Issue 47

R. Fincato et alii, Frattura ed Integrità Strutturale, 47 (2019) 231-246; DOI: 10.3221/IGF-ESIS.47.18 240 Figure 4: Calibration of the material parameters of the DSS on a uniaxial tensile test. a) b) Figure 5: Hysteresis loops for the thin steel pier a) without damage, b) with damage, evolution laws of Eqn. (13) P-D law and Eqn. (15) NP-D law. Fig. 5b shows the effect of the tangential plasticity contribution on the hysteresis loops for the pier, as a consequence of the ductile damage acceleration. The green line refers to the ductile damage evolution of Eqn. (13), the acronym used in the legend P-D stands for proportional damage law, in contrast with the blue line, obtained with Eqn. (15), where the acronym NP-D stands for non-proportional damage law. As it can be seen the green line does not reproduce correctly the experimental results in the last cycles. However, a different calibration of the damage parameters focused to improve the pier behaviour description in the last part of the analysis, led to an underestimation of the material performances in the modelling of the monotonic uniaxial tensile test and in the description of the first five cycles of the column analysis. On the other hand, the solution carried out with a non-proportional damage law is able to catch a realistic hysteresis behaviour of the pier and at the same time to be in good agreement with the experimental results of the tensile test. The difference between the P-D and the NP-D laws can be observed in Fig. 6 where the value of the horizontal load is reported in correspondence of the unloading points. Both the green and blue lines seem to overestimate the elastic response of the structure, however, the difference can be considered as acceptable. The peak is well described in the load envelope of the positive side of the lateral displacements, whereas there is an overestimation of about the 10% of the peak load at the third loading cycle in the negative envelope. The post-peak behaviour described by the NP-D law is in very good agreement with the experimental data.