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RC module reliability

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GabrieleNovembri1027
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RC module reliability

It seems there are many problems with the real reinforcement for concrete columns. I am not sure if it is reliable.

Below a list of problems I found. (see also http://forums.autodesk.com/t5/Robot-Structural-Analysis/the-stirrups-calculated-by-Robot-does-not-se...).

Specifically, I suspect that Robot does not correctly handle shear in the columns. Attached here there is a simple model with a test I did with a 80x80 column (columns 9..12).


Step 1) I calculated reinforcement. The calculation result is shown in the file figureprimo calcolo.JPG

Step 2) for the column group 9..12 I introduced exactly the same reinforcement using “typical reinforcement” and I verified it with Robot. Surprisingly, I received the error message below. Attached here you will find the file rxd of the typical reinforcement used for the test. The reinforcements created with the “typical reinforcement” command and the error are as follows:

secondo calcolo.JPG


They appear (at least to me) absolutely identical, but in the second case Robot reports that the column has insufficient capacity.

 

errore armatura tipo.JPG

 

Which of the two situations is correct ?.  The column appears not verified due to the Shear

 

taglio.JPG

 

If you consider the VRd calculated by Robot this seems to be, in this case, 223.81 (355.26x0.63).  This value seems absurd!. The shear resistance of the section varies also with load combinations while, instead, should always be the same as it is a characteristic of the section of the column. The Shear in this case should instead be verified due the shear resistance of the section that is about 1200 kN.

Moreover, the arrangement of the reinforcements does not meet the standard. I think that the correct arrangement should be like that shown in the following image:

verifica gelfi.JPG


To understand if the reinforcement calculated by Robot is correct due the difficulties to do this by hand, I did a test with a simple free software freely downloadable from the internet that is very popular in Italy and reliable. For the column I adopted reinforcements shown in the previous picture similar to those calculated by Robot but complying with the requirement of DM14/01/2008. The section, with the correct arragement is verified using stirrupswith diameter of 8 mm.

Reintroducing the reinforcements so changed in Robot always occurs an error that appears to be related to the height of critical zone of the column:

verifica gelfi-robot.jpg

 

So ... Is the rc module for column reliable ??

Any suggestion ?

Thanks

 

 

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Thw attachment due dimension of the post

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