Story Eccentricity Table
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Check or modify the story eccentricities of a building structure in a spreadsheet format table. For eccentricity ratios, Story Center for Eccentricity Ratio must be defined in Building Control Data.
When "Story Shear Force Ratio>Consider Story Module"is checked in the "Model/Building/Control Data", accurate shear forces can be obtained for the story having the overlapping Module.
This function has no relation to Structure > Building > Story > Define Module button.
Table Tool in midas Gen offers a variety of powerful built-in functions. Refer to Usage of Table Tool for detail directions. |
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From the Main Menu select Results > Tables > Result Tables > Story > Story Eccentricity. |
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Upon executing the Buckling Mode Shape Table function, Records Activation Dialog prompts. Click after selecting the output entities such as nodes or elements, loading conditions, construction stages, etc.
Note
Refer to Usage of Table Tool and check the following data:
When Modules are not defined
Story: Story ID
Level: Story elevation level
Weight Center: Location of the center of weight
Stiffness Center: Location of stiffness center
Ecc. Dist.: Eccentricity distance
Torsion Stiffness: Torsional stiffness of the story at the stiffness center
El. Radius: Elasticity radius
Ecc. Ratio: Eccentricity ratio
When Modules are defined
Module: Module name is defined in Structure > Building > Story > Define Module button
Story: Story ID
Level: Story elevation level
Weight Center: Location of the center of weight
Stiffness Center: Location of stiffness center
Ecc. Dist.: Eccentricity distance
Torsion Stiffness: Torsional stiffness of the story at the stiffness center
El. Radius: Elasticity radius
Ecc. Ratio: Eccentricity ratio
Note Eccentricity Ratio
(1) Background to Eccentricity Ratio
A lateral seismic load is considered to act through the center of mass in a building plan as shown in Fig. 1. The building structure then undergoes lateral displacements while rotating about the center of the stiffness due to the stiffness eccentricity. If the eccentricity between the centers of mass and stiffness is excessive, displacements at one side of the building may be undesirably large due to the torsion. The eccentricity ratio is defined as the ratio of the eccentricity to the radius of elasticity, which represents torsional resistance. The higher the eccentricity ratio the greater the eccentricity from the stiffness center of the lateral resisting system (frames, bracings, shear walls, etc.) to the mass center.
Fig. 1 Building with Eccentricity
(2) Calculation of Eccentricity Ratio
The eccentricity ratio, Re is considered in each direction at each story. We will simply find the eccentricities at a floor to demonstrate the concept as shown in Fig. 2. The coordinate system does not affect the outcome; so we will locate the origin at the lower left corner here.
Fig. 2 Torsional notations |
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