Abaqus Users - to simulate the behavior of RC Slab 1

[helmi30]

Dear Abaqus users,

Iam modeling and analysing a simply supported RC Slab with Concrete Damaged Plasticity on Abaqus CAE. Concrete slab is modelled with C3D20 solid elements and steel bars are modelled on Truss element T3D2 which are embedded into concrete. My results show very high force vs deflection graph, i.e. the loading force is high (around 800-100kN) when the behavior of slab begins to yield. These values are far out when compared to my experimental test results which is around 80kN. I have chosen a tensile stress of concrete to a minimum value of 0.05 to 0.1% of fcu (41.24N/mm2), i.e. around 2.06 to 4.12 N/mm2, for Abaqus input tensile behavior. My query is that how to lower down the force vs graph curve so that it would match the experimental tests results? Thanks in advance for any kind helps.

 

[helmi30]

Dear Abaqus users,

Iam modeling and analysing a simply supported RC Slab with Concrete Damaged Plasticity on Abaqus CAE. Concrete slab is modelled with C3D20 solid elements and steel bars are modelled on Truss element T3D2 which are embedded into concrete. My results show very high force vs deflection graph, i.e. the loading force is high (around 800-100kN) when the behavior of slab begins to yield. These values are far out when compared to my experimental test results which is around 80kN. I have chosen a tensile stress of concrete to a minimum value of 0.05 to 0.1% of fcu (41.24N/mm2), i.e. around 2.06 to 4.12 N/mm2, for Abaqus input tensile behavior. My query is that how to lower down the force vs graph curve so that it would match the experimental tests results? Thanks in advance for any kind helps.

 

[kellnerp]

Sure your boundary conditions are correct in the FEA?

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."

 

[helmi30]

To my best knowledge, yes, I have put the right boundary conditions into my model. Since the RC Slab is simply supported at all edges, I restrained all nodes at base only in vertical direction (u3 = 0) at the support. The rest remains unrestrained. Abaqus shows a yield load of around 800 -1000 kN higher than experimental with 80kN yield load. Please let me know how to solve this problems. Thanks in advance.

 

[struclearner]

If the material data does not contain plasticity values in it, the force or stress after yield will follow the elasticity curve and will be very high. To get the correct Force & Stress values, materil stress-strain curve need to be defined along with the elstic curve.

I am not a civil engineer, it might be the reason of the problem.

 

[TheMan008]

Lol, DO you think that maybe the truss elements and slab elements are not communicating effectively? What dimensions are the slab? Have you tried the analysis with just the concrete?

 

[helmi30]

Thanks for response. All materials data, both elastic and plastic values are put into Abaqus. Thats why the yield load is high (around 180kN in one case) before the curve begins to deform into plastic region. Compare to experimental test results, the yield load is around 80kN before the behavior of slab enters plastic deformation. I have analysed the concrete slab alone without the steel bars, and the results are very well indeed, i.e. about 100% match with the theoretical results that I have calculated. Please advice me on how to reduce the yield load (loading value before slab enters plastic region). Thanks.

 

[mrgoldthorpe]

In your original questions you say "...very high force vs deflection graph.."

A simple question: how does the initial prediction of load versus 'a measured displacement' compare with the test measurement? In other words, does the FEA at least predict the elastic response of your slab before the onset of yield/damage?

If the answer is "no" there is something fundamentally wrong with the model.

 

[helmi30]

mrgoldthorpe..thanks for reply. The curve between FEA and test shows a close relationship at elastic region (before yielding), less than 10% difference. Such minor error is acceptable due to the fact that the support edges during test are not rigid enough, i.e. vertical deformation at supports are allowed slightly. However, vertical displacements are totally restrained at supports in FEA. The only main and huge difference between FEA and test is the yield load. As I have mentioned before, test yield load gives around 80kN whilst FEA exhibits 180kN. Iam still wondering about this yield load difference.

 

[bkal]

Hi, could you explore what are the major and minor principle stresses in concrete at midspan at extreme fibres. What reinforcement ratio are you modelling, are you applying distributed load or concentrated forces? How many elements do yo uhave through the thickness?

 

[kellnerp]

I restrained all nodes at base only in vertical direction (u3 = 0) at the support.

Are any of these nodes common to the truss elements?

TOP
CSWP, BSSE

http://www.engtran.com

http://www.niswug.org

"Node news is good news."