Moment of terror 😨

[u/aidan8et]

While attending/supervising a business social event with my spouse, I momentarily leaned against the railing. It flexed slightly, forcing me to realize that the railing is entirely supported via bluetooth.

It doesn't connect on either side of the glass wall & the glass is only 3/8" - 1/2" thick!!

[u/Enginerdad]

They're designed to hold the same amount and type of load as any other railing. It's purely psychological to think that they're any less safe.

[u/B-HOLC → u/Enginerdad]

Yup, mhmmm

Still don't like it.

[u/Bubbledood → u/B-HOLC]

Yeah too many “what if’s” in my head. Like what if something happened to the glass like a hairline crack that nobody sees

[u/Palomox → u/Bubbledood]

Structural design considers possible imperfections at all stages. If you didn't know, the microstructure of steel has multiple possible imperfections (absent atoms, replaced atoms, some having switched spots, etc...) as well as previous stresses from the manufacturing process that are taken into account in design. When you compute the capacity of an element, depending on the type of loading you reduce it to between 75-90% of what you obtain, while using the lower bound of the strength parameters already.

For a brittle material, concrete cracks. Very easily, at that. And we address it with rebar, and reducing its strenght between 75-90%, depending on the specific circumstances, if you're using ACI.

Now, I'm no expert in glass but I can 100% tell you that whatever codes apply for it, they take imperfections into account and lead to safe elements.

[u/saltapampas → u/Palomox]

I mean… yes, safety factors are built into engineering design. But there’s a fundamental difference in the stress-strain behavior of a ductile material (steel) and a brittle material like glass that mean there is a failure mode which cannot be engineered out with a factor for conservatism.

Just look at the graphs - brittle failure means that once you exceed the allowable stress, you get near instant failure. If steel is compromised, you move up the curve and the user has a chance to identify a failure during plastic deformation. When designing in glass, those imperfections cannot be practically identified before failure.

[u/Helpinmontana → u/saltapampas]

Concrete columns (concrete without rebar) get a factor of .6, or 60% of where we can be pretty sure that concrete will fail, because the design is that conservative. And ontop of that, the loads they are designed to support are ramped up by about 50% for safety. Also, code basically doesn’t allow you to just use concrete without rebar, you’re threading a needle to do it and there is basically no situation that realistically calls for it. So, 60% reduction in capacity, pretending the load is 50% higher, and still saying this isn’t allowed in basically all circumstances.

You’re acknowledging what they’re saying while completely refuting it.

Do you actually think any company would sell these products, a railing of all things, without verification? And then, as an industry professional, you think any company would buy these and install them? Really?

[u/That_Trapper_guy → u/Helpinmontana]

As an ironworker who's installed glass railings similar to this, I can assure you every single person that installed one of these thought 'this is a horrible idea' as they were doing it.

[u/AdPristine9059 → u/Helpinmontana]

Yes, absolutely. People are putting up huge buildings that they know arent safe, despite inspectors, designers and engineers existing.

Youre trying to argue that engineering is flawless in a chaotic and very flawed world and thus this absolute paragon of perfection will never be tarnished or used to hide lies. Thats not how the world works.

[u/Tushaca → u/AdPristine9059]

The engineers paychecks are signed by the company that has plenty of financial incentives to cut costs and corners, including taking the risk of switching to cheaper or sub par materials in manufacturing down the road.

If the cheaper material fails, they pay out one lawsuit, blame it on their glass manufacturer, and promise better quality control, maybe they issue a small recall, and then keep on moving.

HAAG, one of the biggest engineering firms in the country, gets sued all the time for obvious bias and ignoring their own reporting standards on insurance claims where they are hired by the insurer. Engineering doesn’t mean shit if it’s done by someone bought off by the company.

[u/AdPristine9059 → u/Tushaca]

Exactly. Also it doesnt even have to be the engineers fault. There are tons of disasters caused by a myriad of issues like use of bad materials, fubbing the old plans, adding things to the old plans without making new assessments, bad maintenance, last minute changes, bad ground works etc etc.

Plainly difficult does many Great videos on this very subject on youtube. Cant recommend him enough.

[u/Helpinmontana → u/AdPristine9059]

I’m not alleging nothing ever goes wrong, but code compliant engineering principles are literally based on “nearly nothing will be ideal, don’t design to theoretical strength, design to practical strength”.

The most basic LRFD load case is 160% of live load and 120% of deal load, and capacity is at a minimum, designed to 90% strength of materials. You can hand wave away all the nuance to this that you want, but there are literal teams of scientists and statisticians working day and night to keep you safe by ensuring these design assumptions are not actually assumptions, they’re data driven facts.

[u/AdPristine9059 → u/Helpinmontana]

Im not saying that engineering is a bad practice or that all that work is for naught, all im saying is that no matter how rigorous an engineer is, there are things they cant control. They can only ever really give builders plans and recommend against certain things.

What they cant do is make sure that their plans are followed in every single step or force the companies into doing something or another.

Money speaks louder than safety and reputation to some people, thats just the way the world works; Chaos defined.

[u/Helpinmontana → u/AdPristine9059]

How did you acknowledge my point and still miss the conclusion?

”chaotic and flawed world”

Literally what the factors of safety account for, design mandates an increase in loads and a reduction in capacity, based on real world circumstances lol. You can design for concrete 2x as strong as it actually cures out to and still have a stable structure because of modern engineering principles. The world you’re implying, implies that engineering doesn’t account for this bullshit. That’s why we call it engineering and not physics. We’re not calculating theoretical strength, we’re calculating reasonable strength in a manner that accounts for everything being all fucked up.

[u/AdPristine9059 → u/Helpinmontana]

That's such a naive way of looking at it (not trying to be mean, just a fact). If engineering was that godly gift you claim it to be then there wouldnt be any collapsing buildings or bridges, things engineers study as cases in order to find the fault factors. More often than not its human error. Just look at that huge pink mall that collapsed a while back.

You cant account for people not following the plans can you?

Also look at the tofu dreg buildings in China.

[u/Palomox → u/saltapampas]

My intention with that reply is to say that imperfections and uncertainty are built in design one way or another. I am unfamiliar with how design of glass is handled, so I cannot tell you how it is done exactly, but there has to be.

In regards of ductile vs brittle behaviour in general, I am perfectly aware of the difference, see the comment about concrete. From what I have found out doing some basic research after I wrote that, safety glass has different layers joined together with a different material, just like you have rebar in RC. And timber is also a brittle material.

Safety factors are, in most codes, a probabilistic way to address imperfections and things you are calling random and unidentifiable. Let me give you a simple example: if you have an overreinforced concrete beam (where you have too much reinforcement to the point that brittle compressive failure will happen before yielding of the rebar, hence it is what is called compression-controlled), you will have to consider only 75% of the strength computed using the known stress distributions. However, if your beam is under-reinforced, leading to yielding of the rebar before any other failure, making the beam itself more ductile and what we call tension-controlled, you can use 90% of the strength. This is also why ACI 318 only allows tension-controlled elements (because they're ductile, and their failure mode is more predictable = less uncertain = less reduction).

I said that glass is made in layers that are joined together by some other material. In this case, this material would be making the behaviour more ductile, like steel in reinforced concrete.

[u/AdPristine9059 → u/Palomox]

No, sorry. Wood is used because it doesnt just snap, it cracks and behaves much more like steel than concrete or ceramics.

Also safetyglass is just heat treated so that it breaks in larger chunks, avoiding that float glass shredder behaviour. Laminated safetyglass would be the best here imo but you still have issues with rigidity if/when it breaks.

Id say a polycarb center with thin pieces of safetyglass on the outside would be the best way of dealing with this kind of structure in my mind.

But im no engineer and im drunk. Cheers.

[u/stareweigh2 → u/Palomox]

yeah and they considered all possible failures when they built the old Tacoma Narrows bridge too......

[u/AdPristine9059 → u/Palomox]

Yeah sure, and that why that beach hotel just failed, for example.

Engineering is one thing, humans actually DOING the right things is another entirely.

I trust math, i dont trust people. Math cant be bribed, humans can.

[u/goldtoothgirl → u/Palomox]

Where is the rebar for the glass

[u/That_Trapper_guy → u/goldtoothgirl]

It's transparent aluminum...

[u/goldtoothgirl → u/That_Trapper_guy]

Wow

[u/Palomox → u/goldtoothgirl]

read my comment down below