The most important thing that can be said about rigidity and center of mass is the torsional irregularity that will occur in the building. Torsional irregularity is defined as the case where the torsional irregularity coefficient, which expresses the ratio of the maximum relative story drift at any floor to the median offset in the same direction, is greater than 1.2 for any of two perpendicular earthquake directions. In order to avoid torsional irregularity, care should be taken not to place rigid structural system elements such as curtains in a way that increases the torsional rigidity of the system. It is desirable that the stiffness and center of mass coincide in structural systems. Even if these two centers do not overlap, care should be taken to keep them as close to each other as possible. Changes to the system geometry affect the center of rigidity. For example; change the dimensions of any column and do Analysis+Reinforced Concrete. You will see that the center of rigidity has changed. Changes in system loads affect the center of mass. For example; Change the wall load value on any beam or define a single (point) load on columns or beams. The center of mass will change when the Analysis+Reinforced Concrete is done again. In such a case, torsions occur in the building. Sections are forced and grow unnecessarily. Equipment increases. 2nd order effect occurs in the building.
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