Download the Spreadsheet here.

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What does the Doubly Symmetric Steel Flexural Spreadsheet solve?

This spreadsheet will find the flexural capacity of a Doubly Symmetric I-Shaped Member bend around it's major axis. It is solved using ASD? loads.

This spreadsheet checks for:

  • To see if the web and flange are compact
  • Find the beams Yield Strength
  • Lateral Torsional Buckling (which occurs in compact sections and non-compact sections)
  • Flange Local Buckling (which occurs in non-compact sections)
How to Understand this Spreadsheet
  1. Where to Download
  2. How to use this spreadsheet
  3. Notes
  4. Addendum
  5. Spreadsheet FAQ's

Where to download?

Download the Spreadsheet here.

How to use this Spreadsheet:

''This spreadsheet works in Microsoft Excel 2003 and later. This spreadsheet will solve for Lateral Torsional Buckling it will check to make sure that the steel section is compact and it will check to see if the flange has local buckling? (which only occurs in non-compact sections).

The top portion of the spreadsheet allows you to change your inputs:

Steel I-Beam Flexural Inputs
Fig. 1: Spreadsheet Inputs


bf = width of the flange (inches)
tf = thickness of the flange (inches)
Sx = Section Modulus? of the beam about the strong axis of the cross section (in3)
Zx = The Plastic Section Modulus in the x or strong axis. Zx is similar to the Section Modulus of a member (it is usually a minimum of 10% greater than the Section Modulus) (in3)
ry = The radius of gyration? about the weak axis of the cross section
rts2 = \frac{\sqrt{I_yC_w}}{S_x} = \frac{I_yh_O}{2S_x}
hO = distance between flange centroids = d - tf (in)
J = torsional constant (in4)
Cw = warping constant (in6)

Cb = Beam bending Coeeficient
Lb = Unbraced Length (bracing must resist displacement of the compression flange or twisting of the cross section)
Fy = The yield strength of the steal beam (e.g. A36 has a yield strength of 36 ksi)
E = The modulus of elasticity of the steel beam (e.g. 29000 ksi)

Note: For standard doubly symmetric I-shapes: rts, ry, J, Sx, hO, Iy, Cw, and most of the other variables can all be found in Table 1 of the AISC 360 Steel Construction Manual[1]. This makes these calculations much easier.

The next section will check to see if the beam's flange and web are compact.

Steel I-Beam Compact Section
Fig. 2: Check to see if the beam is compact

If required (Lb > Lp), the third section will find whether or not the beam is in the inelastic or elastic LTB zone and reduce the flexural strength of the beam.

Steel I-Beam LTB
Fig. 3: Check to see if the beam is undergoing Lateral Torsional Buckling

If required (the flange is not compact), the next section will solve for flange local buckling? in the beam.

Steel I-Beam Flange Local Buckling
Fig. 4: Does the Flange have Local Buckling Problems (non-compact only)

Finally, the spreadsheet will provide you the Results Summary which gives you the allowable flexural strength of the beam

Steel I-Beam Flexural Results
Fig. 5: Spreadsheet Results


The following notes must be considered when using this spreadsheet:

  1. For doubly symmetric I-shaped members bent about their major axis
  2. Designed using the AISC 13th edition (AISC 360 specifications)
    • See chapter F in the specifications for complete details
    • Table B4.1 in the Specifications (AISC 360) has also been referenced to find λp & λr. And also to find out if the beams flange & web are compact.
    • Most of the required variables to solve the above complex equations (for standard sized beams) can be found in Table 1 of the manual.


  • V1.0: This is the original version of the column stability factor spreadsheet (designed by A. Cabico)
  • V1.1: Corrected an error in calculating Lr (an extra square was present in the equation)



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