Beam-Column Flexural Capacity Ratios.
For special moment frames, minimum flexural strength of columns are calculated automatically, aacording to Codes.
International Design Codes
ACI 318-19 : Beam-Column Flexural Capacity Ratios per ACI 318-19 with ideCAD
TSC 2018 : Conditions for Columns to be Stronger than Beams (Strong columns)
Notation in ACI 318-19
Ag = gross area of concrete section, in2
fc' = specified compressive strength of concrete, psi
fy = specified yield strength for nonprestressed reinforcement, psi
Mn = nominal flexural strength at section, in.-lb
Mnb = nominal flexural strength of beam including slab where in tension, framing into joint, in.-lb
Mnc = nominal flexural strength of column framing into joint, calculated for factored axial force, consistent with the direction of lateral forces considered, resulting in lowest flexural strength in.-lb
Mpr = probable flexural strength of members, with or without axial load, determined using the properties of the member at joint faces assuming a tensile stress in the longitudinal bars of at leasts 1.25fy and a strength reduction factor ϕ of 1.0, in.-lb
Pu = factored axial force; to be taken as positive for compression and negative for tension, lb
ϕ = strength reduction factor
The columns of special moment frames are considered as part of the seismic-force resisting system. The subject of this title is to reduce the possibility of yielding in columns of special moment frames. Columns not stronger than beams increased likelihood of inelastic action. The worst possible case is when all columns in a given story have flexural yielding at both ends. In this case, it creates a column failure mechanism to cause collapse. In order to avoid this situation, the minimum flexural strength of colums control given in Codes should be satisfy.
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