Verified by the CalcTree engineering team on June 27, 2024
This calculator computes actual and allowable stresses in members when subjected to axial load and/or uniaxial or biaxial bending. Therefore it is applicable to both beams and columns. The final result is computed as a Stress Ratio (S.R) of actual stress to allowable stress. A member with S.R ≤ 1 is deemed adequate against strength checks.
All calculations are performed in accordance with AISC 360, which is the American Institute of Steel Construction (AISC) Specification of Structural Steel Buildings - Allowable Stress Design and Plastic Design - 9th Edition 1989.
Common steel sections in ASIC
Calculation
Technical Notes
This calculator:
requires input for the total depth (
d
), web thickness (
tw
), flange thickness (
tf
), design parameters and member loadings. All remaining section properties are calculated
does not check shear, deflection or torsion and does not consider deduction for holes in members subject to tension
assumes the Modulus of Elasticity for steel (
E
) is 29,000 ksi
is valid for AISC W, S, M and HP shapes that are not contained in the AISC 9th Edition Manual, as well as for non-hybrid and doubly symmetrical I-shape built-up members which have their flanges continuously welded to the web and which do not qualify as plate girders.
'ASIF' is a multiplier of any of the calculated allowable stresses
Fa
,
Fbx
and
Fby
and the Euler column buckling stresses
F’ex
and
F’ey
. It appears only when calculating the Stress Ratio (S.R) where a value of 1.0 is typically used.
Output
Member Properties
A
:26.1252
rt
:4.010142330665608
J
:3.8573316666666666
Cw, in.^6
:15933.40399021285
Lc
:12.987194547792917
Lu
:24.51190476190475
Lb/rt
:35.908949889092504
X-Axis
Sx
:140.43370120571444in3
Ix
:983.0359084400006
rx
:6.134156884510232
Y-Axis
Sy
:49.77148407724138in3
Iy
:360.84325956000004
ry
:3.7164602037060157
Capacity Checks
Axial Compression
Kx*Lx/rx
:23.475108757590473
Ky*Ly/ry
:38.74654701169799
Cc
:106.99879020467306
fa
:0.30621775144305113
Fa
:26.00668785181162
Pa
:679.4299214661484
fa/Fa
:0.011774577108315629
:PASS
Axial tension
Ft
:30
:NA
Flexure (X-Axis)
fbx
:1.708991488079037
Fbx
:32.2795434315458
Mrx
:377.7613131102142
F'ex
:270.9791819446942
fbx/Fbx
:0.05294348390345867
fbx<Fbx?
:PASS
Flexure (Y-Axis)
fby
:0
Fby
:35.69885857886455
Mry
:148.06543094447085
F'ey
:99.46840237097395
fby/Fby
:0
fby<Fby?
:PASS
Combined Check (Stress Ratio)
Stress ratio
:0.06
:PASS
Explanation
The American and British Standards method for design is to compare "allowable stresses" against "actual stresses", where actual stresses are based upon characteristic loads with an overall Factor of Safety (FoS).
The design checks to ACI 360R-22 are based upon ensuring:
actual stress≤FoSallowable stress
Compression Check
Column's slenderness ratio (
rKL
) is a key parameter in calculating the allowable stress, and is defined as the ratio of its effective length (
KL
) and radius of gyration (
r
). These values vary depending on the axis considered (major / minor).
Actual compressive stress,
fa
is calculated by:
fa=AF
The formula varies depending on whether the column is buckling elastically or inelastically, and is determined by the factor
Cc
:
Cc=Fy2π2E
For calculating the allowable axial compressive stress,
For calculating allowable resisting moment (Mr) and Euler stress (F'e):
Mr=12FbSFe′=23(KLr12)212Ep2
Buckling due to bending
Combined Check (Stress Ratio)
The Stress Ratio (S.R.) checks against the combined actions of axial and flexure. A steel section with S.R. ≤ 1 is deemed safe against strength checks.
The effective length of column is the actual unbraced length of the member capable of resisting buckling. This is calculated as a proportion of the actual member length multiplied by Kx and Ky, the effective length factors about the major (x) and minor (y) axis respectively. K is dependent on the restraint conditions at columns ends and can be found in the AISC ASD Manual, as shown below:
Recommended K values - Table C-C2.1 of AISC ASD Manual
Effective lengths,
Lb,Lc
and
Lu
(bending)
The actual unbraced length of the compression flange of the member for X-axis (major) bending is Lb. The "unbraced length" can be more specifically defined as the distance between cross sections braced against twist or lateral displacement of the compression flange.
For most cases, Lb = Ly
For cantilevers braced against twist only at the support, Lb may be taken conservatively as the actual length.
For input values of Lx or Ly or Lb <= 1, the calculator will use Lx or Ly or Lb = 1
Lc is the maximum unbraced length of compression flange at which the allowable X-axis bending stress can be taken as 0.66*Fy or from AISC code Eqn. F1-3 when applicable.
Lu is the maximum unbraced length of compression flange at which the allowable X-axis bending stress can be taken as 0.60Fy when Cb = 1.
Bending coefficients
Cmx and Cmy are the coefficient applied to the X-axis bending term and Y-axis bending term, respectively, in the interaction equation (H1-1) and is dependent upon column curvature caused by applied moments. The Cmx (or Cmy) coefficient value is determined as follows:
Category A - for compression members in frames subject to joint translation (side-sway), Cmx = 0.85.
Category B - for rotationally restrained compression members in frames braced against joint translation (no side-sway) and not subject to transverse loading between their supports in the plane of bending:
Cmx=0.6−0.4×(Mx2Mx1)
Category C - for rotationally restrained compression members in frames braced against joint translation (no side-sway) and subject to transverse loading between their supports in the plane of bending, the following Cmx values are permitted:
For members whose ends are restrained against rotation in the plane of bending, Cmx = 0.85
For members whose ends are unrestrained against rotation in the plane of bending, Cmx = 1.0