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!