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The seismic vulnerability of bridges may be reduced by the application of Geotechnical Seismic Isolation (GSI) below the foundations of the columns and the abutments. However, the role of GSI on the seismic response of bridges has been limitedly examined in literature. Therefore, this research has been conducted to study the effect of applying GSI on the seismic response of bridges to address the aforementioned gap in knowledge. Advanced nonlinear dynamic three-dimensional finite element analyses have been conducted using OpenSees to study the influence of the GSI. The cases of traditional and isolated bridges subjected to earthquakes have been considered to assess the GSI effects. The results showed that the GSI reduces the seismic effect on the column while its effect seems to be less significant for the abutments. In addition, fragility curves for the traditional and isolated cases have been developed and compared to provide insights with a probabilistic-based approach. The results of this paper provide a useful benchmark for design considerations regarding the use of GSI for bridges.

Summary The aim of this paper is to demonstrate the efficiency of a low-cost and sustainable timber-based energy dissipation system with recentering ability, which can be used as a seismic isolation system or a tuned mass damper for the seismic protection of structures in developing or developed countries. The system, defined as Dovetail with SPrings (Dove-SP), utilizes the attractive properties of timber to store CO 2 , thus reducing the carbon footprint of the existing energy dissipation systems: It comprises two timber slabs that are designed to slide against each other in a motion that is restrained by a dovetail sliding joint. Two sliding interfaces that allow this sliding motion at an attractively low friction coefficient are experimentally investigated: A PVC sand-wich (PVC-s) sliding interface, comprising a thin layer of sand that is sand-wiched between two PVC layers and a timber sand-wich sliding interface consisting of a thin layer of sand encapsulated between two beech timber surfaces. A set of low-cost steel springs is designed and installed on both sides of the dovetail joint to recenter the structure back to its original position after the end of an earthquake ground motion excitation. A novel, low-cost and deformable wood material fabricated from delignified balsa wood is used to reduce the pounding effects before the activation of the steel springs. The seismic behavior and the recentering ability of the novel timber-based energy dissipation system subjected to an ensemble of recorded earthquake ground motion excitations was experimentally investigated through a large-scale shaking table investigation at ETH Zurich.

Geotechnical Seismic Isolation (GSI) can be defined as a new category of seismic isolation techniques that involve the dynamic interaction between the structural system and geo-materials. Whilst the mechanism of various GSI systems and their performance have already been demonstrated through different research methods, there is a missing link between fundamental research and engineering practice. This paper aims to initiate the development in this direction. A new suite of equivalent-linear foundation stiffness and damping models under the same framework is proposed for four GSI configurations, one of which is a novel combination of two existing ones. The exact solutions for the equivalent dynamic properties of flexible-base systems have also been derived that explicitly include the foundation inertia and the strain-dependent equivalent damping of foundation materials, which are both significant for GSI systems. The application of the proposed analytical design models has been illustrated through response history analyses and a detailed hand-calculation design procedure has also been outlined and demonstrated.

The 2010–2011 Canterbury Earthquake Sequence caused extensive damage to over 6000 residential buildings in Christchurch and highlighted an urgent need to improve the resilience of the housing sector. As a result, the authors have developed the eco-rubber geotechnical seismic isolation (ERGSI) foundation system for new low-rise buildings. It is a cost-effective and sustainable technology that integrates a horizontal geotechnical seismic isolation (GSI) layer—i.e. a deformable seismic energy dissipative filter made of gravel–rubber mixtures (GRMs)—and a flexible rubberised concrete (RuC) raft footing. The present study aims at evaluating the performance of an ideal ERGSI system in dissipating seismic energy and assessing the seismic response of two-storey RC framed structures placed on the ERGSI system. Firstly, results of laboratory investigations are presented and ideal GRM and RuC for use in ERGSI systems are identified. Hence, OpenSees finite-element numerical investigations and spectral acceleration analyses are undertaken for a 900 mm-thick GRM layer with 40% rubber content by volume. Further, time-history dynamic analyses—carried out by SeismoStruct software—are presented and discussed for two ERGSI-isolated RC framed structures having natural period of 0.3 s and 0.5 s. The results obtained for the ERGSI-isolated structures are finally compared with those obtained for two non-isolated framed structures placed on a traditional foundation (i.e. RC footing placed on a compacted gravel layer). This study demonstrates that the seismic demand (i.e. peak acceleration measured at the structure top-floor, lateral deformation at each floor and base shear) on low-rise buildings can be significantly reduced by using ERSGI foundation systems.

