BricsCAD BIM Analytical Model Explained

Quick answer: An Analytical Model is a simplified wireframe representing only a structure’s load-carrying elements, linear elements like columns, beams, and members become lines (planar elements like walls and slabs aren’t supported yet). BIMANALYTICALMODEL generates one from a full 3D model, starting with an automatic proposal that minimizes rigid links (eccentricities) by shifting, extending, and rotating axis lines, controlled by deviation settings, which you can then adapt further. Recalculate propagates a local change globally, again minimizing rigid links while respecting your edits. The finished model exports to IFC or CIS/2 for use in dedicated structural analysis software. The input model must be fully classified first, since the command assumes load-carrying elements are already indicated in their building element properties, the same classification workflow (BIMIFY) referenced on this hub’s structural steel and BIM QuickDraw pages, now shown in full.

Octave’s own documentation for this article uses a downloadable hangar structure model as its worked example.

Creating an Analytical Model with Strict Deviation Settings

1. Classify your BIM model first, this is required. Run BIMIFY or classify elements manually.
2. Launch BIMIFY; the Bimify command panel opens, letting you run automatic classification and spatial location assignment across the entire model or just selected entities.
3. Launch BIMANALYTICALMODEL.
4. A pop-up window lets you set the level of freedom for generating the model (hovering over an option shows a tooltip explaining its restrictions). Choose Restricted parallel deviation with a maximal deviation in profile directions of 0 mm, so no axis is allowed to deviate from its central position.
5. An interactive preview builds based on that setting, alongside a Visual Settings window where you can tick or untick features to highlight matching axes and nodes in yellow, and adjust node disk size, useful for spotting nearly coinciding nodes.
6. Tick Nearly coinciding with another node in Visual Settings; misaligned centre axes show small rigid links (in purple), a consequence of the strict 0 mm setting. To avoid this, restart with a slightly more flexible setting: Restricted parallel deviation again, but with a maximal deviation of 30 mm this time.
7. Node detection relies on the proximity of structural elements, so nodes can arise where tie rods simply cross. Remove unwanted ones by clicking a node and choosing Remove (box selection works for several at once).
8. Where tie rods still aren’t perfectly aligned with column centrelines, small rigid links persist. Remove them by relaxing the tie rod’s axis to a non-parallel position: click the tie rod, choose Relax restriction, then Non parallel; the extra freedom removes the rigid link by shifting the axis slightly.
9. Where a tilted member connects to a horizontal beam rather than the column it should, disconnect it: click the member, choose Disconnect from node, select the node to disconnect from when prompted, and type O for Ok. Then select the two axes you want connected and choose Connect axes (this reintroduces a small rigid link under the current deviation setting, removable by selecting both nodes and choosing Merge).
10. Repeat step 9 for any side member with the same issue.
11. Remove any remaining coinciding nodes by merging them, which shifts the tilted members’ axes and can introduce rigid links elsewhere. Alternatively, where the Visual Settings’ Not parallel to center axis option shows a member is already allowed to be non-parallel, relax it the same way as the tie rods instead.

Creating an Analytical Model with the Least Restrictive Deviation Settings

1. Repeat the previous procedure through step 4.
2. Choose Any deviation instead, allowing full freedom to avoid rigid links entirely. The preview shows some axes tilted, small truss members off-centre, and column axes shifted toward the profile bounds to connect with smaller side members there.
3. Remove unwanted tie rod nodes the same way as step 7 of the strict procedure.
4. To recentre a column axis that’s shifted toward the profile bounds, click it, choose Add restrictions, then To center, introducing a very local rigid link.
5. In Visual Settings, tick Has rigid links, then type R for Recalculate.
6. In Visual Settings, tick Not centered; if a column is still off-centre because its connection includes a smaller beam too, impose a centre restriction on it as well.

Exporting an Analytical Model

1. Launch BIMANALYTICALMODEL and adjust the model as needed.
2. Once finished, type E for Export and exit.
3. In the document window, name and save the file, choosing either IFC4 (.ifc) or CIS/2 (.stp) as the export format.

Worth knowing before exporting: BricsCAD’s analytical model doesn’t map perfectly onto CIS/2 and IFC concepts.

• Nodes: BricsCAD only models a node where linear elements actually connect (a column with no floor connection there gets no floor node); missing end nodes are added automatically during export for compatibility. BricsCAD nodes always sit exactly on every connected axis, with eccentricities modeled as explicit rigid links instead; export translates each cluster of rigid-link-connected nodes into a single connection node with eccentricities in CIS/2 and IFC terms.
• Axes: BricsCAD uses one single axis per physical element, which can attach to more or fewer than two nodes. During export, an axis with multiple nodes along its length splits into several analysis members, each with one start and one end node.
• Base Position: similar to cardinal points in the CIS/2 standard, but BricsCAD only supports cardinal positions 1 through 9, a subset of the full standard.
• Approximation: BricsCAD’s analysis axis can shift away from a physical element’s centre to nearly any point within certain bounds, so it doesn’t necessarily land exactly on a cardinal point. Export links the section profile to the closest base position instead, meaning a CIS/2 or IFC viewer showing physical members as extrusions along the analysis axes may show a structure that deviates slightly from the one you actually modeled. The exported analysis model is therefore an approximation of the real structure, not an exact copy.

Frequently Asked Questions

Do walls and slabs appear in an analytical model? No, only linear load-carrying elements like columns, beams, and members are supported currently.

What does the input model need before running BIMANALYTICALMODEL? Full classification, either via BIMIFY or manual classification, since the command assumes load-carrying elements are already indicated in their properties.

Why does the exported model sometimes look slightly different from what I actually modeled? Because BricsCAD’s analysis axis can shift to nearly any point within bounds, while export links the section profile to the closest cardinal base position instead, making the exported model an approximation rather than an exact match.

How do I propagate a local edit across the whole analytical model? Use Recalculate, which reruns the global rigid-link minimization while respecting the changes you’ve already made.