Analytical modeling of shear modulus evolution in seismic isolation elastomeric bearings of in-service buildings based on accelerated aging tests

Introduction. Changes in the physical and mechanical properties of rubber bearings during service life represent one of the key factors affecting the efficiency and long-term performance of building seismic isolation systems.

Aim. In this context, the development of analytically justified relationships based on experimental aging data, enabling quantitative assessment of shear modulus variation over the design service life of rubber bearings, constitutes an important scientific task.

Materials and Methods. Based on experimental data obtained from accelerated thermal aging tests of rubber bearings and the time–temperature superposition principle according to the Arrhenius model, the shear modulus was determined for each equivalent service life. The experimental results were subsequently subjected to analytical processing, and an approximating function describing the evolution of the relative shear modulus over time was derived. The parameters of the proposed function were identified using nonlinear regression techniques, followed by statistical evaluation of the goodness-of-fit.

Results. It was established that the variation of the shear modulus of rubber bearings during aging represents a nonlinear process that can be described by a monotonic exponential function of asymptotic type. This function reflects the kinetics of elastomer degradation, characterized by an intensive increase in shear modulus at the initial stage of aging, followed by a transition to a regime of gradual change as thermo-oxidative processes become depleted. The analysis shows that, for an equivalent service life of 50 years, the shear modulus increases by more than 28 % compared to its initial value. The obtained analytical approximation demonstrates a high coefficient of determination and low statistical error values, confirming the adequacy of the selected analytical representation of the experimental data.

Conclusions. An approach to constructing analytical approximating functions describing the evolution of the shear modulus of rubber bearings based on a limited set of accelerated aging test data is proposed. The implementation of this approach enables quantitative assessment of shear modulus variation during service life and may be applied in the evaluation of the long-term performance of seismic isolation systems, as well as in technical condition assessment and residual service life prediction of rubber bearings.

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