Lateral load on conical grain bin top

[PaulArlin]

Converting the top part of a steel grain bin to an open Gazebo. After last night’s wind storm, I’m questioning if the top connected to the posts creates enough of a moment frame to absorb and transfer the lateral wind load. Here in So. Indiana we are in a 90MPH zone.

Diameter is 18’, Side walls are 9 gauge, 2.66” corrugated steel. I’m only using ½ of the top ring, so that’s 18” in height. Roof is conical with a 4.5’ rise (33 degree slope), There are 24 overlapping sections that connect to a 24” open ring for air flow. That will bolt to eight vertical supports that stand 9.5’ above the ground made from 3/8” thick, 4” square steel tube. (4 bolts per post) Footings are 4’ augers with a 12” square base plate on top and a 6” saddle connector to the 4x4.

Load factors for circular and conical structures are hard to find and harder when they aren’t solid like this one. The county building department approved the plans and issued the permit, but….

I’d appreciate thoughts if this will work as described, or do I need to add “beams” between the posts at the top for additional strength? Thanks!

 

[Eng16080]

A sketch would be useful. If I understand correctly, there's a conical roof shell attached to a ring, of 9 gauge corrugated steel. With the steel tube columns attached, I'm not sure that will work well as a moment frame. I would expect some sort of stiffer members to run between the columns (like steel beams). Lacking that, I picture the corrugated steel warping/twisting/buckling under a high enough lateral load. Of course, it depends on what the actual lateral load is. With some quick numbers, maybe it's around 1,500 lbs, which if it were evenly distributed would only be about 170 lbs to each column. This doesn't seem too bad, although take my numbers with a big grain of salt.

Are the "augers" helical piles? Never head that term.

Load factors for circular and conical structures are hard to find and harder when they aren’t solid like this one

If you mean load factors per the required load combinations, they should not change based on a particular geometry. Or are you referring to some factor in calculating the wind load?

 

[WinelandV]

The Cp factors for a conical roof can be found in Figure 29.4-5 of the ASCE 7-16. That factor should then be used with Equation 29.4-4 -- note that the equation assumes that the roof is still on top of the cylindrical portion of the bin (as the eqn includes the GCpi factor for internal pressures).

Please note that is a "v" (as in Violin) not a "y".