Girder Automation

What is Girder Automation?

Girder Automation is the superstructure placement engine inside AutoBRIDGE. Given an AutoBRIDGE Corridor already loaded in Revit, it calculates the exact 3D positions of every structural element across the full bridge length and places them in a single Revit run:

• Girders — Structural framing members spanning between supports, positioned at user-defined lateral offsets across the deck width.
• Crossheads — Transverse cap beams placed at every span node, sitting below the lowest girder bottom by a configurable offset.
• Bearings — Generic Model family instances placed at each girder end, seated at the crosshead level.
• Piers / Columns — Structural Column families placed beneath each crosshead, at configurable lateral offsets from the alignment centreline.

Full Form Layout

Girder Automation is a custom 1020 × 1090 px borderless window. The form has three major zones, arranged vertically: a top combo bar for source and element-type selection, a main work area split into a left canvas panel and a right control panel, and a bottom run bar.

Zone Layout Summary

Selecting the Corridor Source

The first combo box in Zone A (comboBox1) selects the AutoBRIDGE Corridor that defines the bridge centreline. Unlike the Pier Designer, Girder Automation works exclusively with AutoBRIDGE Corridor family instances — it does not support Civil 3D alignments or raw polylines directly.

How the corridor is read

When a corridor is selected, the code calls GetChainagePointsFromFamily() which scans all family instances in the active document for elements whose AutoBRIDGE_Type parameter equals "AutoBRIDGE_Corridor". The instance name is matched against the combo selection. The result is an ordered list of (XYZ Point, double Chainage) tuples representing the centreline geometry in Revit feet.

Selecting Element Types

Zone A contains five combo boxes arranged in two rows. Each picks a Revit family type for a different structural element. Only the Corridor and Girder Type are strictly required to enable the RUN button; the other three are optional and their placement is skipped when left unselected.

What "Config." buttons open

The Crosshead Config. dialog (accessible via a separate button in the right panel) opens a sub-form (CrossheadForm) that exposes three additional crosshead parameters: the family name to use, the beam depth in mm, and how far the crosshead extends beyond the outermost girder on each side.

Configuring Span Layout

Span data defines where along the corridor each span begins and ends, and what skew rotation applies at that station. The right control panel has two ways to define spans.

Method 1 — Numeric Entry + Equal Spacing

Type the desired number of spans in numSpansTextBox. When the value changes, the code in numSpansTextBox_TextChanged divides the total corridor chainage equally into that many spans, producing a customSpanData list of evenly spaced stations. Click Config. (numSpanTabl) to open the Span Configuration Schedule and inspect or fine-tune each node.

Span Configuration Schedule (SpanTableForm)

The schedule dialog (SpanTableForm) shows one row per span node. Each row has two editable columns:

Method 2 — Reference Group (Auto-Detect Spans)

The Ref. Group button (referenceButton) opens a small dialog listing all Revit Groups in the document. Select a group whose lines cross the alignment. The code intersects each group line with each alignment segment and records the distance along the path. The intersection points become span node stations and the angle between the group line and the alignment tangent is used as the skew rotation. This is ideal for bridges where span breaks are already drawn as detail lines or CAD groups.

Min / Max Span Length Limits

The minTextBox and maxTextBox fields in the right panel accept optional span-length limits in metres. When either is provided (value > 0) the plan view rendering highlights spans that fall outside the range. These are visual guides only and do not block placement.

Configuring Girder Layout

Three inputs in the right panel govern how girders are laid out across the deck width within each span.

Deck Width (deckWidthTextBox)

Total transverse width in metres over which girders are spread. The code divides this by (girdersPerSpan − 1) to calculate equal lateral spacing. The deck width is also used to draw the deck hatch in the Plan View and to scale the Section View. Changing this value live-repaints both canvases immediately.

Girders per Span (girdersPerSpanTextBox)

Integer number of girder lines per span. For equal spacing the offsets range from −deckWidth/2 to +deckWidth/2 in (count−1) equal steps. Click Config. (numGirderTabl) to open the Girder Offset Schedule and set custom lateral positions.

Girder Offset Schedule (GirderOffsetForm)

Offsets are measured in metres from the alignment centreline. Negative = left (towards decreasing Y in plan), positive = right. When custom offsets are present the girder count text box updates to match the number of rows. Clearing the custom list (by changing the textbox value) reverts to equal spacing.

