In terms of cost, Risa 3D is more expensive than Ram Elements. Is there anything you can do with Risa 3D that you cannot do with Ram Elements. Thereby eliminating most reasons why ETABs might require significantly fewer modes than RISA. For those of you that have used BOTH Ram Elements (Advanse) and Risa 3D, which do you prefer and why. So, while our Ritz Vector algorithm won't be exactly the same as CSI's / ETABs, it should be in the same ball park. However, RISA added a Ritz Vector dynamic solution option a year or so ago. What you get are not the true dynamic modes of the structure, though they are usually close. This type of solver allows you to use fewer "modes" because you're biasing the solution to specifically exclude modes that do not participate in the direction requested. Now, ETABs used to have an advantage because of their "Ritz Vector" solver for dynamics. But, for modeling of steel building with a rigid floor diaphragm, the mass modeling should be virtually identical between the programs. Hence, why there may still be some different with concrete building using a semi-rigid floor slab. If you're talking about true eigen modes, then RISA cannot take more modes to get to 90% mass participation unless you have modeled your mass differently. But, it should be much more modest than what it used to be. Maybe for pure concrete models, ETAB's may have an advantage over RISA for dynamic solution.
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