> 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-i-girder-bridge-workflow/superstructure-sig/cross-frames-sig/steel-bolster-sig.md).

# Steel Bolster \[SIG]

The Steel Bolster is a short stub-girder that sits beneath a steel I-girder at a bearing location, transferring the girder's bottom-flange reaction down to the bearing (and through it to the pier cap or abutment). It is picked onto a girder and an insertion point; its top face glues to the underside of the girder's bottom flange and its base lands on the bearing.

## Bolster Parameters

**Girder:** The host steel I-girder that the bolster sits beneath. Pick a single girder.

**Insertion Point:** The bearing insertion point the bolster is centered on. The bolster's position and elevation follow this insertion point (including its longitudinal and transverse offsets).

**Plate Girder / Rolled Section \[Plate Girder/Rolled Section]:** Selects how the bolster cross-section is defined. With **Plate Girder**, the plate dimensions below are used. With **Rolled Section**, the section is taken from a chosen rolled I-section instead.

**Rolled Section:** The rolled I-section used when the section type is set to Rolled Section. Must be an I-section.

**Top Flange Width:** Width of the bolster top flange (Plate Girder mode).

**Top Flange Thickness:** Thickness of the bolster top flange (Plate Girder mode).

**Web Depth:** Depth of the bolster web (Plate Girder mode).

**Web Thickness:** Thickness of the bolster web (Plate Girder mode).

**Bottom Flange Width:** Width of the bolster bottom flange (Plate Girder mode).

**Bottom Flange Thickness:** Thickness of the bolster bottom flange (Plate Girder mode).

**Material:** The material shared by the top flange, web, and bottom flange. Materials can either be imported or assigned from previously defined ones.

**BF Length Before Bearing:** Length of the full-depth bottom flange zone measured back-station from the bearing.

**BF Length After Bearing:** Length of the full-depth bottom flange zone measured ahead-station from the bearing.

**Taper Length Before Bearing:** Longitudinal length of the taper on the back-station side, where the web depth ramps down toward the bolster end.

**Taper Length After Bearing:** Longitudinal length of the taper on the ahead-station side.

**Taper Vertical Drop Before Bearing:** Web depth at the back-station taper end (the shallow web depth the taper ramps to).

**Taper Vertical Drop After Bearing:** Web depth at the ahead-station taper end.

## FEA

**Rigid Section:** Section assigned to the rigid link that ties the bearing support node up to the girder bottom flange. The bolster itself is not meshed; load transfers through this rigid line.

## Stiffener

A pair of stiffener plates can be placed on each web face over the bearing.

**Stiffener Used \[YES/NO]:** If 'YES', the stiffener is generated (in 3D and in the quantity) and the parameters below become available. If 'NO', no stiffener is drawn and it is excluded from the quantity.

**Stiffener Thickness:** Thickness of each stiffener plate.

**Stiffener Width:** Width of the stiffener measured out from the web face.

**Distance from Top of Web:** Distance the stiffener is held below the top of the bolster web (shortens it from the top).

**Distance from Bottom of Web:** Distance the stiffener is held above the bottom of the bolster web (shortens it from the bottom).

**Longitudinal Offset from Bearing:** Shifts the stiffener fore/aft along the girder from the bearing station. Set to 0 to keep it centered on the bearing.

**Inner Vertical Clip Height:** Vertical clip dimension at the web-side (inner) corners.

**Inner Horizontal Clip Width:** Horizontal clip dimension at the web-side (inner) corners.

**Outer Vertical Clip Height:** Vertical clip dimension at the free-end (outer) corners.

**Outer Horizontal Clip Width:** Horizontal clip dimension at the free-end (outer) corners.

**Material:** The material assigned to the stiffener plates, used for their weight in the quantity.

## IFC

**Type:** The IFC entity type used when exporting the bolster (e.g. IfcBeam).

**Predefined Type:** The IFC predefined type (e.g. BEAM).

**Parent:** The IFC spatial parent the bolster is grouped under (e.g. SUPERSTRUCTURE).

## Quantities

**Volume:** The total volume of the bolster, including the plates and (if enabled) the stiffener. (Read-only)

**Weight:** The total weight of the bolster, computed from its volume and material density. (Read-only)

**Material:** The bolster material name. (Read-only)


---

# Agent Instructions
This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com.

## Querying This Documentation
If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter:

```
GET https://docs.openbrim.org/templates/steel-i-girder-bridge-workflow/superstructure-sig/cross-frames-sig/steel-bolster-sig.md?ask=<question>&goal=<endgoal>
```

`ask` is the immediate question: it should be specific, self-contained, and written in natural language.
`goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal.

The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.