Story Stiffness Ratio Table

Check or modify the story stiffness ratio of a building structure for seismic loads in a spreadsheet format table.

This function is applicable only when the Story Shear Force Ratio of Member option is selected in Model>Building>Control Data.

Table Tool in MIDAS/Gen offers a variety of powerful built-in functions. Refer to the following items for detail directions:
 

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Results Table

From the Main Menu select Results > Result Tables > Story > Story Stiffness Ratio.

Select Result Tables > Story > Story Stiffness Ratio in the Tables tab of the Tree Menu.

Upon executing the Story > Story Stiffness Ratio 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 Results Table of "Usage of Table Tool" for the usage of Records Activation Dialog.

Refer to Usage of Table Tool and check the following data:

Load Case

Story: Story ID

Level: Story elevation level

Height: Floor to floor height

X-Dir

Average Drift: Average inter-story drift

Story Force

Story Stiffness : Story Force / Average Drift

Story Stiffness Ratio: Story Stiffness in the current story / Story Stiffness in the story below

Soft Story Ratio: Refer to the explanation as stated in the table above (Refer to Note 1.). However, Story Stiffness Ratio for the

roof level (top floor) will not be calculated.

Soft Story: Check whether it is a soft story or not (Refer to Note 1.).

Soft Story >= 1:  NO (Not a soft story)

Soft Story <  1:  YES (Soft story)

Refer to the items under X-Dir for the items relevant to Y-Dir.

Note 1. Calculation example of Soft Story Ratio

Calculate the Soft Story Ratio for 5F from the table results above.

1) When Load Case = EX and Story = 5F

Story Story Stiffness

Max(0.7 X 6F, 0.8 X (6F+7F+8F)/3) = 11198.43

 100112 / 11198.43 = 0.89 < 1   (YES)

2) When Load Case = EY and Story = 5F

Story Story Stiffness

Max(0.7 X 6F, 0.8 X (6F+7F+8F)/3) = 7624.96

 7937.8 / 7624.96 = 1.04 >1   (NO)

Note 2. Stiffness Ratio

The stiffness ratio is calculated in each direction at each story level. First, obtain the inverse of the angle of the inter-story deflection, at each story level, and then compute the numerical average of of all the stories above grade, . The value at each story level is divided by the value, and the result is defined as the stiffness ratio.