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

 

[RFreund]

@samchrun
How did you design it?

Ron,

Can you expand some on how you design these? what do you mean when you say grout block? I guess I'm not visualizing this the stress distribution your describing.

Sorry don't mean to hijack the post.

EIT

 

[samchrun]

I essentially designed it per Ron's description. Triangular stress distibution from top of footing down to bottom of column embedment, resolved the moment with the T-C couple arm and check the actual bearing vs the allowable bearing of the concrete per the ACI and added a few additional ties at the top of the footing for tension.

 

[Ron]

RF...the styrofoam blockout is larger than the column, so there is space to back-grout the hole around the column. I deal with aluminum structures, almost always extruded tubes, so the bottom of the tube gets flared to give a mechanical key within the grout. If uplift is very high, we use a stainless steel pin through the bottom of the tube to give additional mechanical keying.

Analysis is as samchrun noted.

 

[csd72]

Stress on concrete is (Bd^2)/6 where b is the width of the steel and d is the embedment.

 

[slickdeals]

Check out this link

http://www.ncree.org.tw/iwsccc/PDF/08 - Shahrooz.pdf

 

[paddingtongreen]

Okay, but how is level and plumb achieved? In slickdeal's link that is not a problem.

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

 

[slickdeals]

I totally agree with the comments about constructability. It has ZERO tolerance. My link was only regarding how to engineer the problem. (link was originally provided by cap4000 in another thread).

 

[RFreund]

Ahah - I see. Thanks guys!

I got a nice dose of Aluminum design this year because someone wanted to put a 12' sail (canopy) on their existing building. All I have to say is Weld affected this Weld affected that, can I have more strength, is there some way we can do this in steel.
It was a good learning experience though.
And although I was a little nervous about the design (being my first time and all) when I saw the manufactures product I thought - My support is designed for 40psf but that thing is going to fold like a deck of cards with 10psf.

EIT

 

[Ron]

Michael...the company that I do the engineering for has been doing this since 1960...I've been doing their structural design since 1984.....they have it down to a fine art with jigs and temporary supports. Since it is aluminum, the weight is very low, so the extruded, rigid frame bents are relatively easy to erect. For the cantilevered bents, it gets a little more tricky, but not bad.

 

[RHTPE]

I see no confining reinforcing in your pier. What happens when the concrete cracks between the steel column and the face of the pier? I have been doing similar designs for a solar installer here in the Northeast US. They do not want to look beyond the life of the subsidy that helped pay for the solar installation. We have yet to converge on a method that they like and that I can stand behind. Rust will be the downfall of the method you depict, and at some point in the life of the column it WILL crack the concrete surrounding the column. Confining reinforcing (column ties) in the pier is a must IMHO, no matter how you connect the steel column to the pier.

This must be an installtion in the lower latitudes. Here in my area the pivot point for the array is much higher so that the array angle suits the sun's position during the winter. Makes wind analysis much more interesting.



Ralph
Structures Consulting
Northeast USA

 

[oldrunner]

Samcrun:

This is called a ground-set foundation and is very common for flagpoles. Page 14 of the Metal Flagpole Manual published by the National Association of Architectural Metal Manufacturers illustrates some generic dimensions for flagpoles up to 100 feet. We have found these suggestions to be very conservative.

Your configuration is no different from a Pole type of structure and the methods to design footings for these kinds of structures have been around for years. One of my references is Design Notes and Criteria Pole Type Buildings by H.J.Dengenkolb and Associates, San Francisco. (Published 1968).

I assume that you have a geotechnical report for the site and if conditions vary across the site, you will have various embedment depth requirements. One of your biggest problems will be having enough mass of the steel column and the footing itself from pulling out of the soil. Either you develop enough upward friction at the sides of the 24” pier or you add weight of some kind. This kind of a structure is going to have a lot of movement due to the complexities of your wind load, so I would require a cage of stirrups in the hole. I don’t know what kind of fixity you have at the ground level. (Sketch shows asphalt?) If this is not used as the point of rotation, you then do have to be careful where you select the start of the passive pressure of the soil for your lateral pressures. (Get it in writing from the geotech!) The design calculations for this kind of footing is easily set up in a spreadsheet so that you can hand calc the solution and be able to play with the different possibilities – such as depth, diameters, passive and maximum pressures. You should also be checking the bearing pressure – 2 foot diameter of bearing plus whatever friction factor on the sides of the pier may not be enough. You might end up with a bearing cap at the top of the footing to take care of this and also provide enough additional mass if the “wing” of solar panels tries to fly away.

Specifying stud anchors on the side of the steel column is easily determined - we don't count on any friction between the concrete and the steel. There may be some other methods that are cheaper.

Others have already provided you with other good basic design information.

http://www.nma-se.com