Material Model Parameters for the Giuffrè-Menegotto-Pinto Uniaxial Steel Stress-Strain Model

The uniaxial Giuffrè-Menegotto-Pinto (GMP) constitutive steel model is widely used in nonlinear modeling of reinforced concrete components. However, the parameters characterizing this constitutive law are not easily identifiable from mechanical tests. An extensive literature review showed that most authors use the parameter values recommended during the early development of this constitutive model. Therefore, a calibration of the model parameters to steel manufactured in accordance to modern standards represents an important contribution to researchers and engineering professionals. A series of cyclic stress-strain tests were performed on 36 reinforcing steel Grade 60 coupons. To obtain data about statistical variability, the bar specimens were sourced from three different manufacturers. The test results were used to calibrate the model parameters, which were then verified using a set of validation reversed cyclic stress-strain tests. The strain-rate effects were analyzed using equivalent cyclic coupon tests at rates of 0.001/s and 0.02/s. The final calibration results are presented in terms of recommended model parameters for Grade 60 steel reinforcement complying with two commonly used standards.