Standard Substitutions Procedures

[humanengr]

I'm working on an international project which will require the structural steel fabricator to make member size
substitutions due to use of metric sizes or material availability.
Is anyone aware of an industry standard that outlines the procedures for making such substitutions?
I can write my own specs. for substitution and submittal for approval. I'm just checking if there is a published
industry standard.

thank you.

 

[msquared48]

Require the same grade material as you used in the design.

Also, for the new shape, the flange thickness, the area, section modulus and moment of inertia of the new section should equal or exceed those of the original section.

For beams and purlins, the maximum unbraced length of the section for the moment seen must equal or exceed that of the original section.

For connections, if the width of the new flange, or thickness of the web, is less than the original, all affected connections must be checked.

For concrete footings, the footprint of the new column must equal or exceed that of the original column.

Make the steel fabricator responsible for providing you with calculations verifying that the above restrictions have been satisfied.

Mike McCann
MMC Engineering

http://mmcengineering.tripod.com

 

[Michel60]

Good afternoon humaneng,
For international projects, if at all possible, it's best to design using the local materials and shapes from the start and avoid the conversions and substitutions at the end. While it's possible to swap out gravity members with stronger/stiffer shapes it can be a little problematic if you have done capacity designs for frame sections and connections.

If it's not practical to design for the actual members (I've had projects too where every beam and column was "built" in a shop out of three separate plates), you may still want to consider specifying no substitutions on the frame elements. Otherwise you will be needing a much more comprehensive spreadsheet for what section properties and material strengths will be permissible.

regards,
Michel

 

[robklein82]

I am working on a project in Canada with a similar issue. We are using all ISO metric steel as per our client's spec. In some cases our fabricators have substituted in ANSI imperial equivalents. From what I understand the lengths on these members are quite close. We are having issues with some structures that have longer members. I suspect that it is due to tolerance ranges being different from ISO vs ANSI vs MSS.

Is anyone aware of a resource for comparing tolerance levels on different structural members?

 

[bpstruct]

Where is your project? I have done a few projects in the middle east over the last few years....and some of it was a nightmare. NOTHING I specified was available (and I tried to specify what I was told would be available in the local market). I would require them to submit alternate shapes and consider on a case-by-case basis. If your project is like mine was, writing specs for procedures would be a waste of time, because they probably won't follow that either...and you'll still have to consider what ever they can find.

Regarding getting engineered calcs to back up alternates (and I'm speaking only from my limited experience), that too would be a waste of time. I tried that route many times, and finding local engineers was next to impossible for my client (a design/build contractor), and I had to re-engineer based on availability. If your client was like mine and pays for the additional work, it is not the worst thing. But I hate reworking designs either way.