Transverse reinforcement (beams seismic: ACI 318)
Seismic requirements relating to transverse reinforcement take into account properties, strengths and outcomes which are shear related ignoring any reinforcement intended to deal with torsional effects.
Design shear force
The design shear force for members subjected to earthquake effects is obtained by consideration of the minimum required shear strength of the member. The required nominal shear strength of a flexural member part of a Moment Resisting Frame is checked considering the sum of shears resultant from the moment strengths due to reverse curvature bending acting at each end of the beam and from the tributary factored gravity loads.
Beams are checked for shear in three regions:
 Left region, S1;
 Central region, S2;
 Right region, S3.
Shear design is performed considering the Major axis shear force only. Shear Force in the minor axis is checked against the ignorable threshold.
If SFRS Type = Ordinary Moment Frame, then no shear seismic check applies.
If SFRS Type = Intermediate Moment Frame

V_{e}  =  ɸMIN(V_{e,Mn}+V_{e,gravity},V_{e,2E}) 
where 

ɸ  =  Strength reduction factor = 1.0  
V_{e}  =  Minimum design shear force for load combinations including earthquake effects  
V_{e,gravity}  =  Shear due to factored gravity loads from seismic combinations (including vertical earthquake effects) retaining the sign from analysis  
V_{e,2E}  =  Maximum shear resultant from seismic combinations, with doubled earthquake effect [i.e.: V_{e.nonseismic} + V_{e.E} x 2]  
V_{e,Mn}  =  Maximum shear associated with the development of reversed curvature bending due to nominal resisting moments at both ends of the member, considering both the clockwise and counterclockwise cases  

If SFRS Type = Special Moment Frame

V_{e}  =  ɸ(V_{e,Mpr}+V_{e,gravity}) 
where 

ɸ  =  Strength reduction factor = 1.0  
V_{e}  =  Minimum design shear force for load combinations including earthquake effects  
V_{e,gravity}  =  Shear due to factored gravity loads from seismic combinations (including vertical earthquake effects) retaining the sign from analysis  
V_{e,Mpr}  =  Maximum shear associated with the development of reversed curvature bending due to the probable flexural moment strength for both the clockwise and counterclockwise situations, at both ends of the member  

Maximum hoop spacing
The maximum allowed horizontal center spacing of hoops in confinement regions of beams is limited by ACI 318 depending on the type of Seismic Force Resisting System considered.
For Support Regions:
If SFRS Type = Special Moment Frame
The maximum allowed center hoop spacing in support regions, s_{cr,max,sup} is calculated as follows:
According to ACI31808^{1}:

s_{cr,max,sup}  =  MIN(d/4, 8 * d_{b,smallest}, 24 * d_{b,w}, 300mm)  Metricunits 
s_{cr,max,sup}  =  MIN(d/4, 8 * d_{b,smallest}, 24 * d_{b,w}, 12 in.)  USunits  

According to ACI31811^{1}:

s_{cr,max,sup}  =  MIN(d/4, 6* d_{b,smallest}, 150 mm)  Metric units 
s_{cr,max,sup}  =  MIN(d/4, 6 * d_{b,smallest}, 6 in.)  US units  


where 

d  =  Distance from extreme compression fiber to centroid of longitudinal tension reinforcement  
d_{b,smallest}  =  Smallest longitudinal reinforcement bar diameter  
d_{b,w}  =  Link (hoop) diameter  

If SFRS Type = Intermediate Moment Frame
The maximum allowed center hoop spacing in support regions, s_{cr,max,sup} is calculated as follows:

s_{cr,max,sup}  =  MIN(d/4, 8* d_{b,smallest}, 24 * d_{b,w}, 300mm)  Metric units 
s_{cr,max,sup}  =  MIN(d/4, 8 * d_{b,smallest}, 24 * d_{b,w}, 12 in.)  US units  


where 

d  =  Distance from extreme compression fiber to centroid of longitudinal tension reinforcement  
d_{b,smallest}  =  Smallest longitudinal reinforcement bar diameter  
d_{b,w}  =  Link (hoop) diameter  

For Span Regions:
If SFRS Type = Special Moment Frame, or Intermediate Moment Frame
The maximum allowed hoops spacing outside confinement regions, s_{cr,max,span} is calculated as follows:

s_{cr,max,span}  =  d/2 

Maximum allowed lateral link leg spacing
The clear spacing between link legs at right angles to the span is limited in confinement reinforcement regions of members part of Special Moment Frames only.
Footnotes