Unexpected bending resistance of rc frame cross-section

04-Unexpected behaviour/errors
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MatCiar
Posts: 3
Joined: 16 Oct 2017, 11:08

Unexpected bending resistance of rc frame cross-section

Post by MatCiar »

I have modelled a rc rectangular cross-section to perform a static nonlinear pushover of a cantilever. I have adopted a distributed plasticity model (DB finite element) and defined reinforcements exploiting potentials of the software in defining rebars (at the angles, and the cross-sections sides). I found that the resistant bending moment is twice the expected value from the hand calculations (verified also through the Axial Force-Bending Moment Limit Domain).

If necessary I can upload the input file.

Waiting for a reply, best regards
huffte
Posts: 978
Joined: 22 Jul 2011, 10:19
Location: Cookeville, Tennessee, USA
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Re: Unexpected bending resistance of rc frame cross-section

Post by huffte »

Do your hand calculations use the same assumptions for material stress-strain behavior as does the software? Do the hand calculations account for strain hardening in the reinforcement? Do hand calculations account for increased strain limits for confined concrete? If you change to force-based elements, does the difference between hand calculations and software results get closer? Did you subdivide the column (this is often necessary with DB-elements in order to get accurate results, but is not necessary with FB-elements)? Best of luck.
Tim Huff
MatCiar
Posts: 3
Joined: 16 Oct 2017, 11:08

Re: Unexpected bending resistance of rc frame cross-section

Post by MatCiar »

My calculation are correct, based on simple equilibrium conditions.

I have personally found the problem in the modelling, related to the meshing of the cantilever (considering that I was using the DB element).

Now the software well predict the bending moment evaluated through the simple formula M almost equal to As(tensile)*fymax*(d-c), assuming d-c = internal lever arm equal to the distance of reinforcements.....

Best regards.
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seismosoft
Posts: 1184
Joined: 06 Jul 2007, 04:55

Re: Unexpected bending resistance of rc frame cross-section

Post by seismosoft »

Hi MatCiar,
Indeed, 4-5 elements per member are required, in order to achieve adequate accuracy with the infrmDB element class.
Regards,
Seismosoft Support
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