> For the complete documentation index, see [llms.txt](https://docs.openbrim.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.openbrim.org/templates/concrete-box-girder-bridge-workflow/superstructure-cbg/diaphragm-cbg/diaphragm-cbg.md).

# Diaphragm \[CBG]

The Diaphragm object models a transverse concrete diaphragm cast inside a box girder at a given support line. It locates the diaphragm along the girder, sets its up-station and down-station thicknesses, and assigns its material. The diaphragm cross-section is taken from the host box girder at that station (including any cell cutouts), so the diaphragm fills the box outline automatically.

## Diaphragm

**Box Girder:** The Concrete Box Girder this diaphragm belongs to. Pick a single girder; this value is required. The diaphragm inherits its cross-section outline and alignment from the selected girder.

**Support Line:** The support line that locates the diaphragm along the girder. Pick a single support line; this value is required.

**Offset from Support Line:** Longitudinal offset of the diaphragm from the selected Support Line, measured along the alignment. Use a non-zero value to place the diaphragm away from the support line (e.g. an intermediate diaphragm between supports).

**Thickness (Downstation):** Thickness of the diaphragm measured down-station (toward the start of the alignment) from its reference station. Together with Thickness (Upstation) this sets the total diaphragm width along the girder.

**Thickness (Upstation):** Thickness of the diaphragm measured up-station (toward the end of the alignment) from its reference station. Defaults to 15. The full diaphragm spans from the down-station face to the up-station face.

**Material:** The concrete material assigned to the diaphragm, selected from the Materials defined in the Properties section. Drives the self-weight and quantity calculations.

## Quantities

**Volume:** Computed concrete volume of the diaphragm (Read-only; this is an expensive computation that may slow recompute).

**Weight:** Computed self-weight of the diaphragm, derived from its volume and material density (Read-only; this is an expensive computation that may slow recompute).

## IFC

**Type:** The IFC entity used when exporting the diaphragm to IFC. Defaults to IfcBeam.

**Predefined Type:** The IFC predefined type for the exported entity. Defaults to PIER.

**Parent:** The IFC spatial parent the diaphragm is nested under on export. Defaults to SUPERSTRUCTURE.


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