Stiffness Irregularity Check (Soft Story Check) Table
Story Stiffness Ratio of a building structure is tabulated in the Stiffness Irregularity Check (Soft Story Check) Table.
When 'Consider Story Module' under "Story Shear Force Ratio" is checked in the 'Model/Building/Control Data', accurate shear forces can be obtained for the story overlapping the upper Module and the lower Module.
When Modules are defined in Structure > Building > Story > Define Module button, the Module data is displayed in the first column of the table.
When the ratios exceed the allowable limit, they appear in red and 'Irregular' is printed in the Remark.
"Story Shear Force Ratio" in "Model/Building/Control Data" must be checked for this function, which is checked as the Default.
Table Tool in midas Gen offers a variety of powerful built-in functions. Refer to Usage of Table Tool for detail directions.
From the Main Menu select Results > Tables > Result Tables > Story > Stiffness Irregularity Check (Soft Story Check)
Select load cases/combinations for which Stiffness Irregularity
Check is required and the Story Drift calculation method.
Record Activation dialog box
For KBC 2009
Refer to Usage of Table Tool and check the following data:
When Modules are not defined
Load Case: Load case/Combination
Story: Story number
Level: Story Elevation
Height: Story Height
1. Story Drift
Story drift for the selected Load Case
2. Story Shear Force
Story shear force due to the selected Load Case
3. Story Stiffness
If Story Stiffness Method chosen in Irregularity Check Parameter is 1/Story Drift Ratio
Story Stiffness = Story Height / Story Drift
If Story Stiffness Method chosen is Story Shear/Story Drift
Story Stiffness = Story Shear / Story Drift
4. Upper Story Stiffness
0.7 Ku1: 70% of the Story Stiffness at the story immediately above the current story
0.8 Ku123: 80% of the average Story Stiffness of the three consecutive stories immediately above the current story
5. Story Stiffness Ratio
Story Stiffness Ratio = Story Stiffness of the current story / Max (0.7 Ku1, 0.8 Ku123)
Story Stiffness Ratio for the Roof (top story) is not computed. Also, if three stories above the current story do not exist, only 0.7 Ku1 value is computed.
6. Story Drift Angle Ratio
Story Drift Angle Ratio: Story drift angle of the current story is divided by that of the upper story
7. Remark
If the "Story Drift Angle Ratio" exceeds 1.0 and 'Story Stiffness Ratio' exceeds 1.3, "Irregular" is printed, otherwise "Regular" is printed.
Note1
If Story Stiffness (Story Drift) is negative, - is printed
before the value, as shown in the table.
Table is generated as per the following rules:
1. If Story Drift is negative, the corresponding Story Stiffness is displayed with - sign (①).
2. If the Story Stiffness of an upper floor is displayed with - sign then 0.7Ku1 is also displayed with - sign (②).
3. If one of the Stiffnesses of the three upper floors is displayed with - sign then 0.8Ku123 is also displayed with - sign (③).
4. If both 0.7Ku1and 0.8Ku123 are displayed with - sign then Story Stiffness Ratio is also displayed with - sign.
When Modules are defined
The Module column is generated only when the Modules are defined. Results of evaluation of stiffness irregularity are calculated as per the following Note.
Note
1. Results of evaluation of stiffness irregularity for the
top floors of each Module are not generated.
2. Since the Upper Story Stiffness is zero for the story immediately below the top floor of upper Modules, it is always marked as Regular.
3. As per the evaluation method for stiffness using 0.7Ku1, the Upper Story Stiffness is always displayed as 0 for the story immediately below the top floor of each Module.
4. As per the evaluation method for stiffness using 0.8Ku123, Upper Story Stiffness is always displayed as 0 for the three stories immediately below the top floor of each Module.
Module: Module name is defined in Structure > Building > Story > Define Module button
Load Case: Load case/Combination
Story: Story number
Level: Story Elevation
Height: Story Height
1. Story Drift
Story drift for the selected Load Case
2. Story Shear Force
Story shear force due to the selected Load Case
3. Story Stiffness
If Story Stiffness Method chosen in Irregularity Check Parameter is 1/Story Drift Ratio
Story Stiffness = Story Height / Story Drift
If Story Stiffness Method chosen is Story Shear/Story Drift
Story Stiffness = Story Shear / Story Drift
4. Upper Story Stiffness
0.7 Ku1: 70% of the Story Stiffness at the story immediately above the current story
0.8 Ku123: 80% of the average Story Stiffness of the three consecutive stories immediately above the current story
5. Story Stiffness Ratio
Story Stiffness Ratio = Max (0.7 Ku1, 0.8 Ku123) / Story Stiffness of the current story
Story Stiffness Ratio for the Roof (top story) is not computed. Also, if no three stories exist above the current story, only 0.7 Ku1 value is computed.
