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Inverted Pendulum Columns

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It should be noted that if you chose to use the 1997 code, that the redundancy
factor, rho, must be applied as an attempt to ensure sufficient number of
vertical lateral resisting elements.  The requirement for the decreased R (Rw)
value for the lateral design of all elements in the same direction would seem
most appropriate for rigid diaphragms, although, IMO, the distribution should
be done based upon the stiffness of all elements including the diaphragm,
collectors and vertical resisting elements irregardless of diaphragm

It seems L.A. has a good concept:  Use the higher value of R (Rw) for
determining the base shear of the entire structure and then designing the
columns using an overstrength factor, OMEGA (3Rw/8).  This type of structural
system is not very redundant (if the column bulckles, a significant portion of
the structure is effected) and requires prudence and conservatism in design.

Another point to note:  DSA allows Rw=4 to be used if it can be demonstrated
that the strut ties are capable to develop the capacity of the column in
multi-column structures (Table 16A-P).  This would mean that the connection of
the strut to the column and the strut itself would be designed to the maximum
lateral force at the top of  the column resulting from the ultimate moment
capacity of the column at the applied vertical load.

As can be seen, the entire design should be done at LRFD levels throughout,
which is another subject altogether.

It seems appropriate to design the grade beam at the reduced force level.

Of course, this is all only my opinion.

Ted Beckwith
SFA, Inc.