Special RC Cantilevered Moment Frame - Rho/Omega + detailing questions

[Bowsers]

Hello and Greetings

I have been tasked with designing a special reinforced concrete cantilevered moment frame. This is a 14' concrete column over an isolated footing.

I have three issues of design that I am unsure on, and wish to be properly addressed.
1) I have a redundant rho factor applied(1.3), as there are only two columns in this system. This system calls for an omega of 1.25. From what I understand, the purpose of omega is to have higher strength in the connections/footings than the designated SFRS members. I also understand that rho and omega are not to be applied simultaneously, so that the column experiences ductile failure before the connections fail. I don't understand how this would be the case as rho > omega. Would I apply omega on top of rho?
2) The column is framing into an isolated footing, and this appears to fall under aci chap 18.13 , foundation design. I have no been able to point to anything specific indicating that any reinforcing should be present 3" from the top of the footing. Have I missed the provision? There appears to be an unknown-unknown here. Any suggestions?
3) I have a steel pile/rock anchor present connecting to rock to resist uplift forces. The pile specifications appear to all be for RC concrete piles. I'm unsure which detailing provisions govern to be assured there is adequate capacity.

Thanks one and all for any clarity and illumination on working my way through ACI 318-14 chap 18 for the first time.

 

[HTURKAK]

Hi Bowsers (Structural)(OP),

Below find my replies to your questions ;

1- I understand the bldg composed of frames with single span , two columns. The omega factor ( 1.25 ) is applied to the foundation and other elements contributing to the overturning resistance of cantilever column structures. Refer to 12.2.5.2 Cantilever Column Systems.You are also expected to check the structure for redundancy as per 12.3.4.

(.... Foundation and other elements used to provide overturning resistance at the base of cantilever column elements shall be
designed to resist the seismic load effects, including overstrength of Section 12.4.3. )

2- You are expected to design foundation and tie beams etc. which are contributing to the overturning resistance with load combinations that include the overstrength factor .


3- I think the pile is hollow section steel pile and anchored to rock with steel profile and will be designed for tension force due to seismic loading..If this is the case, The pile itself and steel anchor should be designed as per AISC and anchor to the rock should be designed for grout strength and rock anchor strength . I will suggest you to look API RECOMMENDED PRACTICE 2A (Recommended Practice for
Planning, Designing and Constructing Fixed Offshore Platforms )..