7.10.3.13 IfcStructuralItem

ABSTRACT This definition may not be instantiated

7.10.3.13.1 Semantic definition

The abstract entity IfcStructuralItem is the generalization of structural members and structural connections, that is, analysis idealizations of elements in the building model. It defines the relation between structural members and connections with structural activities (actions and reactions).

Relationships between elements in the building model and structural items as their idealizations can be expressed by instances of IfcRelAssignsToProduct.

*Coordinate Systems*:

The following coordinate systems are distinguished:

The so-called global coordinate system is the coordinate system shared by all items and activities which are grouped in a common IfcStructuralAnalysisModel. This coordinate system is established by SELF\IfcProduct.ObjectPlacement. (This coordinate system is not necessarily the same as the IfcProject's world coordinate system.)
The so-called local coordinate system is a coordinate system local to a structural item (connection or member). This coordinate system is established by a Representation (attribute inherited from IfcProduct) in conjunction with further use definitions and attributes of subtypes of IfcStructuralItem.

Representation items in topology representations are always given within the ObjectPlacement, i.e. in so-called global coordinates (global with respect to the IfcStructuralAnalysisModel to which this item belongs).

The usage of local coordinate systems is further defined in subtypes.

*Topology Use Definitions*:

Instances of IfcStructuralItem shall have a topology representation. It includes a placement and a product representation. The IfcProductRepresentation shall be given by an item in a Representation of type IfcTopologyRepresentation.

Local Placement

The local placement for IfcStructuralItem is defined in its supertype IfcProduct. It is defined by the IfcLocalPlacement, which establishes a global coordinate system which shall be common to all items and activities in an IfcStructuralAnalysisModel.

Topology Representation

Instances of IfcStructuralItem shall have a topology representation given by an instance of a subtype of IfcTopologicalRepresentationItem, which should be the single item of IfcTopologyRepresentation.Items. Depending on the dimensionality of the structural item, one of the following types of toplogical representation items shall be used:

Point connections shall be represented by an IfcVertexPoint with an underlying IfcCartesianPoint. The Cartesian point is the reference point of the connection in the so-called global coordinate system. The following labels are used in the IfcTopologyRepresentation:
- RepresentationIdentifier: 'Reference'
- RepresentationType: 'Vertex'
Curve members and curve connections shall either be represented by an IfcOrientedEdge, IfcEdgeCurve, or IfcEdge. The curve to which the IfcEdgeCurve (or an IfcOrientedEdge's underlying IfcEdgeCurve) refers to is the reference curve of the structural item in the global coordinate system. Start and end vertex of the edge shall be IfcVertexPoint_s with underlying _IfcCartesianPoint_s. The following labels are used in the _IfcTopologyRepresentation:
- RepresentationIdentifier: 'Reference'
- RepresentationType: 'Edge'
  NOTE While an IfcEdge (or IfcOrientedEdge with underlying IfcEdge) does not provide an explicit underlying curve geometry, it may be used to imply an underlying straight line as reference curve with the origin of the curve parameter at the start vertex point.
Surface members and surface connections shall be represented by an IfcFaceSurface. The underlying surface defines the reference surface of the structural surface item in the global coordinate system. All edges in the bounds of the face shall conform to the rules for edge representations of structural curve item. The following labels are used in the IfcTopologyRepresentation:
- RepresentationIdentifier: 'Reference'
- RepresentationType: 'Face'

The reference point, reference curve, or reference surface partially or completely defines the local coordinate system of the represented structural item according to the following rules. In all cases, The local x,y,z directions form a right-handed Cartesian coordinate system.

Structural point items

The reference point in the representation is the origin of the local coordinate system of the structural item.
The axes of the local coordinate system are either parallel with and directed like the so-called global coordinate axes, or are oriented according to definitions at the respective subtype of IfcStructuralItem.

Structural curve items

The u parameter origin of the reference curve in the representation is the origin of the local coordinate system of the structural item.
The local x axis is parallel with the tangent on the curve and directed like the u parameter direction.
The local y and z axes are oriented according to definitions at the respective subtypes of IfcStructuralItem.

Structural surface items

The u,v parameter origin of the reference surface in the representation is the origin of the local coordinate system of the structural item.
The local x and y directions follow the tangents on the surface and are in parallel with and directed like u and v respectively.
The local z direction is in parallel with and directed like the surface normal.

Informal Propositions:

The ObjectPlacement_s of all structural items which are grouped into the same instance of _IfcStructuralAnalysisModel shall refer to the same instance of IfcObjectPlacement.

