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)?
------------------------------
Thomas Wolfe P.E., M.ASCE
Stress Engineer
Woodinville WA
------------------------------