Browsing by Author "Restrepo, José I."

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    A numerical model for non-linear shear behavior of high damping rubber bearings
    (Elsevier SCI LTD, 2023) Gallardo Briones, José Alberto; Llera Martín, Juan Carlos de la; Restrepo, José I.; Chen, Michelle
    The dynamic behavior of isolated structures is strongly controlled by the force-deformation constitutive behavior of the isolators. Among the different types of existing isolation devices, High Damping Rubber Bearings (HDRBs) are commonly used in practice, which behavior is highly non-linear and difficult to model analytically. Consequently, this article proposes a simple, but sufficiently accurate, mathematical model for simulating the non-linear shear behavior of HDRBs under large deformations, and an estimation procedure for its parameter values using the geometrical features and mechanical characteristics of the device. First, we briefly describe the phenomena observed in the experimental test data, as well as other phenomena not observed within the range of experimental deformations. Then, the mathematical formulation is presented, which is based on the consideration of two components connected in parallel, a hyperelastic spring and a dissipative component. The governing equation for the former is derived from the expanded formulation of the Mooney-Rivlin model for isotropic hyperelastic materials, and the latter from a Bouc-Wen model with hardening. A novel model is included to account for stiffness degradation, including scragging and Mullins effects, which is developed from experimental data of 924 tested devices. The proposed model fits well the experimental test results of HDRBs with different geometric features and material properties. Based on the evolution laws for the different variables, the model can be successfully used in structural dynamic analysis. To facilitate model calibration, a statistical estimation procedure is proposed to reduce the 17 force- deformation constitutive model parameters of the isolator to 9 unknown parameters, which are computed from the geometric features of the device and mechanical characteristics of the rubber material. This makes the calibration of the force-deformation constitutive model parameters feasible. The estimation procedure successfully predicts the behavior of an average device within a batch of HDRBs, showing good agreement with two different experimental datasets.
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    Modeling the Multiaxial Behavior of High Damping Rubber Bearings (HDRBs)
    (2025) Gallardo Briones, José Alberto; Chen, Michelle C.; Restrepo, José I.; Llera Martin, Juan Carlos de la
    The dynamic behavior of seismically isolated structures is governed by the force-deformation response of the isolation devices.Consequently, significant efforts have been made to accurately simulate the behavior of different types of devices. High dampingrubber bearings (HDRBs) are among the most widely manufactured and used isolators in practice. Given the internal structureof these devices and the characteristic behavior of the rubber compound, HDRBs show highly nonlinear behavior with strongcoupling between deformation directions, which is challenging to simulate numerically. Capturing these complex multiaxialinteractions is essential for reliably predicting device behavior and ensuring the dynamic stability of the isolation system duringseismic events, therefore, a holistic multiaxial modeling approach is critical. This study presents a robust and sufficiently accuratenumerical model for simulating the multiaxial behavior of HDRBs under large deformations. This elaborate model includes:bidirectional shear response that accounts for stiffness degradation with load-direction dependency, including scragging (long-term degradation) and Mullins effect (short-term degradation), and temporary hardening; coupling between axial and shearresponse, including axial stiffness softening due to lateral displacement and shear stiffness variability due to axial load variation;axial instability due to large compressive loads; and cavitation under tensile forces. The proposed model is validated usinga wide range of load patterns applied to an HDRB, as well as experimental results from the literature. The proposed modeldemonstrates good agreement with experimental data, accurately simulating HDRB responses across diverse validation tests, including double bidirectional shear tests in rotated directions, cyclic shear response under different axial loads, tensile loads,bidirectional deformation history with an elliptical orbit, extremely large deformations (beyond the design limits), and dynamicanalyses. The results show that the model provides reliable predictions of the static and dynamic behavior of HDRBs underdifferent load patterns, including deformations until the onset of failure. The proposed model has been implemented in OpenSeesand is openly available at the supplementary repository https://github.com/JAGallardo1992/HDRB_model