Offsetting the Center of Mass (4.5.10)

Owned by Hakan Şahin
Last updated: Sept 29, 2022 by Zeynep Aladağ
2 min read

  • As required by 4.5.10.2 , the earthquake calculation is made automatically in every 4 cases by shifting the storey masses by 5%.

  • In accordance with Article 4.5.10.2 (b) , the horizontal earthquake loads are calculated automatically by shifting (+) and (-) 5%.

  • In modeling the additional eccentricity effect, any of the static and dynamic methods that comply with the regulation can be used for analysis. Method selection is under user control.

There are two different ways to determine the additional eccentricity effect.

1- Static procedure: For  horizontal earthquake loading situations, the torsional moment (Mz) obtained by multiplying the storey forces determined by response spectrum analysis by the rate of exanthicity is applied to the center of the diaphragm. Regardless of whether the diaphragm type is full or semi-rigid, Torsion Moment is applied to the center of the diaphragm in all floors containing diaphragms. As of V10.15, it is applied if the static eccentricity and single loading state calculation method explained in 4.3.6.2 is selected in the analysis settings tab  . Unless a different value is entered in the analysis settings tab   , transactions are made according to the (+) and (-) 5% eccentricity ratio in both horizontal directions as per TBDY 2018 4.5.10.2 .

2- Dynamic procedure:  Determined directly for each mode by response spectrum analysis. It is  included in the internal force and displacements of the horizontal earthquake loading conditions obtained by combining with CQC  or  SRSS methods. According to the logic of the method, at each node where the masses are distributed, the mass at the center of the diaphragm, for the semi-rigid diaphragm, or the mass at the center of the diaphragm, is calculated by shifting (+) and (-) 5%. Since it is obtained by shifting the mass matrix, 4 different modal analyzes are required in the standard procedure.

  • Why is the Extra-eccentricity Effect Applied?

It  is calculated by one of the methods mentioned above in accordance with Article 4.5.10 of TBDY 2018 .

  • The buckling moment of the structure due to ground motion can affect the Z axis.

  • Additional effects arising from the uncertainty of moving loads on the structure should be taken into account.