User Guide

Tutorial 5 – Dynamic Analysis
Version 5.0 111
When you've finished viewing the animations select Single View from the
Window menu.
Response Spectra Analysis
Click on the Solve button and select Response Spectra Analysis and click
Solve.
This brings us to the Response Spectra Selection window:
The first field is a list of the available spectra in the RISA-3D spectra library. For
this analysis, we'll have RISA-3D build a 97-UBC site-specific spectra. See
Figure 16-3 in the UBC for the equations used to build the spectra. See Tables
16-Q and 16-R to obtain the Ca and Cv values.
Click on the down arrow in the Spectra to be Used field and select “UBC 97,
Parametric Design Spectra”.
A detailed explanation for all the fields on this dialog can be found in the
Response Spectra Analysis section of the help file, so we'll only provide a brief
description here.
The “Modes to be Used” field allows you to select which of the solved modes
should be used in the Response Spectra Analysis (RSA). Typically you will
usually leave this field blank to use ALL the solved modes.
The “Spectra Direction” specifies the direction of action for the base excitation
represented by the response spectra. For this model, we'll be applying the spectra
in the X and Z directions so we will leave this as is.
The “Mode No. for Signs” field gives you some control over the signs of the final
RSA results. The modal combination methods available all are derivatives of the
SRSS method (Square Root of the Sum of the Squares), so the final results come
out ALL POSITIVES. This is because an RSA is intended to predict the
MAXIMUM values for the model response. This presents a problem if the RSA
results are being combined with a static solution, which will have both positive
and negative results. RISA-3D gives you the option of assigning signs to the final
RSA results based on the signs for the results for any particular mode. If you
choose not to use this option, just leave it set to “None”.