> 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/steel-tub-girder-bridge-workflow/loading-stg/load-geometry-definitions-stg/surface-stg/quadrilateral-stg.md).

# Quadrilateral \[STG]

This component is typically used to define the geometry of stay-in-place formwork loads and wearing surface loads.

## Surface

**Bridge:** By selecting the bridge object, the component will be able to identify the correct finite elements to use.

**Start Station:** The start station of the surface along the PGL can be specified.

**End Station:** The end station of the surface along the PGL can be specified.

**Start Transverse Offset:** The transverse offset is measured perpendicular to the PGL, where the PGL is defined as 0.

**End Transverse Offset:** The transverse offset is measured perpendicular to the PGL, where the PGL is defined as 0.

**Surface Width:** The surface width remains constant for both the start and end stations. The geometry will be generated with a transverse location equal to PGL Transverse location + (surface width/2) and PGL Transverse location - (surface width/2).\
If you are defining this load for the deck, and if your deck width is constant, you can use your deck width as the surface width.

**Start Skew:** This parameter provides a quick way to define the start skew of the geometry without resorting to arbitrary polygon definitions. If you are defining this load for the deck, you can use the same skew values as those of the support lines here.

**End Skew:** This parameter provides a quick way to define the end skew of the geometry without resorting to arbitrary polygon definitions. If you are defining this load for the deck, you can use the same skew values as those of the support lines here.

## Graphics

This component serves solely for graphical representation to determine the elevation of the loading representation and has no impact on loading computations.

**Reference Elevation:** Elevation on the coordinate system where you wish to create a graphical loading surface.

**Elevation Coordinate System \[Alignment/Global]:** The Elevation Coordinate System is typically your alignment. However, if you have more than one alignment, please select the one you wish to use and input the elevation accordingly


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