When it comes to modeling the structure using semi-rigid diaphragms, does the eccentricity value make a difference? Since the floor diaphragm is sub-meshed into plates (given it's modeled as semi-rigid), the seismic and/or wind forces are NOT applied to the center of mass (as is the case of the rigid diaphragm), but rather distributed to individual nodes that compose the particular story diaphragm. Also, if semi-rigid diaphragms are used, the program does not display the center of rigidity following the 'center of rigidity' analysis (defined in Load Cases). If the loads are distributed spatially in this matter, the torsion on the structure is, in my belief, included based on stiffness matrix of the structure. The concept of center of mass (the location of concentrated lateral load) does not apply nor the location of the center of rigidity. However, if the eccentricities are defined explicitly in Loads>Masses, what is the program doing? (Assuming semi-rigid diaphragms are used). I am not seeing any differences in forces, stresses, reaction in my load cases where X +E and X –E are defined. Should I leave the eccentricity value at zero and let the building experience additional torsion based the spatial distribution of the lateral loads and the stiffness of the vertical elements?
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