IFC 4.3.x development

7.11.3.10 IfcStructuralCurveMember

Change log

IFC4

additions attributes Axis
additions where_rules HasObjectType
modificationsattributes PredefinedType definitionChanged from IfcStructuralCurveTypeEnum to IfcStructuralCurveMemberTypeEnum

7.11.3.10.1 Semantic definitions at the entity

Instances of IfcStructuralCurveMember describe edge members, i.e. structural analysis idealizations of beams, columns, rods etc.. Curve members may be straight or curved.

HISTORY  New entity in IFC2x2.

IFC4 CHANGE  Attribute Axis and WHERE rule added. Use definitions changed.

*Coordinate Systems*:

See definitions at IfcStructuralItem. The local coordinate system is established by the reference curve given by topology representation and by the attribute Axis. The local x axis is parallel with the tangent on the reference curve. The local z axis is located in the surface which is created by sweeping Axis along the reference curve and is directed according to Axis. The local y axis is directed such that x,y,z form a right-handed Cartesian coordinate system.

7.11.3.10.1 Attributes

# Attribute Type Description
IfcRoot
1 GlobalId IfcGloballyUniqueId Assignment of a globally unique identifier within the entire software world.
2 OwnerHistory OPTIONAL IfcOwnerHistory Assignment of the information about the current ownership of that object, including owning actor, application, local identification and information captured about the recent changes of the object,

> NOTE  only the last modification in stored - either as addition, deletion or modification.

> IFC4 CHANGE  The attribute has been changed to be OPTIONAL.
3 Name OPTIONAL IfcLabel Optional name for use by the participating software systems or users. For some subtypes of IfcRoot the insertion of the Name attribute may be required. This would be enforced by a where rule.
4 Description OPTIONAL IfcText Optional description, provided for exchanging informative comments.
IfcObjectDefinition
HasAssignments SET [0:?] OF IfcRelAssigns FOR RelatedObjects Reference to the relationship objects, that assign (by an association relationship) other subtypes of IfcObject to this object instance. Examples are the association to products, processes, controls, resources or groups.
Nests SET [0:1] OF IfcRelNests FOR RelatedObjects References to the decomposition relationship being a nesting. It determines that this object definition is a part within an ordered whole/part decomposition relationship. An object occurrence or type can only be part of a single decomposition (to allow hierarchical strutures only).

> IFC4 CHANGE  The inverse attribute datatype has been added and separated from Decomposes defined at IfcObjectDefinition.
IsNestedBy SET [0:?] OF IfcRelNests FOR RelatingObject References to the decomposition relationship being a nesting. It determines that this object definition is the whole within an ordered whole/part decomposition relationship. An object or object type can be nested by several other objects (occurrences or types).

> IFC4 CHANGE  The inverse attribute datatype has been added and separated from IsDecomposedBy defined at IfcObjectDefinition.
HasContext SET [0:1] OF IfcRelDeclares FOR RelatedDefinitions References to the context providing context information such as project unit or representation context. It should only be asserted for the uppermost non-spatial object.

> IFC4 CHANGE  The inverse attribute datatype has been added.
IsDecomposedBy SET [0:?] OF IfcRelAggregates FOR RelatingObject References to the decomposition relationship being an aggregation. It determines that this object definition is whole within an unordered whole/part decomposition relationship. An object definitions can be aggregated by several other objects (occurrences or parts).

> IFC4 CHANGE  The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.
Decomposes SET [0:1] OF IfcRelAggregates FOR RelatedObjects References to the decomposition relationship being an aggregation. It determines that this object definition is a part within an unordered whole/part decomposition relationship. An object definitions can only be part of a single decomposition (to allow hierarchical strutures only).