7.10.3.13.2 Entity inheritance

7.10.3.13.3 Attributes

#	Attribute	Type	Description
IfcRoot (4)
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 (7)
	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)
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 (5)
6	ObjectPlacement	OPTIONAL IfcObjectPlacement	This establishes the object coordinate system and 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 constrained (e.g. relative to grid axes, or to a linear positioning element). The type of placement is determined by the various subtypes of IfcObjectPlacement. An object placement must be provided if a representation is present.
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	No description available.
	ReferencedInStructures	SET [0:?] OF IfcRelReferencedInSpatialStructure FOR RelatedElements	No description available.
Click to show 21 hidden inherited attributes Click to hide 21 inherited attributes
IfcStructuralItem (1)
	AssignedStructuralActivity	SET [0:?] OF IfcRelConnectsStructuralActivity FOR RelatingElement	Inverse relationship to all structural activities (i.e. to actions or reactions) which are assigned to this structural member.

Table 7.10.3.13.A

7.10.3.13.4 Property sets

Pset_Risk
- RiskName
- RiskType
- NatureOfRisk
- RiskAssessmentMethodology
- UnmitigatedRiskLikelihood
- UnmitigatedRiskConsequence
- UnmitigatedRiskSignificance
- MitigationPlanned
- MitigatedRiskLikelihood
- MitigatedRiskConsequence
- MitigatedRiskSignificance
- MitigationProposed
- AssociatedProduct
- AssociatedActivity
- AssociatedLocation
Pset_Tolerance
- ToleranceDescription
- ToleranceBasis
- OverallTolerance
- HorizontalTolerance
- OrthogonalTolerance
- VerticalTolerance
- PlanarFlatness
- HorizontalFlatness
- ElevationalFlatness
- SideFlatness
- OverallOrthogonality
- HorizontalOrthogonality
- OrthogonalOrthogonality
- VerticalOrthogonality
- OverallStraightness
- HorizontalStraightness
- OrthogonalStraightness
- VerticalStraightness
Pset_Uncertainty
- UncertaintyBasis
- UncertaintyDescription
- HorizontalUncertainty
- LinearUncertainty
- OrthogonalUncertainty
- VerticalUncertainty
Qto_BodyGeometryValidation
- GrossSurfaceArea
- NetSurfaceArea
- GrossVolume
- NetVolume
- SurfaceGenusBeforeFeatures
- SurfaceGenusAfterFeatures

7.10.3.13.5 Concept usage

Concept	Usage	Description
IfcRoot (2)
Revision Control	General	Ownership, history, and merge state is captured using IfcOwnerHistory.
Software Identity	General	IfcRoot assigns the globally unique ID. In addition it may provide for a name and a description about the concept.
IfcObjectDefinition (9)
Aggregation	General	No description available.
Approval Association	General	No description available.
Classification Association	General	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.
Constraint Association	General	No description available.
Document Association	General	No description available.
Library Association	General	No description available.
Material Association	General	No description available.
Material Single	General	No description available.
Nesting	General	No description available.
IfcObject (5)
Assignment to Group	General	No description available.
Object Predefined Type	General	No description available.
Object Typing	General	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. This concept can be applied to the following resources: IfcTypeObject
Object User Identity	General	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.
Property Sets with Override	General	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.
IfcProduct (17)
Body Geometry	General	The body or solid model geometric representation of an IfcProduct is typically defined using a Tessellation or Brep. Subtypes may provide recommendations on other representation types that may be used. The following attribute values for the IfcShapeRepresentation holding this geometric representation shall be used: IfcShapeRepresentation.RepresentationIdentifier = 'Body' IfcShapeRepresentation.RepresentationType = Typically 'Tessellation' or 'Brep'
Box Geometry	General	No description available.
CoG Geometry	General	No description available.
Mapped Geometry	General	No description available.
Product Geometric Representation	General	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.
Product Geometry Colour	General	No description available.
Product Geometry Layer	General	No description available.
Product Local Placement	General	No description available.
Product Relative Positioning	General	If the IfcProduct Product Placement is placed relative to an IfcPositioningElement this relationship covers the information on which IfcPositioningElement positions the IfcProduct.
Product Span Positioning	General	No description available.
Product Topology Representation	General	No description available.
Property Sets for Objects	General	This concept can be applied to the following resources: Pset_Risk Pset_Tolerance Pset_Uncertainty
Quantity Sets	General	This concept can be applied to the following resources: Qto_BodyGeometryValidation
Reference Geometry	General	No description available.
Reference SweptSolid Geometry	General	No description available.
Reference SweptSolid PolyCurve Geometry	General	No description available.
Reference Tessellation Geometry	General	No description available.
Click to show 33 hidden inherited concepts Click to hide 33 inherited concepts

Table 7.10.3.13.B

7.10.3.13.6 Formal representation

ENTITY IfcStructuralItem
 ABSTRACT SUPERTYPE OF (ONEOF
	(IfcStructuralConnection
	,IfcStructuralMember))
 SUBTYPE OF (IfcProduct);
 INVERSE
	AssignedStructuralActivity : SET [0:?] OF IfcRelConnectsStructuralActivity FOR RelatingElement;
END_ENTITY;