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Inverted Pendulum Columns[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: seaint(--nospam--at)seaint.org
- Subject: Inverted Pendulum Columns
- From: <Tjb5424744(--nospam--at)AOL.COM>
- Date: Wed, 29 Jul 1998 12:47:27 EDT
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 flexibility. 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.
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