Hello everyone, i am trying to simulate experimental load-deflection curve of a reinforced concrete beam from literature with an analytical procedure using strain compatibility method.
I assume an initial strain at the extreme compression fibre of the RC beam and with the help of similar triangle concepts corresponding stress,strain in rebar, concrete bottom layer will be evaluated, moment and load are calculated using obtained stress multiplied by corresponding lever arm. The deflections are calculated by Branson's equation. My problem is that analytically obtained load-deflection curves does not match with the experimental curve available in the literature as seen in the attached picture. What could have been possibly gone wrong?
Can someone please help me?
Thank you in advance.
Best Regards
Naveen
Hi Naveen,
I do not really see a reason why they should look the same. Your calculations involve a huge number of approximations. I can name for example the concrete constitutive model used, the loading step, the method for integration of stresses along the section and many others. Even if you use an FEM model, you will probably not get the exact same curve depending on the type and size of your mesh elements.
I would advise to check the following reference:
https://www.scielo.br/scielo.php?script=sci_arttext&pid=S1983-41952017000200415
Best regards,
Dear Aziz Sakr
Thank you very much for your explanation, i get it. I will go through the reference.
Thank you again.
Best Regards
Naveen
Hi, Naveen Revanna
Do one thing plot experimental data with non linear form in graph plotting their is option of that then see or compare your results.
Hi Souraj Gupta
Thank you very much for your response. I will try it.
Best Regards
Naveen
This depends on several factors:
1- What is the software program used in theoretical analysis?
2 - Specifications of the materials entered in the theoretical analysis, and was there an testing and calibration thereof before the process of analyzing the beam? By noticing the two curves you have, I notice that there is a clear difference from the beginning of the behavior of the two models, and this means that there is a defect in the specifications of the material inputs to the software program.
3 - There are some things and errors that occur during reading the experimental test, which may affect the process of comparison with theoretical results.
check this reference, may be it will be helpful
https://www.scielo.br/scielo.php?script=sci_arttext&pid=S1983-41952017000200415
Try to create a non-linear model of the RC beam using the same constitutive realationships of the concrete and steel reinforcement as the experimental data. Then, the load-deflection curve will be approximately identical with the experimental one. Namely, create a non-linear model by inserting fiber hinges (with the appropriate constitutive material laws) at the end-sections of the RC beam and perform a non-linear static analysis.
Dear Alaa al-Habbobi
Thank you very much for taking time to present your inputs, my calculations were carried out using Excel software, iterations were carried out manually using Excel Solver.
No calibration was attempted, Hognestad's stress-strain equation was used to to calculate compression force along with alpha and beta as calculated in some technical papers. Forces in concrete, top compression,tensile reinforcement were equated to obtain Neutral axis depth for every strain value at the extreme compression fibre, corresponing deflections were calculated for every strain increment with the help of modified Branson's and Bischoff's equation.
Dear Athanasios Bakalis
Thank you very much for your time and input on this question.I have understood it, could you please share an article on the procedure you have described?
Thank you.
Dear Athanasios Bakalis
Am very thankful for your instantaneous reply. Thank you for the reference sir.
Best Regards
Naveen
Hello Naveen Revanna,
coud you send me the details of your beam, section, reinforcement, material specifications and a sketch of your mathematical model?
Best regard,
Héctor Urrrego
Dear Naveen Revanna,
I would recommend you to use in this particular case of a reinforced concrete beam the Degrading Trilinear Hysteresis Model.
Prof. Mikayel Melkumyan
Urrego Hector , Excuse me for responding late, could you please share your email?
Best Regards
Naveen
Respected Mikayel Grigor Melkumyan
Thank you for your response, i will read the concepts of the model.
Best Regards
Naveen
@Naveen Revanna . Can you share me your research topic or your setup to analysis that deflection?
Dear Souraj Gupta , Could you please share your email ID?
Best Regards
Naveen
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