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RE: shell stability[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: shell stability
- From: "Brian McDonald" <mcdonald(--nospam--at)exponent.com>
- Date: Tue, 2 Nov 2010 11:23:01 -0700
Sorry for the late response – your tank is probably already constructed.
I had a similar situation several years ago. If I recall correctly, one important issue was imperfection sensitivity. I found that some types of structures, such as shells and shallow arches, might exhibit many closely spaced buckling modes that can interact, resulting in reduced buckling capacity in the presence of even very small imperfections. For our structure, linear elastic FEA buckling analysis (eigenvectors) closely matched hand calculations of Timoshenko buckling, but was very unconservative; nonlinear FEA with imposed, realistic imperfections yielded much smaller buckling capacity. Again if I recall correctly, the AWWA D100 tank design manual had a factor to apply to Timoshenko-like buckling to account for this reduction. A theoretical but very well written description of this effect (attributed to Koiter) is provided in Bazant’s “Stability of Structures” book, Section 4.6.
I guess this is one more thing for Structural Engineers to lose sleep over…
Roark's Fomulas for Stress and Strain has and appropriate entry under paragraph 13.5, "Thin Shells of Revolution under External Pressure", as well as Table 13.1.
It also has a calculated example thereto all right.
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