NBCC - Snow Accumulation - Code becoming too convoluted? 4

[GalileoG]

I have not really been designing these last few years. Working on a design at the moment and have to calculate snow accumulation due to adjacent high roof.

Looked up NBCC/OBC code and noticed just how convoluted the calculation for snow accumulation has become. Am I alone here in thinking the calculations have become unnecessarily complex for something basic? Bananas.

Need to have less PHDs and more practical people writing these codes.

Maybe it's time to hang my engineering hat.

 

[skeletron]

I mean it's definitely become a more detailed calculation as opposed to the 1:5 slope and F-factor determination that was in 1995. But It's not that onerous once you set up a spreadsheet/tool to do the calculation checks. If it is too onerous, there's always online calculators. If you are commenting regarding the corner distributions, or the additional cases based on the "source" and wind direction, I think it's still reflecting the "real" load and the observations over the years based on data.

 

[skeletron]

@Dik: The Code has changed since your last update (just FYI), which may be what the OP has flagged. The requirement is now a little more stringent on source area and direction, requiring 3 cases to be reviewed.

 

[dik]

Thanks skeletron... I'll update when I have time... it's been a while since I last used it... Deleted original post...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

I, for one, would like to see environmental loads made / kept simpler than they've been trending. Our work is inextricably related to reliability theory. However, I feel that we often overlook the aspect of reliability represented by our own propensity to err as fallible human beings. If load requirements need to be 15% higher, or whatever, in order to make them simple enough that any two engineers are likely to arrive at the same answer without too much rigmarole, then that's how I'd like to see things set up. When it comes to developing safe and efficient designs, I'm of the opinion that a talented structural engineer will work most of his or her magic downstream of the determination of the loads.

 

[skeletron]

So if we are already putting emphasis on (insert: full building models; 3D computer analysis; output-input programming to share results; printing/showing explicit numerical calculations) why not take that for the full 8second ride and actually pin-point the true Boolean determinants of your demand?
Your assumption to use (ex1: a smeared average snow load everywhere) or (ex2: corner pressures across the whole side) will usually shake-out with a good amount of safety factor by the time you detail it in good practice (Yes, I agree). But if you have your Programmed Machine Output match your Rational Human Output, than isn't that the same as arriving at the same answer without much rigmarole?

 

[KootK]

@skeletron: was that intended as an actual question or a humorous attempt at imitating a bot? It was almost as convoluted as ASCE wind loads / NBCC snow loads. I'm afraid that I don't know how to respond.

 

[Aesur]

I'm in agreement with KootK here, these codes are becoming more and more difficult to use, mainly because practicing engineers don't have time to sit on these boards to push for simplicity and we rely on PHD's who couldn't design a beam without spending a week theorizing all the ways a beam could react. (yes this is exaggerated, but also close to what seems to be happening). I don't see buildings designed under older, simpler, codes failing all that often (except maybe in higher seismic locations) and I also don't see current buildings providing more optimized designs (less material) using the newer loading methods. A lot of it to me is similar to how a steel beam has "gotten stronger" over the years using newer codes, great... we can use less weight in the steel and it still works stress and deflection wise, but now we need to add that steel back to add mass for vibrations. The PHD's writing the code created a new problem (for them to research) and created more work for us engineers to do with the same or less fees..

 

[MIStructE_IRE]

Its not Just snow. I think all design codes have become way more complicated than they should be. Everything written with computer programme designs in mind and young engineers not having a real feel for the numbers at all. How could they?! It’s too complex.

I used to have a college lecturer who famously carried a copy of the steel code in his front shirt pocket at all times! That’s how small the code was at that time. Now there’s hundreds of pages of absolute drivel - and has it made things more efficient..? I don’t believe design principles have changed at all.

TL;DR - rewrite the bloody codes and make my life easier!

 

[skeletron]

@KootK: Nah. I don't really need a response. I agree that putting loads in simpler form is the ideal direction and that the detailing is key.

With the amount of building modelling going on in a typical project, it appears that the codes are being formed to be "programmed" as opposed to be "rationalized". Whether or not this is a good-thing, it is an accurate-thing.

 

[KootK]

Interestingly, some FEM programs don't even have the ability to input tapered drift loads.

 

[TLHS]

All the edge case environmental load cases are really hard to model in generalized FEA, because they tend to take conceptual understanding of the building to apply the code correctly, which the computer isn't good at. Snow drift is annoying, but getting wind on there takes dozens of cases if you actually wanted to hit all the requirements as well. I also find that you have to apply the loads in annoying ways that are difficult for a checker to confirm.

 

[JLNJ]

There are a LOT of failures due to snow, yet snow loading has traditionally lagged wind and seismic in its complexity and precision. To me it makes sense that the snow code be developed a little more.

Back in the day, you had to go to the NBC for meaningful information on drifts since there was little in the US Codes to address those areas (and they are CRITICAL areas).

 

[bones206]

There was an article in the latest Structure Magazine about forthcoming snow drift "improvements" for ASCE 7-22. I read the article through twice and still have no idea what it says. Something about different drift slope angles for windward and leeward drifts. Can't wait to have 150 different snow load combinations in my RISA models!

 

[canwesteng]

I don't mind NBC snow loading, it's simple enough. ASCE is a massive and sometimes illogical headache, and it sounds like it's only getting worse.

 

[Once20036]

ASCE is also about to switch to a 1.0 load factor in lieu of 1.6, along with the two different angles for drift that now need to be checked.