Storey Shear Strength

[EngTipper.]

I'm trying to figure out if i am going to trigger the type 6 irregularity in NBCC 2020, weak storey for a multistorey concrete building.

In my case shear walls will be continuous from foundation to roof however at the second floor the diaphragm is only connected to around 50% of the walls. The way I'm interpreting this is that since the shear strength that resists the 2nd floor storey shear at that level is around 50% of the level above, this will trigger a weak storey irregularity. Is that right?

Obviously a way around this would be to increase the shear capacity of the walls that are connected to the diaphragm at the second floor but i don't want to do this if not needed.

 

[HTURKAK]

In my case shear walls will be continuous from foundation to roof however at the second floor the diaphragm is only connected to around 50% of the walls. The way I'm interpreting this is that since the shear strength that resists the 2nd floor storey shear at that level is around 50% of the level above, this will trigger a weak storey irregularity. Is that right?

I am also trying to figure out your case. I do not have any experience with NBCC 2020 . However, in your case , the shear walls are continuous from foundation to roof and the storey height is the same . In this case , the interpretation that the shear strength that resists the 2nd floor storey shear would be around 50% of the level above is not reasonable.
I will suggest you , perform drift-based check of the structure with the design lateral loads and find the story drift ratios for each story. If the drift ratio in second floor is less than 1.3 times the drift ratio in the third floor , you can say there is no stiffness irregularity.
If you post the 2nd floor and typical floor plans you may get better responds.

 

[ETABSUSER1551]

Why is your second-floor diaphragm connected to only 50% of the shear walls? I assume this is because there is openings near the diaphragm to core interface?. I believe your situation does not create a 'weak story' since all your lateral load-resisting elements are continuous to the ground, (with no significant changes to wall openings at the lower level). The fact that the second-floor diaphragm connects to only 50% of your shear walls doesn’t make your building less stiff overall; it just means that specific disphragm at that level is slightly more flexible.

 

[milkshakelake]

I'm also not familiar with NBCC. But your shear walls are not less stiff, and you're not creating a weak story condition. They're just having less load applied. If I can reference a similar code, ASCE 7-16 commentary shows some irregularities including soft story, and you don't have these.



There is a book called 2012 IBC SEAOC Structural/Seismic Design Manual (there might be a newer version available). This is a good reference for getting in depth examples. It's useful to look at the pictures there to visually see if you're close to one of the examples.