Improved Reduced System (IRS)
If you compare static analysis with dynamic or seismic analysis, you will see that what you are looking for is completely different.
Seismic design focuses on the overall behaviour of the structure whereas analyzing the full mesh of the model will probably return too much information about local vibrations, which are in fact irrelevant for the overall seismic structural response.
The solution here is to use a different, reduced mesh for the dynamic analysis.
The Improved Reduced System (IRS) method takes into account not only the stiffness matrix of the system, but also the mass matrix, during the reduction process.
This method has proven to give excellent results in dynamic analysis while calculation time is reduced tremendously.
Advantages are:
- only one rotation node per storey;
- vast reduction of the DOF;
- easy to introduce accidental eccentricities;
- output of results per storey.