IfcMemberType

Definition from IAI: The element type (IfcMemberType) defines a list of commonly shared property set definitions of a structural member and an optional set of product representations. It is used to define a structural member specification (i.e. the specific product information that is common to all occurrences of that product type).

> NOTE: The product representations are defined as representation maps (at the level of the supertype IfcTypeProduct, which gets assigned by an element occurrence instance through the IfcShapeRepresentation.Item[1] being an IfcMappedItem.

A structural member type is used to define the common properties of a certain type of a structural member that may be applied to many instances of that type to assign a specific style. Structural member types may be exchanged without being already assigned to occurrences.

The occurrences of the IfcMemberType are represented by instances of IfcMember.

> HISTORY New entity in Release IFC2x Edition 2.

> IFC2x2 ADDENDUM CHANGE: The entity IfcMember has been added to serve as the occurrence object for all member types.

Use definition for steel members

When using the IfcMemberType as the underlying type for steel members within steel construction aware applications the following additional conventions apply:

Material association:
The IfcMemberType is associated with exactly one instance IfcMaterial by the IfcRelAssociatesMaterial relationship. This material association assigns a common material to all occurrences (IfcBeam, IfcColumn or IfcBuildingElementProxy) of the IfcMemberType. If an individual occurrence has its own material assignment (see IfcMember), then this overrides the material assignment given at the IfcMemberType.

Geometric representation:
The IfcMemberType type has (at least) one representation map assigned through the RepresentationMaps relation. The representation map has a full geometric representation given by:

- IfcExtrudedAreaSolid for straight beams,
- IfcRevolvedAreaSolid for curved beams based on circular arcs, or
- IfcSurfaceCurveSweptAreaSolid for all other curved beams.

The attribute ProfileName of the extruded IfcProfile instance may contain a standardized name according to local standards. However, a geometric representation of the profile is necessary as specified below. An importing application is allowed to check for the existence of the profile name: in case of identifying it as a standardized name, the corresponding profile geometry and possibly other cross sectional properties can be read from a library. Otherwise the explicit IFC geometry and possible non geometric IfcProfileProperties have to be used.

Only 'SweptSolid' representation should be used to represent steel members. The following attribute values for the IfcShapeRepresentation holding this geometric representation shall be used:

- RepresentationIdentifier : 'Body'
- RepresentationType : 'SweptSolid'

The following additional constraints apply to the 'SweptSolid' representation:

- Solid: IfcExtrudedAreaSolid shall be supported.
- Profile: IfcArbitraryClosedProfileDef, IfcArbitraryOpenProfileDef, IfcArbitraryProfileDefWithVoids, IfcCircleProfileDef, IfcCompositeProfileDef, IfcIShapeProfileDef, IfcRectangleProfileDef, IfcRoundedRectangleProfileDef, IfcCShapeProfileDef, IfcCircleHollowProfileDef, IfcCraneRailAShapeProfileDef, IfcCraneRailFShapeProfileDef, IfcLShapeProfileDef, IfcRectangleHollowProfileDef, IfcTShapeProfileDef, IfcUShapeProfileDef, IfcZShapeProfileDef and IfcAsymmetricIShapeProfileDef.
- Extrusion: The extrusion axis shall be perpendicular to the swept profile, i.e. pointing into the direction of the z-axis of the position of the IfcExtrudedAreaSolid.

In addition to the full 'SweptSolid' representation a simple representation for the axis of gravity can be used., i.e. as a second IfcRepresentationMap. It represents the neutral axis of stress which is not necessarily in the profiles center of gravity. In this case the following attribute values for the IfcShapeRepresentation holding this geometric representation shall be used:

- RepresentationIdentifier : 'Axis'
- RepresentationType : 'GeometricCurveSet'

Position number:
The position number is specified in the attribute IfcTypeProduct.Tag.

Non geometric profile properties:
Non geometric profile properties (for instance mechanical properties) are specified through IfcProfileProperties (and its specific subtypes). These properties are attached to IfcMemberType by the relationship IfcRelAssociatesProfileProperties. If an individual occurrence has its own profile property assignment (see IfcMember), then this overrides the profile property assignment given at the IfcMemberType.

Quantity related properties:
Quantity related properties, which do not relate to the profile, are specified through IfcElementQuantity (and its specific subtypes). These properties are attached to the IfcMemberType by the relationship IfcRelDefinesByProperties. If an individual occurrence has its own element quantity assignment (see IfcMember), then this overrides the quantity assignment given at the IfcMemberType. The following quantities are foreseen, but will be subjected to the local standard of measurement used:

Name | Description | Value Type
NominalLength | Total nominal length of the member, not taking into account any cut-out's or other processing features. | IfcQuantityLength
CrossSectionArea | Total area of the cross section (or profile) of the member. The exact definition and calculation rules depend on the method of measurement used. | IfcQuantityArea
OuterSurfaceArea | Total area of the extruded surfaces of the member (not taking into account the end cap areas), normally generated as perimeter * length. | IfcQuantityArea
TotalSurfaceArea | Total area of the member, normally generated as perimeter * length + 2 * cross section area. | IfcQuantityArea
GrossVolume | Total gross volume of the member, not taking into account possible processing features (cut-out's, etc.) or openings and recesses. The exact definition and calculation rules depend on the method of measurement used. | IfcQuantityVolume
NetVolume | Total net volume of the member, taking into account possible processing features (cut-out's, etc.) or openings and recesses. The exact definition and calculation rules depend on the method of measurement used. | IfcQuantityVolume
GrossWeight | Total gross weight of the member without add-on parts, not taking into account possible processing features (cut-out's, etc.) or openings and recesses. | IfcQuantityWeight
NetWeight | Total net weight of the member without add-on parts, taking into account possible processing features (cut-out's, etc.) or openings and recesses. | IfcQuantityWeight

EXPRESS specification:

ENTITY IfcMemberType
SUBTYPE OF ( | IfcBuildingElementType);
PredefinedType | : | IfcMemberTypeEnum;
END_ENTITY;

Attribute definitions:

PredefinedType | : | Identifies the predefined types of a linear structural member element from which the type required may be set.

Inheritance graph

ENTITY IfcMemberType;
ENTITY IfcRoot;
GlobalId | : | IfcGloballyUniqueId;
OwnerHistory | : | IfcOwnerHistory;
Name | : | OPTIONAL IfcLabel;
Description | : | OPTIONAL IfcText;
ENTITY IfcObjectDefinition;
INVERSE
HasAssignments | : | SET OF IfcRelAssigns FOR RelatedObjects;
IsDecomposedBy | : | SET OF IfcRelDecomposes FOR RelatingObject;
Decomposes | : | SET [0:1] OF IfcRelDecomposes FOR RelatedObjects;
HasAssociations | : | SET OF IfcRelAssociates FOR RelatedObjects;
ENTITY IfcTypeObject;
ApplicableOccurrence | : | OPTIONAL IfcLabel;
HasPropertySets | : | OPTIONAL SET [1:?] OF IfcPropertySetDefinition;
INVERSE
ObjectTypeOf | : | SET [0:1] OF IfcRelDefinesByType FOR RelatingType;
ENTITY IfcTypeProduct;
RepresentationMaps | : | OPTIONAL LIST [1:?] OF UNIQUE IfcRepresentationMap;
Tag | : | OPTIONAL IfcLabel;
ENTITY IfcElementType;
ElementType | : | OPTIONAL IfcLabel;
ENTITY IfcBuildingElementType;
ENTITY IfcMemberType;
PredefinedType | : | IfcMemberTypeEnum;
END_ENTITY;