Silo Foundation 2

[Ben29]

I was recently asked to design a silo foundation. I have never done this before. The silo is an elevated cylinder that is supported by a steel platform, similar to the image below. It seems to me that whoever designed the steel platform should provide signed/sealed drawings for the platform, as well as reactions for the foundation design (similar to the process for designing metal building foundations). Is that right?

 

[GC_Hopi]

If you anticipate a large loading it is beneficial add supplement anchor reinforcing. Here is the reasoning. This is conservative and helps ensure you can "develop" the anchor forces at the anchor location. Secondly, this makes the contractor think a bit about where the anchors are located especially if you have cast in place anchors. Third, piece of mind since a couple #5 u-bars cost nothing compared to the equipment cost.

 

[JLNJ]

Clients like to turn-key the structural supports for this kind of equipment because they think it will be easier to purchase the platform along with the silo. Simple, right?

We often find that the silo manufacturer does not have the expertise to design the structure, so either you get garbage loading from a mechanical designer using some off-brand program he doesn't understand or you have to wait for the sub-consultant the manufacturer hired to give you the loads. You are lucky to get anything meaningful in terms of wind or seismic loading. The equipment people say things like "sure we can design the structure - what seismic zone is this in?" I explain that seismic "zones" want away with the 1999 UBC and receive blank stares from the equipment guys.

I had an bin guy send me what he thought was a swell finite-element model of a bin support frame with a 20 kip column load. I explained to him that you can't just model one cell of a continuous frame multi-cell structure with shared columns and call it good. His column loads were at least 40 kips each but he simply didn't understand the concept of tributary area. Getting seismic calcs from him was absolutely out of the question.

In the end I told the Owner that his supplier didn't know what he was doing, did my own calcs for the column reactions, and designed the slab on grade accordingly.