footing with a concrete pier, with the steel column embedded into the concrete pier. I assume this is to protect the steel because this is underground but...

Sounds like others interpreted your situation differently.

The more info you give us the better help you will get!

 

[samchrun]

Here is a sketch my project is not quite this scale nor does it invlove a carport structure, essentially the same design concept.

 

[ATSE]

While this is not common, it is done in telecommunications, where a steel pipe (up to 24" diameter) is "wet-set" into very fresh concrete with no spiral or vertical reinforcing.
The concrete is simply cover for the steel and an enlarged bearing surface against the soil. An oversized post socket.

Very quick and cheap, since the base plate and anchor bolts are eliminated. Okay for single, small monopoles.

However, not the appropriate solution if normal structural steel tolerances (horizontal and vertical control, plumb...) are expected.

Your drawings will need to be more specific about tolerances and be more involved in "means and methods" than usual.

 

[hokie66]

The sketch attached seems to show a two step concreting process, with some site welding in between.

I have seen lighting poles done in the manner described by ATSE, but they were concrete poles, not steel.

 

[a2mfk]

I think you'd be better off designing this as an auger cast reinforced pile with CIP anchor bolts, like road signs, traffic lights, and light poles. This is a very common and standard design method, allows leveling and adjustment via the nuts, and you'd have plenty of design guidance from AASHTO/DOT type publications...

 

[csd72]

Agree with all of the above comments.

It is done sometimes but it does have its problems. When I have used this methods for small signs I have designed it as ATSE has suggested - with the concrete just acting as a cover.

 

[JStephen]

I've seen large galvanized transmission towers where the pole was just sticking out of the concrete instead of using a base ring with anchor bolts, but I have no idea how they are arranged under the surface, or what analysis goes into them.

 

[samchrun]

Thanks for all the help guys, typically I would use a base plate and anchor bolts but the client prefers to just embed the column into the footing. From what I understand this is very common in the solar and carport industry. In any case I got some good advice from my former empolyer and have it figured out now.

 

[MiketheEngineer]

And it always seems to start rusting where the steel goes into the concrete. Very hard to fix - but will take years - usually

 

[Ron]

I routinely use embedded columns for aluminum structures. We use styrofoam blockouts for the concrete.

Analysis is straightforward, with resolution of the moment (and shear) at the column insertion point and applying a triangular stress distribution on the grout block. Required depth of embedment can be computed algebraicly from an assumed stress block. You can mechanically anchor against pullout by inserting a dowel through a hole in the column or compute the shear-bond strength of the grout/column interface.

 

[hokie66]

How do you remove the styrofoam?

 

[Ron]

Well, before the environmentalists got all touchy about it, we used an aromatic solvent to melt the styrofoam. Now we just dig it out. We don't oil it because we don't want to compromise the grout-to-concrete bond.