4D in IFC for Beginners: from a bridge with no schedule to a construction animation

You have an IFC 4.3 bridge that says nothing about time. This guide takes that file and, in 13 steps (about 40 minutes), adds a construction schedule, links every task to the geometry and renders an MP4 of the bridge being built. Everything is done by clicking in Bonsai 0.8.5 (free, inside Blender 5.1), and every screenshot below is a real Bonsai screen with the click targets marked 1 2 3.

Starting model: the BR-01 bridge (IFC4X3_ADD2, 203 physical products) with geometry intact and zero work plans, schedules and tasks.

1 · What 4D actually is in IFC

4D = 3D + time. Your model already answers what and where. 4D adds when it gets built.

The key thing to understand: IFC contains no animation. It stores a schedule as plain data. The animation is computed afterwards by software, here Bonsai. So a 4D IFC is really three things that have to be connected:

Naming a task “Foundations A1” does not connect it to any footing. The link (IfcRelAssignsToProduct) has to be made on purpose. That single relationship is the heart of 4D.

The IFC vocabulary you need (and no more)

How the film is derived

For every element that a task builds, Bonsai writes keyframes:

• before the task starts: the element is invisible (not built yet)
• during the task: green (under construction)
• after it finishes: light grey (completed)

2 · What you need

⬇Download the starter kit (IFC 4.3)Start model + finished reference + script · ZIP, 170 KBGet it free →

Tip before you start: the Properties column is narrow by default and clips button labels. Drag the border between the 3D viewport and Properties to the left until it is about 420–520 px wide. For the long forms in Steps 4–9, hover over Properties and press Ctrl+Space to maximise it (same key to restore).

3 · The plan we will enter

Five construction stages. The first two are split into one child task per support (A1, P1–P4, A2), so 5 + 12 = 17 tasks. These are exactly the dates stored in the reference model, so you can compare at the end.

Total span: 5 April → 27 August 2027 = 144 days. Stages are chained T10 → T20 → T30 → T40 → T50 with FINISH_START.

Step 1 · Load the model

⬇Don’t have the file yet? Download the starter kitBridge_START_no_4D.ifc + reference model + script · ZIP, 170 KBGet it free →

Step 2 · Find the scheduling panel

Step 3 · Create the work plan and the work schedule

IfcWorkPlan is a folder; IfcWorkSchedule is where the task tree lives. Right now both lists are empty.

Step 4 · Add the five construction stages

Click the first icon on the schedule row (3 in the previous figure). The panel switches to task editing: schedule tools, task tools and the task tree appear.

Use these names and IDs:

Step 5 · Add a child task for each support

Stages 1 and 2 are done support by support. Child tasks are what you will attach geometry to later; the parent only summarises them (IfcRelNests stores the hierarchy).

Step 6 · Enter the dates

Select a task, click Edit, and pick the clock icon (it is the fourth icon of the tool row below – Enable Editing Task Time).

• 1 auto-select elements when you click a task  ·  2 reorder (A–Z)  ·  3 sequence – dependencies (Step 9)
• 4 clock – task time (this step)  ·  5 task calendar  ·  6 pencil – name / attributes (Step 4)

Use the dates from the plan in section 3: T10.x = 5–9 April, T20.x = 30 April–4 May, and the stage rows for T10, T20, T30, T40, T50.

Step 7 · Link the tasks to the geometry

This is the step that turns a list of names into 4D. It creates IfcRelAssignsToProduct.

ICOM stands for Inputs / Controls / Outputs / Manpower. 4D uses Outputs: what the task produces. The small arrow icon next to + (Select Task Related Products) selects a task’s outputs in 3D, which is a quick way to double-check a link.

Assign leaf tasks, not parents. For T10.x that is the footing, the blinding slab and the crushed-stone bed of each support; for T20.x the walls or pier wall; for T30, T40, T50 the elements listed in section 3.

Step 8 · The railing trap: assign the members too

Assigning the two IfcRailing objects to T50 is not enough. Their 100 posts and handrails are separate IfcMember objects connected to the railing only through IfcRelAggregates (decomposition). Bonsai’s animation reads task assignments only and does not walk down the decomposition. Result: 100 railing members hang in mid-air from the very first frame.

Step 9 · Add dependencies between stages

Dependencies (IfcRelSequence) say what has to finish before something can start. Chain the five stages with FINISH_START.

Afterwards you can use Schedule tools → Re-calculate Schedule so dates follow the dependencies and lags. Re-check the dates: it can move tasks.

Step 10 · Check the data, then save the IFC

Reference result for this bridge: 151 of 151 physical elements had a task. Compare with your count.

Step 11 · Animation settings

The task tree must stay active (Step 4). The Animation Tools panel is hidden until a schedule is active and is collapsed by default.

Other modes: Duration-based (fix the film length) and Multiplier (speed vs. real time).

Step 12 · Create the animation and check it

Bonsai now keyframes visibility and colour of every assigned element, sets the scene frame range and switches viewport shading to Object colour (without it all elements would look the same).

The finished film is the video at the top of this article: hidden, then green, then light grey, stage by stage.

Inspect frame 1 (should be empty), the transition between stages, and the last frame (everything light grey, no green).

Step 13 · Render the MP4

Bonsai builds the animation in the scene; the rendering itself is plain Blender.

Troubleshooting

Shortcuts worth knowing

• Import a ready schedule instead of typing it: File → Import supports CSV, Primavera P6 (.xml / .xer), Asta Powerproject (.pp) and Microsoft Project (.xml). You still do Step 7 (linking to geometry) yourself. Export goes the other way (File → Export: P6 or MS Project XML).
• Snapshot of a single date: Animation Tools → Snapshot Settings → pick a date → Create SnapShot.
• Gantt chart: Schedule tools → Generate Gantt (opens in the browser).
• Script: for a model that already has a schedule, bonsai_4d.py builds the animation and the MP4 in one command and also handles the railing and colour-interpolation issues automatically.

Cheat sheet

If you want to go further than one example, the IFC Infrastructure Masterclass works through the whole delivery workflow across six workshops – objects, relationships, properties, classification and information structure, on real infrastructure models.