PSI - Issue 78

Laura Ragni et al. / Procedia Structural Integrity 78 (2026) 2094–2101

2101

It should be noted that the initial lost displacement decreases as the velocity increases and that the system tends to oscillate around its initial position. The latter case is very close to the ideal case, but a such a flow rate (500 l/m) can not be available outside a laboratory. More expensive systems compared to those used in the tests described in this article can reach flow rates of 50 l/m or 100 l/min, and in rare cases, up to 200 l/min. Obviously, the obtained velocity values turn depend on the pushing forces and thus on the building dimensions. For smaller buildings with a fewer number of bearings and/or bearings with smaller dimensions, higher velocity values would be obtained for a

given flow rate. 4. Conclusions

This article presents an overview of push-and-release tests conducted on a strategic base-isolated building, along with type tests on HDRBs following European seismic standards. Viscous effects were observed and analyzed in detail, then a simple linear viscoelastic model was proposed to interpret the results. Initially, the model was calibrated using type tests on a single HDRB, then extended to simulate in-situ tests by incorporating all elastomeric bearings and slider friction. Key conclusions include: • The model accurately predicts lost displacement during slow loading and the residual displacement due to friction, confirming the minimal long-term drift in hybrid HDRB systems with low-friction sliders. • Simulations with faster loading ramps showed reduced lost displacement and larger oscillations, allowing estimation of isolation period and damping. • For small buildings, high loading velocities can be achieved with standard hydraulic systems. For large buildings, like the CHIP building, achieving similar velocities requires costly equipment. However, the model allows for post-test interpretation using affordable systems. In conclusion the article provides a tool to interpret in situ push and release tests, that are a cost-effective and realistic method to assess performance of the entire isolation system (100% of devices ), thereby verifying that the system meets design expectations. Acknowledgements The financial support for these tests provided by the Italian Department of Civil Protec-tion is gratefully recognized. For the interpretation of tests, partial financial support was re-ceived by the Italian Department of Civil Protection, within the ReLUIS projects 2024-2026. References Athanasiou A. Dynamic identification of the Augusta hybrid base isolated building using data from full scale push and sudden release tests. Ph.D. Dissertation. Italy: University of Catania; 2015. Braga F, Laterza M. Field testing of low-rise base isolated building. Engineering Structures, 2004;26(11):1599-1610. Dall’Asta A, Ragni L. Experimental Tests and Analytical Model of High Damping Rubber Dissipating Devices, Engineering Structures 2006, 28(13):1874-1884. Dall’Asta A, Leoni G, Micozzi F, Gioiella L, Ragni L. A resilience and robustness oriented de-sign of base-isolated structures: The New Camerino University Research Center. Fontiers in Built En-vironment. 2020;6(1):50. Dall'Asta A., Leoni G., Gioiella L., Micozzi F., Ragni L., Morici M., Scozzese F. and Zona A. Push-and-release tests of a steel building with hybrid base isolation, Engineering Structures 2022, 72,114971. De Domenico D., Losanno D., Vaiana Experimental tests and numerical modeling of full-scale unbonded fiber reinforced elastomeric isolators

(UFREIs) under bidirectional excitation. Engineering Structures, 274 (2023) 115118. DM 17 gennaio 2018. NTC 2018: Norme Tecniche per le costruzioni (in Italian), 2018. EN 15129:2009 Anti-seismic devices, European Committee for Standardization, Brussels, 2009.

Tubaldi E, Ragni L, Dall’Asta A, Ahmadi H, Muhr A. Stress softening behaviour of HDNR bearings: modelling and influence on the seismic response of isolated structures: Stress Soften-ing Behaviour of HDNR Bearings. Earthquake Engineering & Structural Dynamics 2017.