BIM Workflow for Contractors

Hi,

I work for a timber framing Software Company in the UK; we use AutoCAD Architecture for our framing product (as well as our own bespoke platform for Roof Trusses). I'm reasonably conversant with what BIM is and what it is trying to achieve, I have a lot of experience with 3D modelling and I know a bit about IFC and Revit etc. What I'm struggling with is real life BIM work flow for a contractor (like a timber frame fabricator) as I'm yet to get my hands dirty on a real life BIM project.

BIM is gathering pace in my industry (mainly residential buildings, houses, flats care homes etc.), until now our customers (timber frame fabricators) have been detailing in 3D but predominately their starting point has been 2D dwg files they received from an Architect. Now we see a growth in UK Architects using ArchiCAD and Revit and wanting to adopt BIM workflows. I have listed below what I currently believe to be a fair reflection of where BIM and in particular IFC is at (since IFC in AutoCAD Architecture is my only option just now)…

1. Most 3D CAD software in the building industry is capable of exporting a decent IFC model
2. Most IFC viewers work well for viewing/merging/overlaying these IFC files and doing collision detection etc.
3. Most CAD software (Revit/ACA/ArchiCAD) is quite poor at Importing/converting these IFC files into their native formats.
4. There are limited possibilities in existing CAD software (like ACA and Revit) for merging and overlaying IFC files, managing revisions etc. When I import an IFC file now, I don’t really want it to create a new project for me (like it does in both ACA and Revit) I want it to be more of an xref/overlay in my existing project that can be refreshed when the Architect makes revisions to his model. I think I saw Tekla has something along the lines of what I would ideally want in ACA (an IFC reference model).

To elaborate on point 3, I tried importing an 8mb IFC file from ArchiCAD into Revit today and it took about 15 minutes, looked like it was not responding but eventually did complete the operation, but it had problems with about 1200 objects which it insisted I deleted or take some action with. The same IFC file would not import at all in AutoCAD Architecture (although I could IFC export the Revit model and import that into ACA but by this time I’m pretty sure I didn’t have a sound model anymore). By comparison the IFC file opens fine in all 3rd party viewers I tested, opens in seconds and is complete and accurate. By the time the timber frame fabricator completes his work I expect the IFC file might be over 100mb and even more unlikely to import with a good result into the Architects native model.

I'm satisfied my customers are able to export IFC files and therefore participate in BIM projects, but I think they are also hoping to be able to improve accuracy and efficiency from receiving an architect’s IFC file. But I’m afraid I don’t see any possibilities to overcome the need for my clients to re-draw the model, even if they could use an IFC file for the basis of their project at the start they sure as hell can’t use it for updating the model as it evolves. Even if I could solve all the software interoperability issues, the way the architect draws a model is can be very different to how the timber frame fabricator needs it and would need a lot of re-working.

Therefore I think I can rule out any conversion of architects model into the timber frame designers native format, and conversion of the timber frame designers model back to the Architects native format, so the only time the model is ever going to be complete is when using IFC viewers to merge the IFC file provided by the Architect and each sub contractor. Is this typical of what the Architect/Client would expect? Am I missing any tools/trick relating to point 4? I know ACA is not marketed as a BIM solution, but from what I can see Revit isn't offereing anything closer to what i want either!

Regards,

Graham.

PS. Sorry for the large amount of text to read! I guess I'm just hoping someone will read it and tell me if I am missing something important relating to IFC import/export and conversion into native file formats, or just confirm my findings that IFC and BIM offers little in the way of efficiency or accuracy for a timber frame fabricator!

Are you aware of the wood frame extension for Revit? visit: http://www.youtube.com/watch?v=aKxaLdD0_6Y


BTW, I spent some time practicing in the UK. Every British architect I worked with considered timber construction (wood frame in the US) to be too expensive to even consider. Did I get the wrong impression?

Hi,

Yes I'm aware of it but I consider it as more of an architects tool, no where near powerfull enough for a UK timber frame fabricator (we have a huge development team writing our timber frame software and we wouldn't even consider the Revit plugin as a competitor application), I don't really see being on the Revit platform much of an advantage as it still has the same IFC issues and lake of revision managment when you need to collaborate with some one another platform?

Also its not really true that wood frame is too expensive here. All our timber frame is offsite construction rather than stick built on site. Most of our wood for wall panels is CLS imported from Canada, in Scotland it is still over 60% of new houses built and perhaps 20% in England. Cost is approx the same as the traditional brick and block methods in most cases!

Thanks,

Graham.

I find that for best results the BIM methodology has to be adjusted according to the requirements and particular circumstances of each project. Design/Build is very different from Design/Bid. Design models are different from construction models which are different from as-built/facility models. Software choices and workflows will determine transfer formats and standards. IFC can be great when it works but sometimes DWG geometry is all that is needed.

As far as the application of IFC specifically to timberframe construction, I think much of the same concerns apply. If you are exporting a frame for design coordination to an Architect using Revit it may be best to use DWG for the geometry and not worry about native Revit families. I imagine you really don't want the Architect changing the timbers anyway. This method also allows for easy updating of the linked files which IFC does not.

For export to ArchiCAD IFC would be the preferred method. The quality of the imported model will typically be much better than Revit manages at this point and it can be set up in a way that is relatively straight forward to update. It still requires an extra file to update the IFC to be linked to the working model but once set up it's not too bad.

I believe Tekla has similar capabilities as ArchiCAD but my experience with it is limited. The BIMsight product works great and clearly indicates a serious commitment to IFC on the part of Trimble/Tekla.

For construction coordination IFC is clearly indicated when using Solibri or BIMsight. NavisWorks (as of 2013) on the other hand doesn't handle IFC so well and the Revit NWC export add-in doesn't produce the best product (unless I'm missing something) so DWG seems to be the best way to go at the moment.

ETA: Just checked in NavisWorks 2014 and the IFC seems at first look to be much better. I haven't checked the latest IFC add-ins to Revit 2014 yet either but from what I've seen in 2013 things are getting better and from what I understand this will continue.

BTW: Do you know Ralph Wessel? He is a UK developer of add-ons for ArchiCAD and has a product called FrameWright which seems pretty good at least for Architectural timber frames. I'm not so sure about fabrication models.

Thanks Matthew, we did find as you say it was much easier working with DWG, as it was easier to manage updates into AutoCAD Architecture (just xref the DWG into your model and replace the file when it changes). Importing/converting into native objects was very slow and not reliable and very difficult to manage updates.

Exporting a 3d dwg from archicad as 3D faces worked much more solidly than using IFC, even though we had to re-draw a lot of the model this is actually a fairly small amount of time compared to detailing the timber frame. The idea of re-using the architects IFC walls/doors/windows etc didn't really work (too slow, not easily updatable and there were far too many modifications that we would need to do to them to make them suitable for framing).

Speaking with other BIM managers at a conference recently, it seems IFC is often not they route the choose (some said they prefer contractors to send them dwfx over IFC which suits me fine!).

Cheers,

Graham