Seismic Analysis of Elevated Silo
Seismic Analysis of Elevated Silo
(OP)
I'm working on the analysis of an elevated sand storage silo. The silo is 65 feet high and 19 feet in diameter. The base of the round section and the top of the cone base is at elevation 29 feet. The bottom of the cone is at elevation 16 feet so truck can pass underneath. The frames are crossed braced only in the upper cone section.
I'm looking at section 15.7.10 of ASCE 7-05. I'm wondering how to calculate the natural period of the structure. I'm not designing the silo frame, just the foundation. The NEHRP section 14.4.7.9.5.2 state AWWA D100 has a method of determining the natural frequency for elevated tanks. I don't have a copy of AWWA D100. Can some who has a copy tell me if the standard would have sufficient information in it to help me determine the natural period for the structure from this limited information?
Are there other traditional methods for calculating the natural period of the silo structure?
Thanks for your help.
I'm looking at section 15.7.10 of ASCE 7-05. I'm wondering how to calculate the natural period of the structure. I'm not designing the silo frame, just the foundation. The NEHRP section 14.4.7.9.5.2 state AWWA D100 has a method of determining the natural frequency for elevated tanks. I don't have a copy of AWWA D100. Can some who has a copy tell me if the standard would have sufficient information in it to help me determine the natural period for the structure from this limited information?
Are there other traditional methods for calculating the natural period of the silo structure?
Thanks for your help.






RE: Seismic Analysis of Elevated Silo
Never, but never question engineer's judgement
RE: Seismic Analysis of Elevated Silo
RE: Seismic Analysis of Elevated Silo
RE: Seismic Analysis of Elevated Silo
RE: Seismic Analysis of Elevated Silo
A couple of approaches come to mind. In the ASCE 7 equations, they are generally of the form V = "this but need not be greater than this". That is, there's an upper bound on the seismic loading regardless of the period. If the seismic accelerations are fairly low, you may be able to work with that upper bound and design your work without getting too overly-conservative.
If you are only designing foundations, the design loads on the foundation would not need to exceed the ultimate strength of the structure. If you can calculate the maximum shear and axial load the columns can generate, that may give you a means of design.
Since the lower part of the structure is not cross-braced, you could treat the entire upper structure as a rigid body, calculate deflection in the unbraced legs only, and derive a period without too much trouble. The actual period should be somewhat longer, and depending on the period, this may be a conservative estimate.