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 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 deflections.

In order to get code calculations the RISA-3D and RISA-2D programs need to know what type of shape would be most similar to yours. This is because the program needs to use the correct code equations for your shape type.

Investigating P-Delta instabilities in RISA-3D (or RISA-2D) can be difficult. The first step is usually to solve the model without the P-Delta effect included to see if there are any obvious deflection problems that could cause issues with a P-Delta analysis.

RISA-3D has the ability to create a finite element plate mesh for you automatically. This is a great tool for modeling elevated slab and diaphragm elements.