Span Gap (gapTextBox)

A clearance in metres inset from both ends of every span before the girder beam starts. For example, 0.20 m means each girder starts 100 mm short of the support centreline on each side. Internally the gap is halved and applied as finalStart = pStart + girderDir × (gap/2) and finalEnd = pEnd − girderDir × (gap/2). This ensures girder ends do not clash with the crosshead solid.

Deck Edge Parameters (comboBox4 / comboBox5)

These optional combos select family parameters from the corridor family that encode the left and right edge distances from centreline. When set, the Plan View uses per-point varying width values for the deck hatch, accurately representing a superelevated or widened deck. Both combos are populated by scanning the corridor family for parameters of SpecTypeId.Length.

Configuring Piers & Columns

The Piers section of the right panel controls how structural columns are placed beneath each crosshead.

Piers per Span Node (piersPerSpanTextBox)

Number of columns placed at each intermediate span node (the start and end nodes are not piers by default — they are abutments). The default value 2 places two columns symmetrically either side of the centreline. Click Config. (numPiersTabl) to open the Pier / Column Offset Schedule and specify exact lateral positions.

Pier / Column Offset Schedule (PierOffsetForm)

Offsets follow the same sign convention as the girder offsets: negative = left of centreline, positive = right. The default configuration at form load is { −2.0, +2.0 } metres.

Pier Base Level (pierBaseTextBox)

Absolute elevation (in metres) at which each Structural Column's base point is placed. The column top is positioned at the crosshead bottom (crosshead Z). The Revit API call doc.Create.NewFamilyInstance(basePoint, symbol, level, StructuralType.Column) uses this elevation as the base point Z coordinate. A value of 0.0 places column bases at the project datum.

Section Preview — Pier view

The Section View canvas (pictureBox2) renders a live cross-section using the pier offsets and base level. Column rectangles are drawn in dark grey, their height proportional to the distance between pier base Z and crosshead bottom Z. The section updates in real time when any pier value changes.

Configuring Crossheads & Previewing

The crosshead configuration controls its vertical position and transverse extent, and the two canvas views give a live confirmation of the overall geometry before you commit to Revit.

Crosshead Offset (CrossheadOffsetTextBox)

Vertical drop in metres from the minimum girder bottom Z at a span node down to the crosshead top face. For example, 2.0 m means the crosshead sits 2 metres below the lowest girder soffit at that node. Internally: crossheadZ = minGirderZ[k] − (crossheadOffsetM / 0.3048). This value is also used as the drop distance for bearing placement.

Crosshead Layout Width (CrossheadLayoutTextBox)

Total transverse length of the crosshead beam in metres. The code places the beam from −layoutWidth/2 to +layoutWidth/2 in the skewed cross direction. The skew angle at the node is applied with a cosine correction: halfCrossFt / cos(skewDeg), so the projected length along the skewed axis is correct.

Plan View Canvas — Live Preview

The Plan View (pictureBox1, painted by pictureBoxGirder_Paint) draws in real time:

• A background grid (minor at 30 ft spacing, major at 5× minor).
• The corridor centreline in red.
• The deck hatch (green fill with dark green border) — width driven by deck-edge parameters or constant deck width.
• Yellow lines for each girder trace within each span.
• Red transverse lines for crossheads at each span node.
• Black dots for pier/column positions below the crossheads.

Section View Canvas — Cross-section

The Section View (pictureBox2, painted by pictureBox2_Paint) renders a front-on cross-section at the current settings:

• Yellow rectangles — individual girder cross-sections at their lateral offsets.
• Blue rectangle — the crosshead, spanning the configured layout width at crosshead Z.
• Cyan squares — bearing pads at each girder–node intersection.
• Dark grey rectangles — pier columns extending from crosshead bottom to pier base Z.

AdditionalValue (AdditionalValueTextBox)

An extra vertical offset (in metres) applied during Section View rendering to shift the displayed geometry up or down for visual clarity. This does not affect placed element elevations — it is a preview-only display adjustment.

Running the Placement

The cyan RUN button (button8) in Zone C executes all placement operations in sequence. It triggers button8_Click which internally calls the same logic as the static RunGirderAutomation() method.

End-to-End Workflow

Right Panel — All Controls

Keyboard & Mouse Reference

Troubleshooting

GirderAutomationResult — Output Object

When called programmatically via Girder.RunGirderAutomation() the static method returns a GirderAutomationResult object with the following fields: