Acceptable Failure Rate for Structural Glass

#1

Does anyone know if there any codes that gives clear guidance on this?

in Canada I use CGSB 12.20-M89 and ASTM E1300, for application of windows the typical acceptable probability of failure is 8 in 1000 once design load exceeds capacity, both codes give vague indication in the commentary that this is intended for window, and if the consequence of failure is more severe, the acceptable prob.fail should be adjusted. GANA glazing manual says it is common to use 1 in 1000 for more critical structural elements. My questions is are there code prescription/requirement on probability of failure for different application, or is this is a judgement call on the engineer of record?

For example, if I design a glass floor with failure rate that is same as those of window, but I have calculated a reasonable post-breakage design resistance (e.g. can resist 50% service load once glass breaks), then I would argue the post-breakage failure is not serious, therefore the 8 in 1000 probability is appropriate. Can anyone weigh in on this with their knowledge?

#2

Welcome to the crowd… it’s not crowded yet, but hopefully will be in the future.

Something in the attached may have some qualitative information on the acceptable failure rate. I would err on the save side since glazing can be lethal and it may travel a fair distance due to the ‘gliding’ effects.

http://www.mah.gov.on.ca/Asset11192.aspx

https://www.egbc.ca/getmedia/b73c4822-09f2-48c5-9085-35db63ae235b/EGBC-Designing-Guards-for-Buildings-V2-0.pdf.aspx

Dik

1 Like
#3

Thank you for the quick response. Also great resources. I have read a few glass design codes including parts from DIN18008, SEI’s glass design guide, parts from Eurocode, ASTM, CGSB, but I am genuinely surprised how comprehensive Hong Kong’s glass code is; I guessbeing released in 2018 really can capture the latest and greatest.

I skimmed through all of these and it looks like only one paper in there by SLChan mentions that 0.1% breakage is commonly used for sloped glass. I have read the same thing from GANA glazing manual and did not know where this originated from. No harm following it, but would be nice to know who came up with this and why.

Many thanks again. Look forward to future discussions!

P.S. can you please elaborate on “gliding”, I could not quite imagine it. Are you talking about the “wet-blanket” effect where an entire piece of laminated glass would fall down in a big piece?

#4

Fragments or large pieces may not fall in a straight line. Aerodynamically they can translate horizontally a bit. Maybe a glide ratio of 15 or so. They can be hazardous, depending on the height of the building, for several feet from the expected point of impact. Think of a ‘heavy’ sheet of paper being dropped from shoulder height, and watch it ‘flutter’ down.

Dik

#5

I see, sliding glass cutting through people like happy tree friends, sounds safe. Luckily

This is off topic, I have designed a number of glass project over the last 3 years now, but unfortunately being the most knowledgeable from engineering perspective in my firm with my limited knowledge, I would really like to figure out how I can learn more about what others do in this field, especially considering all the codes relating glass boils down to “use your best judgement”.

#6

With most engineering issues, you have to have a real understanding of the material properties. Glass is one material in particular. If you’ve been working with it for 3 years, you likely have a reasonable understanding. I’ve only done a few things in glass (still standing).

With most materials, developing an understanding, will allow you to carry the design beyond the normal and you have to be careful in doing this.

Good luck (skill, actually) with your future endeavours. In my years, I’ve found that ‘luck’ shouldn’t be relied on to any extent.

Is there anyone else that can add to this? Glass in not my area of experise.

Dik