Shahab Mojaddad - Masters student, Semnan Branch, islamic azad university, semnan, iran
Ali Hemmati - Assistant Professor, Department of Civil Engineering, Semnan Branch, Islamic Azad University, Semnan, Iran

The strength and ductility of concrete improve under multiaxial compressive stress. This can be done with concrete confinement technique, using steel jackets. Over the past years, several researchers have developed various stress-strain models for concretes confined with longitudinal and transverse reinforcement steel. This article presented the results from the application of a non-linear finite element method (NFEM) to a normal concrete frame, and concrete frames confined via confinement models developed by various researchers. The effect of the stress-strain models proposed by these researchers on linear and non-linear behaviors of the concrete frame, crack pattern of all models, and ductility parameter of the frames were discussed. Laboratory findings of a concrete frame were selected, and its aforementioned parameters were examined after the calibration of the numerical model and ensuring the validity and accuracy of the findings. Finally, the pushover curves of all models were plotted and compared. Then, the crack patterns of all models were interpreted and ductility parameters were computed. Results from the finite element method (FEM) showed that all pushover curves obtained from the finite element analysis had a linear behavior similar to the validated and laboratory models. Among the obtained pushover curves, models developed by Mander et al. (1988), and Saatcioglu and razvi (1992) had the highest conformity with both the calibrated and laboratory models. The reason behind this conformity was that these researchers considered all effective parameters in developing their stress-strain models.

Stress-Strain Curve Model, Longitudinal Steel, Transverse Steel, Ductility, Crack Pattern