Canadian ice and wind-on-ice procedure 5

[mrsutton]

How does the Canadian NBC or engineering practice address the weight of glaze ice on structural components for vertical, wind, and seismic? The NBCC and Alberta Code I've got access to don't seem to even mention ice loading at all--which I find surprising given how much of Canada is so far north. I've got an industrial trussed platform in northern Alberta with grating catwalks where icing could represent a significant load. I'm following ASCE7-16 procedure for ice and wind-on-ice but used ice values from eastern Montana hoping that's reasonable for the site in Alberta just to get a design started.

 

[StrucPEng]

Take a look at CSA S37-13. The document is for antennas and towers but contains a full section on ice loading which could easily be applied to other type of structure as well.

 

[dik]

I generally design for an ice thickness added to the exposed wind face... often 1/2" which makes 1/2" cable 1-1/2"... thanks for the reference to CSA S37... I'll have to check what my current edition is...

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

-Dik

 

[skeletron]

CSA S37-18

There are values for ice thickness. From my copy, it appears Alberta (and a lot of places) has 10mm ice thickness. Then you use that value to increase your projected area based on the shape type. There are a bunch of fluid-dynamic derived equations in S37.

 

[skeletron]

@dik

Heads up for a Manitoban like you:
Ice thickness in S37 ranges from 1/2" to 7/8" in Manitoba, most places hitting 5/8" (16mm).

 

[mrsutton]

Thanks. I've been trying to track down a free copy of the CSA S37 document with no luck as all the pdfs of that code I've found via Google search are behind paywalls. All the articles I've found Googling Canadian ice loads have been academic research papers relating to marine ice floes impeding navigation and pushing on offshore platforms and port/pier structures--interesting though not quite related.

I didn't want to plead for my company to buy a pdf copy of it only to find it's explicitly for telecommunications structures only and not applicable. Using ASCE7 I ended up with a ice thickness of 0.593" which is right about 15mm which seemed reasonable to me but again I'm not a Canadian engineer used to what kind of sub-Arctic ice loads are typically encountered in Canadian engineering practice, so I don't have a good feel for what's in the range of plausibility.

 

[GastonLagaffe]

The NBCC (2015) doesn't have anything about ice accretion indeed, except Article 4.1.6.15, which says to use CSA S37, the standard for Antennas & Towers. I imagine that includes the formulas for weight of ice accretion & effective area. I'm more familiar with S6, which does also include ice accretion provisions.

In S6, essentially all of Alberta has only a 4mm design ice thickness (9.8 kN/m3 weight). I doubt that'll ever govern.

In gravity loading, I generally just multiply the exterior perimeter of the of the section by the design ice thickness to get my weight of ice per meter. If you have a big perimeter, you probably also have a big moment of inertia so it's usually not a problem other than on long cables.

For your grating specifically, you essentially never have to worry about ice accretion. To give you an idea, a 4.8 kPa (100 psf) live load is equivalent to a solid slab of ice half a meter thick! If you really want to be conservative, you could assume every hole in your grating is completely iced-in, but even then it won't be all that much of a load. At least in S6, you don't need even to consider ice accretion & live load at the same time. It makes sense: ice accretion is a very slow process with plenty of time for the structure to deflect and scare away your live load, and even then, you wouldn't expect anything more than an angry worker with a bucket full of salt in one hand and a scraper in the other

For wind loads, the wind load factor is usually much lower when combined with ice accretion. In S6, it goes from 1.4 to 0.75. We get 66mm design ice thickness here and even then, the pure wind load almost always governs on any element wider than about 4-6". With 4mm I would only expect any significant effect on something like a chain-link fence.

 

[skeletron]

If you are working with lots of lattice-type structures, or projections that can catch wind, S37 is pretty good resource. It's definitely tailored to the telecommunication industry but it is also a good companion to the wind tables in the commentaries. And it goes much more in depth. But, it's also very derivative of TIA standards and ASCE recommendations whether CSA wants to admit it or not. Not many of these standards are worth the 150-400$ they command, which is unfortunate. And the digital license for them kind of sucks as well. Bollocks.

 

[dik]

thanks for the heads up... I use the correct thickness... my project notes go from 1/2" to 1" in 1/8" increments... and the added live loading is also tabulate based on the thickness. I just used 1/2, with 1/2 cable for ease of calculating... too lazy to use 1/2" + 2(5/8"). again, thanks...

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

-Dik