Oasys GSA Documentation

# Modelling Implications

The analysis stage facility allows the elements, element properties, restraints and constraint conditions to be specified for particular analysis cases. It is provided to allow the results from models differing in these ways to be combined (e.g. for the analysis of construction stages).

The model is set up in the usual way. In the context of staged analysis the model that is set up without reference to an analysis stage is referred to as the whole model. The following should be considered when setting up the whole model.

  • The elements that constitute an analysis stage will be a list of elements from the whole model so the whole model must be the superset of all analysis stage elements.
  • The element properties used in an analysis stage default to the whole model properties. The properties for a given property number may be replaced for specific stages (see below) so whole model element property numbers should be organised accordingly.
  • Nodal restraints and nodal springs are applied in all stages in which the nodes to which they are applied are active. If it is required that a node be restrained in some stages but not in others then this must be done in the Generalised Restraints module (see below), not in the Nodes module.

Analysis stages are defined in the Stage Definition module. A stage has a name and a list of elements that are to be active for the stage. Other data that contributes to the definition of the stage is as follows.

  • If the properties associated with an element property number are to be different for a specific analysis stage the required property record may be mapped on to the element property number for the stage in the Analysis Stage Properties module. This module does distinguish between different property types so mapping Beam Sections record 10 on to element property number 5 will only affect elements that refer to Beam Section property 5. Note that the element local axes may not vary from stage to stage so, for example, changing the 2D Element Property axis from that specified for the whole model will result in an error.
  • Generalised restraints may be associated with a particular stage. When the stage is set to zero the restraint condition is applied to the nodes in the whole model, irrespective of stage. Otherwise it is applied just in the specified stage. If it is required to apply a restraint to a stage made up of all the elements in the whole model but not to all stages then a stage must be set up containing all of the elements.
  • Rigid constraints may be associated with a particular stage, as for Generalised Restraints. Note that it is valid for the constrained node list to identify nodes that are not active for the stage; a warning is given in this circumstance. The primary node is implicitly active for the stage.
  • Joints may be associated with a particular stage, as for Generalised Restraints. The joint is ignored if either the constrained or primary node is not active for the stage.
  • Constraint equations may be associated with a particular stage, as for Generalised Restraints. The equation is ignored if either the constrained or any primary node is not active for the stage.

Note that when specifying element lists references to element properties in the list (to identify elements with a specified property) are always interpreted as whole model element properties. For example, beam loads applied to elements PB5 are applied to beam and bar elements that have element property number 5 in the whole model even if the analysis of that load case is of a stage for which the beam section property has been mapped to a different record.

Analysis stages are not available for raft analysis.

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