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).
*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.
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.
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.
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.
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:
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,
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.
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.
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 structures only).
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).
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.
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 definition can be aggregated by several other objects (occurrences or parts).
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 definition can only be part of a single decomposition (to allow hierarchical structures only).
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.
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 or when the concrete entity instantiated does not have a PredefinedType attribute. The latter is the case in some exceptional leaf classes and when instantiating IfcBuiltElement directly.
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.
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.
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.
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.
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.
Reference to the representations of the product, being either a representation (IfcProductRepresentation) or as a special case of a shape representation (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.
Reference to the IfcRelAssignsToProduct relationship, by which other products, processes, controls, resources or actors (as subtypes of IfcObjectDefinition) can be related to this product.
Reference to the objectified relationship IfcRelReferencedInSpatialStructure may be used to relate a product to one or more spatial structure elements in addition to the one in which it is primarily contained.
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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.
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).
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.
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:
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.
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.
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:
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, in which all geometric representations are founded.