PSI - Issue 44

Marco Gallo et al. / Procedia Structural Integrity 44 (2023) 618–625

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Marco Gallo et al./ Structural Integrity Procedia 00 (2022) 000–000

The parametric interventions allow to underline once more that the effect of the SSI even in terms of the cost needed to retrofit the bridge piers, which is reduced if the SSI is considered in the structural analysis. Table 7 shows how the demand to capacity ratio D/C is affected by each variable, in terms of concrete thickness and rebar diameters. 8. Conclusion This work allowed to highlight how the seismic vulnerability of viaducts is strongly affected by the base constraint modelling assumption. In fact, considering the SSI, in the face of a greater modelling and computational burden, allows to better simulate the dynamic behaviour of the structure compared to reality, obtaining greater periods of vibrations as a consequence of the decrease in stiffness of the structure in the presence of a deformable soil-foundation compound. Using a linear analysis and seismic action evaluated from the response spectrum it is possible to evaluate lower stresses in structural elements. The effect of the SSI also depends on the soil category and piers slenderness. It has been shown that as the mechanical properties of the foundation soil decrease, the SSI assumes an even greater importance since soils of worse properties determine a less rigid soil-foundation compound, leading to a reduction of stresses compared to the case of fixed base restraints. Furthermore, using the behavior factor q, defined considering the SSI, to obtain the design response spectrum, the seismic actions are also affected by the value assumed for it: performing a non-linear static analysis it is possible to justify the use of a higher value and then evaluate seismic horizontal forces less penalizing. All of these considerations also have a direct effect on the retrofitting interventions design, as they result less invasive and expensive considering the SSI. Acknowledgements This research activities is within the framework of the Research Agreement between Reluis and the Department of Civil Protection of the Italian Government. References Anoyatis, G., Ylonakis, G., 2012. Dynamic winkler modulus for axially loaded pile. Geotechnique Vol. 62, pp. 521-536. Dobry, R., and Gazetas, G., 1988. Simple method for dynamic stiffness and damping of floating pile groups - Geotechnique, Vol. 38, No. 4, pp. 557-574. Gazetas, G. (1999) - Foundation vibrations - Foundation Engineering Handbook, 2nd Edition, Chapter 15, H.-Y. Fang, ed., Chapman and Hall, New York, New York Kaynia, A.M., and Kausel, E. (1982) - Dynamic Stiffness and Seismic Response of Pile Groups - Research Report R82-03, Massachusetts Institute of Technology, Cambridge, Massachusetts. Mylonakis, G., and Gazetas, G. (1999) - Lateral vibration and internal forces of grouped piles in layered soil - Journal Geotechnical and Geoenvironmental Engineering, Vol. 125, No. 1, pp. 16-25 Mylonakis G., Gazetas G. (2000) – Seismic Soil-Structure Interaction: Beneficial or Detrimental? - Journal of Earthquake Engineering, Vol. 4, No. 3 (2000) 277-301 Pais, A., and Kausel, E. (1988) - Approximate formulas for dynamic stiffnesses of rigid foundations - Soil Dynamics and Earthquake Engineering, Vol. 7, No. 4, pp. 213-227 Pitilakis K.D., Karapetrou S.T., Fotopoulou S.D. (2014) - Consideration of aging and SSI effects on seismic vulnerability assessment of RC buildings - Bulletin of Earthquake Engineering, vol.12, no. 4, pp. 1755-1776 Brincker R., Zhang L. & Andersen P. (2001). Modal identification of output-only systems using frequency domain decomposition. Smart Materials and Structures, Vol. 10, pp. 441- 445. Peeters B. & De Roeck G. (2001). Stochastic system identification for operational modal analysis: a review. ASME Journal of Dynamic Systems, Measurement and Control, Vol. 123, pp. 659-667. [D.M.II.TT., 2018]: DECRETO DEL MINISTERO DELLE INFRASTRUTTURE E DEI TRASPORTI del 17 Gennaio 2018: Aggiornamento delle “Norme Tecniche per le Costruzioni”, supplemento Ordinario n. 42 della Gazzetta Ufficiale della Repubblica Italiana del 20 Febbraio 2018. Circolare 21 gennaio 2019, n. 7 - Istruzioni per l’applicazione dell’<> di cui al D.M. 17 gennaio 2018.