Modeling and analyzing structures for dynamic conditions is essential to understanding how a structure will react to loading such as wind and seismic. These analysis types can include simple free vibration analysis as well as more advanced response spectra and time history analysis. RISA-3D is...
In structural engineering, a modal analysis uses the overall mass and stiffness of a structure to find the various periods at which the structure will naturally resonate, along with the frequencies of vibration of the structure. In RISA-3D, the modal analysis is a prerequisite to the response...
The Pacific Earthquake Engineering Research center (PEER) has a large library of measured earthquake records. Below is an example of how to quickly convert one of these records into a format that can be imported into RISA.
Ramp Up Function RISA allows you to define “Ramp Up Functions” to control how the force and frequency vary during this initial startup time. Typically cyclic equipment loading is applied as a reduced force or frequency when it is initially starting up. It would be overly conservative if it were...
New in RISA-3D v14 is the introduction of a Time History analysis feature. Time history functions may be generated directly in the program based on simple sinusoidal functions. More complex functions, however, can be imported from a text file.
Time history analysis solves for normal analysis results (joint displacements, member forces, code checks, etc.) based on loading that varies with time. For some analyses it may be useful to view an animation of the deflected shape of the structure as a function of time. This blog topic serves as a...
RISA-3D v13 includes a new Ritz Vector Solver for the Dynamic analysis. When running a Response Spectrum analysis for seismic design, some structures experience large numbers of local modes that don’t contribute to the lateral response of the structure. The use of load-dependent Ritz vectors...
The applied loads in a response spectrum analysis (RSA) are the applied masses times the accelerations in the response spectra. Each mode of vibration produces its own set of joint reactions. The reactions for each mode obey statics as shown in the portal frame example shown below: Response...
