FRP Confinement Factor

[anantparghi]

Hi There,
To calculate the confinement factor using SeimoStruct, for FRP confined circular section, we need to provide the Jacket thickness (m), FRP elastic modulus (kPa) and Jacket strain.

I am modeling RC circular column (400mm Dia.) with 1, 2, 3 and 4 layer of CFRP and GFRP composites under reverse cyclic load and constant axial load. The CFRP and GFRP composites have an initial stiffness of 266 GPa and 19.13 GPa, and an ultimate strain of 1.63% and 1.80%, respectively.
In the attached excel sheet all the information is give.
https://drive.google.com/file/d/0B3tbcU ... sp=sharing

I would like to keep the same confinement ratios of 0.11, 0.22, 0.33 and 0.44 % and the same confinement pressure of 1.2, 2.4, 3.6 and 4.8 MPa) for CFRP and GFRP jacket, respectively.

For these situation, the CFRP thickness will be same like 0.00011m, 0.00022m, 0.00033m and 0.00044m and to keep the same confinement pressure of the GFRP jacket, I changed the thickness of GFRP jacket of 0.00141m, 0.0028m, 0.00419mm and 0.00559mm. So, now by this different thickness and different materials properties the CFRP and GFRP jacket the confinement pressure and ratio will be the same.

My question is that, if I am entering different thickness and different materials properties of CFRP and GFRP composites, then why the SeismoStruct confinement factor is same? (Logically, GFRP modulus is 19.13 GPa and strain 0.018, and CFRP modulus is 266 GPa and strain 0.0163, and due to higher thickness and higher strain of GFRP the confinement factor might be same?). However, due to the same confinement factor the analysis results will not be change weather it is CFRP of GFRP materials. (Even, I changed the thickness of GFRP). Therefore, I would request you, anybody could please through the idea, I am doing right or wrong ?
Thanks
Anant

[z.gronti]

Dear anantparghi,

Please check if the assigned values are in the correct units. For example the FRP elastic modulus should be assigned in kPa, that is 266000000kPa for CFRP and 19130000kPa for GFRP.

[anantparghi]

Hi Gronti,
Thank you very much for your kind reply. I already verified the units, please see the attached screenshot. https://drive.google.com/file/d/0B3tbcU ... sp=sharing
I am getting same confinement factor for CFRP thickness = 0.000111mm, Elastic modules = 266000000 kPa, and strain = 0.0163

GFRP thickness = 0.0014, Elastic modules = 19130000 kPa, and strain = 0.018.
The confinement factor is almost same. (i. CFRP = 1.4694, and GFRP =1.4700). So in cyclic time history analysis there is not change in stiffness or ductility.
Thanks
Anant

[z.gronti]

Dear anantparghi,

The reason that the confinement factor has the same value for the two different FRP, is because you have chosen their thickness so that you get the same confinement pressure. If you apply the same confinement pressure you will get the same confinement factor, according to no.29 equation given in Mander et al.[1989] paper for the calculation of the section's confinement factor.

[anantparghi]

Hi Gronti,
Thank you very much for your reply. I do agree with your comments which I was also thinking. But, I like to make sure that i ma doing right things.
Thanks
Anant