Snow Drift Analysis

[STRUKT]

Hi Everyone,

We've been working on a project in which we have to take into heavy snow loads. The issue that we have in hands is how should we define the snow drift for the given situation? (please check picture)

As far as we get the snow drift recommendations from the standards take as main reference a 2D scheme between the roofs. Here we have a 3D scheme in which the highest roof has the small footprint in plan view. Should we consider both directions independently? Should we set a distribution between the 2 directions using 45 degree lines from the corners of the highest roof? What are your thoughts about this?

Thank you,
STRUKT

 

[dik]

Something like, and consider it as a complete load, not one at a time:

-----*****-----

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[STRUKT]

The values for the 2 independent directions will be different, so that which load should one consider at the intersections zones (45º lines from the corners of the small roof)?

(how can we insert pictures in line with text how you did before Dik)

Thanks,
STRUKT

 

[dik]

Why would they be different? Upper structure is at a uniform height? or are you considering some other effects... in Canada, given the height, the area of the upper roof and lower roof, the snow accumulation and slope would be the same, all around the upper structure. It's just a matter of applying the load to the lower roof structure. Unless I'm misunderstanding something (occasionally do that).

As far as inserting pictures... I just use windows 'snapshot' <win><shift><s> and past it to irfanview and save it to clipboard... and then load it using 'Image' above.

-----*****-----

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[driftLimiter]

Using the ASCE the down wind fetch length also plays into the accumulated snow drift (windward drift). ASCE also says you if the drifts overlap you take the larger magnitude at the overlapping region not additive.

 

[ryaneng]

Then wherever you have higher loads use a schematic similar to Dik's and show the higher load goes to the point where it applies. Or, if the loading isn't that much higher, just apply the higher load around the entire pop up roof for simplicity.

 

[STRUKT]

According to Eurocode the distances between the roofs limits have influence on the value of drifted snow load to consider. Those distances are different on both directions. So in this particular case and taking Dik picture as reference in XX direction the load will be higher than on YY direction.
They are both flat roofs at different heights, nothing more complex or special here.

Thanks,
STRUKT

 

[dik]

You still design for the loading shown by the envelope acting at the same time.

-----*****-----

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[STRUKT]

Dik,

Could you please share the name of the Standard that you use as reference for the snow load scheme shown above (picture that you shared)?

Thanks,
STRUKT

 

[dik]

It's contained in the National Building Code of Canada that Manitoba has adopted as the provincial code. We are using an earlier version and snow loading has changed, substantially, in the later versions. Jacabus has the loading on their website for the 2015 code. I use SMath program sheets.

https://www.jabacus.com/engineering/c_load2015_index.php

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik