Opening in Pile shaft 2

[palk7 EIT]

Hi,

There is a huge opening of approx. 31'(Height) and 50' Long opening in a secant pile shaft.. The hoop forces (compression- due to soil pressure) are huge around the lines of 35 to 60 Kip/feet (From Geo tech software). This creates a huge moment of 5500 Kip-ft approx. between the openings in the long column (Havent dealt this huge of a force before). So my approach is treating this as a composite column-beam (W-encased inside reinforced concrete)to design this section, is this right? with the shear studs criteria as below:

1. By placing in the shear studs (to achieve composite action), is still my unbraced length the full height (between the openings of top and bot. beam. (moment connx.)), as I dont have any perpendicular bracing to this longitudinal frame in the weak direction or Could I consider the column frame to be continuously braced as the shear studs are placed throught, which bites the concrete when it wants to buckle out of plane.

2. Any recommendation on Guide or software to use to design this composite column.?

Thank you!

 

[JedClampett]

You're in some strange territory there. You might get hoop action or the structure might devolve into a cantilever from the base, especially at the opening sides.
Have you thought about framing the four sides of the opening with members similar to your column. The hoop forces would put the side members in bending, supported by the top and bottom members in compression. If the curve worries you, straighten out the top and bottom members.
As far as software, this doesn't seem like a problem you want to learn on. Personally, I'm very old school. Analyze the rectangular frame for the hoop and gravity forces. You'll get compression and bending in the top and bottom members and mostly bending in the side members. I'd use an encased wide flange, design the steel member for all the forces and the concrete section for all the forces. When someone comments that the sections are big, just say "you're welcome."

 

[palk7 EIT]

Thank you, the Cb factor for moment capacities for this stuff, is it better to leave it at 1 or leave it to program computed Cb values (This gives higher capacity)?

 

[Retrograde]

A detail I have seen for this situation is to frame out the opening with a cast in-situ reinforced concrete block.