Oasys GSA Documentation

# Export : Nastran

The model data can be exported to a a Nastran (opens new window) bulk data file.

# Export

The user can select:

  • Small or large field format.
  • Static, modal dynamic or buckling solution options and number of modes for eigenvalue solutions.
  • Which analysis stage should be exported.
  • To export section properties or section shapes.

# Restrictions

The following restrictions apply:

  • Spacer elements not exported.
  • Spring elements in non-global directions are approximate. The spring is assumed to act in the closest global direction.
  • In spring elements non-axial/torsional effects are ignored.
  • No distinction is made between applied displacements and settlements.
  • The axis is ignored for applied displacements.
  • Beam loads in user axes are transferred in global axes.
  • Face load axes are ignored and pressure assumed normal to surface.
  • Edge loads on 2D elements are ignored.
  • Prestress and in-plane loads are converted to equivalent thermal loads.

# CBAR & CBEAM elements

The principal difference between CBARs and CBEAMs is that the shear centre, neutral axis and centre of mass are all coincident for a CBAR element, but can be defined separately for a CBEAM.

Also, for SOL106 – Pδ analysis – only CBEAM elements may be used.

CBAR elements will generally take PBAR or PBARL property cards, CBEAM elements will generally take PBEAM or PBEAML property cards. The ‘L’ suffix indicates that the property is defined by its dimensions, rather than defining the section properties explicitly. This is useful when element stress output is required, as Nastran automatically chooses the main stress recovery points of the section, or if you want to optimize on a particular dimension. See the Nastran manual for further information.

When converting GSA models into Nastran models the option is given writing either of the four property formats mentioned above. Using the PBEAML card is the only way to ensure that the shear centre, centre of mass and neutral axis are correctly defined for sections that do not have two axes of symmetry, such as angles, channels or tees. Sections that are defined explicitly in GSA are written as PBEAM or PBAR cards, regardless of whether section shape information is requested.

The disadvantage of using PBEAML cards is that some pre-processors may not be able to read and rewrite them.

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