- i model a beam as Over Reinforced Section (ORS), Ast > Ast,lim), using solid65, link8 and solid45 in ANSYS APDL V12, used '"MISO" property to concrete (M20) for stress strain curve, to model crack/crush the first 4 constants are give as =0.35, 0.95, 3.13 & 20. for steel i given "BISO" property. Now when i simulate up to first crack load and check the cracking pattern i observed a crack occurs at the bottom of the beam, but it is a ORS need to be crush/crack at the top surface ( for crushing failure).
- plz anyone suggest why the beam does not crush at the top fiber, instead a crack occurs at the tension fibre, is there any other way to model the ORS in Ansys APDL.
- If you have any journals/thesis did on ORS in ANSYS APDL,Plz attach to me.
- Email: [email protected]
- Thank you
First, let us define the "URA" & "ORS"
"URS" .... An under-reinforced beam is one in which the tension capacity of the tensile reinforcement is smaller than the combined compression capacity of the concrete and the compression steel (under-reinforced at tensile face). When the reinforced concrete element is subject to increasing bending moment, the tension steel yields while the concrete does not reach its ultimate failure condition. As the tension steel yields and stretches, an “under-reinforced” concrete also yields in a ductile manner, exhibiting a large deformation and warning before its ultimate failure. In this case the yield stress of the steel governs the design.
"ORS" ...... An over-reinforced beam is one in which the tension capacity of the tension steel is greater than the combined compression capacity of the concrete and the compression steel (over-reinforced at tensile face). So the “over-reinforced concrete” beam fails by crushing of the compressive-zone concrete and before the tension zone steel yields, which does not provide any warning before failure as the failure is instantaneous.
Therefore, the main difference between the "URS" & "ORS" is that large deformation is monitored for "URS" unlike "ORS"
I suggest the following
1- make two models "URS" & "ORS" to compare the deformation ... If "URS" model shows lager deformation than "ORS"...then it is fine...
2-check the capacity of the compression steel as Mohammad Alhassan highlighted... ensure that the section is really ORS. Increase the tensile RFT more and more to make the section extremely ORS to check the correctness of your model..
3-check if all the Gauss points of the soild65 (at the tension face) were cracked or only one or two Gauss points (near with the reinforcement bar) that were cracked. If only few Gauss points were cracked (near the RFT bar), then it is bond minor cracking and not full tensile cracking of the concrete as you imagine. You may use interface element between the concrete and bars to overcome this issue. Also, you may increases slightly the 3.13 value to forget about tensile cracks. As far as I remember, there are 8 Gauss points in solid65 elements. I expect that the cracks bothering you will be at those gauss points adjacent to the RFT bar. Plot the maximum principal stress for the cracked elements to check my expectation. Focus on reading the deformation .... That is better ...
Cracking starts at the tension side at a load/moment much smaller than the strength of the beam. The failure load is usually more than 3 times the cracking load. The occurrence of cracks does not mean the section is failed.
keep loading the beam and check your failure criteria to make sure that the beam still can be loaded after cracking until failure. As an ORS the concrete at the conmpression side must crush while the tension steel is below yielding. Make sure to take into consideration the influence of compression steel if any.
First, let us define the "URA" & "ORS"
"URS" .... An under-reinforced beam is one in which the tension capacity of the tensile reinforcement is smaller than the combined compression capacity of the concrete and the compression steel (under-reinforced at tensile face). When the reinforced concrete element is subject to increasing bending moment, the tension steel yields while the concrete does not reach its ultimate failure condition. As the tension steel yields and stretches, an “under-reinforced” concrete also yields in a ductile manner, exhibiting a large deformation and warning before its ultimate failure. In this case the yield stress of the steel governs the design.
"ORS" ...... An over-reinforced beam is one in which the tension capacity of the tension steel is greater than the combined compression capacity of the concrete and the compression steel (over-reinforced at tensile face). So the “over-reinforced concrete” beam fails by crushing of the compressive-zone concrete and before the tension zone steel yields, which does not provide any warning before failure as the failure is instantaneous.
Therefore, the main difference between the "URS" & "ORS" is that large deformation is monitored for "URS" unlike "ORS"
I suggest the following
1- make two models "URS" & "ORS" to compare the deformation ... If "URS" model shows lager deformation than "ORS"...then it is fine...
2-check the capacity of the compression steel as Mohammad Alhassan highlighted... ensure that the section is really ORS. Increase the tensile RFT more and more to make the section extremely ORS to check the correctness of your model..
3-check if all the Gauss points of the soild65 (at the tension face) were cracked or only one or two Gauss points (near with the reinforcement bar) that were cracked. If only few Gauss points were cracked (near the RFT bar), then it is bond minor cracking and not full tensile cracking of the concrete as you imagine. You may use interface element between the concrete and bars to overcome this issue. Also, you may increases slightly the 3.13 value to forget about tensile cracks. As far as I remember, there are 8 Gauss points in solid65 elements. I expect that the cracks bothering you will be at those gauss points adjacent to the RFT bar. Plot the maximum principal stress for the cracked elements to check my expectation. Focus on reading the deformation .... That is better ...
Pandi Mani
Regarding your massage,
Please use Etable command ... to check the crack at them (16 not cracked - 1 crushed - 2 ... - 3....)
https://www.sharcnet.ca/Software/Ansys/17.0/en-us/help/ans_elem/Hlp_E_SOLID65.html
check the image
Also, may plot the stress in the cracked element, you will find that not all the element stress >= 200 .. only near bars
Pandi Mani
Also, check the axial stress SAXL in the RFT bars....
For URS, the stress should be exceed the yield steel stress
For ORS, the stress should be less than yield steel stress
Check both the stress and the deflection.. Moreover, check the plastic strain in the RFT bars
For URS, the plastic strain should be >0
For ORS, the plastic strain should be =0
To read the axial (normal) stress and the plastic strain for link8, use Etable
To learn Etable command for link8 and plotting the stress, check the end of the following simple example
https://sites.ualberta.ca/~wmoussa/AnsysTutorial/BT/Truss/Truss.html
Best wishes
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