Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Silo Floor Loading

Silo Floor Loading

Silo Floor Loading

I am looking for the load profile as a function of radius (and height) on a grain silo floor.  I gather that the shape of this loading profile is something like a "bell curve" as a consequence of Janssen's equation.

Perhaps more to the point, how does one determine how much of the mass at any given height is sitting on the floor, versus "hanging" on the walls? It would seem that with extreme pressures on the grain near the floor, that material will stay with the floor, rather than slide on the floor and create additional pressure on walls.  On the other hand, the grain near the top of the silo will almost certainly apply additional pressure on the walls during seismic loading.

This sounds pretty cryptic but I hope it makes enough sense to get some pointers on where to look.

Thanks in advance

Bob Carlson

RE: Silo Floor Loading

Flat-bottomed silo or silo with conical or wedge hopper?

RE: Silo Floor Loading


Flat bottom bin/silo.  Typically larger Diameter than height.



RE: Silo Floor Loading

I'm going to take a stab at this - it sounds like you are trying to determine:
  1. The vertical pressure exerted by the grain at the slab level of a grain silo during a seismic event, and
  2. The lateral pressure of the grain on the silo walls during a seismic event.
The grain will act a lot like a sand - not exactly, because the individual sand grains aren't compressible while the "grain grains" clearly are.  This difference means that some common geotechnical engineering principles have to be re-considered before they can be applied to your circumstance.

On the vertical pressure: since the shaking during a seismic event can cause the grain to act like a fluid, I think you have to assume the full weight of the grain will act on the slab, with relatively small amounts acting on the silo itself.  This would not apply if the grain was somehow compressed so that it actually "fluffed" during the shaking; but I don't see a mechanism for that compressed condition to occur prior to a seismic event.

I also think that assuming something less than a hydrostatic pressure distribution - with the pressures calculated assuming an equivalent fluid weight based on the density of the grain - could result in an underestimation of the loads.  The grain will try to reach a density where neither contraction nor dilation occurs during shearing stresses within the grain mass during a seismic event.  I would expect the grain to increase in density, meaning the grain will contract in volume.  Arching is unlikely for this circumstance.

But my comments are loaded with suppositions, some (all?) of which may be wrong.

Please see FAQ731-376  by VPL for tips on how to make the best use of Eng-Tips Fora.

RE: Silo Floor Loading

For silos which have a height greater than 1.5*diameter, then the Janssen equations apply, and the floor load would be the least of (unit weight of material * height of meterial) or q = ((gamma * R)/(muprime * k))*[1-e^(-muprime*k*Y/R)] * Cd.

gamma = unit weight of material
R = hydraulic radius
muprime = wall friction factor
k = lateral pressure ratio
Y = depth below surface
Cd = overpressure factor (1.5 for steel floors, 1.35 for concrete)
q = vertical pressure (typically psf)

If the height is less than 1.5 * diameter, then the normal Rankine pressures would apply, where wall friction is neglected, and the floor load would be just the weight of the material times it's height.  This is out of ACI 313-97.  You can also reference Gaylords Structural Engineering Handbook, 4th edition, for a description also.

RE: Silo Floor Loading


On November 14, 2003 BobCarlson wrote,
Flat bottom bin/silo.  Typically larger Diameter than height.

Since Diameter > Height, then clearly Height < 1.5*Diameter.  Janssen equations don't apply.

But a pressure reduction does appear to apply; I found the following on the Internet:


It looks like the change from the 1991 to 1997 code was primarily a move from assuming "active" pressures to "at rest" pressures.

It looks like you need to read and understand ACI 313-97...

Please see FAQ731-376  by VPL for tips on how to make the best use of Eng-Tips Fora.

RE: Silo Floor Loading

Although I have some that have heights approaching 1.5*D it looks like the consensus is ACI 313-97 will get me pointed in the right direction.

Thanks for the help.


Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


eBook - Integrating the Engineering Ecosystem
Aras Innovator provides multiple options for integrating data between systems, depending on the scenario. Utilizing the right approach to meet specific business requirements is vital. These needs range from authoring tools, federating data from various and dissimilar databases, and triggering processes and workflows. Download Now
Research Report - Simulation-Driven Design for SOLIDWORKS Users
In this engineering.com research report, we discuss the rising role of simulation and the paradigm shift commonly called the democratization of simulation. In particular, we focus on how SOLIDWORKS users can take advantage of simulation-driven design through two analysis tools: SOLIDWORKS Simulation and 3DEXPERIENCE WORKS. Download Now
White Paper - Industry 4.0 and the Future of Engineering Education
With industries becoming more automated, more tech-driven and more complex, engineers need to keep their skills and knowledge up to date in order to stay on top of this wave—and to be prepared for the Industry 4.0 future. The University of Cincinnati offers two online Master of Engineering degree programs designed specifically for practicing engineers. Download Now
eBook - The Design Gridlock Manifesto
In this eBook, you’ll learn 6 ways old CAD technology slows your company down and hear how design teams have put those problems to rest. “The Design Gridlock Manifesto” shares first-hand modern CAD experiences from 15 companies around the world. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close