Summary This paper introduces a novel seismic isolation system based on metamaterial concepts for the reduction of ground motion‐induced vibrations in fuel storage tanks. In recent years, the advance of seismic metamaterials has led to various new concepts for the attenuation of seismic waves. Of particular interest for the present work is the concept of locally resonant materials, which are able to attenuate seismic waves at wavelengths much greater than the dimensions of their unit cells. Based on this concept, we propose a finite locally resonant Metafoundation, the so‐called Metafoundation, which is able to shield fuel storage tanks from earthquakes. To crystallize the ideas, the Metafoundation is designed according to the Italian standards with conservatism and optimized under the consideration of its interaction with both superstructure and ground. To accomplish this, we developed two optimization procedures that are able to compute the response of the coupled foundation‐tank system subjected to site‐specific ground motion spectra. They are carried out in the frequency domain, and both the optimal damping and the frequency parameters of the Metafoundation‐embedded resonators are evaluated. As case studies for the superstructure, we consider one slender and one broad tank characterized by different geometries and eigenproperties. Furthermore, the expected site‐specific ground motion is taken into account with filtered Gaussian white noise processes modeled with a modified Kanai‐Tajimi filter. Both the effectiveness of the optimization procedures and the resulting systems are evaluated through time history analyses with two sets of natural accelerograms corresponding to operating basis and safe shutdown earthquakes, respectively.
Fluid-filled tanks in tank farms of industrial plants can experience severe damage and trigger cascading effects in neighboring tanks due to large vibrations induced by strong earthquakes. In order to reduce these tank vibrations, we have explored an innovative type of foundation based on metamaterial concepts. Metamaterials are generally regarded as manmade structures that exhibit unusual responses not readily observed in natural materials. If properly designed, they are able to stop or attenuate wave propagation. Recent studies have shown that if locally resonant structures are periodically placed in a matrix material, the resulting metamaterial forms a phononic lattice that creates a stop band able to forbid elastic wave propagation within a selected band gap frequency range. Conventional phononic lattice structures need huge unit cells for low-frequency vibration shielding, while locally resonant metamaterials can rely on lattice constants much smaller than the longitudinal wavelengths of propagating waves. Along this line, we have investigated 3D structured foundations with effective attenuation zones conceived as vibration isolation systems for storage tanks. In particular, the three-component periodic foundation cell has been developed using two common construction materials, namely concrete and rubber. Relevant frequency band gaps, computed using the Floquet-Bloch theorem, have been found to be wide and in the low-frequency region. Based on the designed unit cell, a finite foundation has been conceived, checked under static loads and numerically tested on its wave attenuation properties. Then, by means of a parametric study we found a favorable correlation between the shear stiffness of foundation walls and wave attenuation. On this basis, to show the potential improvements of this foundation, we investigated an optimized design by means of analytical models and numerical analyses. In addition, we investigated the influence of cracks in the matrix material on the elastic wave propagation, and by comparing the dispersion curves of the cracked and uncracked materials we found that small cracks have a negligible influence on dispersive properties. Finally, harmonic analysis results displayed that the conceived smart foundations can effectively isolate storage tanks.
Metamaterials represent a new trend in the field of seismic engineering. Their capacity to attenuate waves at the superstructure level is highly desirable and sought after in recent years. One of their main drawbacks to date, is the excessive size of the necessary resonators and, consequently, the uneconomic design they require. In order to tackle this problem, we apply the concept of negative sti↵ness to a metamaterial-based foundation system and analyse the potential improvements such a mechanism may have on the metamaterial as well as the coupled structural behaviour. Since negative sti↵ness is a property that cannot be achieved through conventional measures, a novel mechanism, designed for the implementation in periodic metamaterial-based structures, is proposed herein. The inevitable nonlinearity of the mechanism will be discussed and taken into account, while the advantages of the negative sti↵ness element (NSE) will be treated analytically and verified numerically. Additionally, through an optimization in the frequency domain and nonlinear time history analyses (THAs), the performance of the system coupled with a fuel storage tank is elaborated. With only 50% of the theoretically allowable NSE value, the foundation system could be reduced to 1/3 of its size. Furthermore, the nonlinear e↵ect of the device has proven to diminish the band gap of the periodic system, which led us to introduce nonlinearity parameters that can help avoid the strongly nonlinear
The recent advance of seismic metamaterials has led to various concepts for the attenuation of seismic waves, one of them being the locally resonant metamaterial. Based on this concept, the so-called metafoundation has been designed. It can effectively protect a fuel storage tank from ground motions at various fluid levels. In order to show the effectiveness of the proposed design, the response of the metafoundation is compared to the response of a tank on a traditional concrete foundation. The design process of conceiving the metafoundation, optimizing it for a specific tank, and its seismic response are described herein. Furthermore, the response of a tank during a seismic event can cause severe damages to pipelines connected to the tank. This phenomenon can be of critical importance for the design of a seismic tank protection system and must be treated with care. Since the coupled structure (tank + foundation + pipeline) exerts highly nonlinear behavior, due to the complexity of the piping system, a laboratory experiment has been conducted. More precisely, a hybrid simulation (HS) that uses the metafoundation and a tank as a numerical substructure (NS) and a piping system as a physical substructure (PS) was employed. To make the results relatable to the current state of the art, additional experiments were performed with concave sliding bearings (CSBs) as an isolation system in the NS. The metafoundation offered a clear attenuation of tank stresses and, in some cases, also reduced the stresses in the piping system.
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