Side Mounted Welded Handrail 3

[McMichael05]

Wondering if anyone could provide some guidance/ design examples to help me out in determining if the weld is adequate for a 200lb point load at the top of the handrail.
Thanks

 

[canwesteng]

I don't think that's the right weld symbol, unless you intend for them to completely fill in the groove to a depth of 3/16" and then finish with a 3/16" fillet weld. Otherwise, just take the height of the guardrail, find the moment and shear reaction at the base, and determine the capacity of the weld using the elastic section modulus of your weld group.

 

[r13]

The all around symbol is incorrect. I think you meant "weld this side and the other side"

 

[JoelTXCive]

If you are welding the round pipe to the flat web of the channel, I believe you need a flare bevel groove weld and not a fillet

 

[phamENG]

Here's a good report on determining the effective throat of a flare bevel groove weld:

Link

 

[sbisteel]

Worked design examples can be found in this literature:

https://www.naamm.org/store/product/3/metal-stairs-manual

 

[r13]

Another detail I would like to bring it up for discussion is the placement of the handrail on inside face of the stringer. To me, there are two problems: 1) What is the clear width of the stair? 2) A person's foot can be caught by the protrude rail post and its bracket, a safety hazard.

 

[McMichael05]

Thanks for the responses.
Yeah, i knew that the fillet weld was not appropriate for this situation, it just gets detailed that way.
So when you are looking at J2.2 in AISC, it says that the effective throat needs to be 5/8R or 5/16R, for this case what would that R be? is it the radius of the pipe?

 

[phamENG]

That's not what it needs to be, it's what it can be under normal, prequalified welding procedures. And yes, as the footnote of the table states:

R=radius of joint surface...,in

You have to then use that effective throat in the rest of the calculations required by chapter J and an analysis of the guardrail post to see if it's sufficient.

it just gets detailed that way

That's doesn't seem like a great attitude, but then I don't know your role in all of this. Who is detailing it like that? If you're working for the EOR and reviewing a submittal, I'd call them out on it. If your doing calcs for the detailer, I'd call them out on it. If the fabricator did that themselves, I'd question the fabricator's qualifications for welding.

I can't find it now, but I read an article a while back about this very issue. It included an anecdote about an engineer who designed a repairs and retrofits to an old transmission tower built from pipes and angles. He detailed all of the welds as fillets rather than the more appropriate flare bevel. There were several hundred field welds. The contractor must have had a junior estimator put together the bid (or they were one of those change order hungry outfits), but they missed it and bid the project as detailed. Well the welder showed up expecting a few days of field welding (fillets can be done much faster than flare bevels). He immediately saw the problem. It took him closer to 2/3 weeks, but due to scheduling it didn't get done for much longer. The owner sent the change order and a claim for damages to the engineer. By the time it was all said and done and his insurance policy had covered it, he was effectively un-insurable and had to close down his business. All over a little weld symbol.

 

[McMichael05]

Yeah i do plan on calling it out. I work at a consulting firm and the architect sent it to me as is. I know they understand it cant technically be a fillet, but they do detail it that way sometimes, but i do call it out just in case!

 

[phamENG]

Got it. I always get annoyed when architects try to call out welds and bolted connections. One of my favorites was a lag screw in a metal stud...

 

[JLNJ]

I would guess your weak point will not be at the weld. I would look carefully at:

The aluminum handrail spanning between supports. Especially if there are welds.
The 5/8" bracket supporting the handrail in flexure.
The 1 1/4" pipe vertical post in flexure.
The local bending of the channel web to distribute the rail reaction. Worse if this is an MC channel as compared to the more stout C shape.

 

[r13]

It looks like the stair treads will be cast-in-place concrete. I wonder why you need steel stringer, is that just there to hold the guardrail, or for architectural reasons?