> IFC4 CHANGE  The inverse attribute datatype has been changed from the supertype IfcRelDecomposes to subtype IfcRelAggregates.
HasAssociations SET [0:?] OF IfcRelAssociates FOR RelatedObjects Reference to the relationship objects, that associates external references or other resource definitions to the object.. Examples are the association to library, documentation or classification.
IfcObject
5 ObjectType OPTIONAL IfcLabel The type denotes a particular type that indicates the object further. The use has to be established at the level of instantiable subtypes. In particular it holds the user defined type, if the enumeration of the attribute PredefinedType is set to USERDEFINED.
IsDeclaredBy SET [0:1] OF IfcRelDefinesByObject FOR RelatedObjects Link to the relationship object pointing to the declaring object that provides the object definitions for this object occurrence. The declaring object has to be part of an object type decomposition. The associated IfcObject, or its subtypes, contains the specific information (as part of a type, or style, definition), that is common to all reflected instances of the declaring IfcObject, or its subtypes.

> IFC4 CHANGE  New inverse relationship, change made with upward compatibility for file based exchange.
Declares SET [0:?] OF IfcRelDefinesByObject FOR RelatingObject Link to the relationship object pointing to the reflected object(s) that receives the object definitions. The reflected object has to be part of an object occurrence decomposition. The associated IfcObject, or its subtypes, provides the specific information (as part of a type, or style, definition), that is common to all reflected instances of the declaring IfcObject, or its subtypes.

> IFC4 CHANGE  New inverse relationship, change made with upward compatibility for file based exchange.
IsTypedBy SET [0:1] OF IfcRelDefinesByType FOR RelatedObjects Set of relationships to the object type that provides the type definitions for this object occurrence. The then associated IfcTypeObject, or its subtypes, contains the specific information (or type, or style), that is common to all instances of IfcObject, or its subtypes, referring to the same type.

> IFC4 CHANGE  New inverse relationship, the link to IfcRelDefinesByType had previously be included in the inverse relationship IfcRelDefines. Change made with upward compatibility for file based exchange.
IsDefinedBy SET [0:?] OF IfcRelDefinesByProperties FOR RelatedObjects Set of relationships to property set definitions attached to this object. Those statically or dynamically defined properties contain alphanumeric information content that further defines the object.

> IFC4 CHANGE  The data type has been changed from IfcRelDefines to IfcRelDefinesByProperties with upward compatibility for file based exchange.
IfcProduct
6 ObjectPlacement OPTIONAL IfcObjectPlacement Placement of the product in space, the placement can either be absolute (relative to the world coordinate system), relative (relative to the object placement of another product), or constraint (e.g. relative to grid axes). It is determined by the various subtypes of IfcObjectPlacement, which includes the axis placement information to determine the transformation for the object coordinate system.
7 Representation OPTIONAL IfcProductRepresentation Reference to the representations of the product, being either a representation (IfcProductRepresentation) or as a special case a shape representations (IfcProductDefinitionShape). The product definition shape provides for multiple geometric representations of the shape property of the object within the same object coordinate system, defined by the object placement.
ReferencedBy SET [0:?] OF IfcRelAssignsToProduct FOR RelatingProduct Reference to the IfcRelAssignsToProduct relationship, by which other products, processes, controls, resources or actors (as subtypes of IfcObjectDefinition) can be related to this product.
PositionedRelativeTo SET [0:?] OF IfcRelPositions FOR RelatedProducts
ReferencedInStructures SET [0:?] OF IfcRelReferencedInSpatialStructure FOR RelatedElements
IfcStructuralItem
AssignedStructuralActivitySET [0:?] OF IfcRelConnectsStructuralActivity FOR RelatingElement Inverse relationship to all structural activities (i.e. to actions or reactions) which are assigned to this structural member.
IfcStructuralMember
ConnectedBy SET [0:?] OF IfcRelConnectsStructuralMember FOR RelatingStructuralMemberInverse relationship to all structural connections (i.e. to supports or connecting elements) which are defined for this structural member.
IfcStructuralCurveMember
8 PredefinedType IfcStructuralCurveMemberTypeEnum Type of member with respect to its load carrying behavior in this analysis idealization.
9 Axis IfcDirection Direction which is used in the definition of the local z axis. Axis is specified relative to the so-called global coordinate system, i.e. the _SELF\IfcProduct.ObjectPlacement_.

