Question
How is torsional dynamic amplification achieved in static seismic loading?
Answer
In static seismic loading, the horizontal torsional moments are automatically calculated within the program when the seismic load is entered.
However, if you want to apply dynamic amplification of torsion (KBC 2009, 0306.5.6.4), you need to find the eccentricity factor and enter the torsion dynamic amplification factor. The method for applying the torsional dynamic amplification factor for static seismic loads is as follows.
First, find the eccentricity ratio. When finding the eccentricity ratio, you can choose from three methods (mass, axial force, and shear force) to find the floor centre (centre of mass), and you must check Eccentricity Ratio (Model > Building > Control Data) to apply it. This eccentricity ratio is provided by Japanese standards and can be found in the online manual under Results > Results Tables > Story > Story Eccentricity.
Next, after the analysis, check the eccentricity distance (Results > Results Tables > Story > Story Eccentricity) and dynamic amplification factor (Results >Results Tables > Story > Torsional Amplification Factor) and enter them in the Eccentricity and Dynamic Amplification Factor tabs of Model > Building > Control Data > Seismic, respectively.