Hello everyone,
I am trying to make a model using ABAQUS for RC beam column joint, but I keep getting joint shear failure despite using 3 stirrups (D=8mm) inside the joint core.
Given that, the experimental specimen which I compare my model to has beam flexural failure.
May someone help me with the reason and how I can fix this issue?
Thanks in advance.
Mohamed Maher, There are a few possible reasons why you may be getting joint shear failure instead of beam flexural failure in your ABAQUS model of an RC beam-column joint:
- Insufficient joint shear reinforcement: The joint shear reinforcement (stirrups) may not be sufficient to carry the shear forces in the joint. This can be due to the number of stirrups, the size of the stirrups, or the spacing of the stirrups.
- Incorrect material properties: The material properties for the concrete and steel in your model may not be accurate. This can lead to the joint failing in shear before the beam reaches its flexural capacity.
- Incorrect boundary conditions: The boundary conditions for your model may not be correct. This can lead to the joint being overstressed and failing in shear.
- Incorrect mesh density: The mesh density in your model may not be high enough, especially in the joint region. This can lead to inaccurate results and joint shear failure.
To fix this issue, you can try the following:
- Increase the joint shear reinforcement: Add more stirrups to the joint, increase the size of the stirrups, or reduce the spacing of the stirrups.
- Check the material properties: Make sure that you are using the correct material properties for the concrete and steel in your model. You can find these properties in the literature or from your experimental data.
- Check the boundary conditions: Make sure that the boundary conditions for your model are correct. You can do this by comparing your model to the experimental setup.
- Refine the mesh: Increase the mesh density in your model, especially in the joint region. This will improve the accuracy of the results and reduce the risk of joint shear failure.
You may also want to try using a different concrete damage model in ABAQUS. The default concrete damage model in ABAQUS (the Concrete Damaged Plasticity model) is known to sometimes predict joint shear failure even when beam flexural failure is expected. There are a number of other concrete damage models available in ABAQUS, such as the Concrete Smeared Crack model. You may want to experiment with different concrete damage models to see if this improves the accuracy of your results.
I conducted a research study on 68 models ( An animation given here for a model; https://www.youtube.com/watch?v=nz9IY0FAs9w&ab_channel=CivilAcademia ), with various types of Special Moment-Resisting Frames (SMRF), Intermediate Moment-Resisting Frames (IMRF), and joints that do not conform to building codes, but unfortunately, I was unable to have it published. Attached are some results (DamageT) demonstrating the significance of the aforementioned points. Among them, reinforcement stands out as the most crucial factor.
Mohamed Maher, Based on the experimental test image you provided, the RC beam-column joint failed with flexural-shear failure experimentally, which is characterized by both beam flexure cracks and shear cracks at the joint area.
To resolve this issue in ABAQUS, you should first check the following:
Concrete dimensions: Make sure that the concrete dimensions in your model match the experimental data.
Rebar area: Ensure that the rebar area in your model is the same as in the experimental specimen.
Boundary conditions: Verify that the boundary conditions in your model are correct, including the clear distance between upper and lower column supports, the distance between the beam inflection point and column face, and the existing column axial load as it can change the failure mode.
If all of the above are correct, then you should revise your CDP model and use other CDP models, changing the CDP model parameters, especially the "Dilation angle".
The following articles may help you in revising your model and calculating the joint shear capacity:
https://doi.org/10.1177/13694332211050979
https://doi.org/10.1016/j.engstruct.2023.116497
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