PSI- Issue 9

Riccardo Fincato et al. / Procedia Structural Integrity 9 (2018) 136–150 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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The structure is subjected to two types of loads: a compressive load P , constant, and kept for the whole duration of the experiment and a horizontal load H , directed along the x direction and with an increasing amplitude. The idea of Nishikawa et al. was to reproduce the conditions of a seismic solicitation hitting a bridge pier, where P represented the dead load of the infrastructure over the steel column and H represented a simplify shock wave. The magnitude of P was set to be 0.124 the squash load P y . The parameters H y and δ y in Table 1 represent the horizontal load and horizontal displacement when the specimen yields close to the base.

a)

b)

Figure 2 a) Model and geometry of the bridge pier, b) loading sequence for the model calibration.

Table 1. Structural parameters of the specimen. h

3,403 [mm] 8.70 [mm] 891.3 [mm]

t

D

P/P y

0.124

H y δ y

414.9 [kN]

10.5

3.2. The material parameters calibration

The DSS requires the calibration of 13 parameters for the elastoplastic behavior and 4 material constants for the definition of the MC failure envelope. Few material parameters, such as the Young’s modulus, Poisson’s ratio and the yield stress were assumed directly from Nishikawa’s experimental work. The remaining constants were calibrated minimizing the difference between the numerical and experimental curves obtained in uniaxial tensile tests in (Goto et al., 2010; Van Do et al., 2014). The results of the calibration are reported in the Figure 3 whereas Table 2 and 3 report the values of the parameters. The four constants R e , u , c and χ in Table 2 are proper of the subloading surface model. They regulate the amount of plastic deformation generated in the sub-yield state, the details are available in Hashiguchi (2009) and in Tsutsumi et al. (2006). The characterization of the MC criterion cannot be done by using the experimental results from one single test (i.e. uniaxial extension) since a unique definition of the failure envelope requires at least few points in the   , , f    space. Therefore, the ductile damage parameters were preliminary set for the uniaxial tensile test and then adjusted to fit the pier behavior. The blue curve in Figure 3 represent the final stage of calibration obtained after the adjustment of the damage parameters in the pier analyses. As it can be seen the FE simulation overestimate the material performances reported by Van Do et al. (2014), however the blue curve seems to be in good agreement with the results reported in Goto et al. (2010) for the SS400 steel. Moreover, the authors run some numerical analyses fitting the uniaxial curve in Van Do et al. (2014), however, the subsequent analyses on the pier sample gave an unsatisfactory