Test with reinforcement design results

[TSOFA]

Hi again,

My initial goal is to design a RC cantilever of variable thickness. I run some tests of how to do that. All my structures have the same geometry with small differences. At the attached picture pic1:

model 1: The slab is divided to zones of different thicknesses, in order to simulate the variable thk of the slab

model 2: The slab is simulated as a slab of variable thk from 27cm to 12cm

model 3: As model 2 but without supporting beam

model 4 As model 3 but with a constant thk of 15cm

Questions from the observation of the models:

-Model 1 &2 has really different results of design reinforcement, even though it supposed to be similar (pic 2)

-At model 2  the reinforcement close to the supported beam doesn't seem to be the one that is expected when the slab is rigidly connected to a stiffer element as the beam (pic3)

-For model 4 there is an error message during the design "Incoherent data for the panel no 8, Incomplete results for panel no. 8 (pic 4).

From all the above, the outcome is that I don't feel secure  for the results of RC design when it comes to a cantilever with variable thickness . What is the best way to approach a design like this with Robot?

Thanks in advance

  model: https://we.tl/t-T3NfCaXSqG

 

@Krzysztof_Wasik 

[Krzysztof_Wasik]

Hi @TSOFA 

I have the following suggestions

- Correct variable thickness definition (it should be defined individually for each slab) 2 and 3

- Switch off Reiforcement adjust for deflection.

- Slab 3 has nodal supports (from columns) for which reduction over supports does not work due to sloped panel. I would use rigid links to distrbute column forces to more than one slab node

- Slab 4 - if your intention was to use average thickness it should be between 18 and 19 cm to reflect structure selfweight.

- Problems with reinforcement (while calculations) are caused by small distance between reinforcement layers, I would try to reduce bar diameters to correct it.

Slab 4 has uniform small thickness

[TSOFA]

Thanks a lot! your answer cleared a lot of things to me!

All the above testing took place in order to clarify the results of a model with non regular geometry. I have to design an corridor at the perimeter of an existing church, which has columns only at the external side and the roof is a cantilever. 

(see pic 1)

The roof slab has a variavle thk 30cm-15cm from RC beam to the free edge. I followed your guidance, i switched off the reinforcement due to deflection etc.

What doesn't look right is that the elastic deflection  and the deflection taking account the creep are equal! So, what is the case? The calculation of the model for the church is not right? 

at the model with the testing at the post above, the elastic deflection is 3.7cm and the deflection taking account the creep is 5.1cm. 

To a slab that is supported at 4 sides, the ratio between elastic deflection and deflection taking account the creep is usually 1:3. Why the ratio here is so small?

More over as you can see at the pic below, there is a deflection of -0.8cm where the slab is connected to the RC supported beam. This is normal due to similar stiffness between slab and beam, or the connection between FE elements and Beam is not right?

I am sorry for the long post and thanks again for your help!!

model of church: https://we.tl/t-qW3wGlb8Ly

[Krzysztof_Wasik]

Hi @TSOFA 

Use tapered slab simulation with series of panels with uniform thickness.

Problem was discussed on forum couple years ago.

Refer to

Slab with variable thickness - wrong deflections 

or

Slab with variable thickness deflection

[TSOFA]

I did the slab with zones and the as you can see an area of slab has too high reinforcement. I understand that the slab at that area is narrow, but is not very long.

model: https://we.tl/t-L2xUhv1GTp 

[Krzysztof_Wasik]

Hi @TSOFA 

Switch off reinforcement adjust for deflection.

[TSOFA]

Hi, 

The results that you see is after I turned off reinforcement due to delfection. 

I think that the problem is that this narrow area is crashed, thats why the reinforcement is so huge! 

What I did is to erase this area ( green circle) and run the model again. Now, the pick of reinforcemet is as shown below (red circle)

I am not sure if this is because the edge there is crushed or is due to "bad meshing". What is your opinion on that?

Is the connection between panels and RCbeams correct?

model: https://we.tl/t-FqXQOarOlj

Thanks again!!

[Krzysztof_Wasik]

Hi @TSOFA 

In the previous model, the huge reinforcement of panel 110 was caused by activated Reinforcement adjust for deflection.

after Reinforcement adjust for deflection deactivation. Calculated reinforcement drops down

After

[TSOFA]

First of all you are right! By mistake the reinforcement parameters were "my RCfloor" instead of "my RC roof" that i had turned off the reinforcement adjustment for displacement!

The problem (again, sorry for that!) is that if you design the slabs also under ACC combinations and correct reinforcement parapeters, the reinforcement at the edge of the narrow area is high!

Do you think that this is the case, or is something wrong with the meshing or the model?

[TSOFA]

hi @Krzysztof_Wasik 

I added one RC wall at the model in order to get better results of reinforcement. The problem is that I have some picks of reinforcement ( see red marks) that I don't know if they should be neglected or is a problem of meshing and it should be investigated. 

model: https://we.tl/t-afvD6ltcNK  

Thanks in advance!