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Bridge

The object "bridge" represents a horizontal plate causing diffraction from sources located below or above. This object was the only way in former releases of CadnaA to model a screening plate lifted above the ground.

Due to the option „Self-Screening“ of the objects „Road“ and „Railway“ the object „Bridge“ became dispensable for modeling of bridge plates (see section „Self-screening“ of roads, chapter Roads, and of railways, chapter Railways).

The object „Bridge“ has the following properties:

  • The bridge is a horizontal plate being a closed polygon. All sound rays not intersecting the bridge remain unaffected.
  • When a sound ray by a source lies above the bridge plate intersects the plate the diffraction is calculated for receiver points not directly below the bridge’s plate.
  • For sound rays from sources lying below the bridge intersecting the plate to receiver points above the bridge the diffraction is calculated due to the bridge’s edge.
  • Diffraction into the space below the bridge is not considered. Therefore, resulting levels below the bridge are irrelevant!
  • The bridge plate is assumed to have a plane surface being parallel to the reference plane regardless of the terrain’s contour.
  • The height of the bridge is always taken from the first polygon point (dialog Bridge|Geometry). Heights entered for further polygon points are not relevant.
  • The bridge plate is considered as if it were a building’s roof. When the bridge’s height attribute is set to „Roof“ (dialog Bridge|Geometry) the height above the bridge’s level is entered.
  • On the vertical grid or on the cross section the bridge plate is not displayed.

The sound diffracted downwards from roads or railway lines on top of the bridge are calculated correctly considering the diffraction around the bridge’s edges. Rays passing below the bridge causing an immission on the opposite side are considered automatically.

Due to the „floating barrier“-option even barriers on a bridge can be modeled (see Floating Barrier).

Example

Path: Examples\Obstacles\Bridge