Seismic protection of buildings using the Geotechnical Seismic Isolation (GSI) system placed between the natural soil and the building foundation has recently emerged as an innovative and economical alternative to the traditional base isolation system. The present study aims to experimentally investigate the effectiveness of the GSI system composed of horizontal layers of Sand Rubber Mixture (SRM), a high damping energy-absorbing material reinforced with geogrids for seismic protection of mid-rise buildings. A series of 1-g laboratory shaking table tests were carried out on a five-story model framed structure placed on the GSI system in a laminar shear box filled with sand subjected to input excitation of 0.1 Hz to 10 Hz frequency range. The shake table tests were carried out under different base conditions of model structure: (1) pure sand, (2) SRM-GSI system and, (3) geogrid reinforced SRM-GSI system. The seismic performance of the model structure was compared for test beds with and without the GSI system by evaluating and analysing the recorded acceleration-time histories. The results indicate that while both SRM-GSI and geogrid reinforced SRM-GSI system effectively reduces the acceleration response of the buildings; however, the geogrid reinforcement was highly effective in reducing vertical ground settlement and contributing to improved lateral stiffness compared to the SRM-GSI case. The introduction of the geogrid reinforced SRM-GSI system tends to reduce the lateral displacements on the superstructure by 35%, besides minimizing the foundation rotation. In addition, the geogrid reinforced SRM-GSI system significantly reduces the interstorey drift of the model framed structure. Overall, the effectiveness of the geogrid reinforced SRM-GSI system in reducing seismic damages and permanent displacements of typical mid-rise buildings was experimentally demonstrated in the present study.

We present the results of the forced-vibration experiments performed at the large-scale prototype structure of EuroProteas founded on gravel-rubber mixture (GRM) layers acting as a means of Geotechnical Seismic Isolation (GSI). Three GRM with different rubber content per mixture weight (0%, 10%, and 30%) but the same mean grain size ratio were used as foundation soil. Each GRM-structure system was subjected to harmonic forces in a wide range of excitation frequencies and force amplitude. It was found that a 0.5 m thick GRM foundation soil layer with 30% rubber content can effectively isolate the structure. The strong effect of the rubber fraction was expressed in the detected period elongation and the dominating rocking component which leads to a more “rigid-body” response of the structure. Moreover, the developed base shear and base moment are significantly reduced regardless of the excitation frequency, while the increased damping of the system and the important energy dissipation demonstrate the effectiveness of the GRM foundation soil layer. Overall, the experimental results demonstrated that the use of GRM as a GSI system can be considered as a low-cost alternative seismic isolation technique.

The paper focuses on the detailed analysis of the dynamic characterisation of polyurethane to evaluate the effects of polyurethane injections into soil with the aim of geotechnical seismic isolation. To determine the dynamic properties, resonant column (RC) tests were performed at the University Kore of Enna (Italy) on specimens of pure polyurethane with different values of density and subjected to different mean confining pressures. The results obtained by means of RC tests, in terms of shear modulus G and the damping ratio D as a function of shear strain γ c , allowed to develop an analytical formulation for G-γ c and D-γ c curves, taking into account the linear relationship with density, of both the maximum value of shear modulus G max and the minimum value of damping ratio D min . The analytical formulation derived from the experimental results is applied for ground response seismic analyses of cohesive soils injected with polyurethane, using a finite element code. The numerical results show that the polyurethane injections reduce the value of maximum acceleration on the ground surface and the reduction varies with the thickness of the soil modified by polyurethane injections.

