STAAD File: Conventions

Description

Some differences between conventions used in STAAD and Straus7 are described below.

Beam Local Axis

The corresponding beam axis mappings are:

Straus7	STAAD
+1	-Z
+2	+Y
+3	+X

For L Sections, the correlation changes to:

Straus7	STAAD
+1	-Y
+2	-Z
+3	+X

Beam Global Orientation

The default STAAD beam convention is as follows: when the local x-axis is parallel to the global Y-axis, as in a column, the local z-axis is in the positive global Z-axis direction. When the local x-axis is not parallel to the global Y-axis, the local z-axis is parallel to the global X-Z plane and the local y-axis is in the same positive direction as the global Y-axis.

The beam orientation may differ from this convention by the specification of a beta angle or a reference point. In Straus7, the former is similar to specifying a principal axis angle, whilst the latter is similar to adding a reference node to a Beam3 type beam.

See Beam Elements: Local and Principal Axes for the Straus7 beam orientation convention.

Plate Local Axis

The local axis system in Quad4 elements in STAAD is the same as that used by the quadrilateral elements in Straus7.

The triangular elements, however, use a different convention. In STAAD, the local x-axis is parallel to the first two nodes. In Straus7, the local x-axis in the Tri3 element is directed from the first node to the bisector of the opposite edge (mid-way between the second and third nodes).

Problem Types

Truss problems use truss elements.

Plane problems are imported so that the global freedoms only allow for translation in the global X and Y directions and rotation in the global Z direction.

Floor problems are imported as Space problems.

Units

Only length and force units are specified in STAAD.

There is no defined mass unit. Instead a mass unit is derived from the force unit.

Coordinate Systems

Node (joint) coordinates can be entered in Cartesian, cylindrical or reverse cylindrical coordinates.

Groups

Groups specified in STAAD will be imported provided their definition is contained within the keywords, START GROUP DEFINITION and END GROUP DEFINITION.

Nodes are grouped using the keyword JOINT. If the STAAD node group name is numeric it will be imported and assigned as Straus7 node IDs. If the node group name is alphanumeric it will assigned as the next available ID in Straus7 and the mapping added to the Import Log file.

Beams are grouped using the keyword MEMBER.

Beams can be grouped using the keyword FLOOR.

Plates are grouped using the keyword ELEMENT.

Entity and Load Case Numbering

Entities such as joints, members and elements may be numbered in a non-consecutive fashion in STAAD. In Straus7, imported entities are mapped to consecutive numbers in the order they appear. For example, if the first four joints in a STAAD file are numbered as 843, 903, 1200, 1201, they will appear in Straus7 as nodes numbered 1, 2, 3, 4. The STAAD node number is then assigned as the node ID attribute in Straus7. Note that this ID can be overwritten by the ID representing the group, as described in the Groups section above.

Note that load case numbers are similarly mapped in consecutive order once imported.

Miscellaneous Differences

The following commands are not supported: PERFORM ROTATION, INACTIVE, DELETE, CHANGE.