Commentary of Width-to-Thickness Limitations per AISC 341-16 with ideCAD

How does ideCAD control width-to-thickness Ratios according to AISC 341-16?

Symbols

F_y = Specified minimum yield stress
R_y = Ratio of the expected yield stress to the specified minimum yield stress, Fy
R_t = Ratio of the expected tensile strength to the specified minimum tensile strength, Fu
Pa = Required axial strength using ASD load combinations, kips (N)
P_u = Required axial strength using LRFD load combinations, kips (N)
P_y = Axial yield strength, kips (N)
C_a = Ratio of required strength to available axial yield strength
E= Modulus of elasticity of steel = 29,000 ksi (200 000 MPa)

Local buckling, when repeated like low-cycle fatigue caused by an earthquake, can cause very high localized stresses that can cause premature failure of an element intended to behave in a ductile manner. In order for horizontal structural system elements to achieve sufficient plastic deformation without local buckling under the effects of earthquakes, the width-thickness ratios of the compression elements must meet the conditions given in Table D1.1.

The width-to-thickness ratios of steel elements are automatically controlled and reported with steel elements reports according to Table D1.1.

Limiting Width-to-Thickness Ratios for Compression Elements for Moderately Ductile and Highly Ductile Members

Limiting Width-to-Thickness Ratios for Compression Elements for Moderately Ductile and Highly Ductile Members
Description of Element	Width-to- Thickness Ratio	Limiting Width-to-Thickness Ratio		Example
		λhd Highly Ductile Members	λmd Moderately Ductile Members
Flanges of rolled or built-up I-shaped sections, channels and tees; legs of single angles or double-angle members with separators; outstanding legs of pairs of angles in continuous contact	b/t			Open
Flanges of H-pile sections per Section D4	b/t	not applicable		Open
Stems of tees	d/t
Walls of rectangular HSS used as diagonal braces	b/t
Flanges of boxed I-shaped sections	b/t
Side plates of boxed I-shaped sections and walls of built-up box shapes used as diagonal braces	h/t
Flanges of built up box shapes used as link beams	b/t
Webs of rolled or built-up I shaped sections and channels used as diagonal braces	hw/t
Where used in beams or columns as flanges in uniform compression due to axial, flexure, or combined axial and flexure: Walls of rectangular HSS Flanges and side plates of boxed I-shaped sections, webs and flanges of built-up box shapes	b/t     h/t
Where used in beams, columns, or links, as webs in flexure, or combined axial and flexure: Webs of rolled or built-up I shaped sections or channels [b] Side plates of boxed I-shaped sections Webs of built up box sections	h/tw     h/t     h/t	For Ca ≤ 0.114 For Ca > 0.114 where	For Ca ≤ 0.114 For Ca > 0.114 where
Webs of built-up box sections used as EBF links	h/t
Webs of H-Pile sections	h/tw	not applicable
Walls of round HSS	D/t