Seismosoft | Earthquake Engineering Solutions

Hello everyone. I would like your help: I have modeled a building of 4-level steel frames (without bracings). The slab is concrete and I have modeled it as a rigid diaphragm. When analyzing the building with eigenvalues the predominant period (mode 1) gives me equal to 0.88 s (normal value) BUT the MAXIMUM MODAL displacement for that mode gives me a value of 0.04 mm. While in ETABS I made the same model and obtained a maximum displacement of 0.9 mm. I have already checked the modulus of elasticity and the grade of the steel. So, what could be the problem?

Thank you!

In eigenvalue what is important is the relative value of the nodal deformations, rather than their actual value, i.e. the shape of the deformed shape. Obviously, different programs choose different methods of normalizing the displacements. Refer on a good textbook on modal analysis for a better understanding of the results.
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