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[Xansys] Negative slope stress-strain curve for concrete
 
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akram.hassan
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Joined: 08 Jun 2015
Posts: 3

PostPosted: Sat Jun 20, 2015 10:12 am  Reply with quote

Hi all:
I need help please. Im trying to model RC beam strengthened with CFRP
laminates for my PhD dissertation. I want to use the simplified compressive
stress-strain curve for concrete, widely known in ANSYS analysis for
concrete, but my adviser wants me to include non-confined/ confined
concrete effects (stress-strain curve with descending (negative) branch). I
built the concrete stress-strain model with the descending part (for
un-confined concrete),using multi-linear stress-strain input with
Von-misses isotropic non-linear model, but when I hit run, ANSYS gave an
error message stating that "negative slope is not acceptable for solution".
I have read several papers and the authors of those papers claim they have
included the descending branch in their concrete stress-strain models.
Does any one know how to include a negative (descending) stress-strain
material in ANSYS, in the multi-linear stress-strain curve for Von-misses
nonlinear material?

Akram Jawdhari
PhD student
University of Kentucky
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ayo.brimmo
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Joined: 01 Jul 2013
Posts: 38
Location: Masdar City, Abu Dhabi

PostPosted: Sun Jun 21, 2015 1:01 am  Reply with quote

Akram,

From what I understand, this is not possible on ANSYS. Harish gave a good explanation of why this is so in one of the previous threads.

It also amazed me when someone claimed to have done this in a conference I once attended.

Ayo Brimmo
Masdar, UAE

Quote:
On 20 Jun 2015, at 21:12, Hassan, Akram R <akram.hassan@uky.edu> wrote:

Hi all:
I need help please. Im trying to model RC beam strengthened with CFRP
laminates for my PhD dissertation. I want to use the simplified compressive
stress-strain curve for concrete, widely known in ANSYS analysis for
concrete, but my adviser wants me to include non-confined/ confined
concrete effects (stress-strain curve with descending (negative) branch). I
built the concrete stress-strain model with the descending part (for
un-confined concrete),using multi-linear stress-strain input with
Von-misses isotropic non-linear model, but when I hit run, ANSYS gave an
error message stating that "negative slope is not acceptable for solution".
I have read several papers and the authors of those papers claim they have
included the descending branch in their concrete stress-strain models.
Does any one know how to include a negative (descending) stress-strain
material in ANSYS, in the multi-linear stress-strain curve for Von-misses
nonlinear material?

Akram Jawdhari
PhD student
University of Kentucky
+-------------------------------------------------------------+
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| The Online Community for users of ANSYS, Inc. Software |
| Hosted by PADT - www.padtinc.com |
| Send administrative requests to xansys-mod@tynecomp.co.uk |
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| Hosted by PADT - www.padtinc.com |
| Send administrative requests to xansys-mod@tynecomp.co.uk |
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Ayo Brimmo
Research Engineer
Masdar Institute of Science and Technology
UAE.
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Moe
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PostPosted: Sun Jun 21, 2015 4:36 am  Reply with quote

Hi,

Just a quick question, why are using
Von-misses to capture the response of concrete material? Isn't it used for metals and ductile materials?

M. Z. Naser,
PhD student,
Michigan State University

Quote:
On Jun 20, 2015, at 1:12 PM, Hassan, Akram R <akram.hassan@uky.edu> wrote:

Von-misses
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ayman.al-tantawy
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Joined: 02 Dec 2014
Posts: 3

PostPosted: Mon Jun 22, 2015 3:33 am  Reply with quote

Dear Akram..

don't use isotropic hardening when you need to model descending portion in stress strain curve, use kinamatic hardening. and for concrete don't use von mises yeild criteria, it's yeild surface translate. use any expanding yeild surface criteria (there are another option in ansys down von mises - unfortunately i didn't remember the name - ).

I wish it will solve you peoblem.

Ayman Al-Tantawy
MSc. , M.ACI
Structural Design Engineer, PACE




akram.hassan wrote:
Hi all:
I need help please. Im trying to model RC beam strengthened with CFRP
laminates for my PhD dissertation. I want to use the simplified compressive
stress-strain curve for concrete, widely known in ANSYS analysis for
concrete, but my adviser wants me to include non-confined/ confined
concrete effects (stress-strain curve with descending (negative) branch). I
built the concrete stress-strain model with the descending part (for
un-confined concrete),using multi-linear stress-strain input with
Von-misses isotropic non-linear model, but when I hit run, ANSYS gave an
error message stating that "negative slope is not acceptable for solution".
I have read several papers and the authors of those papers claim they have
included the descending branch in their concrete stress-strain models.
Does any one know how to include a negative (descending) stress-strain
material in ANSYS, in the multi-linear stress-strain curve for Von-misses
nonlinear material?

Akram Jawdhari
PhD student
University of Kentucky
+-------------------------------------------------------------+
| XANSYS web - www.xansys.org/forum |
| The Online Community for users of ANSYS, Inc. Software |
| Hosted by PADT - www.padtinc.com |
| Send administrative requests to xansys-mod@tynecomp.co.uk |
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akram.hassan
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Joined: 08 Jun 2015
Posts: 3

PostPosted: Mon Jun 22, 2015 1:26 pm  Reply with quote

Moe wrote:
Hi, Thats what has been used so far, I have looked at countless number of papers and they all use isotropic hardening--von misses plasticitiy--multilinear stress-strain curve. But your correct, Von misses criteria is mostly used for metals.

Just a quick question, why are using
Von-misses to capture the response of concrete material? Isn't it used for metals and ductile materials?

M. Z. Naser,
PhD student,
Michigan State University

Quote:
On Jun 20, 2015, at 1:12 PM, Hassan, Akram R <akram.hassan@uky.edu> wrote:

Von-misses
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