Common seismic requirements (Seismic: AISC 341)
AISC 341-22
Required strength
The required strength (including overstrength effects) for a member should be determined from:
The expected yield stress Ry × Fy
The expected tensile strength Rt × Fu
| Grade | Fy | Ry | Rt |
|---|---|---|---|
| A36 | 36 | 1.5 | 1.2 |
| A53B | 35 | 1.6 | 1.2 |
| A500B | 42 | 1.4 | 1.3 |
| A500B | 46 | 1.4 | 1.3 |
| A500C | 46 | 1.3 | 1.2 |
| A500C | 50 | 1.3 | 1.2 |
| A501 | 36 | 1.4 | 1.3 |
| A529 | 50 | 1.2 | 1.2 |
| A529 | 55 | 1.1 | 1.2 |
| A572 | 42 | 1.3 | 1.0 |
| A572 | 50 | 1.1 | 1.1 |
| A572 | 55 | 1.1 | 1.1 |
| A913 | 50 | 1.1 | 1.1 |
| A913 | 60 | 1.1 | 1.1 |
| A913 | 65 | 1.1 | 1.1 |
| A992 | 50 | 1.1 | 1.1 |
| A1085 | 50 | 1.25 | 1.15 |
Seismic classification - all members
When required by the seismic checks, the classification of elements of the cross section for various member types is as follows.
Compiled from Table D1.1a and D1.1b of AISC 341-22
| Section | Element | Width thickness ratio | Application | λhd – highly ductile | λmd – moderately ductile |
|---|---|---|---|---|---|
| I (rolled) | Flange | bf /(2×tf) | Beams, Columns, Braces | 0.30 × √(E/(Ry × Fy)) | 0.38 × √(E/(Ry × Fy)) |
| Web | h/tw | Braces | 1.49 × √(E/(Ry × Fy)) | 1.49 × √(E/(Ry × Fy)) | |
| Columns, Beams when NOT part of a Moment Frame |
Ca = αs × Pr/(Ry × Fy× Ag) LRFD αs = 1.0 ASD αs = 1.5
Ca ≤ 0.113 2.45 × √(E/(Ry × Fy)) × (1 - 1.04×Ca)
Ca > 0.113 2.26 × √(E/(Ry × Fy)) × (1 - 0.38 × Ca) but ≥ 1.56 × √(E/(Ry × Fy)) |
Ca = αs × Pr/(Ry × Fy× Ag) LRFD αs = 1.0 ASD αs = 1.5
Ca ≤ 0.113 3.76 × √(E/(Ry × Fy)) × (1 - 3.05×Ca)
Ca > 0.113 2.61 × √(E/(Ry × Fy)) × (1 - 0.49 × Ca) but ≥ 1.56 × √(E/(Ry × Fy)) |
|||
| Columns, Beams when part of a Moment Frame |
Ca as above
2.5 × √(E/(Ry × Fy)) × (1 - Ca)2.3 |
Ca as above
5.4 × √(E/(Ry × Fy)) × (1 - Ca)2.3 |
|||
| H-Pile | Flange | bf /(2 × tf) | Beams, Columns | Not Applicable | 0.45 × √(E/(Ry × Fy)) |
| Web | h/tw | Beams, Columns | Not Applicable | 1.5 × √(E/(Ry × Fy)) | |
| Flange | bf/(2 × tf) | Braces | Not Classified | Not Classified | |
| Web | h/tw | Braces | Not Classified | Not Classified | |
| RHS and SHS | Walls |
(bf -3×t)/t and (d-3×t)/t |
Braces |
0.65 × √(E/(Ry × Fy)) | 0.76 × √(E/(Ry × Fy)) |
| Walls as flanges |
(bf -3×t)/t or (d-3×t)/t |
Columns, beams | 0.55 × √(E/(Ry × Fy)) | 1.00 × √(E/(Ry × Fy)) | |
| Walls as webs# |
(bf -3×t)/t or (d-3×t)/t |
Columns, beams |
Ca = αs × Pr/(Ry × Fy× Ag) LRFD αs = 1.0 ASD αs = 1.5
Ca ≤ 0.113 2.45 × √(E/(Ry × Fy)) × (1 - 1.04×Ca)
Ca > 0.113 2.26 × √(E/(Ry × Fy)) × (1 - 0.38 × Ca) but ≥ 1.56 × √(E/(Ry × Fy)) |
Ca = αs × Pr/(Ry × Fy× Ag) LRFD αs = 1.0 ASD αs = 1.5
