Experimental parameter calibration, uncertainties propagation and parameter sensitivity of a phenomenological model for elastomeric bearings

Abstract eng:
Elastomeric bearings are among the most used seismic isolators, and the considerably grown number of applications in recent years witnesses the confidence of the modern engineer with such design approach. On the other hand, recent full-scale experimentation of isolators has focused the attention to unexpected collapses, basically due to: (i) the influence on the device response of a number of factors usually not considered in the current state of practice, (ii) scale effects, (iii) assemblage effects, (iv) the unavoidable percentage of random variations in mechanical characteristics. All of the above considerations highlight the importance of a proper assessment of the isolator response, and above all of the investigation of its behavior variability due to the presence of internal non-homogeneities. Some rubber layer often appears to be subjected to high deformations and can be unevenly damaged, modifying the global stress distribution. This phenomenon is due to both the tilting of the middle bearing layers when the bearing is deformed in shear and to the small variations of mechanical characteristics and geometric imperfection of the steel and rubber layers. Such variations, which may localize high deformations, are ascribable to the operating conditions and/or to the manufacturing dispersion, and thus appearing random in nature. Within the current endeavor, a phenomenological model has been developed able to reproduce the force-deformation state of each layer of the device, which may constitute the base for a probabilistic modeling of the isolator, simulating the uneven random distribution of mechanical characteristics within the isolator itself. The proposed model includes geometric nonlinearities in the formulation and material nonlinearities in the layers constitutive laws, defined by a number of parameters which are calibrated coupling a system identification approach and a global sensitivity analysis in the interpretation of the experimental test results on full-scale bearings carried out at the EUCENTRE TREES Lab of Pavia (Italy).

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