I'm modelling a RC beam structure using LSDYNA. I want to include the rebar bond-slip relation in the model. The *CONTACT_1D has different parameters, such as Bond Shear Modulus GB, Maximum shear strain displacement SMAX, and Exponent in Damage Curve EXP.
- Are there any recommended values backed up from your experience ? Any guidance through the calculation of those parameters ? I read few literature and they refer to FIB Model Code for Concrete 2010, clause 6.1.1 and Table 6.1-1. But no any clue regarding relating those to GB, SMAX, or EXP. And also, what are the units for each? Is it MPa or MPa/mm for GB ? mm or unitless for SMAX ? Because I came across both units in some literature.
- Is it a must to have mesh conformity between rebar and concrete to implement a correct *Contact_1D ?
Hi Muhanned,
Am not experienced in LSDYNA, however in general those parameters could be obtained either by fracture mechanics based models or empirical models which are directly derived from pull out experimental test data through strain gauges and equilibrium equations of the bond interface. I believe there are many research articles and references online that contain pull-out bond slip models. for example as a start you can check the link below for a couple of pullout bond slip papers.
Article Influência da adição de fibras de aço na tensão de aderência...
Conference Paper 3d finite element modelling of bond-slip between rebar and c...
Thanks Ahmed Mirghani , appreciated.
I checked several research articles addressing bond-slip relationship based on experiments, yet the parameters used in LSDYNA differs a bit from the experimental ones. It's more correlated to mathematical expressions. Particularly for the shear strain modulus (since most articles discussed axial pull-out strain). It turns out that other parameters can be obtained through curve fitting in the numerical model; no specific values to be recommended. But I will research it more. Thanks again for passing through, Ahmed.
Hey Muhannad Husain
My answer >
According to some researchers they take the pull out testing values that are available as literature source for bond shear modulus, the max elastic slip and damage co-efficient.
Please contact in my email id ([email protected])for such literature.
1. How do you give the bond stress slip values? And what parameters are you presently using for Contact_1D (GB , Smax, EXP ) would you please enlighten ?
2. How do you will to set the bond relationship between Reinforcement and concrete ? CLIS or ACNC or BIS or linkage elements ?
I am also working on something like this, may be we can help each other.
Hi Abhirup Bhattacharjee ,
Thanks for your cooperation, will email you soon.
Regarding your inquiries:
1- You can find the bond stress value from the FIB Model Concrete Code 2010, table 6.1 for ribbed deformed bars (according to the interface bonding condition). From the same table you can find Smax. For GB, You may then simply use the formula Smax=Bond Stress/GB. Note that it's unit sensitive. EXP is case dependent, no recommended values given the fact that it's often used to fit your curve based on trial approach.
2-For the rebar coupling in concrete, you may use *CLIS. Recent versions of LSDYNA solvers recognize *CBIS (shown slightly better results). So far, I haven't dealt with ACNC or BIS. If you're interested in rebar coupling, you may check Len Schwer's article entitled "Modelling Rebar: The forgotten sister in RC" (https://www.dynalook.com/13th-international-ls-dyna-conference/constitutive-modeling/modeling-rebar-the-forgotten-sister-in-reinforced-concrete-modeling). Will publish one article soon addressing same topic with focus on prestressed tendons coupling, if you're interested may notify you once it's available.
Cheers!
Hello @Muhannad,
How is you experience with the Contact_1D parameters.
For my RC beam with point load, it is giving me very poor and wrong results. I've attached a .k file and a movie from the results showing eff. plastic strain.
Any key pointers would be really appreciated.
Hi Abhirup Bhattacharjee ,
After briefly checking your k file, I came out with the following:
1-For rebars coupling, I noticed you employed two different coupling approaches for the same part of rebar, which is incorrect. You shall only stick to one coupling methodology for a rebar element; never couple with CLIS and CBIS altogether.
2-For the *CONTACT_1D, your definition for the master nodes shall include only concrete nodes whom the rebar nodes are connected to; defining the whole concrete part nodes as master nodes is conceptually flawed. Kindly refer to the attached figure.
3-Again for *CONTACT_1D, are you sure about your input parameters? especially ERR (too large). Usually it is just a fraction. Re-check and refer to this article:
"Bond slip modelling and its effect on numerical analysis of blast-induced responses of RC columns", Yanchao Shi, Structural Engineering and Mechanics, Vol. 32, No. 2 (2009)
4-What kind of loads your beam is subjected to? If it's an ordinary service loading, you may set the LOAD_CURVE to reach its full magnitude in a very short time period (say, from 0.00 to 20.00) and then maintaining its magnitude until the solution terminates.
5-The UNITS defined in the CSCM_CONCRETE must comply with the units in the whole model inputs. Re-check again.
6-You may add a CONTROL_TIMESTEP
7-It's better to have INTOUT & NODOUT=STRESS in the EXTENT_BINARY card.
Employ all of the mentioned comments in your model, hopefully it's gonna give better results.
Regards,
Again once again, lots of appreciation for your prompt response and the time Muhannad Husain
1. But, How do you manage to write the scripts for Beam in solid relationship for including the bond slip relationships? by using Define_Function ?
If yes, do you know of any good literature showing it ?
2. For using Lagrange_in_solid, how do you geometrically select the master nodes which are well inside the model? I mean how do you see through your cross section and mark the nodes explicitly?
Thanks in Advance.
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