Higher participation factors indicate more important modes. Here is where you can tell which modes are important in which directions.
Remember that the RSA involves calculating separately the response forĮach mode to the applied base excitation represented by the spectra. Mass Participationįactors reported on the Frequencies Spreadsheet reflect how muchĮach mode participated in the Response Spectra Analysis solution. In the “high” frequency range tend to converge to the maximum ground acceleration A constant spectral acceleration is used because modes In a constant Spectra Acceleration from the largest defined spectral frequency If the modal frequency is above the largest defined spectral frequency,Ī spectral velocity will be used for the modal frequency that will result Range will tend to converge to the maximum ground displacement.
If the modal frequency isīelow the smallest defined spectral frequency, a spectral velocity willīe used for the modal frequency that will result in a constant Spectraĭisplacement from the smallest defined spectral frequency value.Ī constant spectral displacement is used because modes in the “low” frequency The range of the selected spectra, RISA will extrapolate to obtain spectral Frequencies OutsideĪnalysis is solved using modal frequency values that fall outside Learn more about this method, an excellent reference is Structuralĭynamics, Theory and Computation by Dr. Static procedure so there really isn't any reason to use the static procedure. The response spectra method is easier, faster and more accurate than the The response spectra method satisfies this dynamics requirement. Model to any arbitrary base excitation, particularly earthquakes.īuilding codes require a dynamics based procedure for some structures. These modal responses are then combined to obtain the model's overallĪcceptance as an accurate method for predicting the response of any structural The maximum responses for each mode are calculated independently. In the response spectra analysis procedure,Įach of the model's modes is considered to be an independent SDOF system. Maximum deflections, and thus, the maximum stresses for the system. By "any SDOF system", it is meant a SDOF system Spectrum, it is possible to predict the maximum response for any SDOF The maximum response of any single degree of freedom (SDOF) system toĪ dynamic base excitation. “-” if you want the summed results subtracted. Positive) added to the other loads in the load combination. Use “+” if you want the summed RSA results (which will be all The "RSA SRSS" flag for the combination to "+" or The multiple RSA results using an SRSS summation. If you do this you can also have RISA- 3D combine To scale the spectral results enter the spectra-scaling factorĬan include more than one spectra solution in a single load combination.In the BLC column enter " SX", " SY", or " SZ" as the BLC entry ( SXįor the X direction RSA results, SY for the Y direction RSA results, etc.).Running the response spectra analysis go to the desired combination on The Dynamic Solver options are located in the Model Settings - Solution tab Advanced options.To create a load combination on the Load Combination spreadsheet To view model results such as forces/deflections/reactions you will need Spreadsheet and the participation yielded by the RSA is listed. Of the solution you are returned to the Frequencies and Participation Then specify the otherĪ more thorough explanation of the Eigensolution options refer to Dynamic Analysis - Eigensolution. The spectra to be used for each direction. Indicate which directions you want to perform your response spectra analysis. Model can be approximated as a summation of the responses of the independentĭynamics (Eigensolution / Response Spectra) from the Solve Procedure is based on the assumption that the dynamic response of a structural In general, the response spectra analysis
Dynamic Analysis - Response Spectra Dynamic Analysis - Response SpectraĪnalysis may be performed after the dynamic analysis to obtain forces,