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Automatic assignment of Junction Types

In CadnaB, a junction type is assigned to the modeled junctions by means of junction detection. Depending on the junction type, the flank transmission is automatically calculated by CadnaB. A list of junction types that can be detected by CadnaB can be found in Junction Types.

Identification of junction types

After starting the calculation, CadnaB examines the currently existing elements connections in order to identify junction types and assigns them to each junction. For information on the available joint types see Junction Types. The algorithms used to calculate the junction transmission index applies strictly to perpendicular junctions only. This assumption is, however, often not met in real buildings.

CadnaB proceeds as follows to identify junction types depending on the order n (= number of coupled elements):

  • order n=2: Junctions of order n=2 are identified, but not taken into account when calculating the junction transmission. This primarily concerns junctions within the separating element (e.g. material/thickness changes or corners in the separating element between rooms or the room corners as junctions between two external elements). In contrast, changes in material/thickness or corners as a junction types of walls are recognized as such and calculated (see Wall).
  • order n=3: For rotation-invariant junctions of the T type, CadnaB proceeds as follows:
    • T-junction, vertical: The search occurs for the two elements that are more or less collinear (+/- 45°), i.e. having the largest angle between each other. The element running towards these two element then forms the junction with these two.
    • T-junction, horizontal: analogous procedure as above, but since there are always 90° angles, special cases are not dealt with.

Note

The consideration which of the three elements represents the separating element does not occur in this step, since initially only the logics for the rotation-invariant junctions is affected. In a subsequent step - on the basis of the room pairs detected - the actual junction types are generated (taking into account whether the separating and/or flanking element(s) are rigid heavy or lightweight flexible).

  • order n=4: For junctions of the cross type, the algorithms of the cross junctions are used regardless of the angle between the separating and the flanking elements.
  • order n>4: currently not possible, returns an error (-1)

The subsequent transmission calculation just includes first-order transmission paths, regardless of the junction type. If - depending on the junction type - specific transmission paths (Ff, Df, Fd) are not relevant for the identified junction type, this is automatically considered in the calculation.

Alignment with Kij,min

After determining the vibration reduction index Kij, it is compared with the minimum required value Kij,min.

If the Kij value determined is lower than the minimum Kij,min, the minimum value is used for the calculation.

DIN 4109: To determine Kij,min, Equation (17) from DIN 4109-2:2018-01 is applied. When Kij,min is used, a note is added to the calculation report (see Chapter 5.4.5 “Activate / Open Protocol”).

ISO 12354: To determine Kij,min, Equation (23) from EN ISO 12354-1:2000 is applied.