I think you mean the situation where the 2nd basement floor is rigid while the 3rd basement floor is rigid. That is, if the rigid curtains on the 3rd basement floor do not continue on the 2nd basement floor (or not), then we enter -3.[ /quote] TDY 2007 article 2.7.2.4 and item 2.8.3.2 the definition of rigid floor is a bit open. Regulation article "The stiffness of the basement floors is very high compared to the upper floors There is an expression such as .." in buildings where there are shear walls and the basement floors operate as rigid diaphragms in the horizontal plane. Based on this expression, there are basement perimeter curtains throughout the 3rd basement floor. Therefore, the 3rd basement floor should be considered rigid. There are rigid shears on the 1st and 2nd basement floors that are not on the upper floors. However, they do not cover the entire building. Therefore, the engineer will take the initiative whether these floors are considered rigid. When the relevant floors are considered rigid (when the rigid floor number is entered), the vibration modes on these floors will not be taken into account. .So structure 7-story bookmark It will be solved like this. If the floors are not considered rigid (if the rigid floor number is entered as -3), the building will be solved as 9 floors. Meanwhile, the horizontal force TDY acting on the floors accepted as rigid shall be calculated according to the formula specified in Article 2.7.2.4 b and Figure 2.6 . I hope that has been revealing. Good work