Steel columns embedded in concrete 1

[bruinboy]

I'm doing an analysis of an existing free-standing carport structure. The designer used 2-8"x2 1/4"x 14GA. CEE's as columns supporting a shallow slope roof. The wind uplift load will be very large and I'm concerned that the way he attached the columns won't provide enough strength. He embedded the columns 2'-4" into a 4'-6" deep and 2' diameter concrete footing. Can anyone provide me with a reference regarding the strength of steel columns embedded in concrete, both for tension and moments? I am also concerned with earthquake forces as this structure is located in California. The same columns support equally sized beams but are only connected by screws (no welds, etc to transfer moments). Anyone know of a way to achieve a moment connection between these channel type steel beams?

 

[Ron]

I routinely design rigid frame aluminum structures with the columns embedded in concrete. Analytically, my procedure is to use a bond strength (taken as 10 percent of the tensile strength of the concrete) and column surface area to develop the load, then compute the failure of a concrete cone using the area of a 45 degree failure cone in shear.

You'll probably find that your application will work fine with that depth of embedment. I would be more concerned about corrosion at the interface for the light gage material.

 

[dbuzz]

bruinboy, this paper may be of interest:
Pratt, A. and Alexander, S
Plunge Columns
Concrete, April 2003, pp 8-12
The Concrete Society, UK

Ron, as a side issue, aluminium reacts poorly in contact with concrete. What do you use to protect the aluminium components?

 

[bruinboy]

dbuzz, I was wondering if you could provide a link to Concrete April 2003...can't seem to find it.

Ron, bond strength equals 10% of tensile strength of CONCRETE?

 

[dbuzz]

http://www.concrete.org.uk

http://www.concrete.org.uk/downloads/contents/apr2003.pdf

 

[Ron]

dbuzz...we coat the aluminum with a heavy, clear coat of acrylic. Our proof tests show that actual load capability is almost twice the computed capacity.

bruinboy....10% is conservative for this application though it cannot be compared to the bond achieved in rebar.