Would you brace this thing?

[n3jc]

Hi, im wondering would you guys brace a steel canopy that is anchored in a wall?
On a field I have seen both - braced and unbraced structures like this, but the beams (cantilevers) are usually shorter than mine is (1,80 m).

Wind forces (perpendicular to beam axis) are small so im wondering is it really necessary to brace this thing (lets say with diagonals in plane)? Also in a case I design a bracing i also have to connect steel beams at the end (blue lines in image bellow) so the forces can get transfered.

There is gonna be a glass on top of steel beams.

 

[TehMightyEngineer]

Nah, I'd look into using the glass as a diaphragm.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[EngineeringEric]

Weak Axis bending of the beams?

 

[BAretired]

Glass or plexiglass? How will it be fastened to the beams? Will it be strong enough to walk on?

BA

 

[n3jc]

Glass, something like this:

There will be no walking on top.

 

[TehMightyEngineer]

I might also suggest a post in the glass engineering forum:

http://www.eng-tips.com/threadminder.cfm?pid=329

Might better attract the right people.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[TLHS]

I would always assume someone will come along and walk on those things. Maybe not a full occupancy load, and maybe not something you document, but have the strength there in case a couple of guys end up on top. I've seen too many window washers jump on top of those things to clean them.

 

[BAretired]

I agree that someone is likely to walk on the glass for cleaning or maintenance on the adjacent structure.

It is still not clear how the glass is attached to the beams. On the photo, it seems to be resting on top of some metal pegs. If so, that is not a suitable connection for a roof deck.

BA

 

[TLHS]

Oh, and what I would do would entirely depend on the nature of the rest of the structure. I might not brace in plane, but I'd likely run a continuous member along the face of the building wall. It'll make interface with the bulding and construction fitup significantly easier. This is, of course, assuming you don't have a good backspan. I'm assuming you don't, since it looks like a metal canopy on a wood building.

With a wood frame structure, I'd probably also run tension members back to the building to support the front edge of the canopy, because getting the moment connection at the wall would be tricky. You can probably do it without a framing member running along the front edge of you get creative, even though you only have maybe three spots to drop the tension members in. It'd be a lot easier if you put a framing member along the front edge though.

 

[slickdeals]

I would agree with designing for weak axis bending in this beam. Diaphragm is only good if you attach it back to the structure along it's length.

 

[JoelTXCive]

Birds are going to poop on that glass; and then someone is going to have to clean it. I could see maintenance people putting some load on it.

 

[bhugey]

Consider movement allowed by the point supported glass system. Will there be sealant at glass joints? If not, likely forgiving.
IF the weak axis bending movement of the beams is ok for the glass, no bracing
i agree that specifying some amount of maintenance loading is prudent.
i am in snow country, so i would consider drifted snow, which may exceed any maintenance loading

 

[XR250]

I can see using the glass as a diaphragm. I have worked on a large pre-fab conservatory foundation where the glass was intended to provide the lateral stability. (fortunately, I was only designing the foundation)

 

[EdStainless]

In most of these the glass floats, there are rubber bushings at the connection pegs (allow for differential expansion, glass doesn't like to be twisted).
Full length connection along the front edge is common, and sometimes mid-span also.
I have watched a few of these go up in our area recently.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[bigmig]

The bushing connections (rubber) will eliminate your ability to conservatively count the glass as a diaphragm. They will be heating up / cooling off so their viscosity or stiffness (assuming they are a rubber compound) will always be changing. You will have partial joint fixity on the ends of your steel members just based on the welds used to connect them....assuming you have a cross piece running where you drew the blue line. The sum of the joint stiffness will give you an idea as to how "stiff" it will be in a lateral event. How much sway (or racking) can the glass handle bushings handle before they want to bottom out or tear apart or crack the glass? Compare that to your partial joint fixity model (running with Risa etc). With the slim profile I would expect the horizontal loads to be pretty minimal.

 

[racookpe1978]

Even if you can enforce a "No Step Here" rule (like on an airplane wing) with a permanent placard or fade-resistant lettering, somebody is going to lay a ladder against the edge of the glass/plexiglass panels - probably where the blue line is in the image - and climb up and clean the top of the panel. That will put a vertical load, and a crushing twisting load on the edge of the panels.

 

[LittleInch]

Only comment I have which is not strictly structural but the drawing at the top seems to show a cantilevered section of glass plate beyond the last beam. Not seem anything like that before and looks very dangerous to me.

Also the glass needs to have some sort of slope on it to drain off. A flat plat will leave puddles on top which then discolour or worse, the water tracks over the edge and then drips on people underneath, somewhat spoiling the intent of the thing.

if the beams are relatively well fixed to the wall and / or you add a front beam which has some level of moment capacity, I can't see a reason to brace it, but that is quite long for a glass panel so will need some flexibility in the fixings.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[klaus.]

Must be a fully fixed cantilever beam ...so should be ok for lateral load too ...no need for bracings
For the glass you need to follow certain rules since glass is 'over head'
But I guess you are familiar with glass design.... and glass codes