> NOTE  It is desirable and usually possible that many instances of IfcStructuralCurveConnection and IfcStructuralCurveMember share a common instance of IfcDirection as their Axis attribute.

7.11.3.10.2 Entity inheritance

dot_inheritance IfcStructuralCurveMemberVarying IfcStructuralCurveMemberVarying IfcStructuralCurveMember IfcStructuralCurveMember IfcStructuralCurveMemberVarying->IfcStructuralCurveMember IfcStructuralMember IfcStructuralMember IfcStructuralCurveMember->IfcStructuralMember IfcStructuralSurfaceMember IfcStructuralSurfaceMember IfcStructuralSurfaceMember->IfcStructuralMember IfcStructuralItem IfcStructuralItem IfcStructuralMember->IfcStructuralItem IfcStructuralConnection IfcStructuralConnection IfcStructuralConnection->IfcStructuralItem IfcProduct IfcProduct IfcStructuralItem->IfcProduct IfcProduct_children 8 more... IfcProduct_children->IfcProduct IfcObject IfcObject IfcProduct->IfcObject IfcObject_children 5 more... IfcObject_children->IfcObject IfcObjectDefinition IfcObjectDefinition IfcObject->IfcObjectDefinition IfcContext IfcContext IfcContext->IfcObjectDefinition IfcRoot IfcRoot IfcObjectDefinition->IfcRoot IfcTypeObject IfcTypeObject IfcTypeObject->IfcObjectDefinition IfcPropertyDefinition IfcPropertyDefinition IfcPropertyDefinition->IfcRoot IfcRelationship IfcRelationship IfcRelationship->IfcRoot

7.11.3.10.3 Definitions applying to General Usage

7.11.3.10.3.1 Classification Association

Any object occurrence or object type can have a reference to a specific classification reference, i.e. to a particular facet within a classification system.

7.11.3.10.3.2 Identity

IfcRoot assigns the globally unique ID. In addition it may provide for a name and a description about the concept.

7.11.3.10.3.3 Material Profile Set Usage

The material of direct instances IfcStructuralCurveMember (in contrast to instances of the subtype IfcStructuralCurveMemberVarying) is defined by IfcMaterialProfileSetUsage and attached by the IfcRelAssociatesMaterial.RelatingMaterial. It is accessible by the inverse HasAssociations relationship. Composite profile beams can be represented by refering to several IfcMaterialProfiles within the IfcMaterialProfileSet that is referenced from the IfcMaterialProfileSetUsage. In case of tapered members, the material profile usage subtype IfcMaterialProfileSetUsageDual is used which specifies IfcMaterialProfileSets separately at the start and the end of the tapered member.

The material (IfcMaterial) in each IfcMaterialProfile(Set) is specified minimally by a name which corresponds with an agreed upon standardized structural material designation. An external reference to the source which specifies the material designation should be provided. Alternatively, structural material properties may be provided by means of IfcMechanicalMaterialProperties and IfcExtendedMaterialProperties.

The profile (IfcProfileDef) in each IfcMaterialProfile(Set) is specified minimally by a name which corresponds with an agreed upon standardized structural profile designation. An external reference to the source which specifies the profile designation should be provided. Alternatively or additionally, explicit profile geometry should be provided by using respective subtypes of IfcProfileDef. Alternatively or additionally, structural profile properties may be provided by means of subtypes of IfcProfileProperties.

An IfcProfileDef is a two-dimensional geometric object with a xp,yp coordinate system. The profile is inserted into the curve member model thus that the origin of xp,yp is located at the member's reference curve and that xp,yp are parallel with and directed like the local y,z.

NOTE  Due to convention in structural mechanics, axis names of IfcStructuralCurveMember differ from axis names of building elements like IfcBeamStandardCase: The extrusion axis of IfcStructuralCurveMember is called x while the extrusion axis of IfcBeamStandardCase is called z. Hence x,y,z of IfcStructuralCurveMember correspond with z,x,y of IfcBeamStandardCase.

