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# cantilevered column system

## cantilevered column system

(OP)
hello,

i have a one story builidng which i am investigating if a cantilevered column system is better than special moment frame. the seismic design category is D.
i guess no requirement for beam column joint. asce7-10 specifies that it must be detailed to fit the requirements of SMRF.
Does this mean i need to detail the reinforcement accordingly while designing the column as ordinary or intermediate frame ?
Thank you

### RE: cantilevered column system

Table 12.2-1 Design Coefficients and Factors for Seismic Force-Resisting Systems,G. CANTILEVERED COLUMN SYSTEMS; IMF or OMF is not allowed for SDC D.

Special reinforced concrete moment frames are allowed with height limit of 35 ft.

This means; R=2.5 , Overstrength factor Ω0 =1.25 , Cd = 2.5 and comply with detailing req's specified at 14.2.

### RE: cantilevered column system

(OP)
thank you hturkak. So i need to design the column as special column and not only adopt the reinforcemeent arrangement of SMRF ?
the problem i am facing with the SMRF is that the columns are quite big for one story (i am still getting an overstressed joint shear even with column 500x500). Is it common to provide a thicker joint at the top of the column ?

(OP)
500x500mm

### RE: cantilevered column system

Based on my experience, for single story building, OMF and IMF can still work as I believe its height is less than 35'.
I would still open an option for ordinary cantilever column too.
SMF is definitely a heavy deign for a single story building.
Often, what i usually do is, place cantilever columns and make the base fixed by placing grade beams,
simply because the construction (apparently) process gets tricky as you start using Cantil. Col to OMf, IMF then SMF.

### RE: cantilevered column system

#### Quote (structural87 (Structural)(OP))

.....So i need to design the column as special column and not only adopt the reinforcemeent arrangement of SMRF ?
the problem i am facing with the SMRF is that the columns are quite big for one story (i am still getting an overstressed joint shear even with column 500x500). Is it common to provide a thicker joint at the top of the column ?

I want to remind the definition ; section 11.2 ( CANTILEVERED COLUMN SYSTEM: A seismic force resisting system in which lateral forces are resisted entirely by columns acting as cantilevers from the base.)

Pls look to part G of Table 12.2-1 for the detailing req's 12.2.5.5 and 14.2 . For R.C SMRF, ACI limits the cross-section dimensions ,material quality, area and spacing of reinforcement, location of splices, spacing of transverse reinforcement.

I want to remind also, foundations for cantileverd column systems shall be designed with the overstrength factor , 1.25. and the system shall be checked for redundancy..

Regarding your querry, ( i am still getting an overstressed joint shear even with column 500x500). Is it common to provide a thicker joint at the top of the column ? ) .I could not imagine..The cantilever systems should not have rigidly connected beams at the top..

If you post the system, at least some descriptive sketches, you may get better responses..

### RE: cantilevered column system

yes, new shop drawing for columns.

### RE: cantilevered column system

structural87,

Don't you have walls that can be utilized/designed to meet requirement for special reinforced concrete walls. Then you can use dual system designation, with the requirement that the special reinforced concrete moment frames shall be capable of resisting 25% of prescribed seismic force.

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