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RE: EQ resistant Design

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For a "definitive" answer on these subjects I suggest you get a copy of
"Three Dimensional Dynamic Analysis of Structures" from Prof. Edward L.
Wilson (www.csiberkeley.com).

On the recommendations in Chapter 5 ( Orthogonal effects in 3d analysis) it
says:

... For all structural systems, it has been shown that the design of
members using the 100/30 or 100/40 percent combination rules to account for
orthogonal effects are dependent on the user's selection of the reference
system. The alternative code method, which uses the SRSS combination of two
100 percent analyses with respect to any user defined orthogonal axes,
produces forces which are not a function of the reference system and
results in a design that has equal resistance to seismic motions from all
directions.
... It is apparent that the use of the percentage rules does not introduce
major errors. However, they have no theoretical justification. Since the
SRSS method of combining two orthogonal CQC analysis is very simple to
apply and has a sound theoretical basis, it is recommended that it be used. ...

Pedro Santos
raiz1(--nospam--at)mail.telepac.pt


At 21:16 20-03-2002 -0600, you wrote:
>simultanious application of 100% of the seismic
>load in one direction and 30% of the seismic load in the other direction.
As long as I'm getting some education in this area, why 30%. Why not
simply provide the horizontal acceleration and require that it be applied
at the severest orientation? I'm almost as baffled by this provision as I
am about the utility of another analysis approach I won't mention.



Christopher Wright P.E.    |"They couldn't hit an elephant from
chrisw(--nospam--at)skypoint.com        | this distance"   (last words of Gen.
___________________________| John Sedgwick, Spotsylvania 1864)
http://www.skypoint.com/~chrisw


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