> 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/cable-stayed-bridge-workflow/superstructure-csb/girders-csb/girder-csb.md). # Girder \[CSB] ## Girder To model custom girders, the parameters below can be defined. ### Girder Parameters **Girder Layout:** This parameter can be used to specify the girder layout for the girder to be modeled. **Girder Start-End Section:** * **Reference Support Line:** A minimum of two rows of definitions must be made for a girder to be generated correctly. Support lines, one being the start and one being the end station, for a section must be defined. * **Longitudinal Distance Along Girder Line Layout:** For varying girder sections, if a section is needed until a certain station and then a variation (for instance, a linear variation) is needed after a certain point, this parameter can be used to define the constant section length along the girder layout. * **Section:** This parameter can be used to assign the section to the girder at the specific station. A section can be imported or assigned from the previously defined ones under **Properties > Sections**. * **Variation (from previous point) \[None/Linear/Parabola/Circular]:** The variation must be defined for varying sections. If this parameter is set to "None," the girder will be generated as a constant section girder. * **Radius (for Circular Variation):** For variations defined with the "Circular" option, the radius can be specified by this parameter. Otherwise, this parameter will be N/A. **Material:** Material assigned to the girder. This definition affects both the 3D model and the Finite Element Analysis (FEA). Materials can be imported or assigned from the ones defined under **Properties > Materials**. ### FEA **Supports:** In OpenBrIM, all bearings are generated at the center of the bottom of a custom girder. This applies when there is one bearing per girder at a specific station. To change the location or assign additional bearings, this parameter can be used. **Long. Mesh Size:** The maximum distance between nodes in the longitudinal direction is specified using the longitudinal mesh size. In most cases, a smaller mesh size can be generated based on the bracing locations, deck pouring or deconstruction definitions, or section change locations. **Expansion joint end releases:** Defines nodes along the girder where an expansion joint or hinge is modeled. The girder mesh creates two coincident nodes at the given station and connects them with springs; spring stiffness values are assigned in each translational and rotational direction. **Rigid Section:** This parameter's definition is used only when there are two or more bearings at the same station. Rigid beams are employed to link the bottom nodes of girders with bearing locations/supports. **Mesh at section edges \[No/Yes]:** When set to **Yes**, additional mesh nodes are inserted at the stations where the girder section changes, improving analytical accuracy at those locations. **# of Result Extraction St.:** The result extraction station settings are solely for viewing FEA composite results in either the spreadsheet or FEA view, and do not impact standard finite element analysis results like member end forces, node displacement, and node reactions. For girder code checks, exact code check stations will be utilized for FEA composite results. ### Moveable Bridge These inputs model a girder of a moveable (bascule) leaf. The Moveable Deck and the floor beams of the leaf take the same **Rotation Support Line**, **Opening Angle** and **Rotation Axis Elevation**, so the leaf turns as one rigid body. ![A bascule leaf in elevation: the rotation axis along the Rotation Support Line at the Rotation Axis Elevation, the closed leaf (Opening Angle 0) and the leaf opened by the Opening Angle](https://2645910244-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FGR3Y2oTOZjlXFJKoQ7ar%2Fuploads%2Fgit-blob-e71e8c0948edf92d0493d67ff76fc17deee4b84f%2Fmoveable-leaf-rotation.png?alt=media) **Moveable Bridge \[No/Yes]:** Set to **Yes** for a girder of a moveable leaf: the girder then turns rigidly with the leaf about the **Rotation Support Line** by the **Opening Angle**. In the closed position (**Opening Angle** 0) its nodes and result lines are placed along the alignment, as the Moveable Deck's are, so the live load reaches it. A moveable girder rests on a Moveable Deck, and a Moveable Deck accepts only girders set to **Yes**; expansion joint end releases are not modelled on a moveable girder. Default **No**: the girder is fixed and existing models are unchanged. **Rotation Support Line:** The support line the leaf turns about: the rotation axis is horizontal, along this support line. Shown when **Moveable Bridge** is **Yes**. **Opening Angle (+ lifts the girder's side of the support line):** The angle the leaf is turned by. **0** is the closed position; a positive angle lifts the girder's side of the support line, which opens the leaf. **Rotation Axis Elevation:** The elevation of the rotation axis (the trunnion), in the same elevation system as the alignment profile. ### Quantities Quantities derived from the parameter definitions are exposed as read-only values under this tab. **Min Section Area:** Minimum cross-sectional area along the girder length (Read-only). **Max Section Area:** Maximum cross-sectional area along the girder length (Read-only). **Total Surface Area:** Total outer surface area of the girder (Read-only). **Min Cross Section Perimeter:** Minimum cross-section perimeter across the girder length (Read-only). **Max Cross Section Perimeter:** Maximum cross-section perimeter across the girder length (Read-only). **Volume:** Total volume of the girder (Read-only). **Min Length Path:** Minimum path length along the girder (Read-only). **Length @COG Path:** Path length along the girder's center of gravity (Read-only). **Max Length Path:** Maximum path length along the girder (Read-only). **Weight:** Total weight of the girder, computed from volume and material density (Read-only). ### IFC **Predefined Type \[Beam/Cornice/Diaphragm/Edgebeam/Girder\_Segment/Hatstone/Hollowcore/Joist/Lintel/Piercap/Spandrel/T\_Beam/Userdefined/Notdefined]:** IFC predefined type for the girder. Used when exporting to IFC. **Parent \[Bridge/Superstructure/Deck/Substructure/Foundation/Approach\_Structure/Retaining\_Structure]:** IFC parent container for the girder in the exported model hierarchy. ### Referencing Objects **Structure States:** Construction/deconstruction states referencing this girder (Read-only). **Temporary Supports:** Temporary Support objects supporting this girder (Read-only). **Decks:** Concrete deck objects referencing this girder (Read-only). **Tendons:** Tendon objects placed in this girder (Read-only). **Strands:** Strand objects placed in this girder (Read-only). **Bracings:** Bracing objects connecting to this girder (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. 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