Elevated steel silo structure design

[JoeH78]

Dear Colleagues,

I've been asked to design a elevated steel silo, silo diameter is 27feet, hopper is elevated at 40feet above ground level, total height is approx 80feet and total weight of silo+material is 650 ton, as per the local local codes peak ground acceleration is 0.3g and reduction factor can be taken as 4, preliminary design points that super structure can be modelled as circular with HEM 700 for steel columns and circular beams(average %70 demand / capacity ratio) ( as a cylindrical shape as shown in attached picture.

Regarding the given information, I feel uneasy about the following items
#1) Although calculations shows that cylindrical shapes is enough for overturning cheks I think that diagonal coloumns must be provided as well for stability of overturning

#2) What type of detail you can suggest for the beam(HEM700) to column web(HEM700) connection, since its a weak axis of column I don't think that simple gusset plate will work in that case, somehow rigidity must be increased on column web side at that point.

#3) PLease refer to 2nd image at the attachement, green section is circular girder section (HEM700) where silo peripheral hopper ring will rest, it really doesn't coincidence with the girder web axis, so those portion will create eccentricity at the beam flange n order to eliminate that I'll place stiffeners say at each 2 feet along the circular girder, do you think that I'll be enough.

I would like to hear your comments as well,

Regards,

 

[JoeH78]

Here is the 2nd image

 

[JStephen]

Depending on the dimensions and loads, the structure could be build with or without the diagonals. But they will also decrease the period and may increase the seismic load, may reduce deflection, so they definitely need to be included in the design, not just added it. You could get some wind vibration issues as well, with or without them.

Is this an existing skirt-supported silo that you are now elevating on a tower? That's what it looks like, maybe I'm mis-interpreting the figure. If it's new and if it's welded steel, the legs would normally attach to the container without a skirt.

 

[JoeH78]

Depending on the dimensions and loads, the structure could be build with or without the diagonals. But they will also increase the period and may increase the seismic load, may reduce deflection, so they definitely need to be included in the design, not just added it. You could get some wind vibration issues as well, with or without them.

Width is 27 feet hopped cylinder, 40feet tall and 650tons total loads IMHO having it with diagonals is better. But there is one thing that I wasn't verbose for the diagonals, actually there are two type of elements which can be treated as diagonals in the figure, I meant that CHS positioned in beween main girders and columns(X shaped) are for increasing the stability of structure against seismic loads. The outer oblique element on the left(HEM700 profile same size as columns and girders) is to prevent the overturning.

I havent analyzed it throughly but knowing that tentatively that wind load can hardly induce any resonance with such heavy load.

Is this an existing skirt-supported silo that you are now elevating on a tower? That's what it looks like, may
be I'm mis-interpreting the figure. If it's new and if it's welded steel, the legs would normally attach to the container without a skirt.

It's totally new structure and silo will be weld manufactured, interestingly the manufacturer specified that only 8xM30 size ( not specified even bolt class ) must be used. Normally they have to puncture the top and bottom flange to fix the skirting to the steel structure. 8 number of M30 bolts seems affordable for the whole periphery but I'm afraid tha manufacturer will change its idea and will require much more number of bolts. In this case I think that they have to use special connector to it, because perforating the main girder for each 10cm doesn't sound liek a good idea, probably you meant that with saying "attach to container without skirt". Can you elaborate that detail a bit more ?

Can you share your projects of with which height and weight you build the silos?

 

[JoeH78]

Dear colleagues I'll really appreciate your comments.