## Compute the compressive strength of confined concrete

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parasismique
Posts: 56
Joined: Tue Dec 13, 2016 7:14 am
Location: University of Tlemcen-Algeria

### Compute the compressive strength of confined concrete

Dear all,

I’m trying to validate a fibre FE model that analyse the cyclic pushover response of 415 RC column of Lehman et al. . In a general way, I followed the modelling strategy proposed by Wang et al. .
To model the confined concrete, I used Mander et al. model  to compute the compressive strength given by eq. 29. The obtained value is equal to 42 MPa, which gives ɛcc of 0.66% and ɛcu of 1.56%.
Strangely, the obtained values are different to that obtained by Wang et al.  (compressive strength of 61 MPa and ɛcc of 1.36% and ɛcu of 1.85%).
Moreover, the FE model does not work in OpenSees when using my values!
The MATLAB script used to compute the compressive strength of confined concrete is given bellow.

 D. Lehman, J. Moehle, S. Mahin, A. Calderone, and L. Henry, “Experimental Evaluation of the Seismic Performance of Reinforced Concrete Bridge Columns,” J. Struct. Eng., vol. 130, no. 6, pp. 869–879, 2004.
 Z.-H. Wang, L. Li, Y.-X. Zhang, and S.-S. Zheng, “Reinforcement model considering slip effect,” Eng. Struct., vol. 198, p. 109493, 2019.
 J. B. Mander, M. J. N. Priestley, and R. Park, “Theoretical stress-strain model for confined concrete,” J. Struct. Eng, vol. 114, no. 8, pp. 1804–1826, 1988.

The matlab script:
% Compute of Compressive Strength of Confined Concrete, f'cc by Mander eq
%f'cc=f'c0(-1.254+2.254*sqrt(1+((7.94*f'l)/f'c0))-2*f'l/f'c0)
s=0.032; %spacing (Column Lehman 415)
Dcol=0.6096;
cover=0.03302;
dbar=0.01588;
dbarT=0.006;
fyh=607;
numBar=22;
Hcol=2.44;
fc0=30.3; % f'c0: unconfined concrete compressive strength
%Vcore=Score*Hcol
%-------------------------------------------
% Ke coefficient given by eq. 14 or 15
% s : center to center spacing or pitch of spiral or circular hoop
% s': clear vertical spacing between spiral or hoop bars
% s : spiral spacing or pitch
s1=s-dbarT;
% ds: diameter of spiral between bar centers
ds= Dcol-2*cover-dbarT;
% Rhocc : ratio of area of longitudinal reinforcement to area of core of section
%------
% Acc: the area of concrete core eq.12
% Area of longitudinal reinforcement
Areinf=(pi*dbar^2)/4*numBar;
% Effectively confined core Diameter (fig.2)
DeffCore=ds-s1/2;
% Ae : the area of an effectively confined concrete core eq. 12
%Ae=(pi/4)*ds^2*(1-(s1/2*ds))^2;
Ac=(pi*ds^2)/4;
Rhocc= Areinf/Ac
% spiral spacing or pitch
Ke=(1-(s1/2*ds))/(1-Rhocc)
%--------------------------------------------
% RhoS: ratio of the volume of transverse confining steel to the
% volume of confined concrete core eq.17
%----------
% Asp: area of transverse reinforcement bar (Formule of Tore in google)
% Asp=4*pi^2*(dbarT/2)*(Dcol/2-cover-dbarT/2);
Asp=(pi*dbarT^2/4);
RhoS=(4*Asp)/(ds*s)
%--------------------------------------------
% fyh : yield strength of the transverse reinforcement
%--------------------------------------------
% f'l: lateral confining pressure on concrete
% f'l is given by eq. 19
f1l=1/2*Ke*RhoS*fyh
%---------------------------------------------
% fc0: Compressive Strength of unconfined Concrete (Experimental value)(MPa)
% Compute of Compressive Strength of Confined Concrete, f'cc (eq. 29)
ratio=(-1.254+2.254*sqrt(1+(7.94*f1l)/fc0)-2*f1l/fc0)
fcc=fc0*ratio