Missing diagonal bars in slab opening 2

[Damotozey]

Hello great minds, I have been having sleepless night after a visit to a construction site.I noticed the third-floor slab openings for stairway didn’t have diagonal bars, just vertical and horizontal bars. My question is without the diagonal bars will there be cracks which could result to collapse of the floor.I’m new to site visits for flat slab system.

 

[KootK]

It's kind of weird in Canada sometimes. On imperial work you're sometimes forced to mix metric rebar callouts with imperial dimensions.

 

[hokie66]

But what does the '10.0' signify?

 

[Tomfh]

Diagonal is more efficient at resisting the cracking because it's perpendicular to the crack, but both ways work.

 

[Tomfh]

I would argue that it's not such a big difference since the lion's share of any restraint cracking is a result of restraint to shrinkage.

Yes it's one and the same.

 

[dik]

The number 3 denotes the quantity, the 15M denotes the bar size and the 10.0 denotes a length of 10'-0"... if c10.0 it would be a standard hooked bar with a straight part length of 10'-0". It's covered in my drawing notes. Sorry Hokie

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[hokie66]

OK. I think KootK said it best "It's kind of weird in Canada".

 

[SteynvW]

On a slightly unrelated note, I am more concerned with the lack reinforcing going over the that column adjacent to the stair.
Hopefully fixing is not finished yet.

 

[Damotozey]

@steynvw if you’re referring to this element shown in here:

It’s actually a shearwall not a column.

@Dik, please I asked a question regarding the statement you made abt multiple Irregular opening, I asked if the diagonal bars attached to the other end might impact the side with just horizontal and vertical bars? Or the horizontal and vertical bars will be sufficient in this case?

 

[MotorCity]

I think that these diagonal bars at openings are something that we use to make us feel like we did SOMETHING in an attempt to arrest the inevitable cracks at the corner of openings. Somebody probably looked at one of those fancy FEA output diagrams with all of the fancy colors and noticed high stress concentrations at the corners, and thus the diagonal bars were born. I am guilty of using them but mostly because I feel like I'd be the first one to not use them. On my future projects, I will reference this thread as a precedence for not using corner bars

 

[dik]

They've been in place long before FEA was common.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

Without a lot more information, I cannot answer this; it's getting into the realm of providing consulting services.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Damotozey]

@Dik

I’m sorry if you felt some type of way with my questions. I was just curious to understand what could happen in a scenario where a side has diagonal bars and the other side without a diagonal bar but with sufficient horizontal and vertical bars. Thank you for your input so far. I really appreciate

 

[dik]

It's not that... when you have a series of irregular openings in a slab... several flexural or shear items may come to bear. It takes the problem, from common useage into what could be some serious structural concerns.

So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[KootK]

I was just curious to understand what could happen in a scenario where a side has diagonal bars and the other side without a diagonal bar but with sufficient horizontal and vertical bars.

Since dik's side stepping this part of it, I guess you're stuck with my answer until someone else chimes in.

Won’t stress be transferred from the part with diagonal to the part without?

Nah. You're grossly overestimating the amount of design effort that goes into the specification of the diagonals. It's just boiler plate "2 - #5 x 4'-0" T&B at all corners" kind of stuff.

1) I'm sure that an asymmetrical layout probably does alter the stress distribution in some minor, and largely unknowable, way.

2) I guarantee you that the original designer put no real design effort into the diagonal bars when he or she specified them. As such, I would argue that there's little to be gained from trying to chase this down to such a granular level of detail as you're attempting too. If you're truly curious to know the effect, you'll probably have to bust out some of your own FEM modelling to chase it down. Practically speaking, this is not something that will be of concern to the original slab designer or to the design community in general.

 

[Damotozey]

@kootk
Thank you for your response. You’ve done justice to my question. I appreciate

@dik, thanks for your response.

 

[Ninjahedge]

I would throw this to the wind, as well.

Since this is designed to prevent cracks at the corner, I would imagine it would also be useful at any corner that would be subjected to deflectional warping, such as at the edge of an elevator core hallway where the only way the lateral load gets to the shear walls is through the hallway.

As was said by others, this probably won't do more than control cracking at that corner since I have never seen these bars designed, just placed in typical details.