Column-Beam Moment Ratio Check for SMF per AISC 341-16 with ideCAD

How does ideCAD control the Column-Beam Moment Ratio according to AISC 341-16?

Moment ratio is automatically controlled and reported in accordance with AISC 341-16 §E3.

Symbols

ΣM^∗_pc = sum of the projections of the nominal flexural strengths of the columns above and below the joint
ΣM^∗_pb = sum of the projections of the expected flexural strengths of the beams at the plastic hinge locations to the column centerline, kip-in.
A_g = gross area of column, in.² (mm²)
F_yb = specified minimum yield stress of beam, ksi (MPa)
F_yc = specified minimum yield stress of column, ksi (MPa)
M_pr = maximum probable moment at the location of the plastic hinge, as determined in accordance with AISC 358,
M_v = additional moment due to shear amplification from the location of the plastic hinge to the column centerline based on LRFD or ASD load combinations, kip-in. (N-mm)
P_c = the nominal compressive strength
P_r = required axial compressive strength according to Section D1.4a, kips (N)
Z_c = plastic section modulus of the column about the axis of bending, in.³ (mm³)
Z = Plastic section modulus about the axis of bending, in.³ (mm³)
α_s = LRFD-ASD force level adjustment factor 1.0 for LRFD and 1.5 for ASD

Conditions for Strong-Column and Weak-Beam (SC/WB)

For the highly ductile steel frames or reinforced concrete structural systems with shearwalls and steel frames, the beam-column connections must provide the condition of the Strong-Column and Weak-Beam (SC/WB) approach, depending on the earthquake direction. In beam-to-column connections, the following relationship must be fulfilled:

Where ΣM*_pc is the sum of the nominal flexural strength of the columns above and below the joint to the beam centerline with a reduction for the axial force in the column, the determination of ΣM*_pc from the Eq (E3-2) is permitted. When the centerlines of beams in opposite directions in the same joint do not coincide, the mid-line between centerlines should be used. For the ΣM*_pb, the sum of the expected flexural strengths of the beams at the plastic hinge locations to the column centerline. The determination of ΣM_pb^* from the Eq (E3-3) is permitted.

The equation given below determines the nominal compressive strength, Pc.

The required axial strength is P_rc = P_uc (LRFD) or P_rc = Pac (ASD), as applicable.

In calculating column flexural strength capacities, the required compressive force P_ac (ASD) or P_uc (LRFD) are obtained from the load combinations, which makes these bending moment capacities the lowest in accordance with the direction of the earthquake.

Strong-Column and Weak-Beam (SC/WB) Frame Mechanism per AISC 341-16 with ideCAD

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Strong-Column and Weak-Beam (SC/WB) Frame Mechanism per AISC 341-16 with ideCAD

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