Flat slab design - long term elastic modulus - deflection

[skellyRSA2023]

Hi,

when design an RC flat slab generally when using looking at deflections I use the long term elastic modulus say short elastic modulus values for E, which I would have thought would give conservative deflection values , however I have run the model with a C40 concrete with a E value of 28,000 short term and 7,000 long term and I am getting less deflection with the long term E value? is this correct? I would have though this would be the opposite? any help or suggestions would be appreciated. 

Thanks,

Simon. 

[Krzysztof_Wasik · Accepted solution]

Hi @skellyRSA2023 

I cannot see your model but good practice for material properties modification is to define new material name.

Probably you have not changed material name while E modification and in that case material properties are not updated automatically in model.

While material modification, new material name should be defined "C40 -reduced" then material should be changed in panel thickness definition dialog.

Panels deflection should be bigger once material E is reduced.

For RC slab long therm deflection calculation, RC required reinforcement module can be used.

See slab design section of   RC design in Robot Structural Analysis

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