Ca ≤ 0.113 3.76 × √(E/(Ry × Fy)) × (1 - 3.05×Ca)
Ca > 0.113 2.61 × √(E/(Ry × Fy)) × (1 - 0.49 × Ca) but ≥ 1.56 × √(E/(Ry × Fy)) |
|
| CHS | D / t | Braces | 0.053 × E/(Ry × Fy) | 0.062 × E/(Ry × Fy) | |
| D / t | Columns | 0.038 × E/(Ry × Fy) | 0.070 × E/(Ry × Fy) | ||
| C (rolled) | Flange | bf / tf | Braces | 0.30 × √(E/(Ry × Fy)) | 0.38 × √(E/(Ry × Fy)) |
| Web | h / tw | Braces | 1.49 × √(E/(Ry × Fy)) | 1.49 × √(E/(Ry × Fy)) | |
| Tees | Flange | bf / (2×tf) | Braces | 0.30 × √(E/(Ry × Fy)) | 0.38 × √(E/(Ry × Fy)) |
| Stem | d / tw | Braces | 0.30 × √(E/(Ry × Fy)) | 0.38 × √(E/(Ry × Fy)) | |
| Angles | Both legs |
L1 / t and L2 / t |
Braces | 0.30 × √(E/(Ry × Fy)) | 0.38 × √(E/(Ry × Fy)) |
| Double angles | Outstand leg – legs in continuous contact | L1 / t (long leg B to B) or L2 / t (short leg B to B) |
Braces | 0.30 × √(E/(Ry × Fy)) | 0.38 × √(E/(Ry × Fy)) |
| Double angles | Both legs – legs separated | L1/t and L2 / t |
Braces | 0.30 × √(E/(Ry × Fy)) | 0.38 × √(E/(Ry × Fy)) |
# For RHS/SHS columns in SCBF and OCBF, the classification is conservatively based on the ‘flange rules’ for both long and short sides. RHS/SHS in any other SFRS applications are currently beyond scope.
In the above table the terms have their usual meaning as follows:
- bf = width of flange and for RHS width of shorter side
- tf = thickness of flange of I/H, channel or Tee
- h = height of web inside flanges (d – 2 × tf) of I/H or channel
- tw = thickness of web
- d = depth of SHS and for RHS depth of longer side
- t = thickness of hollow section RHS, SHS, CHS
- D = diameter of CHS
- L1 = Short leg (from root to toe) of single angle
- L2 = Long leg (from root to toe) of single angle
- E = modulus of elasticity of steel – 29000 ksi
- Fy = minimum yield stress
- Pr = Required axial strength (ASD or LRFD)
- Ag = gross area of section
AISC 341-16
Required strength
The required strength (including overstrength effects) for a member should be determined from:
The expected yield stress Ry × Fy
The expected tensile strength Rt × Fu
| Grade | Fy | Ry | Rt |
|---|---|---|---|
| A36 | 36 | 1.5 | 1.2 |
| A53B | 35 | 1.6 | 1.2 |
| A500B | 42 | 1.4 | 1.3 |
| A500B | 46 | 1.4 | 1.3 |
| A500C | 46 | 1.3 | 1.2 |
| A500C | 50 | 1.3 | 1.2 |
| A501 | 36 | 1.4 | 1.3 |
| A529 | 50 | 1.2 | 1.2 |
| A529 | 55 | 1.1 | 1.2 |
| A572 | 42 | 1.3 | 1.0 |
| A572 | 50 | 1.1 | 1.1 |
| A572 | 55 | 1.1 | 1.1 |
| A913 | 50 | 1.1 | 1.1 |
| A913 | 60 | 1.1 | 1.1 |
| A913 | 65 | 1.1 | 1.1 |
| A992 | 50 | 1.1 | 1.1 |
| A1085 | 50 | 1.25 | 1.15 |
Seismic classification - all members
When required by the seismic checks, the classification of elements of the cross section for various member types is as follows.
