How does ideCAD control width-to-thickness Ratios according to AISC 341-16?
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The width-to-thickness ratios of steel elements are automatically controlled and reported with steel elements reports according to Table D1.1. |
Symbols
Fy = Specified minimum yield stress
Ry = Ratio of the expected yield stress to the specified minimum yield stress, Fy
Rt = Ratio of the expected tensile strength to the specified minimum tensile strength, Fu
Pa = Required axial strength using ASD load combinations, kips (N)
Pu = Required axial strength using LRFD load combinations, kips (N)
Py = Axial yield strength, kips (N)
Ca = 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 |
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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 | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.32\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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| | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.40\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Flanges of H-pile sections per Section D4 | b/t | not applicable | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.48\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Stems of tees | d/t | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.32\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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|
| | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.40\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Walls of rectangular HSS used as diagonal braces | b/t | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.65\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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| | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.76\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Flanges of boxed I-shaped sections | b/t | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.65\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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|
| | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.76\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Side plates of boxed I-shaped sections and walls of built-up box shapes used as diagonal braces | h/t | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.65\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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|
| | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.76\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Flanges of built up box shapes used as link beams | b/t | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.65\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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|
| | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.76\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Webs of rolled or built-up I shaped sections and channels used as diagonal braces | hw/t | | Mathinline |
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| body | --uriencoded--$$ \normalsize 1.57\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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| | Mathinline |
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| body | --uriencoded--$$ \normalsize 1.57\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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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 | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.65\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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|
| | Mathinline |
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| body | --uriencoded--$$ \normalsize 1.18\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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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
| Mathinline |
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| body | --uriencoded--$$ \small 2.57\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D(1-1.04C_a) $$ |
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For Ca > 0.114
| Mathinline |
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| body | --uriencoded--$$ \small 0.88\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D(2.68-C_a) $$ |
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| Mathinline |
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| body | --uriencoded--$$ \small \ge1.57\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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where
| Mathinline |
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| body | --uriencoded--$$ \small C_a=\frac%7BP_u%7D%7B\phi_cP_y%7D \; \; (LRFD) $$ |
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| Mathinline |
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| body | --uriencoded--$$ \small C_a=\frac%7B\Omega_c P_a%7D%7BP_y%7D \; \; (ASD) $$ |
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| Mathinline |
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| body | $$ \small P_y=R_yF_yA_g $$ |
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| For Ca ≤ 0.114
| Mathinline |
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| body | --uriencoded--$$ \small 3.96\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D(1-3.04C_a) $$ |
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For Ca > 0.114
| Mathinline |
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| body | --uriencoded--$$ \small 1.29\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D(2.12-C_a) $$ |
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| Mathinline |
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| body | --uriencoded--$$ \small \ge1.57\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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where
| Mathinline |
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| body | --uriencoded--$$ \small C_a=\frac%7BP_u%7D%7B\phi_cP_y%7D \; \; (LRFD) $$ |
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| Mathinline |
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| body | --uriencoded--$$ \small C_a=\frac%7B\Omega_c P_a%7D%7BP_y%7D \; \; (ASD) $$ |
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| Mathinline |
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| body | $$ \small P_y=R_yF_yA_g $$ |
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Webs of built-up box sections used as EBF links | h/t | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.67\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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| | Mathinline |
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| body | --uriencoded--$$ \normalsize 1.75\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Webs of H-Pile sections | h/tw | not applicable | | Mathinline |
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| body | --uriencoded--$$ \normalsize 1.57\sqrt%7B\frac%7BE%7D%7BR_yF_y%7D%7D $$ |
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Walls of round HSS | D/t | | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.053\frac%7BE%7D%7BR_yF_y%7D $$ |
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| | Mathinline |
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| body | --uriencoded--$$ \normalsize 0.062\frac%7BE%7D%7BR_yF_y%7D $$ |
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