IFC 4.3.x development

7.11.3.5 IfcStructuralActivity

Change log

IFC4

modificationsinverses AssignedToStructuralItem definitionChanged from IfcRelConnectsStructuralActivity FOR RelatedStructuralActivity to SET OF [0:1] IfcRelConnectsStructuralActivity FOR RelatedStructuralActivity

7.11.3.5.1 Semantic definitions at the entity

The abstract entity IfcStructuralActivity combines the definition of actions (such as forces, displacements, etc.) and reactions (support reactions, internal forces, deflections, etc.) which are specified by using the basic load definitions from the IfcStructuralLoadResource.

The differentiation between actions and reactions is realized by instantiating objects either from subclasses of IfcStructuralAction or IfcStructuralReaction respectively. They inherit commonly needed attributes from the abstract superclass IfcStructuralActivity, notably the relationship which connects actions or reactions with connections, analysis members, or elements (subtypes of IfcStructuralItem or IfcElement).

NOTE  Instances of IfcStructuralActivity which are connected with an IfcElement are subject to agreements outside the scope of this specification.

NOTE  The semantics of IfcStructuralActivity are only fully defined if an activity instance is connected with exactly one structural item. The inverse attribute AssignedToStructuralItem can only be empty in incomplete models or in conceptual models which are not yet ready for analysis.

HISTORY  New entity in IFC2x2.

IFC4 CHANGE  Cardinality of attribute AssignedToStructuralItem relaxed from 1 to 0..1 in order to allow for schema-compliant incomplete models as well as conceptual models without load—item relationships.

*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 an 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 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 activity belongs).

Locations of the load objects in the AppliedLoad attribute (if of type IfcStructuralLoadConfiguration) are always given in local coordinates.

Directions of the load objects in the AppliedLoad attribute refer to global or local coordinates according to the GlobalOrLocal attribute.

The ObjectPlacement and Representation are sometimes not explicitly instantiated; instead they may be implied as described below. Global and local coordinate systems are then determined in the same way as with explicit placement and representation.

*Topology Use Definitions*:

Instances of IfcStructuralActivity which are connected with a structural item of same dimensionality, i.e.

shall not have an ObjectPlacement nor a Representation. It is implied that the placement and representation of the IfcStructuralActivity is the same as the ones of the IfcStructuralItem.

Instances of IfcStructuralActivity which are connected with

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

Instances of IfcStructuralActivity which are connected with

shall have a shape representation as specified below. It includes a placement and a product representation. The IfcProductRepresentation shall be given by items in a Representation of type IfcShapeRepresentation. Shape representation and topology representation may be combined.

Local Placement

The local placement for IfcStructuralActivity 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 IfcStructuralActivity which act on parts of a surface item shall have a topology representation given by a face with underlying surface geometry, IfcFaceSurface, which should be the single item of IfcTopologyRepresentation.Items. The surface establishes a local coordinate system of the activity:

  • The origin of surface parameters u,v is the origin of the local coordinate system.
  • 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.
  • RepresentationIdentifier: 'Reference'
  • RepresentationType: 'Face'

Instances of IfcStructuralActivity which act on a curve on a surface item shall have a topology representation given by an edge (IfcEdge or subtype), which should be the single item of IfcTopologyRepresentation.Items. The curve geometry shall be compatible with the surface geometry of the connected item. In conjunction with this surface, the curve establishes a local coordinate system of the activity:

  • The origin of the curve parameter u is the origin of the local coordinate system.
  • The local x direction follows the tangent on the curve and is directed like u.
  • The local z direction is in parallel with and directed like the surface normal of the connected surface item.
  • The local x,y,z directions form a right-handed Cartesian coordinate system.
  • 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.

Instances of IfcStructuralActivity which act on a single point on a curve or surface item shall have a topology representation given by an IfcVertexPoint, which should be the single item of IfcTopologyRepresentation.Items. The point geometry shall be compatible with the curve or surface geometry of the connected item. The local coordinate system of the activity is oriented by the curve or surface geometry of the connected item as described above for activities with edge or face topology.

  • RepresentationIdentifier: 'Reference'
  • RepresentationType: 'Vertex'

Shape Representation

Instances of IfcStructuralActivity which act on a surface item and are specified by isocontours (level sets) shall have a shape representation given by a set of curves on a surface, IfcPCurve. The basis surface shall comply with or preferably be identical with the surface of the structural item to which the activity is connected. The representation identifier and type of this geometric representation is:

  • RepresentationIdentifier: 'Level set'
  • RepresentationType: 'GeometricCurveSet'

7.11.3.5.1 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
IfcStructuralActivity
8 AppliedLoad IfcStructuralLoad Load or result resource object which defines the load type, direction, and load values.

In case of activities which are variably distributed over curves or surfaces, IfcStructuralLoadConfiguration is used which provides a list of load samples and their locations within the load distribution, measured in local coordinates of the curve or surface on which this activity acts. The contents of this load or result distribution may be further restricted by definitions at subtypes of IfcStructuralActivity.
9 GlobalOrLocal IfcGlobalOrLocalEnum Indicates whether the load directions refer to the global coordinate system (global to

the analysis model, i.e. as established by _IfcStructuralAnalysisModel.SharedPlacement_)

or to the local coordinate system (local to the activity or connected item, as established by

an explicit or implied representation and its parameter space).

> NOTE , the informal definition of _IfcRepresentationResource.IfcGlobalOrLocalEnum_ doe s not distinguish between "global coordinate system" and "world coordinate system". On the other hand, this distinction is necessary in the IfcStructuralAnalysisDomain where the shared "global" coordinate system of an analysis model may very well not be the same as the project-wide world coordinate system.

> NOTE  In the scope of _IfcStructuralActivity.GlobalOrLocal_, the meaning of GLOBAL_COORDS is therefore not to be taken as world coordinate system but as the analysis model specific shared coordinate system. In contrast, LOCAL_COORDS is to be taken as coordinates which are local to individual structural items and activities, as established by subclass-specific geometry use definitions.
AssignedToStructuralItemSET [0:1] OF IfcRelConnectsStructuralActivity FOR RelatedStructuralActivityReference to the IfcRelConnectsStructuralActivity relationship by which activities are connected with structural items.

7.11.3.5.2 Entity inheritance

dot_inheritance IfcStructuralAction IfcStructuralAction IfcStructuralActivity IfcStructuralActivity IfcStructuralAction->IfcStructuralActivity IfcProduct IfcProduct IfcStructuralActivity->IfcProduct IfcStructuralReaction IfcStructuralReaction IfcStructuralReaction->IfcStructuralActivity 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

7.11.3.5.3 Definitions applying to General Usage

7.11.3.5.3.1 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.

7.11.3.5.3.2 Identity

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

7.11.3.5.3.3 Object Predefined Type

7.11.3.5.3.4 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.

7.11.3.5.3.5 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.

7.11.3.5.3.6 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.

7.11.3.5.3.7 Product Placement

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

7.11.3.5.3.8 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.

7.11.3.5.3.9 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.

7.11.3.5.3.10 Revision Control

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

7.11.3.5.4 Formal representations

ENTITY IfcStructuralActivity
 ABSTRACT SUPERTYPE OF (ONEOF
	(IfcStructuralAction
	,IfcStructuralReaction))
 SUBTYPE OF (IfcProduct);
	AppliedLoad : IfcStructuralLoad;
	GlobalOrLocal : IfcGlobalOrLocalEnum;
 INVERSE
	AssignedToStructuralItem : SET [0:1] OF IfcRelConnectsStructuralActivity FOR RelatedStructuralActivity;
END_ENTITY;