Occasionally, loads are applied to elements that are not properly connected to the diaphragm (e.g., a beam modeled without a support connection or a slab not meshed with walls).
The Mass Summary is your best detective tool. Here are four common mistakes it catches: etabs mass summary by story
Cause: You defined mass source from load patterns but forgot to assign any load pattern to the roof diaphragm. Or, you used a rigid diaphragm but the beams are not connected to the diaphragm constraint. Occasionally, loads are applied to elements that are
After running modal analysis, ETABS provides "Modal Participating Mass Ratios." For a valid model, the sum of modal mass ratios in the X and Y directions must exceed 90% of the total mass from the Mass Summary. If not, the analyst must add more modes. Or, you used a rigid diaphragm but the