6. Story Drift Angle Ratio
Story Drift Angle Ratio: Story drift angle of the current story is divided by that of the upper story
7. Remark
If "Story Drift Angle Ratio" exceeds 1.0 and 'Story Stiffness Ratio' exceeds 1.3, "Irregular" is printed, otherwise "Regular" is printed.
Note1
If Story Stiffness (Story Drift) is negative, - is printed
before the value, as shown in the table.
Table is generated as per the following rules:
1. If Story Drift is negative, the corresponding Story Stiffness is displayed with - sign (①).
2. If the Story Stiffness of an upper floor is with - sign then 0.7Ku1 is also displayed with - sign (②).
3. If one of the Stiffnesses of the three upper floors is with - sign then 0.8Ku123 is displayed with - sign (③).
4. If both 0.7Ku1and 0.8Ku123 are with - sign then Story Stiffness Ratio is displayed with - sign.
Note2
Examples of Soft Story Ratio calculations
Among the results in the above table, Soft Story Ratio at the
5th floor is calculated.
1) Load Case = EX, Story = 5F
Story |
Story Stiffness |
8F 7F 6F 5F |
16479.3 13870.4 11644.4 10011.2 |
Max (0.7 X 6F, 0.8 X (6F + 7F + 8F) / 3) = 11198.43
10011.2 / 11198.43 = 0.893 < 1
2) Load Case = EY, Story = 5F
Story |
Story Stiffness |
8F 7F 6F 5F |
10566.8 9490.5 8536.3 7937.8 |
Max (0.7 X 6F, 0.8 X (6F + 7F + 8F) / 3) = 7624.96
7937.8 / 7624.96 = 1.04 >1
For NTC 2012 & 2008
When Modules
are not defined
Load Case: Load case/Combination
Story: Story number
Level: Story Elevation
Height: Story Height
1. Story Drift
Story drift for the selected Load Case
2. Story Shear Force
Story shear force due to the selected Load Case
3. Story Stiffness
If Story Stiffness Method chosen in Irregularity Check Parameter
is 1/Story Drift Ratio
Story Stiffness = Story Height / Story Drift
If Story Stiffness Method chosen is Story Shear/Story Drift
Story Stiffness = Story Shear
/ Story Drift
4. Story Stiffness Ratio
Story Stiffness Ratio for nth story = (Kn-Kn-1) / Kn-1,
where Kn is the story stiffness of nth story
5. Remark
When the story stiffness of a particular story is greater
than 1.1 times or lower than 0.7 times the stiffness of the
story below, then the story will be defined as irregular.
When Modules are defined
The Module column is generated only when the Modules are defined.
Results of evaluation of stiffness irregularity are calculated
as per the following Note.
Module: Module name is defined in Structure > Building
> Story > Define
Module button
Load Case: Load case/Combination
Story: Story number
Level: Story Elevation
Height: Story Height
1. Story Drift
Story drift for the selected Load Case
2. Story Shear Force
Story shear force due to the selected Load Case
3. Story Stiffness
If Story Stiffness
Method chosen in Irregularity Check Parameter is 1/Story Drift
Ratio
Story Stiffness = Story Height / Story Drift
If Story Stiffness Method chosen is Story Shear/Story Drift
Story Stiffness = Story Shear / Story Drift
4. Story Stiffness Ratio
Story Stiffness Ratio for nth story = (Kn-Kn-1)
/ Kn-1,
where Kn is the story stiffness of nth story
5. Remark
When the story stiffness of a particular story is greater than 1.1 times or lower than 0.7 times the stiffness of the story below, then the story will be defined as irregular.
Examples
of Soft Story Ratio calculations
Among the results in the above table, Soft Story Ratio at the
5th floor is calculated.
