This article describes how the Model Structure rule works and how you can configure the rule. The Model Structure rule is a simple but useful rule, which is used to validate the model content for further checking or information takeoff calculation.
The structure of a BIM model is described in the IFC standard. The standard sets the requirements for how different entities are related and organized in a hierarchical structure. For example, the standard requires that the IFC model contains only one site entity, and that there are no empty storeys (floors without components). When the first versions of a BIM model are created at the start of a project, it's necessary to validate that the model structure meets the requirements of the IFC standard. Also, it's considered good BIM policy to always check the model content before the model is shared with other stakeholders.
The article covers the following topics:
The rule is used to validate that the model has been structured according to the IFC standard. The rule can also check that all the doors and windows are connected with the correct wall on the correct floor level. In addition, the rule can detect some geometrical issues in the model.
The rule runs the selected checks on the model structure. Some of the parameters are TRUE/FALSE checks, while others verify that certain data is unique so that it can be utilised in checking or information takeoff. If a component-specific parameter, such as Check Floor Names, is selected, the focus is on that component (in this case floors) within the selected discipline.
The Model Structure rule is a simple rule to configure, for the rule parameters are checkbox options. First, select the discipline(s) to check and then select the checks you wish the rule to perform.
Before you select the target discipline, the model must be associated with a matching discipline in the Model Tree view.
To ensure the correct IFC structure, it's highly recommended to select at least the Check Containment hierarchy option.
Discipline: Select the discipline(s) you wish to check from the list.
Check Containment Hierarchy: Checks that the model follows the hierarchy required by the IFC standard:
The model needs to have a site instance which contains a building.
The building needs to contain storeys with related building elements (ifcComponents).
Direct Relation to Building Floor: Checks that all components in the model have a 'Contains' relation directly to a building storey. For example, it's not acceptable that furniture is related to a space only (which is related to a building storey).
Check Empty Floors: Checks that there are no empty or orphan storey instances in the model.
Check Floor Elevations: Checks that the model doesn't have multiple building storeys located in the same elevation.
Check Floor Names: Checks that the model doesn't have multiple building storeys with the same name.
Verify Material Layers Thicknesses: Checks that the sum of material layer thicknesses is the same as the thickness of the component itself. All walls, slabs, and roofs are checked.
Doors/Windows in Same Floor than Wall: Checks that the doors/windows related to the wall, roof or slab are included in the same building storey.
Check Maximum Polygon Number: Searches all components that have more polygons than the given maximum number.
Maximum Polygon Number: The given maximum number of polygons in any component. The value is used only if Check Maximum Polygon Number is checked.
Check Space Boundaries: Checks that all spaces have correct space boundaries.
Check Orphan Doors and Windows: Checks if the model has doors or windows without a relation to a wall (or some other 'hoisting' object, such as a roof for skylights).
Check Door Opening Direction: Checks that all doors in the model have the opening direction defined. Opening direction of doors is needed in some rules, for example #208 Accessible Door rule.
Allow only one site: Checks that each IFC model contains only one site instance. For more information, see the information buildingSMART website.
Check whether site has Geometry or not: Checks if the site has required geometry (user requirement).
Require Unique IFC GUIDs: Checks that there are no duplicates of IFC GUIDs (Global Unique Identifier) in a specific model or all models. Select Not Checked, Unique in One Model or Unique in All Models from the drop-down menu.
The rule reports moderate () severity issues of each selected parameter, if the requirement is not met. You can set component-specific severities in the Severity Parameters view.
Critical severity issues are reported if there are:
Incorrect layer thickness
Exceeded polygon number
Missing space boundaries
Multiple site instances
Missing Required site geometry
Duplicate GUIDS in models
Moderate severity issues are reported, if there are:
Errors in Containment Hierarchy
Missing Direct relation to building storey
Incorrect storey definition of doors/windows related to walls
Low severity issues are reported, if there are:
Multiple storeys at same elevation
Missing storey names
Orphan door reports
Missing Door Opening Direction
The rule is usually used as the parent rule to ensure the correct model hierarchy before further checking. You can read more about gatekeeper rules here.