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Steel shapes: Drafting or engineering dimensions

When it comes to structural steel design and detailing drawings there are two seperate sets of steel shape dimensions- primarly for non-tube shapes like I, C, T, W shapes. I was wondering what users in this group use for product design? If you are using the engineering values how do you go about detailing? There are two sets of numbers to use.

Engineering DimensionsEngineering DimensionsDetail DimensionsDetail Dimensions

12 REPLIES

Re: Steel shapes: Drafting or engineering dimensions

[ Edited ]

I don't know where you got the drawing with the apparently rounded fractions but we use the decimal table.

I've always wondered how to model the flange shown in the attached channel spec as an example which applies to many shapes. Seems like a lot of missing info.

channelspec.JPG

Bruce Shand
ST9 MP8 - Insight - Win10 - K4200

Re: Steel shapes: Drafting or engineering dimensions

I find that RoyMech is a great resource for this kind of stuff with accurate dimensions, though it might be more relevant for UK standards.

 

@bshand it's got fully qualified dimensions for the types of channel you show which might be of interest, though again, perhaps different in the US.  In the UK, "Parallel Flange Channel" or PFC which doesn't have the tapered flanges (i.e. the flange inside and outside faces are parallel) has replaced the old fashioned channel section - alot easier to design around for bolting etc.

Re: Steel shapes: Drafting or engineering dimensions

@Alex_H, Thanks for that link. It is UK oriented but useful. It has an illustration of a channel with complete dimensions, even the angle of the taper. I've never seen that before but there's a disclaimer that it's been superseded by a newer standard and that one suffers from the same lack of info. Although if there has been a change in Britain to parallel sides that would make things simpler. I looked in our shop and much of the channel material is tapered. I wonder how much US and UK differ for imperial stock. I would think metric would conform to the same or very similar standard but I don't know.

Bruce Shand
ST9 MP8 - Insight - Win10 - K4200

Re: Steel shapes: Drafting or engineering dimensions

I attached a set of AISC spreadsheets with all the shape data with a few exception.

 

The radius of the edges of channels and angles are missing, and the side slope of channels is 9.46 Deg. I typically use a radius of 1/4" or 3/16" or 1/8" targeting a radius a bit smaller than the thickness of that part. Then you still have a flat edge for mates.

 

In reality, the radius has a huge manufacturing tolerance (AISC/ANSI), so it varies from mill to mill. I find the largest variance in R for HSS - rectangular.

 

Once you unzip, look at the AISC viewer.

 

I used that to create frame sections. 

 

 

Re: Steel shapes: Drafting or engineering dimensions

@12GAGE, Wow! What a screenfull! A little TMI but I'm not complaining. Thanks, my friend.

Bruce Shand
ST9 MP8 - Insight - Win10 - K4200

Re: Steel shapes: Drafting or engineering dimensions

Thanks, I've got the AISC cd somewhere with the tables as well. The question still stands. Do people use the drafting dimensions, engineering dimensions or both? In the steel construction drafting world everything is pretty much rounded to 1/16 or 1/8th inch. So when you provide detail you get weired looks when your beams are not rounded and the manufacturing guys chuckle..."must be an engineer asking for the impossible again!" ;-)

 

In the past designer life we had to use the engineering dimensions for things like weights, CGs for lifting, neutral axis, etc. But like I mentioned above the manufactures would charge us for redetailing the shop fab drawings using the drafting dimensions....and heaven forbid that you show the bottom view of a beam! You could end up getting all your holes, slots, and welded plates in located opposite of what you needed.

Re: Steel shapes: Drafting or engineering dimensions

I use the dimensions from the attached spreadsheets because it complies with AISC fab and design standards. What other set of measurements are you using specifically? Where are you getting "drafting" dimensions from.

 

In side SE, I work to 7 decimal digits (inches). Then I display everything at 3 digits. In that way, I get dimensions that are dead nuts. I also have to build in tolerances into the design knowings how things actually are fabricated. That's the fun part. In reality all structural steel is cut +- 1/16"

Re: Steel shapes: Drafting or engineering dimensions

@12GAGE, Where did you get 9.46 degrees for channel flanges?

Bruce Shand
ST9 MP8 - Insight - Win10 - K4200

Re: Steel shapes: Drafting or engineering dimensions

[ Edited ]

From a thread about 2 years ago on this forum when I was putting together my "frame" files.

I determined what it was back then. Today I just looked at what I had in the files. 

 

Another way you could look at this is looking up channel nuts. There is only a single "channel nut slope" that is used for the inside of bolts passing through channel sides. They all use the same angle. 

 

The real unknown is the radius used at the end of the slope. For channels I just picked radii that best fit the dimensions given in the AISC spreadsheet. Again I undersize this so that I end up with a flat spot for mates.

 

If I am remembering right, the width of the side flanges are the average when looking and the straight portion of the sides.....so the middle of the stright line should be at the width of the sides.

 

I also made a few adjustments to end up with the correct weight/foot of the shape.

Channels are the least specified using the attached spread sheets.