Compiled from Table D1.1 of AISC 341-16
| Section | Element | Width thickness ratio | Application | λhd – highly ductile | λmd – moderately ductile |
|---|---|---|---|---|---|
| I (rolled) | Flange | bf /(2 × tf) | Beams, Columns, Braces | 0.32 × √(E/(Ry × Fy)) | 0.40 × √(E/(Ry × Fy)) |
| Web | h/tw | Braces | 1.57 × √(E/(Ry × Fy)) | 1.57 × √(E/(Ry × Fy)) | |
| Columns, Beams |
LRFD Ca = Pu/(φc×Ry × Fy×Ag) φc = 0.9 ASD Ca=Ωc×Pa/(Ry × Fy×Ag) Ωc = 1.67 Ca≤ 0.114 2.57 × √(E/(Ry × Fy)) × (1-1.04×Ca) but for SMF only ≤ 2.57 × √(E/(Ry × Fy)) Ca> 0.114 0.88 × √(E/(Ry × Fy)) × (2.68-Ca) but ≥ 1.57 × √(E/(Ry × Fy)) |
LRFD Ca= Pu/(φc × Fy×Ag) φc = 0.9 ASD Ca= Ωc × Pa/(Fy×Ag) Ωc = 1.67 Ca≤ 0.114 3.96 × √(E/(Ry × Fy)) × (1-3.04×Ca) but for IMF only ≤ 3.96 × √(E/(Ry × Fy)) Ca> 0.114 1.29 × √(E/(Ry × Fy)) × (2.12-Ca) but ≥ 1.57 × √(E/(Ry × Fy)) |
|||
| RHS and SHS | Walls |
(bf -3×t) /t and (d-3×t)/t |
Braces |
0.65 × √(E/(Ry × Fy)) | 0.76 × √(E/(Ry × Fy)) |
|
(bf -3×t)/t and (d-3×t)/t |
Columns | 0.65 × √(E/(Ry × Fy)) | 1.18 × √(E/(Ry × Fy)) | ||
| CHS | D/t | Braces | 0.053 × E/(Ry × Fy) | 0.062 × E/(Ry × Fy) | |
| Columns | 0.053 × E/(Ry × Fy) | 0.077 × E/(Ry × Fy) | |||
| C (rolled) | Flange | bf / tf | Braces | 0.32 × √(E/(Ry × Fy)) | 0.40 × √(E/(Ry × Fy)) |
| Web | h / tw | Braces | 1.57 × √(E/(Ry × Fy)) | 1.57 × √(E/(Ry × Fy)) | |
| Tees | Flange | bf /(2 × tf) | Braces | 0.32 × √(E/(Ry × Fy)) | 0.40 × √(E/(Ry × Fy)) |
| Stem | d / tw | Braces | 0.32 × √(E/(Ry × Fy)) | 0.40 × √(E/(Ry × Fy)) | |
| Angles | Both legs | L1 / t and L2 / t |
Braces | 0.32 × √(E/(Ry × Fy)) | 0.40 × √(E/(Ry × Fy)) |
| Double angles | Outstand leg – legs in continuous contact | L1 / t (long leg B to B) or L2 / t (short leg B to B) |
Braces | 0.32 × √(E/(Ry × Fy)) | 0.40 × √(E/(Ry × Fy)) |
| Both legs – legs separated | L1 / t and L2 / t | Braces | 0.32 × √(E/(Ry × Fy)) | 0.40 × √(E/(Ry × Fy)) |
In the above table the terms have their usual meaning as follows:
- bf = width of flange and for RHS width of shorter side
- tf = thickness of flange of I/H, channel or Tee
- h = height of web inside flanges (d – 2 × tf) of I/H or channel
- tw = thickness of web
- d = depth of SHS and for RHS depth of longer side
- t = thickness of hollow section RHS, SHS, CHS
- D = diameter of CHS
- L1 = Short leg (from root to toe) of single angle
- L2 = Long leg (from root to toe) of single angle
- E = modulus of elasticity of steel – 29000 ksi
- Fy = minimum yield stress
- Pu = required axial strength using LRFD (seismic) combinations
- Pa = required axial strength using ASD (seismic) combinations
- Ag = gross area of section
AISC 341-10
Required strength
The required strength (including overstrength effects) for a member should be determined from:
The expected yield stress Ry × Fy
The expected tensile strength Rt × Fu
| Grade | Fy | Ry | Rt |
|---|---|---|---|
| A36 | 36 | 1.5 | 1.2 |
| A53B | 35 | 1.6 | 1.2 |
| A500B | 42 | 1.4 | 1.3 |
| A500B | 46 | 1.4 | 1.3 |
| A500C | 46 | 1.4 | 1.3 |
| A500C | 50 | 1.4 | 1.3 |
| A501 | 36 | 1.4 | 1.3 |
| A529 | 50 | 1.2 | 1.2 |
| A529 | 55 | 1.1 | 1.2 |
| A572 | 42 | 1.3 | 1.0 |
| A572 | 50 | 1.1 | 1.1 |
| A572 | 55 | 1.1 | 1.1 |
| A913 | 50 | 1.1 | 1.1 |
| A913 | 60 | 1.1 | 1.1 |
| A913 | 65 | 1.1 | 1.1 |
| A992 | 50 | 1.1 | 1.1 |
| A1085 | 50 | 1.4 | 1.3 |
seismic classification - all members
When required by the seismic checks, the classification of elements of the cross section for various member types is as follows.