1) Load Case = EX, Story = 6F
Story |
Story Stiffness |
8F 7F 6F 5F |
16479.3 13870.4 11644.4 10011.2 |
1.1 x stiffness of 5th floor= 11012.3 ; 0.7 x stiffness of 5th floor=7007.8
11644.4>11012.3 ; So Irregular story
2) Load Case = EY, Story = 6F
Story |
Story Stiffness |
8F 7F 6F 5F |
10566.8 9490.5 8536.3 7937.8 |
1.1 x stiffness of 5th floor= 8731.6 ; 0.7 x stiffness of 5th floor=5556.5
5556.5<8536.3<8731.6 ; So Regular story
For NSR-10
When Modules
are not defined
Load Case: Load case/Combination
Story: Story number
Level: Story Elevation
Height: Story Height
1. Story Drift
Story drift for the selected Load Case
2. Story Shear Force
Story shear force due to the selected Load Case
3. Story Stiffness
If Story Stiffness Method chosen in Irregularity Check Parameter
is 1/Story Drift Ratio
Story Stiffness = Story Height / Story Drift
If Story Stiffness Method chosen is Story Shear/Story Drift
Story Stiffness = Story Shear
/ Story Drift
4. Upper Story Stiffness
0.6K (Upper): Story
Stiffness of upper story multiplied by 0.6
0.7K (Upper): Story Stiffness of upper story multiplied by 0.7
5. Upper 3 Story Stiffness
(Avg.)
0.7K (3 Stories): Average
story stiffness between three stories above multiplied by
0.7
0.8K (3 Stories): Average story stiffness between three stories above multiplied by 0.8
6. Remark
When the story stiffness of a
particular story is greater than or equal to 0.6 times and
less than 0.7 times the stiffness of the story above, then
the story will be defined as "Irregular".
When the story stiffness of a particular story is greater than
or equal to 0.7 times and less than 0.8 times the average
stiffness of three stories above, then the story will be defined
as "Irregular".
When the story stiffness of a
particular story is less than 0.6 times the stiffness of the
story above, then the story will be defined as "Extreme
Irregular".
When the story stiffness of a particular story is less than
0.7 times the average stiffness of three stories above, then
the story will be defined as "Extreme Irregular".
Note
Stiffness Irregularity Check table is provided to check if there is a story in which the lateral stiffness is less than 70% but more than or equal to 60% of the stiffness of the story above or less than 80% but more than or equal to 70% of the average stiffness between three stories above. “Extreme Stiffness Irregular” will be displayed where there is a story in which the lateral stiffness is less than 60% of that in the story above or less than 70% of the average stiffness of the three stories above.
When Modules are defined
The Module column is generated only when the Modules are defined.
Results of evaluation of stiffness irregularity are calculated
as per the following Note.
Module: Module name is defined in Structure > Building
> Story > Define
Module button
Load Case: Load case/Combination
Story: Story number
Level: Story Elevation
Height: Story Height
1. Story Drift
Story drift for the selected Load Case
2. Story Shear Force
Story shear force due to the selected Load Case
3. Story Stiffness
If Story Stiffness
Method chosen in Irregularity Check Parameter is 1/Story Drift
Ratio
Story Stiffness = Story Height / Story Drift
If Story Stiffness Method chosen is Story Shear/Story Drift
Story Stiffness = Story Shear / Story Drift
4. Upper Story Stiffness
0.6K (Upper): Story Stiffness
of upper story multiplied by 0.6
0.7K (Upper): Story Stiffness of upper story multiplied by 0.7
5. Upper 3 Story Stiffness
(Avg.)
0.7K (3 Stories): Average story stiffness between three
stories above multiplied by 0.7
0.8K (3 Stories): Average story stiffness between three stories above multiplied by 0.8
6. Remark
When the story stiffness of a
particular story is greater than or equal to 0.6 times and
less than 0.7 times the stiffness of the story above, then
the story will be defined as "Irregular".
When the story stiffness of a particular story is greater than
or equal to 0.7 times and less than 0.8 times the average
stiffness of three stories above, then the story will be defined
as "Irregular".
When the story stiffness of a
particular story is less than 0.6 times the stiffness of the
story above, then the story will be defined as "Extreme
Irregular".
When the story stiffness of a particular story is less than
0.7 times the average stiffness of three stories above, then
the story will be defined as "Extreme Irregular".
Note
Stiffness Irregularity Check table is provided to check if there is a story in which the lateral stiffness is less than 70% but more than or equal to 60% of the stiffness of the story above or less than 80% but more than or equal to 70% of the average stiffness between three stories above. “Extreme Stiffness Irregular” will be displayed where there is a story in which the lateral stiffness is less than 60% of that in the story above or less than 70% of the average stiffness of the three stories above.