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PROCEEDINGS OF THE FIFTEENTH INTERNATIONAL CONFERENCE ON CIVIL, STRUCTURAL AND ENVIRONMENTAL ENGINEERING COMPUTING
Edited by: J. Kruis, Y. Tsompanakis and B.H.V. Topping
The Effect of a Grouted Isolating Barrier on the Seismic Performance of a Reinforced Concrete Structure
V. Nappa1, U. Vitiello2, D. Asprone2, E. Bilotta1 and A. Flora1
1Department of Civil, Construction and Environmental Engineering, University of Naples "Federico II", Italy
V. Nappa, U. Vitiello, D. Asprone, E. Bilotta, A. Flora, "The Effect of a Grouted Isolating Barrier on the Seismic Performance of a Reinforced Concrete Structure", in J. Kruis, Y. Tsompanakis, B.H.V. Topping, (Editors), "Proceedings of the Fifteenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 287, 2015. doi:10.4203/ccp.108.287
Keywords: seismic isolation, soil grouting, existing buildings, PLAXIS 2D, SAP2000.
Passive structural systems installed at the foundation level of existing buildings are a common solution to protect them against earthquakes. However, installation procedures are expensive and not always feasible, as for instance in the case of valuable buildings. In this paper, an alternative and innovative solution for the seismic isolation of existing buildings is presented: the idea is to create a barrier buried in the ground, made of grouted soil, able to properly filter the seismic input. This can be obtained by using soft grouts, having a dynamic impedance much lower than that of the natural soil. Previous papers published by some of the authors have shown that the soft barrier can be effective, tending to filter the high frequency components of the amplitude spectrum without modifying in a significant way the low frequency ones. This implies that ground treatment has to be tuned on the characteristics of the structure to be protected, above all its natural frequencies. In this paper, the case of a simple four-story building with a reinforced concrete structure and a shallow slab foundation resting on a sandy soil is considered. Analyses are carried out with the commercial codes PLAXIS 2D and SAP2000, considering a fixed base, the foundation on the soil and finally the existence of a soft barrier. It is shown that the natural frequencies of the structure are largely influenced by the characteristics of the subsoil. Once the soft barrier is created in the soil, a sharp decrease of the first natural frequency of the structure is obtained, similarly to the effect of traditional isolators. In the paper, dynamic analyses with different input motions are considered. It is confirmed that the soft barrier, whose dynamic impedance was assigned considering some experimental results obtained by the authors and previously published, is able to filter higher frequencies, while it has a minimum or even nil effect in the case of low frequency input signals.
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