Compiled from Table D1.1 of AISC 341-10
| Section | Element | Width thickness ratio | Application | λhd – highly ductile | λmd – moderately ductile |
|---|---|---|---|---|---|
| I (rolled) | Flange | bf / (2 × tf) | Beams, Columns, Braces | 0.30 × √(E/Fy) | 0.38 × √(E/Fy) |
| Web | h / tw | Braces | 1.49 × √(E/Fy) | 1.49 × √(E/Fy) | |
| Columns, Beams |
LRFD Ca= Pu/(ɸc×FyAg) ɸc = 0.9 ASD Ca = c × Pa/(Fy × Ag) Ωc = 1.67 Ca ≤ 0.125 2.45 × √(E/Fy) × (1 - 0.93 × Ca) but for SMF only ≤ 2.45 × √(E/Fy) Ca > 0.125 0.77 × √(E/Fy) × (2.93 - Ca) but ≥ 1.49 × √(E/Fy) |
LRFD Ca = Pu/(ɸc × FyAg) ɸc = 0.9 ASD Ca = c × Pa/(Fy × Ag) Ωc = 1.67 Ca ≤ 0.125 3.76 × √(E/Fy) × (1 - 2.75 × Ca) but for IMF only ≤ 3.76 × √(E/Fy) Ca > 0.125 1.12 × √(E/Fy) × (2.33 - Ca) but ≥ 1.49 × √(E/Fy) |
|||
| RHS and SHS | Walls |
(bf -3×t)/t and (d-3×t)/t |
Braces |
0.55 × √(E/Fy) | 0.64 × √(E/Fy) |
|
(bf -3×t)/t and (d-3×t)/t |
Columns | 0.55 × √(E/Fy) | 1.12 × √(E/Fy) | ||
| CHS | D / t | Braces | 0.038 × E/Fy | 0.044 × E/Fy | |
| Columns | 0.038 × E/Fy | 0.07 × E/Fy | |||
| C (rolled) | Flange | bf / tf | Braces | 0.30 × √(E/Fy) | 0.38 × √(E/Fy) |
| Web | h / tw | Braces | 1.49 × √(E/Fy) | 1.49 × √(E/Fy) | |
| Tees | Flange | bf / (2tf) | Braces | 0.30 × √(E/Fy) | 0.38 × √(E/Fy) |
| Stem | d / tw | Braces | 0.30 × √(E/Fy) | 0.38 × √(E/Fy) | |
| Angles | Both legs | L1 / t and L2 / t |
Braces | 0.30 × √(E/Fy) | 0.38 × √(E/Fy) |
| Double angles | Outstand leg – legs in continuous contact | L1 / t (long leg B to B) or L2 / t (short leg B to B) |
Braces | 0.30 × √(E/Fy) | 0.38 × √(E/Fy) |
| Both legs – legs separated | L1 / t and L2 / t |
Braces | 0.30 × √(E/Fy) | 0.38 × √(E/Fy) |
In the above table the terms have their usual meaning as follows:
- bf = width of flange and for RHS width of shorter side
- tf = thickness of flange of I/H, channel or Tee
- h = height of web inside flanges (d – 2 × tf) of I/H or channel
- tw = thickness of web
- d = depth of SHS and for RHS depth of longer side
- t = thickness of hollow section RHS, SHS, CHS
- D = diameter of CHS
- L1 = Short leg (from root to toe) of single angle
- L2 = Long leg (from root to toe) of single angle
- E = modulus of elasticity of steel – 29000 ksi
- Fy = minimum yield stress
- Pu = required axial strength using LRFD (seismic) combinations
- Pa = required axial strength using ASD (seismic) combinations
- Ag = gross area of section
AISC 341-05
Required strength
The required strength (including overstrength effects) for a member should be determined from:
The expected yield stress Ry × Fy
The expected tensile strength Rt × Fu
| Grade | Fy | Ry | Rt |
|---|---|---|---|
| A36 | 36 | 1.5 | 1.2 |
| A53B | 35 | 1.6 | 1.2 |
| A500B | 42 | 1.4 | 1.3 |
| A500B | 46 | 1.4 | 1.3 |
| A500C | 46 | 1.4 | 1.3 |
| A500C | 50 | 1.4 | 1.3 |
| A501 | 36 | 1.4 | 1.3 |
| A529 | 50 | 1.2 | 1.2 |
| A529 | 55 | 1.1 | 1.2 |
| A572 | 42 | 1.3 | 1.1 |
| A572 | 50 | 1.1 | 1.1 |
| A572 | 55 | 1.1 | 1.1 |
| A913 | 50 | 1.1 | 1.1 |
| A913 | 60 | 1.1 | 1.1 |
| A913 | 65 | 1.1 | 1.1 |
| A992 | 50 | 1.1 | 1.1 |
seismic classification - all members
When required by the seismic checks, the classification of elements of the cross section for various member types is as follows.
