Flexural requirements (columns seismic: ACI 318)
Minimum flexural strength
Columns that are part of Special Moment Frames are required by ACI 318 to have a minimum amount of flexural strength depending on the connecting beams flexural capacities so as to promote the formation of beam yielding mechanisms in the case of an earthquake. This is done by establishing a ratio between the beam and column moment strengths in the moment resisting frame direction.
The design of the main reinforcement in a column is done for the top, middle and bottom region of the stack and moment capacity is calculated for the factored axial force in each region for the Major and Minor directions.
If SFRS Type = Special Moment Frame then flexural strength checks are performed at the joints:

Σ M_{nc,l}  =  M_{nc,l,bot} + M_{nc,l,top} 
Σ M_{nc,r}  =  M_{nc,r,bot} + M_{nc,r,top}  
where  
Σ M_{nc,l} , Σ M_{nc,r }  =  Sum of the Nominal Flexural Strengths of the columns framing into the joint in the relevant direction.  
M_{nc,l,bot}, M_{nc,r,bot}  =  Nominal Moment Strength of the stack below the joint obtained for the axial force value consistent with the minimum Nominal Moment Strength respectively for the left and right sway cases.  
M_{nc,l,top}, M_{nc,r,top}  =  Nominal Moment Strength of the stack above converging on the same joint for the axial force value consistent with the minimum Nominal Moment Strength respectively for the left and right sway cases.  

The sum of the beam strengths are obtained as follows:

Σ M_{nb,l}  =  M_{nb,l} + M_{nb,l}+ 
Σ M_{nb,r}  =  M_{nb,r} + M_{nb,r}+  
where  
Σ M_{nb,l} , Σ M_{nb,r}  =  Sum of the Nominal Flexural Strengths of the beams framing into the joint in the relevant direction.  
M_{nb,l} , M_{nb,r}  =  Nominal Moment Strength at the joint from the beam on the left from current reinforcement arrangement respectively for the left and right sway cases.  
M_{nb,l}+ , Mnb,r+  =  Nominal Moment Strength at the joint from the beam on the right from current reinforcement arrangement respectively for the left and right sway cases.  

The minimum strength ratio between columns and beams in both left and right sway cases is checked as follows:

Σ M_{nc,l}  ≥  6/5 * Σ M_{nb,l} 
Σ M_{nc,r}  ≥  6/5 * Σ M_{nb,r}  

Maximum allowed area of reinforcement
The maximum area of longitudinal reinforcement in columns part of Special Moment Frames is limited as follows.
If SFRS Type = Special Moment Frame
Then calculate maximum area of steel, A_{s,max} as follows:

A_{s,max}  =  0.06 * A_{g} 

where 


A_{s,max}  =  Maximum allowed area of reinforcement 

A_{g}  =  Gross area of the concrete section. 

Maximum allowed longitudinal bar center spacing
Limitations on the longitudinal bar spacing emerge from the code requirement for maximum allowed crosssection center link spacing of the confinement reinforcement due to the method of link leg distribution across the column section.
If SFRS Type = Special Moment Frame
Then check maximum longitudinal reinforcement bar distance, scr,max as follows:

s_{cr,max}  =  350 mm  Metricunits 
s_{cr,max}  =  14 in  USunits  

Nonreversing plastic hinges
Nonreversing plastic hinges are regions along the stack of the column where flexural yielding is likely to occur.
Splices
Columns that are part of Special Moment Frames have restrictions on the allowed locations of lap splices.
Strength design of mechanical splices and restrictions to the use of welded splices as required by ACI 31811 apply to Special Moment Frames