Friday, January 7, 2011

The 'I' in BIM - Steel Tonnage

This is the first post of 2011 of my series The 'I' in BIM, this post will focus on calculating steel tonnage with Revit Structure. Revit can be used to calculate steel tonnage, the beam section weight is already defined within the type properties of each family, the only problem is it isn't a parameter that can be scheduled, that is an easy fix though, it requires a simple modification to the family file, the addition of a shared parameter that looks for the weight (W) parameter in the family type properties. Step one is to edit the family, and add a new parameter.

Create a shared parameter that will represent the beam / column "Mass per metre - kg/m", and set the parameter type to number. In this instance I named the parameter Wtkg.


The next step is to make sure the parameter you have just added has a formula to make it equal the beam weight (W) this is simply done by clicking family types and adding the letter W in the formula column. In this example it means that Wtkg = W


The family can now be saved and loaded into your project. It is time to create your schedule. Add the usual parameters to your schedule such as type mark or type, you will also have to add the length and your newly created parameter, in this example that is Wtkg.


Now it is time for the mathematical part, you need to create a calculated value. Click the calculated value tab and you will see the window below. Set the discipline to common, set the type to number and add a formula. The beam weight (W) multiplied by the beam length, this is then divided by 1000 to convert the final value into tonnes.


Once you have set the schedule sorting, grouping, and filters, you will have something along the lines of the image below.


Note - Be cautious when scheduling the tonnage for anything that is not a UB or a UC section. The out of the box families for Angles, SHS and RHS sections have incorrect properties for the beam weight (mass per m) so it would be wise to check the steel weight properties in the families with a steel stock book, and make the changes as required.

5 comments:

  1. What's the diffrence in using the Volume and multipling it by 7.85?

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  2. The SG (specific gravity / specific density) of steel is typically 7.85, but it varies slightly depending on the type of steel. The method I have described is the formula that is generally more commonly used in the industry.
    I have never seen anyone use the method you describe before, but if it works for you, then there is no reason to change it.

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  3. The problem with using Volume (I think) is that revit uses the medium level of visability to calculate volume hence it leaves off the root radius.

    TBH though i'm not sure how revit calculates the 'W' parameter either.

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  4. The 'W' value is industry standard, provided by the steel suppliers and can be checked against any steel stock book globally.

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  5. Hi,

    I've just played around with both option ('weight x length' vs. 'volume x 7.85')

    so far the results seem to be similar for beams

    How would you go about columns as they dont have a 'length' parameter?

    Many thanks.

    Stephan

    ReplyDelete