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RE: Concrete Frame Rigidity

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I use SAP90 or SAP2000 to find excentricities. You can do the following:

1. Model your structure using master joints at each diaphragm´s center of mass.
2. Allow displacements of the master joints in the direction in which you want to find the excentricity and restrain the other displacements.
3. Add the corresponding horizontal loads to each center of mass and run the program.
4. Look at the output. You will find reactions at each restrained master joint. The excentricity can be calculated by e=Mt/V, where: Mt is the torsional moment (moment in an axis perpendicular to the diaphragm) and V is the total shear force at the interstory level.
5. Repeat the same to find the excentricity in the other direction.

Arturo