Cold-Formed Z-Purlins (Z) - Section Properties Table

What is in the Z-Purlin table

This page lists every Z-Purlins (cold-formed) size to Continental Steel, 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

16

Mass range (kg/m)

1.8 to 15.2 - from Z10010 up to Z35030

Depth range (mm)

102.0 to 350.0

Major-axis stiffness, I (cm⁴)

1.55 to 32.8 - a factor of 21 across the range

Published to

Continental Steel

The spread is worth noticing: the heaviest Z-Purlin weighs 8.6x the lightest but carries roughly 21x 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 a Z-Purlin designation

A Z-Purlin designation is serial size then mass per metre - Z20015. The first two figures are the NOMINAL serial size in millimetres (depth × width); the last is the real mass per metre in kg/m.

The nominal size is shared across a serial group: every section in one group rolls from the same set of rolls, so the outside depth and width stay near-constant while the web and flange thicken to add mass. That is why two sections with the same first two numbers have different real depths in the table above, and why a heavier section is usually a drop-in for a lighter one in the same group.

What each column in the table means

The table above publishes 13 properties for every Z-Purlin 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.

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.

Principal-axis properties, u-u and v-v

For angles the rectangular axes are not the principal ones. u-u is the true strong axis and v-v the true weak axis, and it is v-v that governs compression buckling.

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 a Z-Purlin 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 Z-Purlin sections