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Re: Dynamic base shears, is it considered?

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1994 UBC Code Section 1629.5.3 allows scaling of dynamic results to
minimum code base shear values. The response spectrum base shears are
often higher than the Code static base shears. I think you got confused
here, Dynamic base shears should be checked at the ultimate stress level
with ductility taken into account (i.e. the R factor), while the Code
static base shears should be checked at the allowable stress level.

As far as I know, when I was working for a firm designing highrises here
in LA, it is standard practice to scale the dynamic results to Code base
shears and checked v.s. allowable stresses.  Sometimes we also check the
dynamic results v.s. ultimate( yield)capacity level and calculate the
D/C ratios to see whether they are acceptable. I believe the standard of
practice hasn't changed that much.

Tom Chiu,SE


Seimone Jurjis wrote:
> I have a project where this case has come up.  The geotechnical engineer
> determined
> the response spectrum where the base shears shot up above the code mins.
>  My question is
> where in the UBC does it allow to scale the results down to the code
> minimums?  Is it typical
> practice to design structures with the minimum base shear given in the
> code when the seismic
> review grants a higher load?
> Thankyou in advance
> Seimone Jurjis PE