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FEA
RC beam nonlinear with Mohr-Coulomb
Hi,
I'm modelling a reinforced concrete beam in 4 point flexure testing and comparing fem with experimental results. It's just a simple modelling because I'm still learning fem (I must include stirrups and improve force, constrains and mesh conditions, among other things...).
EXPERIMENTAL BEAM: 70x140x1200mm rc beam containing 2 steel rebars (12,5mm each) in the tension zone. Rupture occured at 36kN with crushed concrete in compression zone between the applied load.
MODELLING: embedded steel reinforcement; concrete compression-only material (parameters in mecway file attached); nonlinear 3d analisys (parameters in mecway file attached); fyk=500MPa (equal to experimental value); fck=30MPa (equal to experimental value); Mohr-Coulomb (MC) parameters: T1=1MPa (asssumed), T3=-30MPa (adapted from mecway: 29,775MPa measured in top center node), phi=30degrees (assumed), fck=30MPa
I' m considering this for the results analisys:
1- The von Mises effective stress is compared to the material yield stress for steel. Failure in steel rebars is predicted
to occur when the von Mises value reaches the yield stress.
2 - The MC stress is is compared to the material compressive strength for concrete. Failure in concrete is predicted
to occur when the MC value in compression zone reaches compressive strength.
3- The 1st principal stress (T1) gives the maximum tensile stress induced in the beam due to the loading conditions; The 3rd principal stress (T3) relates to the maximum compressive stress due to the loading conditions.
4 - Safety factor (SF) for ductile materials = Yield strength/(higher value between Von Mises and T1)
Safety factor for brittle materials = Compressive strength/(higher value between MC in compression zone and T3)
CONCLUSIONS FROM THE MODELLING: at 36 kN steel rebars are still ok (SF=500/213,5=2,34); T3 exceed fc so concrete crushes in compression zone between the applied load. Maximum displacement (2,85mm at rupture load) is not ok with experimental results (4,0mm measured at 30kN).
(As a side note: if I remember correctly it was reported in calculix that compression-only material is ok for stresses moddeling but not good for displacements).
It seems coherent to me in terms of stresses but I'd like an expert opinion...
Best regards
I'm modelling a reinforced concrete beam in 4 point flexure testing and comparing fem with experimental results. It's just a simple modelling because I'm still learning fem (I must include stirrups and improve force, constrains and mesh conditions, among other things...).
EXPERIMENTAL BEAM: 70x140x1200mm rc beam containing 2 steel rebars (12,5mm each) in the tension zone. Rupture occured at 36kN with crushed concrete in compression zone between the applied load.
MODELLING: embedded steel reinforcement; concrete compression-only material (parameters in mecway file attached); nonlinear 3d analisys (parameters in mecway file attached); fyk=500MPa (equal to experimental value); fck=30MPa (equal to experimental value); Mohr-Coulomb (MC) parameters: T1=1MPa (asssumed), T3=-30MPa (adapted from mecway: 29,775MPa measured in top center node), phi=30degrees (assumed), fck=30MPa
I' m considering this for the results analisys:
1- The von Mises effective stress is compared to the material yield stress for steel. Failure in steel rebars is predicted
to occur when the von Mises value reaches the yield stress.
2 - The MC stress is is compared to the material compressive strength for concrete. Failure in concrete is predicted
to occur when the MC value in compression zone reaches compressive strength.
3- The 1st principal stress (T1) gives the maximum tensile stress induced in the beam due to the loading conditions; The 3rd principal stress (T3) relates to the maximum compressive stress due to the loading conditions.
4 - Safety factor (SF) for ductile materials = Yield strength/(higher value between Von Mises and T1)
Safety factor for brittle materials = Compressive strength/(higher value between MC in compression zone and T3)
CONCLUSIONS FROM THE MODELLING: at 36 kN steel rebars are still ok (SF=500/213,5=2,34); T3 exceed fc so concrete crushes in compression zone between the applied load. Maximum displacement (2,85mm at rupture load) is not ok with experimental results (4,0mm measured at 30kN).
(As a side note: if I remember correctly it was reported in calculix that compression-only material is ok for stresses moddeling but not good for displacements).
It seems coherent to me in terms of stresses but I'd like an expert opinion...
Best regards
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Comments
First of all, congratulations for the job done.
I downloaded your model and I have realised that gravity should be add (even having a neglectable effect in vertical deformations).
Another point, if you temporally substitute the parameter s1 for 0 in your formula(MC stress), you will get a nicer plot of concrete stresses. You will check out the concrete solid easier and faster. You will notice that the concrete is about to crunch over the top of the beam amid the nodal loads(29MPa-30MPa).
MANUEL
Thanks a loto for your feedback. Your help has been really greatful and useful.
I'll try your sugestions for this case and soon I'll post the updated results.
Best regards,
Jacinto
I cannot wait to see the new results!!
MANUEL
I've done some changes in Mecway (added self-weight and changed mesh) and considered one more tested beam (experimental). I've attached the mecway files.
Results:
EXPERIMENTAL four-point bending flexural test: rc beam 1 failed at 32kN; rc beam 2 failed at 36kN.
MECWAY (considering applied force as previously plus self-weight)
A ) Coarse mesh ("rev" filename)
ymax=-2,87mm
S3=-30,31MPa
Failure between 35kN and 36kN
B ) Refined mesh ("refined" filename)
ymax=-3,32mm
S3=-36,49MPa
Failure between 30kN and 35kN
So, in this case mesh refinement seems to be important (failure and maximum deflection more "accurate").
What do you think?
Best regards