Using excessive compression reinforcement to control long term deflection in RAPT

[huan0606]

Hi Everyone,

I was wondering if anyone knows how does RAPT calculate the compressive reinforcement effect in calculating the long term deflection.

For a simply supported beam, if my Asc is 5 times x Ast, I could almost eliminate all the long term deflection.

However, based on AS3600, kcs=2-1.2Asc/ASt>0.8, which means I could only utilise 100% of Asc.

it seems that RAPT does not have a limit on the amount of compression reinforcement to be used in reducing long term deflection.

I know it is simply wrong to have a lot of compression reinforcements that you dont even need for strength.

i have also tried a simply supported beam without any load on it in rapt, and specifying 2 times more Asc than Ast,my beam just warped to the opposite direction .

I just want to make sure that the result from RAPT is convincing.

Thank you.

 

[rapt]

I suppose everyone is waiting for me to answer this one!

If you study long term deflection theory (not the code simplifications, the actual theory), you would be able to answer this for yourself. Even if you read the RAPT manual you would be able to figure it out. If you think RAPT is using the AS3600 kcs logic, you should read the manual to see how the program works before using it.

Yes, it is illogical to use 5 times as much compression reinforcement as tension reinforcement. But that logic is common sense, not calculation. By calculation, using extremely large areas of compression reinforcement could actually cause upward deflection due to the shrinkage warping effects. That is what RAPT's calculations are showing. It is not suggesting that the solution is sensible. It does not comment on the common sense aspect of a design. It shows the effect of what the designer has asked it to do. It assumes that engineers provide the common sense part of the design and understand the design methods it is using.