These objects are explained in more detail in the local buckling .HME documenthttp://hypersizer.com/help/Content/Failure/buck-local.php
Please email us to get the username and password to download this document from our online help system.
For the analysis of a hat stiffened panel:
1. Open span - Top facesheet between the flanges of two adjacent stiffeners
2. Closed span - Top facesheet between the flanges of the same stiffener
3. Spacing span - open span + bonded combo. This is basically all the skin not including the closed span.
Let me know if this is unclear.