Intro
A skew grillage is quick to describe and slow to build. The support lines shift along the span across the deck width, every longitudinal girder has to be split at each cross-member, the end crossbeams have to reach every girder, and the node and element numbering has to stay consistent throughout. The whole sequence must then be repeated whenever the skew, span, or girder count changes.
The Skew Grillage Geometry Generator turns that process into one parametric definition. Span, deck width, girder count, transverse spacing, and skew angle produce the complete grillage, shown in a live orthographic preview with its node and element counts, and written to the CIVIL NX model as connected nodes and beam elements in a single confirmed step.
Developed with
- MIDAS CIVIL NX 2026 (v1.0.2)
Benefits of this plugin
- Parametric from end to end — change the skew, span, deck width, girder count, or transverse spacing and the entire grillage regenerates instantly, including the cross-member layout, terminal rows, and skew boundary beams.
- Seen before it is built — an orthographic 3D preview opens in the top view and displays node and element counts, girder spacing, typical bay spacing, and support offset live as the inputs change, so mistakes can be caught before anything reaches the model.
- Correct connectivity — longitudinal girders are split at every transverse intersection, producing a structurally connected grillage rather than crossing but unjoined beams. The final bay is shortened automatically where the selected spacing does not divide the span evenly.
- Two cross-member conventions — transverse members can either follow the skew support lines or run perpendicular to the girders. In the perpendicular option, terminal cross-beams are generated automatically so that every girder is tied in at both supports.
- Tidied before committing — measure the true distance between any two preview nodes, and merge transverse rows that are too close together by deleting redundant nodes and reconnecting the girders.
- Safe on a live model — starting node and element IDs are checked for collisions, an existing model is detected and reported before anything is replaced, missing materials and sections are created in the model's own units, and a failed element write rolls back the newly created nodes.
How to use this plugin?
- Open a new model in CIVIL NX and start the plugin.
The connection details are supplied automatically. Use Connection if the status badge does not read CIVIL NX connected. - Enter the deck geometry.
Define the span length, deck width, number of longitudinal girders, and transverse spacing. The span is measured along every girder between the two support lines. - Set the skew angle.
Drag the slider or enter an exact value between -60° and +60°. A value of 0° is perpendicular to the girders, while a positive angle moves the +Y support end in the +X direction. Choose the transverse-member direction.
Select one of the following options:- Parallel to skew — all cross-members follow the support lines.
- Perpendicular to girders — cross-members span the common girder overlap, and terminal cross-beams are added at each support point.
- Position the grillage under Model origin.
Origin X, Origin Y, and Origin Z place the start of the deck centreline in the CIVIL NX global coordinate system. All values default to 0. Changing them applies a pure translation and leaves all reported geometry metrics unchanged. - Set the assignment IDs under Model assignment.
Enter the material ID, longitudinal section ID, transverse section ID, first node ID, and first element ID. Leave Create missing default properties selected to create any missing material or section automatically in the model's current unit system. Check the preview.
The preview opens looking straight down. Select 3D or drag to orbit, scroll to zoom, and use Reset view to return to the top view.- Measure reports the 3D distance and coordinate differences between any two nodes.
- Merge beams removes a redundant transverse row and reconnects the longitudinal girders through it.
- Create the geometry.
Select Create Geometry, review the summary of nodes and elements to be added, and confirm the operation. If the model already contains nodes or elements, a second warning displays the existing counts before anything is replaced. - Download the API payload when required.
Select Download API payload to save the generated node and element data as a JSON file for review or reuse outside the plugin.
Conclusion
The Skew Grillage Geometry Generator removes the slow, error-prone part of grillage modelling: resolving skew offsets manually, splitting every girder at every cross-member, and renumbering the model whenever a parameter changes.
Define the deck once, verify it in the preview, and rebuild it in seconds whenever the skew, span, or girder arrangement changes. This leaves the engineer's time for analysis rather than geometry creation.