User Guide

Tutorial 5 – Dynamic Analysis
Version 5.0 113
The procedure we use is based on the requirements in Section 1630 of ’97 UBC.
If you are not familiar with these requirements or if you use another building code
you will want to refer to the code to understand the basis for the procedure.
The reasons for having to calculate scaling factors are twofold. First, if a
“normalized” spectra was used to calculate the spectral results, you must scale the
normalized results to match your site specific criteria. Second, the UBC sets
minimum values for the design base shear.
In a nutshell, what has to be done is:
1) Calculate the UBC static design base shear (V).
2) Obtain the unscaled RSA Elastic Response base shear.
3) Scale the RSA base shear such that it satisfies the requirements of
sections 1631.5.4.
After applying the UBC requirements, the calculation for the scaling factors
(SF's) gives:
SF
x
= 0.32
SF
z
= 0.32
(Remember that you can get the details for the scaling factor calculation from the
Help file as described above.)
Load Combinations with RSA Results
These scale factors will now be applied to our spectral results so we can combine
them with our static results.
To see how this is done return to the Load Combinations by selecting it from the
Spreadsheet menu.
The load combinations look like this:
What we have done on the last two lines is combine the spectra analysis results
(SX and SZ) with the combination of loads previously defined in load
combination 2 (L3).
Note that “0.09” is 30% of the “0.32” scale factor. Using 100% dynamic response
in one direction with 30% in the other direction is a common way of accounting