PurposeIn recent years, three-dimensional (3D) seismic base isolation system has been studied extensively. This paper aims to propose a new 3D combined isolation bearing (3D-CIB) to mitigate the seismic response in both the horizontal and vertical directions.Design/methodology/approachThe new 3D-CIB composed of laminated rubber bearing coupled with combined disk spring bearing (CDSB) was proposed. Comprehensive analysis of constitution and theoretical derivation for 3D-CIB were presented. The advantage of CDSB is that the constitution can be flexibly adjusted according to the requirements of the bearing capacity and vertical stiffness. Hence, four different combinations of CDSB were designed for the 3D-CIB and employed to isolate nuclear reactor building. A comparative study of the seismic response in terms of seismic action, acceleration floor response spectra (FRS), peak acceleration and relative displacement response was carried out.Findings3D-CIB can effectively reduce seismic action, FRS and peak acceleration response of the superstructure in both the horizontal and vertical directions. Overall, the horizontal isolation effectiveness of 3D-CIB was slightly influenced by vertical stiffness. The decrease in the vertical stiffness of the 3D-CIB can reduce the vertical FRS and shift the peak values to a lower frequency. The vertical peak acceleration decreased with a decrease in the vertical stiffness. The superstructure exhibited a rocking effect during the earthquake, and the decrease in the vertical stiffness may increase the rocking of the superstructure.Originality/valueAlthough the advantage of 3D-CIB is that the vertical stiffness can be flexibly adjusted by different constitutions, the vertical stiffness should be designed by properly accounting for the balance between the isolation effectiveness and displacement response. This study of isolation effectiveness can provide the technical basis for the application of 3D-CIB into real engineering of nuclear power plants.

The mixture of sand-expanded polystyrene (EPS) beads has emerged as an alternative seismic isolation geomaterial due to its high compressibility and energy absorption capacity features. The objective of this study is to determine the effectiveness of a new proposed geotechnical seismic isolation material, EPS beads-sand mixtures, on the seismic performance of the medium-rise buildings by shake table tests. A 1/10 scaled five-story building model was used in order to determine the effects of the EPS-beads as an isolation material. The seismic isolation layers were created surrounding the foundation of a mid-rise building model with sand-EPS beads mixtures at varying thicknesses. The influence of various parameters, particularly the earthquake characteristics of input motions, the EPS beads content, and the thickness of the isolation layer were investigated. As a result of the extensive experimental program, it was revealed that the EPS40 with the 15 cm isolation thickness significantly reduced the peak accelerations and the inter-story drifts. The utilization of the EPS beads-sand mixture layer surrounding the foundation may be accepted as an alternative seismic isolation material. In addition, the results of this first study were also evaluated according to rubber-sand mixtures as another GSI material in the literature. The results showed that the proposed GSI material is very sensitive to the changes of EPS content and earthquake characteristics. This study is very important as it shows that EPS beads-sand mixtures can be accepted as a potential seismic isolation material.

The anti-seismic problem of rural residential buildings is the weak link of seismic retrofitting in China. Recently, geotechnical seismic isolation (GSI) technology based on rubber–sand mixtures (GSI–RSM) using rubber–sand mixtures (RSM) between the structural foundation and the foundation soil has been proven to have the possibility of potential applications in rural residential buildings. Many theoretical studies exist on the effectiveness of seismic isolation of the GSI–RSM system, but few studies on either the seismic response test of model buildings placed on the RSM layer or the large-scale shaking table test exist. Therefore, this study considers a large shaking table test performed on a 1/4 single-story masonry structure model with and without a GSI–RSM system by selecting a standard input ground motion and varying input acceleration amplitudes. The test results show that the GSI–RSM system can reduce the seismic response of superstructures. The isolation effect of the GSI–RSM system is low in small earthquakes and increases with increasing earthquake magnitude. Overall, the RSM layer can filter part of the high-frequency components of the earthquake to transmit to the superstructure and consume more seismic energy by generating friction slip in the interaction with the structural foundation.