Many, but not all, cantilever column structures are also inverted pendulum structures. What is special about an inverted pendulum structure is that the mass at the top of the structure has considerable rotational mass moment of intertia that is resisted only by the column (or columns). The elevated water tanks of Chapter 15 is the most common but not only case. Buildings sometimes use cantilever column systems where two or more columns in a row support floor framing. In essence these are moment frames without the beams being connected for moment resistance. In that case, the rotational inertia effects addressed by section 12.5.3 are not an issue. Note that above, I said (or columns). Water tanks are sometimes constructed with multiple legs (columns) typically cross braced. If the structure is slender enough, the inverted pendulum provision should still apply.
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Ronald Hamburger, SE
Consulting Principal
Simpson Gumpertz & Heger
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Original Message:
Sent: 04-30-2026 05:59 PM
From: Thomas Wolfe
Subject: ASCE 7-22 Inverted Pendulum Structures
I am looking for some clarification regarding the application of ASCE 7-22 Section 12.5.3 "Inverted Pendulum-Type Structures". This paragraph says that "Regardless of the structural system selected, inverted pendulum systems... shall comply with this section." It then goes on to specify to calculate the moment at the base per Section 12.8 and to vary it uniformly from the base to the top where the moment shall be 1/2 the moment calculated at the base. Other than the Cantilevered Column system, Item G in Table 12.2-1, I don't see another system type in the table that would qualify as Inverted Pendulum unless you had some system that you classified under Type H "Systems not specifically detailed for seismic resistance". The subject gets a bit more complicated in that in Table 15.4-2 (Non Building Structures Not similar to Buildings) there is a specific structure type for Inverted Pendulum systems (and it excludes elevated tanks and vessels). This structure type has R value of 2. So, if I was in table 12.2-1 and I selected structure type H and the particular structure qualified as an inverted pendulum, would I use the R-value from Table 12.2-1 (R=3) or the R-value from Table 15.4-2 (R=2)?
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Thomas Wolfe P.E., M.ASCE
Stress Engineer
Woodinville WA
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