Using Spanman - what is the definition of 1 and 2 rows bridging

[Mikeoz]

I found https://spanman.net/
A calculator for Australian Building code span loads!

You can supply any email for trial, no need to give details or activate.
Just give the site an email address and use.

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My question:

When you use Purlin Single Span to Calculate C Section.
https://spanman.net/Members/purlin-single-span

I choose Country Australia, Building type Garage.
Span 4220mm, Spacing 1000mm.
Roof Custom Setting 33kg/m2.
Ceiling (none).
Design Material = Cold Formed / Light C Section.


The results are returned for using C Section using minimum material with:
1 Row Bridging.
Or,
2 Rows Bridging.
Or,
Just the C Section size without bridging.

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SOLUTIONS
Name ___________- kg/m - Depth (mm)
C10015 2 rows bridging 2.6 102
C15012 1 row bridging 2.9 152
C10019 2 rows bridging 3.3 102
C15015 1 row bridging 3.6 152
C20015 1 row bridging 4.5 203
C15019 1 row bridging 4.5 152
C15024 1 row bridging 5.7 152
C20019 1 row bridging 5.7 203
C25019 ___________6.5 254
C20024 1 row bridging 7.2 203
C25024 ___________8.2 254
C30024 ___________10.1 300
C30030 ___________12.8 300
C35030 ___________15.2 350
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I am assuming the C Section recommendations with no bridging can support load independently?

What do they mean by 1 or 2 row bridging?

Mike