> 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/truss-bridge-workflow/construction-tb/substructure-construction-tb/delta-frame-unit-construction-tb.md).

# Delta Frame Unit Construction \[TB]

This object erects delta frame units (**Delta Frame Unit**) and their lateral bracings (**Lateral Bracing**) in a construction stage of the staged construction analysis. The parts it erects are added to the structure at that stage and their self weight is applied.

{% hint style="info" %}
**What erects what**

* **Girder/Floor/Support Beam Construction (Complete)** and **Truss Construction** do not erect delta frame units or their lateral bracings; this object does.
* The girder part of a unit can also be erected by picking the unit in **Girder/Floor Beam/Bracing Construction (Selected)**. Erect each part of a unit in one construction object only: every erection adds the self weight again, so the unit reports an issue on its **Structure States** when its girder part, or its legs, are erected twice.
* The bearing under a unit and the bearings standing on its girder steps are erected with **Bearing Construction**, and the deck with **Deck Construction**.
* Cross frames between units are not erected here. Pick them by name in **Girder/Floor Beam/Bracing Construction (Selected)**, in the stage of the later of the two units.
* A unit that stands only on its bearing can turn about it. Erect it in the stage of the girder it continues at the splice, or support it with a temporary support until then. The analysis does not stop on such a mechanism: it reports a rigid body rotation and reactions that look like a wrong self weight.
  {% endhint %}

## Delta Frame Unit Construction

**Stage:** The construction stage in which the selected units and bracings are erected. A value is required.

**Delta Frame Units:** The units to erect at this stage, picked from the model. Several units can be erected together.

**Unit Parts \[Girder and Legs/Legs/Girder]:** Which parts of the selected units are erected. **Girder and Legs** (the default) erects the girder part and both legs. **Legs** erects only the legs, for example when the girder part is erected in another stage or by another construction object. **Girder** erects only the girder part; no lateral bracings are erected with this option.

**Lateral Bracings \[Selected/Between the Selected Units]:** Which lateral bracings are erected with the units. **Between the Selected Units** (the default) erects every lateral bracing whose two units are both in **Delta Frame Units**. A bracing with only one of its units in the list is not erected here: erect it with another Delta Frame Unit Construction that selects both of its units, or pick it by name. **Selected** erects only the bracings picked in **Selected Lateral Bracings**. Only editable when **Unit Parts** is not Girder.

**Selected Lateral Bracings:** The lateral bracings to erect at this stage, picked from the model. Only editable when **Lateral Bracings** is Selected.

**Unit Self Weight Factor:** Factor applied to the self weight of the erected unit parts. A value of `1.0` applies the full self weight; values greater than `1.0` scale it up and values less than `1.0` reduce it proportionally.

**Lateral Bracing Self Weight Factor:** Factor applied to the self weight of the erected lateral bracings, in the same way. Only editable when **Unit Parts** is not Girder.

**Stiffness \[No/Yes]:** With **Yes** (the default), the erected members are added to the structure at this stage and carry load from then on. With **No**, only their weight is applied and they do not take part in the structure.


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