Structural Glass Canopy
Structural Glass Canopy
(OP)
Hi,
I need to run some numbers on a glass canopy design. Its supported on 4 corners by spiders but I have never done calcs like this before.
Has anyone got the critical formulas I need to run the numbers. I assume deflection and bending stress calculations are the most critical?
Any information would be appreciated.
Thanks.
I need to run some numbers on a glass canopy design. Its supported on 4 corners by spiders but I have never done calcs like this before.
Has anyone got the critical formulas I need to run the numbers. I assume deflection and bending stress calculations are the most critical?
Any information would be appreciated.
Thanks.






RE: Structural Glass Canopy
Here's a starter doc: Link. If you're just confirming a glass thickness and panel size availability for your architect, I'd just run it by a local glazing contractor.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Structural Glass Canopy
Any idea what allowable deflection I should allow for the supporting steel frame, (it's a cantilever).....?
RE: Structural Glass Canopy
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Structural Glass Canopy
For the steel outrigger (assuming that's what you have), I would apply vertical deflection per the IBC category "roof members supporting ceiling"---L/240 for wind/uplift (add in the 0.42 10-year conversion factor), L/180 for dead plus live. This is my interpretation of how the limit is intended; don't think it's spelled out in the Code.
RE: Structural Glass Canopy
RE: Structural Glass Canopy
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Structural Glass Canopy
After debating on it for a long while, my last workplace purchased Mepla, it was around $7,000. When it came to panels with holes supported by standoffs and fixtures, we found the models it turned out were overly conservative most of the time compared to what we had been doing over the history of the design consultancy. If we designed by it, it would have led to way overly conservative designs that no glazing contractor would have ever built.
The $7000 mepla software became shelf-ware.
From my experience, standard FEA packages (S-frame, solidworks) were adequate, and in many ways even more versatile than Mepla.
RE: Structural Glass Canopy
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Structural Glass Canopy
definitely takes the stress out of calculating it by hand. (well, technically mathcad. still super time consuming)
RE: Structural Glass Canopy
I have 10mm toughened glass on 1.5mm interlayer on 6mm toughened glass. Also what would permissible bending and shear stresses be for toughened glass? And permissible deflection limits?
Any help welcome.
RE: Structural Glass Canopy
RE: Structural Glass Canopy
RE: Structural Glass Canopy
I would send some caution your way. There is (IMO) a lot of research that needs to go into understanding glass before heading into design. Not to say you can't do it or you may have a simple project to start with, but I've read numerous books and tech reports to help me better understanding things as there is no real "code" for glass.
Also you usually want an FEA package that can handle non-linearity as the deflections are usually larger than the thickness of the glass.
EIT
www.HowToEngineer.com
RE: Structural Glass Canopy
Transverse shear is generally a non-issue. Longitudinal shear stress between layers comes into play as RFreuend mentioned. Basically, there are two fundamental cases where your behavior will be less than 100% composite due to inter layer effects:
1) High temperatures.
2) Long duration loads (snow on skylights etc).
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Structural Glass Canopy
regarding whether the less conservative models were right.
We would regularily run 3 different models in 3 different programs, and receive 3 different results. All 3 programs had their own limitations on creating a "true" form of the glass we were modelling, and all had limitations in accurately modelling the connection restraints.
using solidworks, we could draft a perfect version of the glass panel, there would be a variable density mesh near the connections (the main point of interest). however, connections were limited to fully fixed (possibly due to our limited version of the program).
using S-frame, we were free to select the type of FEA, define our own mesh density, define our connections as preferred. the panel was simplified. input glass properties and model in non linear fashion. Again, results must be interpreted.
The differences in inputs and restraints, and their outcomes for stress and deflection always seemed to make sense working between Sframe and Solidworks.
with mepla, stressed were kind of all over the place, depending on the sort of problem. but typically high. Deflections typically seemed unreasonably high. The biggest thing, MEPLA was a black box. I have never worked with FEA that simple to use. It was simple because the user was limited - you couldn't dive too deep into what sorts of functions the program was carrying out. Our conclusion - if we cant see what its doing, and its spitting out funny numbers, what reason do we have to trust it?
My guess? I think there must have been some safety factors built into it to exclude the developers from liability... call me a conspiracy theorist or paranoid, but things just didn't add up using it.
This was just my experience working for a specialty structural glass consultancy.
RE: Structural Glass Canopy
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Structural Glass Canopy
Glass was my first job, I left it to try out "traditional" structural, ie, wood, concrete, steel, masonry.
When you boil it down they are both pretty similar. Ive found sexy-ness and engineering appeal rarely line up . 50 story facades design packages were a laborous bore to grind through, as can be glass clad "architectural masterpieces". Some of my most memorable engineering was designing connection details for typical windows into questionable 80yr old hollow masonry structure.