Seismic mass for aggregate storage bin

[atrizzy]

I'm trying to decide the appropriate live load component of seismic mass for an aggregate storage bin.
The design is in Canada and the 25% allowance for LL provided in NBC seems like it could be too light. Can anyone point me towards a standard that might address this or a similar design case?

Thanks in advance!

 

[JoshPlumSE]

So, I haven't worked on Canadian projects at all, but I've done a decent amount of industrial projects in the US (or at least using US codes) that encountered similar issues.

We generally used a number of different criteria:
1) We'd create one gravity load check for the maximum gravity load. We usually called this the "hydrostatic test" load case. But, we never checked this for lateral because these were generally one time short term loads. And, the probability that an earthquake or severe wind storm would hit at that same time is astronomically low.
2) Most of the time, we'd use the "normal operating" weight of the structure for lateral load. The only caution I would use with this is if you think it likely that the bin could spent a couple of months per year fully filled. If that's possible, then I'd probably use the full load.... Or, a "Max Operating" type load which is close to fully. If it's unlikely to happen for more than a week or so at a time then I'd say that you can probably use a "normal operating load" instead.
3) We often had an "empty" load that we'd use with wind to check overturning. With the idea that the bin may sit empty for months at a time when that facility went unused.

 

[atrizzy]

Thanks Josh,

FYI, I've just come across ACI 313(1991) which is a standard for concrete aggregate storage silos and suggests 80%LL for seismic. Not sure if the latest 2016 version still suggests that.

Yikes...

 

[Guppyz]

Check 4.1.8.2 of NBCC-15 for reference to seismic participating load (W). It states 60% for storage load and 100% if the contents are stored in a container.

 

[atrizzy]

How did I miss that, Guppyz, thank you.

 

[dauwerda]

Although not applicable to your project, The current revision (2016) of ACI 313 states:

"6.3.8 Seismic forces—Silos and stacking tubes shall be designed to withstand the seismic forces in accordance with ASCE/SEI 7. [highlight #FCE94F]The design shall consider the full range of material loading, from empty to full[/highlight]. It shall be permitted to consider the interaction between the silo and the stored material using an appropriate structural analysis procedure found in ASCE/SEI 7. Unless otherwise determined by analysis, the effective density of the stored material, used to compute seismic forces in accordance with ASCE/SEI 7-10, shall be equal to γ. Provisions of ACI 318 shall be satisfied for seismic design of concrete silos."