Mechanical Steel Tubing as a Structural Member

[lma2h]

Let me begin by pleading ignorance when it comes to Mechanical Steel Tubing.

I have client who has installed a three-story spiral staircase in a residence. They have used Mechanical Steel Tubing for the column. It appears to be a 3" pipe, but the client is uncertain how the steel was produced (AISI 1026, AISI 1020, AISI 1010).

As a structural engineer who is being asked to stamp a letter to the adequacy of this column, I am quite nervous. I work in a world of ASTM standards and it doesn't appear from other threads that the carbon content allows me to design this column as I would otherwise. I am also nervous about the welding done as part of the installation of the staircase.

Does anyone have a steel equivalent to these AISI or any advice on finding information as to whether it is advisable or not to use this type of material for structural implications. Any help would be appreciated.

 

[swall]

Can you get any information on the source(s) for the steel tubing? That may help you find out if any of it was produced to an ASTM spec or other structural standard.

 

[EdStainless]

I would ask for two things:
Marking or other grade/spec ID on the tube.
Weld coupons for destructive testing.

Without both of those you can't evaluate the design and construction.
We all know that it is probably fine, but that isn't what they are asking you to say.

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Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net

 

[metengr]

Yes, check with your local building code.

 

[lma2h]

I appreciate the quick responses.

Prior to posting on this site I had asked the fabricator for any and all information pertaining to the steel that has been installed. He indicated he would be providing me with said info. I am suspect at this point, but will come back if I get information.

Confused to the reference to the local building code? We are operating under the 2003 IBC. I can use this to determine the loads, but can't get far if I am unsure of the material properties.

At this point, I believe it is either AISI 1010 or AISI 1018. From what I have read, I am more nervous about the welding done than anything. Are these concerns warranted based on your expertise. I am just not at all familiar with welding techniques for these materials.

 

[metengr]

lma2h;
There is more to the building code than materials. You need to find out what welding code or standards is required - for example AWS D1.1? Second point, you need to evaluate the weld joint details ( example - fillet welds, partial penetration groove welds, full penetration groove welds?)

In reading your post, as as observer, I would be very concerned until you answered my questions above.

 

[lma2h]

Thanks for the continued input.

Based on the 2003 IBC, the reference welding code is AWS D1.1-2000. I guess I assumed this was implied based on the applicable building code.

All welding appears to be fillet welds.

Trust me, I am very concerned. Wish they would have called prior to actually installing the stair.

 

[Rjeffery]

I would ask for the welder's certification papers, then I would have the welds 100% visually inspected and possably either MT or PT evaluated (only after obtaining material certifications for the steel.) The fabricator should be able to provide supplier/mill paperwork for material type and schedule (wall thickness).

 

[metengr]

Go back and ask for document submittals to verify MOC, and ask for detailed fabrication drawings. If these are fillet welds, ask for the AWS procedure - it may be pre-qualified. If so, review to be sure. Ask for information as to the weld rod used for this job, and welder qualification.

You will need to review adequacy of the fillet weld size based on the fabrication drawings and your OWN expertise..

 

[lma2h]

All good info. Thanks again.

 

[EdStainless]

The welds are the biggest question, but maybe you should do a bit of analysis. If the loads are all in compression or shear on the welds then you may not be too bad. If they are in tension or bending then you can explain to people why stairs are often bought pre-fabed from suppliers that make them in factories with designs and verifiable weld processes.

= = = = = = = = = = = = = = = = = = = =
Still trying to help you stop corrosion.
formerly Trent Tube, now Plymouth Tube
eblessman@plymouth.com
or edstainless@earthlink.net