To place purlins in Advance Steel, click Purlins on the Home tab (Extended Modeling panel), select all the rafters that support them, press Enter and pick a reference point. Advance Steel places the purlins and opens a dialog where you set the section, heavy end bays, span type, laps and where the purlins start and end.
Purlins are the secondary members that run across the rafters, evenly spaced, and carry the roof deck. On a pre-engineered or portal frame building there can be hundreds of them, so placing them one by one makes no sense. Advance Steel has a Purlins tool that lays them all out at once across the rafters you pick. Here’s how it works and what each setting does.
Where is the Purlins tool?
On the Home tab: Extended Modeling panel > Purlins.
Or on the Extended Modeling tab: Structural Elements panel > Purlins.
How do I place purlins in Advance Steel?
- Click Purlins.
- Select all the rafters that will support the purlins and press Enter.
- Pick a reference point, and answer whether you want to select an additional reference beam.
- The purlins are created and a dialog box opens where you can adjust them.
What do the Sections tab settings do?
This is where you choose what the purlins are made of.
Section size
The shape type and size of the purlins.
Heavy end bay
Check this box if the end bays need a heavier section than the middle bays. End bays often take more load, so this is common.
Heavy end size
The shape type and size used for the end bay purlins.
Span type
How the purlins span across the rafters. Single Span is the default. The other options cover purlins spanning more than one bay, with the splice placed to the left, right or centered.
Model role
The model role assigned to the purlins. The default is Cold Rolled Purlin. The model role matters later for numbering, lists and drawings, so set it right here.
Overlap
Check this if the purlins should lap over each other at the supports.
What do the Alignment tab settings do?
This tab controls where the purlins start and end.
Reference
What the purlins line up with. The default, System Line, aligns them to the system line of the end rafters. Outer Edge extends them to the outside edge of the end rafters.
Stub
Whether to add extra short purlins that stick out past the end rafters. The default is None, so nothing is added.
Stub length
Only active if you add stubs at one or both ends. It sets how long they are.
Overhang first support
Use this to make the purlins overhang past the first support, on the left side.
Purlin size, spacing, laps and overhangs come from the engineer’s drawings. The tool just builds what you tell it, so check the design before you model it.
What mistakes should I avoid with purlins?
- Placing them one by one. The tool keeps them together, so changing the spacing or size later is one edit.
- Wrong model role. If the model role is wrong, purlins get numbered and listed with the wrong parts. Set it in the dialog.
- Forgetting the heavy end bays. Check the design drawings for heavier end-bay purlins.
- Missing the laps. If the purlins lap at the supports, check Overlap, or the lengths on your cut list will be short.
If the roof uses open-web joists instead of purlins, see the joist tool explained.
