> 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/box-girder-cbg/concrete-box-girder-cbg.md). # Concrete Box Girder \[CBG] The Concrete Box Girder object models a cast-in-place or segmental concrete box girder running between two support lines. It carries the girder's geometry (section, alignment, support-line offsets), its finite-element meshing controls, longitudinal and shear reinforcement, and read-only links to the bents, diaphragms, strands, tendons, and barriers that reference it. ## Girder Parameters **Start Support Line:** The support line where the girder begins. Pick a single support line; this value is required. **End Support Line:** The support line where the girder ends. Pick a single support line; this value is required. **Start Suportline Offset (Longitudinal):** Longitudinal offset of the girder start from the Start Support Line, measured along the alignment. Positive values move the start up-station. Editable only when there is no integral bent at the start support line. **End Suportline Offset (Longitudinal):** Longitudinal offset of the girder end from the End Support Line, measured along the alignment. Positive values move the end down-station. Editable only when there is no integral bent at the end support line. **Section:** The cross-section assigned to the girder, selected from the Sections defined in the Properties section. A value is required. See [Box Girder Section Geometry](#box-girder-section-geometry) below for what the section's dimensions mean. **Use Custom Alignment \[No/Yes]:** When set to Yes, the girder's left and right edges follow user-supplied edge alignments instead of being derived from the section width about the PGL. Enables the Right Edge Alignment and Left Edge Alignment inputs. **Right Edge Alignment:** Alignment that defines the right edge of the girder. Visible and editable only when Use Custom Alignment is Yes; it must not be left empty in that case. **Left Edge Alignment:** Alignment that defines the left edge of the girder. Visible and editable only when Use Custom Alignment is Yes; it must not be left empty in that case. **Soffit Option \[Parallel to Deck=0/Constant Depth(From PGL)=1]:** Controls how the bottom slab (soffit) elevation is derived. **Parallel to Deck** keeps the soffit at a constant depth below the deck surface, so it follows the deck's cross slope and profile; **Constant Depth(From PGL)** holds the soffit at a constant depth below the PGL instead (default: Parallel to Deck=0). **Deck Material:** Material assigned to the deck (top slab) of the box girder. A value is required. **Soffit Material:** Material assigned to the soffit (bottom slab) of the box girder. A value is required. ## Box Girder Section Geometry ![Importing a box girder section](https://2645910244-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FGR3Y2oTOZjlXFJKoQ7ar%2Fuploads%2Fgit-blob-e220ea7a1d335e7bb213fa28c5de9639881a7788%2FSectionImportBoxGirder.gif?alt=media) The **Section** picked above comes from the **Box Girder Section (Multicell)** database, a parametric family of concrete multi-cell box sections (1 through 7 cells: "1 Cells" … "7 Cells"). All variants share the same dimension set — the only difference between them is the number of cells. The girder reads these dimensions to build both its 3D solid and its shell finite-element mesh (top slab, bottom slab, exterior and interior webs), and they can vary station-to-station through the girder's section list, so the box can taper or widen along the span. All dimensions are measured in the section's transverse Y–Z plane: positive horizontal away from the PGL (profile grade line), and depth downward from the top of the deck. **Section Type** controls the profile of the exterior webs: * **Vertical:** the outer webs run straight down (vertical outer walls). * **Slope:** the outer webs lean inward toward the soffit; the horizontal lean over the section depth is set by `B7`. * **Chamfer:** like Slope, but the bottom outer corners are cut back (chamfered) rather than running to a single sloped line. ### Dimension parameters | Parameter | Meaning | | ------------------------------------- | ---------------------------------------------------------------------------------------- | | Section Type\[Vertical/Slope/Chamfer] | Exterior-web profile (see above). | | Depth of Section (H1) | Overall section depth, from the top of the deck to the bottom slab. | | Depth 1 (H2) | Top-slab thickness at the root of the overhang (where the overhang meets the outer web). | | Depth 2 (H3) | Fascia / overhang-tip depth at the outer deck edge. | | Depth 3 (H4) | Bottom-slab thickness; the bottom of each cell sits this far above the soffit. | | Depth 4 (H5) | Top-slab thickness over the cells; the top of each cell sits this far below the deck. | | Left to PGL Width (L1) | Left half-width — horizontal distance from the PGL to the left deck edge. | | Right to PGL Width (R1) | Right half-width — horizontal distance from the PGL to the right deck edge. | | Width 1 (B2) | Top-flange overhang width (deck cantilever beyond the outer web). | | Thickness between Cutout (B3) | Interior web thickness, i.e. the wall between two adjacent cells. | | Chamfer for Cutout Top (B4) | Chamfer/fillet at the top corners of each cell. | | Chamfer for Cutout Bottom (B5) | Chamfer/fillet at the bottom corners of each cell. | | Thickness of Section (B6) | Exterior web thickness (measured along the web, accounting for slope). | | Thickness 2 (B7) | Horizontal slope offset of the exterior web, used by the Slope and Chamfer types. | | Thickness 3 (B8) | Extra horizontal offset used only by the Chamfer