Let’s be honest: How do we normally start a new design project? By modeling walls? Not really.
We usually start with a top down down approach:
• How much money do we have available?
• When should it be finished?
• And finally, what can we afford following the first two constraints?
Most time during the creation of a BIM model is spent on dealing with haptic elements like walls and spatial elements like rooms. But when it comes to the actual construction of the building – whether prefabricated or on-site – the temporal component needs increased attention.
Construction schedules and work plans have always been a main instrument for construction companies. Therefore it is no big surprise that IFC also covers this important topic, but in a different way than many think of when they hear “4D BIM”.
How would most people working with BIM models implement a 4D strategy? Model everything, give each component a time stamp for its construction, done.
Well, as if schedule planning was this easy. And who says there’s only one “time property” to plan? What’s the earliest, the latest date, the actual date for construction? Different properties? This gets our of hand easily. And definitely nobody in scheduling works that way.
How does IFC deal with tasks?
Tasks are entities on their own, as you already might guess by now. If you need to plan something, it should have its own identity. This makes perfect sense: you usually make rough timetables before you even model a single wall.
This is not exotic in nature, the whole concept is quite close to how programs like MS Project are set up.
Tasks are identifiable activities carried out during your project. That could be the construction of a wall or the whole design phase. It has a status, a work method attribute, info whether it is a milestone or not, an assigned priority, a predefined type info and a reference to a task time (all optional, so don’t feel obligated to fill in data that you don’t know or need).
Tasks take time
IfcTaskTime then has 20 attributes containing all the data you already know from other scheduling software: early start and finish, scheduled start and finish, late start and finish, whether it is on the critical path or not, extent of completion etc.
Sounds like you could create a whole scheduling app based on IFC? Head over to blenderbim.org, they already did.
It’s all about connections
There are a lot of things that you can “do” with tasks. You can define successors and precedessors, including time lags (using a custom start/finish configuration, too). Combining task to summary tasks is also possible – the convention is that all tasks add up to one “root” summary task in the end.
Just like in “normal” scheduling program you can assign resources to each task (material, construction equipment, labor resources etc.). Resources will be part of a future article.
Tasks can have their own property sets, so you can assign as many extra data as you need. Classifications, documents can be referenced, too.
By now you sure see the power and flexibility that comes with the IFC schema, don’t you?
We finally want to connect our building elements to our tasks in order to get those nice construction simulations. How to do that?
Another question first: how do elements and activities relate at all? They can be the result, the input or something that is consumed / occupied during the task. And that’s exactly what you can express using IFC. Now, try to document such relationships with element properties.
Do you want to enrich you tasks with even more data? Use cost items to plan and track the monetary aspects of your activities. Use work plans to specify during which hours per day the task is carried out.
So, next time someone tells you 4D BIM is just about adding time stamps to your model show them this article. Because with IFC it could be much more.