Monday, June 13, 2011

Revit & Structural Analysis

I have always maintained that the Structural Analysis 'bi-directional' link between Revit Structure and the numerous analytical packages out there is a myth.



Engineers analytical requirements are not as precise as the detailer at the front end of the project.

An engineers analytical model could be 10mm, 50mm, even 100mm out, whereas a construction / documentation model has to be 100% accurate. After all, this is what is used to work out tricky buildability area, take accurate steel weights and concrete volumes, not to mentions detailing difficult connections.

It is due to this very reason that I have always taken a stance that an analytical model exported to Revit, only has its uses at the early stages of a project. Tender stage for example, the analytical model will be fairly accurate (it has to be if the engineer wants to give a good estimate of the actual costs involved.) It is so easy and time saving if the tender documents are produced from an exported analytical model.

You could produce a set of annotated GA's for a large building in well under a week. The cost savings for the consultant alone will be huge, compared with traditional 2D or starting from scratch.

I have then always taken the stance that the Tender model is 'binned' (archived) and a fresh model is constructed after tender, whilst the Engineer continues to 'tweak' his / her analytical model as and when required through to Construction issue.

Mark Fox over at
Revit FOX has thrown an interesting spanner in the works with his post Revit / Analysis Software - The Missing Link.

He explains his way of working, which the concepts / philosophy is more or less the same as mine, but he does things the opposite way round. He uses the 'one' export from Revit to the analysis software, at quite an advanced stage.

....Firstly, the model should always be created in Revit. My reason is simple. Whilst Engineers are very fussy about some things, there are also some they couldn't care less about; the accuracy of the analytical model generally falls into the ‘I’m not that bothered’ category. Mr Engineer is often ‘not that bothered’ if members they model are 100mm one way or the other. Analytically and from a design POV it generally makes very little difference to them. So why let them start the model and then give it to Mr Technician who then spends hours correcting it? Just start in Revit in the first place right?....

This has led me to think about a second step in the process I follow, combining both of the above points into one approach.

Once the tender documents are produced and the tender model is 'binned,' the construction model can start to take shape, and can be exported to the analysis package.

Whilst this is not a true bi-directional link, it would mean both technician and engineer are working on models that are more or less exactly the same.

Like all of these things, time is always a problem, so the workflow would have to be set up early on, but I do think this approach could work quite well.

2 comments:

  1. Glenn,

    I have worked in the Structural drafting field for over 20 years and I must say that I am perplexed that people are not taking more advantage of the Revit analysis link. As a drafter, I of course have had it drummed into my head that my drawings must be drawn precisely to scale. From your short article, it seems that the engineers and not embracing this concept. In the past firms that i worked for we developed the attitude that if you were going to take the time to model something, model it exactly. It took awhile and the owners of the companies to set this practice in place, but eventually the engineers followed the procedure. It did take a little extra time for the engineers to model structural items correctly, but the time saved in transferring markups and the like were tremendous. the last firm i worked for, we almost completely eliminated markups for structural size changes. If member sizes changes we would re-import the model from RAM Structural System to Revit all the say through the construction document phase. Did we have a few problems? Sure we did at first until we figured out how the links all worked. But in the end, the time saved was worth the headaches.

    The whole key to the process was to inform the drafters that they were now helping the engineers and needed to learn a little about how the building is designed and for the engineers to learn a little about drafting and what it takes to draw an accurate building. I think that we called it 'Teamwork'. Just my thought that it can work and work well if every one is onboard with the idea.

    Kevin Billings

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  2. Kevin,

    Thanks for your comment, clearly there are some Engineers out there who make the bi-directional link work!

    I am sadly yet to meet an Enginer who models the analytical model 100% accurate, as the 'drafting' model has to be.

    and until this comment, I am yet to hear of anyone who is successfully using Revit and analysis software as a bi-directional tool.

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