Compiled from I-8-1 of AISC 341-05 and Table B4.1 of AISC 360-05.
| Section | Element | Width thickness ratio | Application | λps – seismically compact | λps – conventionally compact |
|---|---|---|---|---|---|
| I (rolled) | Flange | bf / (2 × tf) | Beams, Columns[1], Braces | 0.30 × √(E/Fy) | 0.38 × √(E/Fy) |
| Web | h / tw | Columns[2], Beams, Braces |
LRFD Ca = Pu/(ɸc × FyAg) ɸc = 0.9 ASD Ca = c × Pa/(Fy × Ag) Ωc = 1.67 Ca ≤ 0.125 3.14 × √(E/Fy) × (1 - 1.54 × Ca) but for SMF only ≤ 2.45 × √(E/Fy) Ca > 0.125 1.12 × √(E/Fy) × (2.33 - Ca) but ≥ 1.49 × √(E/Fy) |
3.76 × √(E/Fy) | |
| RHS and SHS | Walls |
(bf - 3t) / t and (d-3t) / t |
Columns, Braces | 0.64 × √(E/Fy) | 1.12 × √(E/Fy) |
| CHS | D / t | Columns, Braces | 0.044 × E/Fy | 0.070 × E/Fy | |
| C (rolled) | Flange | bf / tf | Braces | 0.30 × √(E/Fy) | N/A |
| Web | h / tw | Braces |
LRFD Ca = Pu/(ɸc × FyAg) ɸc = 0.9 ASD Ca = c × Pa/(Fy × Ag) Ωc = 1.67 Ca ≤ 0.125 3.14 × √(E/Fy) × (1 - 1.54 × Ca) Ca > 0.125 1.12 × √(E/Fy) × (2.33 - Ca) but ≥ 1.49 × √(E/Fy) |
N/A | |
| Tees | Flange | bf / (2 × tf) | Braces | 0.30 × √(E/Fy) | N/A |
| Stem | d / tw | Braces | 0.30 × √(E/Fy) | N/A | |
| Angles | Both legs | L1 / t and L2 / t |
Braces | 0.30 × √(E/Fy) | N/A |
| Double angles | Outstand leg – legs in continuous contact | L1 / t (long leg B to B) or L2 / t (short leg B to B) |
Braces | 0.30 × √(E/Fy) | N/A |
| Both legs – legs separated | L1 / t and L2 / t |
Braces | 0.30 × √(E/Fy) | N/A |
Note 1: The relaxation on the compactness limit for columns in SMF as per note “b” to Table I-8-1 is not taken into account.
Note 2: These limits are not modified by Note [j] to Table I-8-1 i.e. this dispensation is not taken into account.
In the above table the terms have their usual meaning as follows:
- bf = width of flange and for RHS width of shorter side
- tf = thickness of flange of I/H, channel or Tee
- h = height of web inside flanges (d – 2 × tf) of I/H or channel
- tw = thickness of web
- d = depth of SHS and for RHS depth of longer side
- t = thickness of hollow section RHS, SHS, CHS
- D = diameter of CHS
- L1 = Short leg (from root to toe) of single angle
- L2 = Long leg (from root to toe) of single angle
- E = modulus of elasticity of steel – 29000 ksi
- Fy = minimum yield stress
- Pu = required axial strength using LRFD (seismic) combinations
- Pa = required axial strength using ASD (seismic) combinations
- Ag = gross area of section