Monday, 27 July 2009

Learning Curve ~ Steel Channel Serial Size Question

I recently received the following question about UK serial sizes and materials not being included in Revit:-

“Hi Alan,

Just on the subject of UK serial sizes.

While I find that most steel sizes quoted to me by Engineers are the same as the serial sizes and weights in the Revit families, the C channel sizes are always slightly different - e.g. 180 x 75 x 20 channel specified by Engineer, nearest in Revit is 178 x 76.

Have you come across this - or can you suggest why this should be - my local Engineer cannot see why they should be different.”

The answer is progress and marketing.

The Channel Sections your Engineer is specifying is based on the current Dimension and Properties from the Corus brochures and is based on a Parallel Flange Channel to BS4-1:2005.

The sections you are finding under:-

\Metric Library\Structural\Framing\Steel are Channels to BS4 Part1:1980

Take a peek just below the Corus Advance folder under Steel i.e.

\Metric Library\Structural\Framing\Steel\Corus Advance

And you will find UKPFC-Parallel Flange Channels

Being an old engineer I liked the old channels especially for use in external exposed locations as the rain and water would run off the sloping bottom flange.

Parallel Flange Channels were only introduced about five or six years ago, perhaps if your Local Engineer is a young chap who only knows the PFC and not it’s predecessor.

According to the 4th Impression of the Historical Structural Section Handbook printed in 1991 there has been changes to the dimensions of the Channel Section in 1904,1921,1932 and 1962

Whenever there is a change of basic dimensions there will always be a crossover period until all the stocks of the old profile have been sold and only the new profile as available.

Due to the difference in profile the Section Properties for I and Z will be slightly different, and one should not be used instead of the other without checking with the Engineer.

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