IfcStructuralItem

BACnet MVD

#### IfcStructuralItem

Natural language names

| Tragelement / Tragverbindung / Auflager (allgemein)
| Structural Item

##### Semantic definitions at the entity

Entity 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.

> HISTORY New entity in IFC2x2.

> IFC4 CHANGE Use definitions and informal proposition added.

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 IfcVertexPoints with underlying IfcCartesianPoints. 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 coordiante 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 coordiante 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:

1. The ObjectPlacements of all structural items which are grouped into the same instance of IfcStructuralAnalysisModel shall refer to the same instance of IfcObjectPlacement.

> NOTE This rule is necessary to achieve consistent topology representations. The topology representations of structural items in an analysis model are meant to share vertices and edges und must therefore have the same object placement.

> NOTE A structural item may be grouped into more than one analysis model. In this case, all these models must use the same instance of IfcObjectPlacement.

Attribute definitions

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---
| AssignedStructuralActivity | IfcRelConnectsStructuralActivity @RelatingElement | S[0:?] | Inverse relationship to all structural activities (i.e. to actions or reactions) which are assigned to this structural member. |  | X

##### Inherited definitions from supertypes

Entity inheritance
Attribute inheritance

# | Attribute | Type | Cardinality | Description | B
--- | --- | --- | --- | --- | ---
IfcRoot
1 | GlobalId | IfcGloballyUniqueId |  | Assignment of a globally unique identifier within the entire software world. | X | X

2

OwnerHistory

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.

X

X

3 | Name | 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. | X | X
4 | Description | IfcText | ? | Optional description, provided for exchanging informative comments. |  | X
IfcObjectDefinition
| HasAssignments | IfcRelAssigns @RelatedObjects | S[0:?] | 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. |  | X

Nests

IfcRelNests
@RelatedObjects

S[0:1]

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.

X

IsNestedBy

IfcRelNests
@RelatingObject

S[0:?]

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.

X

X

HasContext

IfcRelDeclares
@RelatedDefinitions

S[0:1]

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.

X

IsDecomposedBy

IfcRelAggregates
@RelatingObject

S[0:?]

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.

X

X

Decomposes

IfcRelAggregates
@RelatedObjects

S[0:1]

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.

X

X

| HasAssociations | IfcRelAssociates @RelatedObjects | S[0:?] | 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. | X | X
IfcObject

5

ObjectType

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.

X

IsDeclaredBy

IfcRelDefinesByObject
@RelatedObjects

S[0:1]

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.

X

X

Declares

IfcRelDefinesByObject
@RelatingObject

S[0:?]

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.

X

IsTypedBy

IfcRelDefinesByType
@RelatedObjects

S[0:1]

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.

X

IsDefinedBy

IfcRelDefinesByProperties
@RelatedObjects

S[0:?]

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.

X

IfcProduct
6 | ObjectPlacement | 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. | X | X
7 | Representation | 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. | X | X
| ReferencedBy | IfcRelAssignsToProduct @RelatingProduct | S[0:?] | Reference to the IfcRelAssignsToProduct relationship, by which other products, processes, controls, resources or actors (as subtypes of IfcObjectDefinition) can be related to this product. |  | X
IfcStructuralItem
| AssignedStructuralActivity | IfcRelConnectsStructuralActivity @RelatingElement | S[0:?] | Inverse relationship to all structural activities (i.e. to actions or reactions) which are assigned to this structural member. |  | X

##### Definitions applying to Design Transfer View

Concept inheritance

# | Concept | Template | Model View
--- | --- | --- | ---
IfcRoot
| Revision Control | Revision Control | Design Transfer View

##### Definitions applying to BACnet View

Concept inheritance

# | Concept | Template | Model View
--- | --- | --- | ---
IfcRoot
| Revision Control | Revision Control | Design Transfer View

##### Formal representations

XML Specification
`<xs:element name="IfcStructuralItem" type="ifc:IfcStructuralItem" abstract="true" substitutionGroup="ifc:IfcProduct" nillable="true"/>
<xs:complexType name="IfcStructuralItem" abstract="true">
<xs:complexContent>
<xs:extension base="ifc:IfcProduct"/>
</xs:complexContent>
</xs:complexType>
`
EXPRESS Specification
`ENTITY IfcStructuralItem
ABSTRACT SUPERTYPE OF(ONEOF(IfcStructuralConnection, IfcStructuralMember))
SUBTYPE OF (IfcProduct);
INVERSE
AssignedStructuralActivity : SET [0:?] OF IfcRelConnectsStructuralActivity FOR RelatingElement;
END_ENTITY;

EXPRESS-G diagram

`

References: IfcStructuralActivityAssignmentSelect

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