If the profile is meant to be inserted centrically in terms of structural section properties, it is necessary that the origin of xp,yp is identical with the geometric centroid of the profile (commonly also called centre of gravity). If subtypes of IfcParameterizedProfileDef are used which are only singly symmetric or are asymmetric, an explicit translation by IfcParameterizedProfileDef.Position.Location is required then.

If the profile is inserted at its geometric centroid, IfcMaterialProfileSetUsage.CardinalPoint shall be set to 10.

Otherwise, the profile is inserted eccentrically and a different cardinal point should be set accordingly.

NOTE  Another eccentricity model is available independently of eccentric profile specification: The reference curve of the member may be located eccentrically relative to the reference points of the connected IfcStructuralPointConnections. The connection relationship is then established by IfcRelConnectsWithEccentricity. Whether one or the other or both eccentricity models may be used is subject to information requirements and local agreements.

7.11.3.10.3.4 Object Predefined Type

7.11.3.10.3.5 Object Typing

Any object occurrence can be typed by being assigned to a common object type utilizing this concept. A particular rule, restricting the applicable subtypes of IfcTypeObject that can be assigned, is introduced by overriding this concept at the level of subtypes of IfcObject.

7.11.3.10.3.6 Object User Identity

An attribute Name and optionally Description can be used for all subypes of IfcObject. For those subtypes, that have an object type definition, such as ifcBeam - IfcBeamType, the common Name and optionally Description is associated with the object type.

7.11.3.10.3.7 Product Geometric Representation

The geometric representation of any IfcProduct is provided by the IfcProductDefinitionShape allowing multiple geometric representations. It uses the Product Placement concept utilizing IfcLocalPlacement to establish an object coordinate system, within all geometric representations are founded.

NOTE  A detailed specification of how to apply the local placement and which shape representaions are applicable is provided at the level of subtypes of IfcProduct and is further determined by the model view definition and implementer agreements.

7.11.3.10.3.8 Product Placement

The Product Placement establishes the object coordinate system and is required, if a geometric shape representation is provided for this product.

7.11.3.10.3.9 Property Sets for Objects

Any object occurrence can hold property sets, each being a set of individual properties having name, description, value(s) and unit(s). A reference to applicable property sets, being part of this specification, is introduced at the level of sub types of IfcObject.

7.11.3.10.3.10 Property Sets with Override

Any object occurrence can hold property sets, either directly at the object occurrence as element specific property sets, or at the object type, as type property sets. In this case, the properties that are provided to the object occurrence are the combinations of element specific and type properties. In case, that the same property (within the same property set, is defined both, in occurrence and type properties, the property value of the occurrence property overrides the property value of the type property.

7.11.3.10.3.11 Reference Topology

Direct instances of IfcStructuralCurveMember shall have a topology representation which consists of one instance of IfcEdge or a subtype, representing the reference curve of the curve member. See definitions at IfcStructuralItem for further specifications.

Informal Propositions:

  1. The reference curve must not be parallel with Axis at any point within the curve member's domain.

The local coordinate system is established by the reference curve given by topology representation and by the attribute Axis. The local x axis is parallel with the tangent on the reference curve. The local z axis is located in the surface which is created by sweeping Axis along the reference curve and is directed according to Axis. The local y axis is directed such that x,y,z form a right-handed Cartesian coordinate system.

Topology
'IfcEdge'

7.11.3.10.3.12 Revision Control

Ownership, history, and merge state is captured using IfcOwnerHistory.

7.11.3.10.3.13 Structural Connectivity

StructuralConnection
'IfcStructuralPointConnection'

7.11.3.10.4 Formal representations

ENTITY IfcStructuralCurveMember
 SUPERTYPE OF (ONEOF
	(IfcStructuralCurveMemberVarying))
 SUBTYPE OF (IfcStructuralMember);
	PredefinedType : IfcStructuralCurveMemberTypeEnum;
	Axis : IfcDirection;
 WHERE
	HasObjectType : (PredefinedType <> IfcStructuralCurveMemberTypeEnum.USERDEFINED) OR EXISTS(SELF\IfcObject.ObjectType);
END_ENTITY;