IfcMaterialLayerSetUsage

Definition from IAI: Determines the usage of IfcMaterialLayerSet in terms of its location and orientation relative to the associated element geometry. The location of material layer set shall be compatible with the building element geometry (i.e. material layers shall fit inside the element geometry). The rules to ensure the compatibility depend on the type of the building element.

EXAMPLE For a cavity brick wall with shape representation SweptSolid, the IfcMaterialLayerSet.TotalThickness shall be equal to the wall thickness. Also the OffsetFromReferenceLine shall match the exact positions between the two shape representations of IfcWallStandardCase, i.e. the IfcShapeRepresentation's with RepresentationIdentifier="Axis" and RepresentationIdentifier="Body".

NOTE Refer to the implementation guide and agreements for more information on matching between building element geometry and material layer set usage.

The IfcMaterialLayerSetUsage is always assigned to an individual occurrence object only (i.e. to relevant subtypes of IfcElement). The IfcMaterialLayerSet, referenced by ForLayerSet can however be shared among several occurrence objects. If the element type is available (i.e. the relevant subtype of IfcElementType, then the IfcMaterialLayerSet can be assigned to the type object. The assignment between a subtype of IfcElement and the IfcMaterialLayerSetUsage is handled by IfcRelAssociatesMaterial.

Use Definition

The IfcMaterialLayerSetUsage is primarily intended to be associated with planar building elements having a constant thickness. With further agreements on the interpretation of LayerSetDirection, the usage can be extended also to other cases, e.g. to curved building elements, provided that the material layer thicknesses are constant.

Generally, an element may be layered in any of its primary directions, denoted by its x, y or z axis. The geometry use definitions at each specific types of building element will determine the applicable LayerSetDirection.

EXAMPLE For a standard wall with extruded geometric representation (vertical extrusion), the layer set direction shall be perpendicular to extrusion direction, and can be derived from the direction of the wall axis. With the DirectionSense (positive or negative) the individual IfcMaterialLayer are assigned consecutively right-to-left or left-to-right. For a curved wall, "direction denoting the wall thickness" can be derived from the direction of the wall axis, and it will remain perpendicular to the wall path. The DirectionSense applies as well.

NOTE The LayerSetDirection for IfcWallStandardCase is always AXIS2 (i.e. along the y-axis).

Mls usage
Fig 1: shows an example of the use of IfcMaterialLayerSetUsage aligned to the axis of a wall.

EXAMPLE For a slab with perpendicular extruded geometric representation, the LayerSetDirection shall coincide with the extrusion direction (in positive or negative sense). The material layer set base is the extruded profile and should be consistent with the IfcExtrudedAreaSolid.Position. With the DirectionSense (positive or negative) the individual IfcMaterialLayer are assigned consecutively right-to-left or left-to-right to the base.

NOTE The LayerSetDirection for standard IfcSlab is always AXIS3 (i.e. along the z-axis).

Mls usage
Fig 2: shows an example of the use of IfcMaterialLayerSetUsage aligned to a slab.

EXAMPLE For a slab with non-perpendicular extruded geometric representation, the guidelines above apply as well. The material layer thickness and the OffsetFromReferenceLine is always measured perpendicularly, even if the extrusion direction is not perpendicular. Therefore the total material layer thickness is not equal to the extrusion depth of the geometry.

Mls usage
Fig 3: shows an example of the use of IfcMaterialLayerSetUsage aligned to a roof slab with non-perpendicular extrusion.

EXPRESS specification:

ENTITY IfcMaterialLayerSetUsage;

ForLayerSet

IfcMaterialLayerSet;

LayerSetDirection

IfcLayerSetDirectionEnum;

DirectionSense

IfcDirectionSenseEnum;

OffsetFromReferenceLine

IfcLengthMeasure;

END_ENTITY;

Attribute definitions:

ForLayerSet	:	The IfcMaterialLayerSet set to which the usage is applied.
LayerSetDirection	:	Orientation of the layer set relative to element reference geometry. The meaning of the value of this attribute shall be specified in the geometry use section for each element. For extruded shape representation, direction can be given along the extrusion path (e.g. for slabs) or perpendicular to it (e.g. for walls). NOTE the LayerSetDirection for IfcWallStandardCase shall be AXIS2 (i.e. the y-axis) and for standard IfcSlab it shall be AXIS3 (i.e. the z-axis).
DirectionSense	:	Denotion whether the layer set is oriented in positive or negative sense relative to the material layer set base. The meaning of "positive" and "negative" needs to be established in the geometry use definitions. See examples at IfcMaterialLayerSetUsage for a guideline as well.
OffsetFromReferenceLine	:	Offset of the material layer set base line (MlsBase) from reference geometry (line or plane). The offset can be positive or negative, unless restricted for a particular building element type in its use definition or by implementer agreement. The reference geometry for each relevant subtype of IfcElement is defined in use definition for the element. Examples are given in the use definition of IfcMaterialLayerSetUsage.

Inheritance graph