Concrete Slab-to-Wall Joint Rigidity 2

[CovertShear]

Greetings

How do you go guys consider the connections between a monolithic concrete slab and a external concrete wall in terms of rigidity (for example as bellow):

You design them as rigid, semi-rigid ?

I know in masonry wall connections, the rigidity is decided by the "clamping" vertical force in the wall from the storey above wall siting on the joint.

But in concrete, it feels like the rebar should carry over the tensions of a fully rigid connection.

In the past, I have been designing them as semi-rigid, but I would like to hear your methods.

 

[dik]

For highrise, if the slab is 'clamped' between the stair/elevator shaft walls, I've always considered the slab as fixed... for other applications, I consider it as pinned, but throw in nominal top reinforcing.

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

-Dik

 

[CovertShear]

@dik

That is what I have been taught as well, but I cant recall the reasons why pinned.

I vaguely remember it (rigidity) being an detailing issue, as in usually the slab rebar is not anchored in the wall underneath, hence the hogging rebar development length is not met?

Or it could be purely a E*Iy stiffness issue as with steel, but I don't know.

My 2D FEM models default the joints as rigid if I dont tell them otherwise with pins.

 

[dik]

If cast into a keyway, then I'd consider it pinned... If you put top reinforcing at the 'pinned' location, it's conservative... you have added reinforcing in both the +ve end span and -ve first interior support.

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

-Dik

 

[HTURKAK]

It depends on relative stiffness of slab and walls , detailing requirements..In case of similar stiffness, you may choose simple pin or detail the connection to provide rigidity.

The sketch implies the reinf . is probably WWF and if so ,it is hard to provide rigid conn.










If you put garbage in a computer nothing comes out but garbage. But this garbage, having passed through a very expensive machine, is somehow ennobled and none dare criticize it. ( ANONYMOUS )

 

[CovertShear]

Keyway i can understand being pinned.

But what if the slab isn't poured into the wall through a keyway, but poured sitting on the wall like this (pic), still pinned?

 

[CovertShear]

@HTURKAK



It depends on relative stiffness of slab and walls

I think this is what I had in mind, do you know of any publication or a design book I could use for a "relative stiffness of 2 concrete members" research?

Yeah, it only feels natural that the thicker (stiffer) the wall, the more rigid the connection, sadly with commercial buildings here the wall to slab thickness ration is somewhere around "1".
So I guess the only way left is to provide a rebar detailing with properly anchored top reinforcement for a rigid connection?

 

[HTURKAK]

- True.. Below find slab -edge wall connection detail . ( excerpt from Standard Method of Detailing
Structural Concrete , Institution of Structural Engineers )..

My points to your sketch ,
- It implies Parallel wall structural system . The conn. btw . slab -to external wall could be detailed as rigid for gravity loading but , this system is not effective for lateral loading. You must have walls at transversal direction to resist lateral loading.
- If this is tunnel formwork system,in general WWF mesh reinf is used for the wall and slab reinf . In this case , the conn. of slab to exterior wall may be assumed pin conn. but provide some hogging reinf .mesh .
- The parallel wall structural systems were designed at slide rule era , with unit frame using moment dist. method which is based on (relative stiffness of 2 concrete members ).








If you put garbage in a computer nothing comes out but garbage. But this garbage, having passed through a very expensive machine, is somehow ennobled and none dare criticize it. ( ANONYMOUS )

 

[CovertShear]

True.. Below find slab -edge wall connection detail . ( excerpt from Standard Method of Detailing Structural Concrete , Institution of Structural Engineers )

Oh yes, that's it, that's what I had in mind about detailing a rigid connection, but couldn't put my finger on it. Thank you.


- It implies Parallel wall structural system . The conn. btw . slab -to external wall could be detailed as rigid for gravity loading but , this system is not effective for lateral loading. You must have walls at transversal direction to resist lateral loading.

Sure, laterally it couldn't resist wind forces or seismic forces very much, that's true. My inquiries were indeed mostly towards "gravity loads".

- If this is tunnel formwork system,in general WWF mesh reinf is used for the wall and slab reinf . In this case , the conn. of slab to exterior wall may be assumed pin conn. but provide some hogging reinf .mesh .

I dont think Ill come across a tunnel design in my practice anytime soon, but a good point nevertheless.

- The parallel wall structural systems were designed at slide rule era , with unit frame using moment dist. method which is based on (relative stiffness of 2 concrete members ).

That's before my time for sure, I might look into it eventually.



Anyway, thank you both @HTURKAK and @dik

 

[dik]

Correction... fully continuous, not fixed... if going into a stair or elevator shaft... they are nearly fixed end conditions, due to their relative stiffness. I was thinking of shafts and not exterior wall bearing walls.

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

-Dik

 

[HTURKAK]

I think you misunderstand the tunnel formwork system , which is used for bldg construction ,the walls and slab casted together ..

https://outinord.fr/siteanglais/pdfang/TUNELSTANDARD.pdf

If you put garbage in a computer nothing comes out but garbage. But this garbage, having passed through a very expensive machine, is somehow ennobled and none dare criticize it. ( ANONYMOUS )

 

[CovertShear]

@HTURKAK

I think you misunderstand the tunnel formwork system , which is used for bldg construction ,the walls and slab casted together ..

Oh I see, of course I misunderstood the technical nomenclature.