Why does AutoPIPE provide an option to “Ignore friction GR” on the Nonlinear analysis dialog?
This feature was logged as an enhancement under:
TFS-E 111529 / CAE-CR-2902: Add support friction acting during gravity loadcase
As mentioned in AutoPIPE help:
"Effect of friction on gravity movement cannot be accurately defined since the movement depends on the initial pipe placement. Ignoring friction would be equivalent to lifting the pipe to release the normal forces causing friction and then placing the pipe again on the support. The default is to ignore friction for gravity load."
Another words, if this field is checked ON, AutoPIPE assumes that all supports are frictionless and the pipe system is free to move orthogonally to those supports until something else stops it (e.g. an anchor or support perpendicular to the pipe).
The reason the field is checked by default is for backward compatibility of AutoPIPE models predating v8.5.
Bentley AutoPIPE