Too big deflections of T-beam with compression load according to Eurocode

[Ronald286]

Hello,

What does it mean, if i try to switch crack diagram and it doesn't appear? It means there are no cracks in the beam? How in this case Robot shows deflection for this beam about 6cm! Beam without cracks. When i see simple result for deformations for this beam after static calculations, it shows only 0,7cm. We can reduce elastic modulus according to creeping of concrete, let reduce it 4 times. So you will have 0,6x4=2,8cm. And here i even ignore stiffness of provided reinforcement. Why robot shows about 6 cm? Please, look attached file and give a comment.

[Ronald286]

Support, any comments? I also did simplified hand calcs(for uncracked section) and i got about 3,4cm. Looks RSA not able to claculate deflections correctly according to eurocode. If no, please, can you identify my mistake. Thank you!

[Artur.Kosakowski]

What does it mean, if i try to switch crack diagram and it doesn't appear? It means there are no cracks in the beam?

Correct.

How in this case Robot shows deflection for this beam about 6cm! Beam without cracks. When i see simple result for deformations for this beam after static calculations, it shows only 0,7cm. We can reduce elastic modulus according to creeping of concrete, let reduce it 4 times. So you will have 0,6x4=2,8cm. And here i even ignore stiffness of provided reinforcement. Why robot shows about 6 cm? 

The reason is that in the current version of Robot the axial force is disregarded in calculations of beam's deflection according to EC2. This causes its value to be larger than you expected it to be.

[Ronald286]

Thanks for answer!

Rafal said it works fine according to Eurocode. He said you have verifications tests for these. And now you say it doesn't work. So, what these verification tests about????? I confused! Looks you can't trust support's answers anymore and must to do double check for EVERY answer.

Please, can you give me more detailed explanation. So, in my file beam doesn't have cracks. Correct? But Robot calculate deflection with taking into account cracks in sections? I.e. ignores compression load(only in calculation of deflections)? Correct? So, why in this case I have different values for deflections when I consider compression load and when I don't consider it? Seems RSA takes into account compression load in calculations of deflection, but does it not correctly. So, can you explain me what kind of verification tests you have for this case? Or you don't have it?

[Artur.Kosakowski]

This situation was caussed by taking into account all SLS combinations (instead of QPR only) when the option "Display diagrams for all combinations" was switched on (done automatically when axial force is included in the design).

Corrected in SP4 for Robot 2015.