Abstract:SUMMARY
New types of fiber‐reinforced rubber‐based seismic isolators have been a research interest for a number of engineers in the past decade. These new types of isolators can have similar seismic performances compared with the conventional ones. In most of the previous researches, the fiber‐reinforced rubber‐based isolators is usually manufactured with placing fiber sheets between precut rubber layers with the use of a bonding agent. This research differs from the previous researches in terms of manufacturi… Show more
“…In this work, we investigate a new type of seismic isolation based on a metamaterial concept that may offer an alternative to classical seismic isolators. Although the performance of classical isolators on superstructures has been studied in depth, they require two strong floors, exert a very high stiffness against the vertical component of an earthquake, and seem to be ineffective for large structures subjected to rocking . As a result, we propose an isolation system that does not require the use of additional strong floors or specialized devices.…”
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.
“…In this work, we investigate a new type of seismic isolation based on a metamaterial concept that may offer an alternative to classical seismic isolators. Although the performance of classical isolators on superstructures has been studied in depth, they require two strong floors, exert a very high stiffness against the vertical component of an earthquake, and seem to be ineffective for large structures subjected to rocking . As a result, we propose an isolation system that does not require the use of additional strong floors or specialized devices.…”
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.
“…17 Karimzadeh Naghshineh et al, (2014) also have used this test set up to conduct vertical compressive tests. 25 Figure 7.Four-block lap shear test specimen.…”
Natural rubber (NR)–based vulcanizates have been used as base isolation materials for many years. Combining good damping properties, low cost, and availability with acceptable mechanical and aging performance, these materials have always been the first choice for base isolation applications. In this research, we try to formulate a natural rubber base recipe with increased damping properties, which can fulfill mechanical and aging requirements of base isolation systems. For this purpose, a series of blends have been formulated by incorporating chloroprene (CR) or butadiene (BR) and acrylonitrile butadiene rubber (NBR) into the natural rubber base. Filler content accelerator type and vulcanization system have been chosen to optimize damping while maintaining a reference point. All vulcanizates have been tested for their mechanical properties. Moving die rheometer (MDR) and rubber process analyzer (RPA) have been used to obtain general cure data as well as storage (G′) and loss modulus and loss angle (η). Crosslink densities have been calculated using RPA and Lee and Pawlowsky’s Coran approach. Dynamic material tests have been performed to obtain dynamic shear properties, equivalent damping ratio, and shear modulus. The results indicated that NR/NBR and NR/CR compounds with viscous damping values of 10.4% and 8.9% at frequency of .5 Hz can lay bases for formulating high-damping rubber (HDR) materials for base isolation systems due to their increased damping and rather good mechanical and relaxation performance.
“…SREIs, whose reinforcements are rigid, when subjected to compression action, show only the bulging of the elastomer layers between two consecutive steel layers without deformation of the latter (Figure 1a) [30]. However, in U-FREIs, whose fiber fabrics are not pre-tensioned, the elastomer deformation is initially accompanied by the deformation of the fiber fabric layers.…”
Section: Similarities and Differences Between Sreis And U-freismentioning
Fiber-reinforced elastomeric isolators (FREIs) are composite devices consisting of an alternation of elastomer layers and fiber reinforcement layers. They have mechanical properties comparable to those of conventional Steel-Reinforced Elastomeric Isolators (SREIs). The mechanical and construction characteristics of FREIs, together with their lower cost, make them potentially usable on a large scale. However, for their actual use, it is necessary to take into account the current regulations regarding seismic isolation. The application of FREIs provides the absence of anchoring to the structure, but the European Technical Standard UNI EN 15129 requires that the isolators are attached to the structure by mechanical fastening only. In this research work, a constraint device that fulfills this requirement but, at the same time, does not significantly alter the mechanical behavior of FREIs is investigated. The properties of the selected device and its installation method are presented. The results of both a simple compression test and a combined compression and shear test performed on two isolators reinforced by quadri-directional carbon fiber fabrics and two isolators reinforced by bi-directional fabrics are presented. The tests were performed in the absence and presence of the constraint device in order to investigate the modifications produced by the device.
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