AISC S-Shapes (American Standard Beam) - Section Properties

What is in the S table

This page lists every AISC S-Shapes (American Standard Beam) size to AISC Shapes Database v16.0, with the full set of section properties for each one. The table is sortable on any column and searchable by designation, and each size links to its own page with the complete property set, a worked capacity check and dimensions for detailing.

Sizes in this table

28

Mass range (lb/ft)

5.7 to 121.0 - from S3X5.7 up to S24X121

Depth range (in)

3.0 to 24.5

Major-axis stiffness, I (in⁴)

2.5 to 3,160 - a factor of 1,264 across the range

Published to

AISC Shapes Database v16.0

The spread is worth noticing: the heaviest S weighs 21.2x the lightest but carries roughly 1,264x the major-axis stiffness. Bending stiffness grows far faster than weight, which is the whole reason the range is shaped this way - going deeper buys stiffness much more cheaply than going heavier.

How to read an S-shape designation

An AISC designation is the shape letter, the nominal depth in inches, then the weight in pounds per foot: S12X40.8. The first number is a NOMINAL depth, not the measured one - shapes rolled from the same family share a nominal depth while their real depth varies with flange thickness, which is why the depth column in the table above rarely matches the name exactly.

The second number is the only part that is exact: it is the weight per foot, and it is what distinguishes two shapes of the same nominal depth.

What each column in the table means

The table above publishes 16 properties for every S size. These are the ones that decide a design:

Mass per metre

Self-weight of the section, and the basis on which steel is bought - so it is the first cost signal when comparing two sections that both pass.

Cross-sectional area, A

Governs axial capacity and, with mass, tells you how efficiently the shape uses its steel.

Second moment of area, I (major axis)

Resistance to bending about the strong axis. It is what deflection is proportional to, so a serviceability check is driven by this number rather than by strength.

Second moment of area about the minor axis

The weak-axis stiffness. It sets lateral-torsional buckling behaviour and matters whenever the compression flange is not continuously restrained.

Elastic section modulus, Wel

Moment capacity while the extreme fibre stays elastic - the value to use for a Class 3 section, and for any check where yielding is not permitted.

Plastic section modulus, Wpl

Moment capacity once the whole section has yielded - the value used for Class 1 and 2 sections, and typically 10-20% above the elastic modulus.

Radius of gyration, i

The slenderness term: effective length divided by i gives the slenderness that drives buckling. The minor-axis value normally governs a column.

Torsion constant, J

St Venant torsional stiffness. Closed shapes carry torsion through a shear flow around the perimeter and have a J orders of magnitude above an open shape of the same weight.

Warping constant, Cw

The second half of torsional resistance in an open section, and an input to lateral-torsional buckling. It is what makes an I-section usable in torsion at all.

Every one of these is a property of the shape alone. None of them depends on the steel grade - grade enters only when a property is multiplied by a design strength to give a capacity, which is what the Capacity tab above does.

Choosing an S size

Which property governs depends on what is being checked, and it is rarely the one people reach for first:

Bending strength

Compare plastic modulus Wpl for Class 1 and 2 sections, elastic Wel for Class 3. Depth buys this cheaply.

Deflection

Compare second moment of area I. A section that passes strength can still fail serviceability, and this is usually the check that decides the size.

Compression

Compare the MINOR-axis radius of gyration. A deep section with a narrow flange is efficient in bending and poor as a column.

Torsion

Compare J. If the load is genuinely torsional, a closed section beats an open one so decisively that the comparison is rarely close.

Cost

Compare mass per metre first, then surface area per metre - protective treatment is charged by area, not weight.

Elastic section modulus

$W_{el} = \frac{I}{c}$

Radius of gyration

$i = \sqrt{\frac{I}{A}}$

Slenderness

$\lambda = \frac{L_{cr}}{i}$

Open the Capacity tab above with a size selected to run these as a full EC3 check rather than comparing the raw properties by eye.

Common questions about S sections