BIM (building information modelling)

BIM, or building information modelling, is a way of designing a building or a bridge as a 3D model made of objects, in which each wall, beam, door and pipe carries data about itself: its size, its material, its maker and its cost. A drawing made in older software is a set of lines. A BIM model is closer to a database of the building. Every later tool, from cost estimating to checking the site, can read that data from the model.

Here is how it works in general. The architect builds the model in BIM software, using ready-made objects. A wall object knows its length, height, thickness and material. A door object knows its width and its fire rating. Structural engineers add the columns and beams in their own model. The engineers for the building services, such as plumbing, electrical wiring and air conditioning, add the pipes, cables and ducts in theirs. The models are then combined, and the software looks for clashes: places where two objects take up the same space, such as a pipe that runs through a beam. A clash found on screen is fixed in a few minutes. Found after the concrete is poured, it can cost lakhs of rupees. The drawings for the site are produced from the model, so a change made once appears on every drawing. Everyone on the project then works from the same model, often shared on a construction management platform. When the building is finished, the model can be handed to the owner, who uses it to maintain the building.

Take, for example, the design of a hospital. Combining the models shows that a duct for an operating theatre runs into a beam, and the engineers move the duct before anything is built.

Consider a metro viaduct. Civil infrastructure design software models each pier and girder, and the same model is later kept up to date with data from the finished structure.

Say a builder wants to know how far the work has really got. Construction progress monitoring scans the site and compares the scan with the BIM model, floor by floor.

How is BIM different from computer-aided design (CAD)? In ordinary 2D CAD, a wall is two parallel lines, and the software does not know that they are a wall. In BIM, the wall is an object that knows what it is, so the software can count it, price it and check it. That is why a quantity takeoff can be read from a BIM model instead of being measured by hand. BIM is also different from a digital twin. A BIM model describes the building as it was designed and built. A digital twin is kept up to date with live data from the real structure after it opens, such as its energy use or the strain on a bridge.