ترجمه مقاله اثرات اندرکنش خاک و سازه بر عملکردهای لرزه ای قاب های مقاوم خمشی بتن آرمه - نشریه الزویر

The paper investigates the influence of Soil-Structure-Interaction (SSI) effects on the seismic performances of 2D reinforced concrete (RC) moment resisting frames (MRFs), which were investigated by means of non-linear dynamic analyses. The goal was pursued by means of a parametric study in which (1) the soil properties, (2) the modelling technique of the SSI effects, (3) the seismic design level of the structures were varied. The soil classes suggested by Eurocode 8 were taken as reference to define the mechanical properties of soil. As concerns the SSI modelling, both a sub-structures approach and a direct approach were considered. Finally, structures of 4 and 8 floors designed for vertical loads only or according to the Italian regulations for constructions (NTC-08) were considered. RC-MRFs founded on soft soils were considered, because SSI effects on the seismic response are expected higher. The study shows that SSI affects the seismic demand in terms of maximum base shear and maximum inter-story drift ratio with different significance depending on the modelling approach.

1. Introduction

In this paper, the results of a parametric study performed with the aim to investigate the effects of the Soil-Structure Interaction (SSI) on the seismic performances of reinforced concrete (RC) moment resisting frames (MRFs) are shown. Nonlinear dynamic analyses were performed varying (i) the soil properties, (ii) the modelling technique of SSI effects, (iii) the seismic design level of the structures. As concerns the soil, the different classes suggested by Eurocode 8 [1] were referenced, while as concerns the modelling technique of SSI effects, both a “direct” approach and a “sub-structures” were considered. Finally, structures of 4 and 8 floors designed for vertical loads only or according to the current Italian regulations for constructions [2] were considered. Before showing the results of the analyses, the reference structures are introduced, as well as the selected records and the mechanical properties of the soil deposits assumed for the numerical analyses. Moreover, some explanations about the numerical models implemented in OpenSees are provided.

5. Conclusions

In this study, SSI effects on the seismic demand of reinforced concrete moment resisting frames were investigated by means of a parametric study in which: (i) the soil properties, (ii) the modelling technique of SSI effects and (iii) the seismic design level of the structures were varied. In particular, nonlinear dynamic analyses were performed.

The study shows that, based on the modelling approach adopted, SSI can affect more or less the estimation of the seismic demand with respect to a fixed-base model. The adoption of a refined complete FEM model can lead to reductions in the estimation of the seismic demand, with respect to a fixed-base model, up to 50% in terms of maximum inter-story drift ratio and up to 20% in terms maximum base shear. A simplified modelling of SSI effects by means of a Beam on Nonlinear Winkler Foundation (BNWF) model can affect the evaluation of the seismic demand only in case of 8 floors buildings founded on very soft soils, whereas rocking response tends to prevail over sliding response of the foundation. Anyway, the reductions with respect to a fixed-base model (up to 20% in terms of both maximum base shear and maximum inter-story drift ratio) are lower than those predicted by a complete FEM model. The difference between the two modelling approaches is related to the different characterization of the overall damping, as shown in Fig.4, in which the acceleration of a point on the top of the structure, and the corresponding Fourier spectrum, is plotted for a specific record. The BNWF model, because of the lack of coupling between vertical and lateral modes of foundation response and because of its incapability to take into account the frequency variability of foundation impedances, seems to under-estimate the energy dissipation due to SSI.