typical architect 1

[pmtrevisan1]

hello great minds.

I have a brilliant architect that want to use the attached as an entry to one of his buildings. The proposed frame is 22' tall and 10' wide, made from 2" x 36" steel plates. I have a few concerns with this being, welding will entail some quite interesting aspects (heating, cooling, lamellar tearing etc), more importantly the frame will experience wind loads applied to the weak axis of the plates, so never a good thing, lastly the plates themselves will act as columns, and as they are super thin buckling is a concern.

I was going to propose to revise this into a custom built hollow tube, with 3/4" plates, but i still do not think the weak axis bending will be adequate.

Any thoughts, or is this just destined to fail.

thanks..
FYi project will be in ottawa, ontario, and is going to be free standing, roughly 6" from the building face

P

 

[hokie66]

"Brilliant architect"? Isn't that an oxymoron?

But being serious, have you done the numbers on the frame? It may work, notwithstanding the fabrication issues. If not, can you provide some small braces to bridge the 6" gap to the building? Maybe use glass or plexiglass to make them less obvious.

 

[dik]

Seismic loading could be an issue... with something that heavy and something that high...

Dik

 

[TLHS]

Make the beam/cross piece at the top wider so that there's no gap between it and the building, and tie it into the building. It won't make a significant visual difference and will act as a canopy for the entrance but will significantly increase the strength.

If the architect really doesn't want that, have a beam cantilever out of the building above the top beam of the frame at midspan. Only continue it to about half way through the thickness of the frame and nobody will be able to see it from below.

The slenderness in compression is definitely a concern. I've used things past slenderness limits for self supporting structures with minimal external loads before, but those are very small and not life safety items. You'd need to do a very careful second order analysis if you wanted to be comfortable with this and also take a close look at deflections. It's definitely worrying with an initial quick run on numbers.

If you can sneak another brace in there somehow, it'd make things a lot nicer.

 

[Ron]

This appears to be a monument or sculpture, not a building support entity. With that in mind, welding is your issue as you have noted. I have been involved with welding inspection of many structures with thick sections (large structures at theme parks, automated guideway transit structures and similar) and pre-heat and post-heat temperatures must be carefully controlled to prevent cracking.

 

[JStephen]

Wind vibration due to the flexibility might be an issue.
I wonder, could a person standing there and pushing periodically get it going like an inverted swing?
You could adjust the period some by using aluminum, if that would help.

 

[pmtpemb]

great thoughts. much appreciated.
Ron--> I agree with you that it's not a building however I still will need to develop capacity of the components unless there is a provision in the bldg that allows less capacity.
hokie --> thought youd like that. I think I will propose a tube section with alittle more width. if I can get the arch to agree to 4" I can make it work and also use TLHS suggestion of discreet braces as well as tying the top to the bldg.
keep you posted and thanks to the info much appreciated.

cheers.
p

 

[dik]

And a caution for other 'steel sculptures'... if made out of corten steel... corten rusts and stains the surrounding. There was a highrise apartment in Winnipeg that use corten for lower cladding and it rusted and stained the sidewalk... not likely the intent.

Also have to be aware that if in an agressive environment, corten can corrode faster because the oxide layer is continually being removed.

Dik

 

[dik]

Why use 3/4 plates, if 1/4" will do?

Dik

 

[pmtpemb]

I'll propose a section based on capacity with options discussed above for bldg tie in.
and see what the arch says.

cheers.
p

 

[azcats]

Could it be built out of several aligned HSS members and then skinned with a solid sheet material to achieve the look the arch desires?

 

[bigmig]

2nd Azcat. Frame it then skin it.

 

[Canuck65]

I had a project some years ago with thick cantilevered, curved steel plate. The plate thickness was 1.5" thick and each plate to plate weld was about 24' long. The welding was completed by a very capable company in Ontario and the welds were reviewed and approved by a welding inspector. The final product looked very good and after powder coating the welds/joints could not be seen. Many points brought up by others (vibration due to wind, slenderness, etc...) were considered at the design stage.

There is a relatively large art sculpture with two curved plates at Toronto Pearson International airport. It is an interior location, so no significant wind or snow loading. The plates are cantilevered quite high (maybe not 20 ft, but greater than 10ft.)

 

[pmtpemb]

thanks for the suggestions. and beleive it or not the architect agrees that this as currently proposed isnt going to work and will revise his design

must say quite impressed with him as he is one of the few that actually listens to my common sense.

cheers great minds...

p