type (default 0). | The cell count and cell width are not entered directly — they are derived from the dimensions above: * **Cell count** is fixed by which section you pick (1 Cells … 7 Cells). * **Cell width** is the remaining width split evenly between the cells: `((|L1| + |R1|) − 2·B2 − (cell count − 1)·B3 − 2·(B6 / cos(edge slope))) / cell count`. In words: take the full deck width, remove the two overhangs, the interior webs between cells, and the two exterior webs, then divide by the number of cells. * **Edge slope** (the tangent of the exterior-web lean) is `B7 / (H1 − H2)` for Slope/Chamfer types. ## FEA **Supports:** The Insertion Points that act as supports (bearings) for the girder in the analysis model. Selected from a list; each must reference a Deck. At least one support is required. **Long. Meh Size:** Target longitudinal mesh size along the girder. Smaller values produce a finer mesh and longer solve times. **Rigid Section:** Section used for the rigid links that connect the girder to the substructure at support locations. A value is required. **# of Result Extraction St.:** Number of stations along the girder at which composite analysis results are extracted. **Additional Result Extraction St.:** Extra stations (entered in a table, measured along the alignment) at which results should be extracted, in addition to the evenly spaced stations above. **Trans. Mesh Size \[0=same as Long.]:** Maximum finite-element size in the transverse direction. Leave at 0 to use the same mesh size as the longitudinal direction (default: 0). **Mesh Algorithm \[GridMesh/MeshAdapt/Automatic/Initial mesh only/Delaunay/Frontal Delaunay/Frontal Delaunay for Quads/Packing of Parallelograms/Quasi structured Quad]:** Meshing algorithm used to generate the shell finite-element mesh. GridMesh (the default) produces a structured grid; the other options select the corresponding unstructured/quad meshing strategies. ## Hinge Joint **Joint Option \[Full-Depth=0/Half-Depth=1]:** Selects the type of in-span joint in the girder. **Full-Depth** separates the girder over its full depth; **Half-Depth** creates a hinge (seat) joint where the lower portion carries the seat (default: Full-Depth=0). **Apply To \[3D Only (joint and its bearings not in analysis)=0/3D + FEA=1]:** Controls whether the hinge joint and its bearings are represented in the analysis as well as the 3D model. Applicable when Joint Option is Half-Depth (default: 3D + FEA=1). **Support Line:** Support line at which the hinge joint is located. Required when Joint Option is Half-Depth. **Orientation \[Front(seat toward start)=0/Back(seat toward end)=1]:** Direction the hinge seat faces — toward the start or the end of the girder. Applicable when Joint Option is Half-Depth (default: Front=0). **Hinge Length:** Length of the hinge along the girder (default: 72). **Hinge Seat Gap:** Gap between the hinge seat and the supported girder end (default: 12). **Hinge Gap:** Gap across the joint between the two girder faces (default: 2). **Hinge Depth:** Depth of the hinge measured from the section reference (default: 36). **Hinge Joint Material:** Material assigned to the hinge joint region. **Post Tension Blockout Length:** Length of the post-tensioning blockout at the hinge (default: 36). **Expansion Joint End Releases:** Table of end releases applied at the expansion joint. Applicable when Joint Option is Full-Depth, or when the half-depth joint is applied to the 3D model only. ## Referencing Objects These read-only fields list the objects that reference this girder. They are populated automatically and are not edited directly. **Structure States:** Construction structure states that reference this girder (Read-only). **Bents:** Integral bents connected to this girder (Read-only). **Diaphragm:** Diaphragm objects placed on this girder (Read-only). **Temporary Supports:** Temporary support objects acting on this girder during construction (Read-only). **Strands:** Girder Strand objects assigned to this girder (Read-only). **Bracings:** Bracing objects on this girder (Read-only). **Barrier:** Barrier objects placed on this girder (Read-only). **Tendons:** Girder Tendon and Cap Tendon objects routed through this girder (Read-only). ## Reinforcement **Show \[Yes/No]:** Toggles the 3D display of the girder reinforcement. **Longitudinal Reinforcement Data:** Table defining the longitudinal reinforcement rows (bar size, count, spacing, reference edge, offsets, and transverse offset from center). **Shear Reinforcement Data:** Table defining the shear (stirrup) reinforcement used for the code check. This data drives the code check and is not rendered in 3D. ## Quantities **Deck Area:** Computed top-slab (deck) area of the girder (Read-only; this is an expensive computation that may slow recompute). **Form Work Area:** Computed formwork area of the girder (Read-only; this is an expensive computation that may slow recompute). **Volume:** Computed concrete volume of the girder (Read-only; this is an expensive computation that may slow recompute). **Weight:** Computed self-weight of the girder, derived from the volume and the section material density (Read-only; this is an expensive computation that may slow recompute). ## IFC **Type:** The IFC entity used when exporting the girder to IFC. Defaults to IfcBeam. **Predefined Type:** The IFC predefined type for the exported entity. Defaults to BEAM. **Parent:** The IFC spatial parent the girder is nested under on export. Defaults to SUPERSTRUCTURE. --- # Agent Instructions This documentation is published with GitBook. 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