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Base isolation techniques have emerged as the most effective seismic damage mitigation strategies. Several types of aseismic devices for base isolation have been invented, studied, and used. Out of several isolation systems, sliding isolation systems are popular due to their operational simplicity and ease of manufacturing. This article discusses the historical development of passive sliding isolation systems, such as pure friction systems, friction pendulum systems, and isolators with other sliding surface geometries. Moreover, multiple surface isolation systems and their behavior as well as the effectiveness of using complementary devices with standalone passive isolation devices are examined. Furthermore, the article explored the various modeling techniques adopted for base-isolated single and multi-degree freedom building structures. Special attention has been given to the techniques available for modeling the complex phenomena of sliding and non-sliding phases of sliding bearings. The discussion is further extended to the development in the contemporary areas of seismic isolation, such as active and hybrid isolation systems. Although a significant amount of research is carried out in the area of active and hybrid isolation systems, the passive sliding isolation system still has not lost its appeal due to its ease of adaptability to the structures.

Background & objectives: Little data are available regarding the frequencies of the blood group antigens other than ABO and RhD in the Indian population. Knowledge of the antigen frequencies is important to assess risk of antibody formation and to guide the probability of finding antigen-negative donor blood, which is especially useful when blood is required for a patient who has multiple red cell alloantibodies. This study was carried out to determine the frequencies of the D, C, c, E, e, K, k, Fy a , Fy b , Jk a , Jk b , M, N, S and s antigens in over 3,000 blood donors. Methods: Samples from randomly selected blood donors from Delhi and nearby areas (both voluntary and replacement) were collected for extended antigen typing during the period January 2009 to January 2010. Antigens were typed via automated testing on the Galileo instrument using commercial antisera. Results: A total of 3073 blood samples from donors were phenotyped. The prevalence of these antigens was found to be as follows in %: D: 93.6, C: 87, c: 58, E: 20, e: 98, K: 3.5, k: 99.97, Fy a : 87.4, Fy b : 57.6, Jk a : 81.5, Jk b : 67.4, M: 88.7, N: 65.4, S: 54.8 and s: 88.7. Interpretation & conclusions: This study found the prevalence of the typed antigens among Indian blood donors to be statistically different to those in the Caucasian, Black and Chinese populations, but more similar to Caucasians than to the other racial groups.

Inspired by the hunting strategy of spiders utilizing cobwebs, this study proposes a novel bionic cobweb structure (BCS) that facilitates the layer-by-layer nonlinear amplification of physical attributes for its embedded isolation components. By integrating a conventional quasi-zero stiffness (QZS) isolator within the BCS, a bionic QZS isolation system is achieved, exhibiting amplified negative stiffness and damping characteristics. The influences of BCS parameters on negative stiffness and damping are systematically investigated. A dynamic equation of the isolation system is formulated, incorporating the cubic trinomial stiffness and cubic quadrinomial damping terms. The displacement transmissibility is derived by the average method and verified via the Runge–Kutta method. The results manifest the effectiveness of the BCS nonlinear amplification effect on the enhancement of vibration isolation performance, accompanied by good coupling between the amplified negative stiffness and damping. Increasing the number of BCS layers, enlarging the initial angle θ i of the i-layer BCS, augmenting the pre-compression δ 20 of the negative stiffness springs, and shortening the connecting rod L s , synergistically contribute to a superior amplification of negative stiffness for better counterbalancing the substantial positive stiffness encountered in heavy-load scenarios. Furthermore, the amplified damping exhibits an anti-resonant characteristic, effectively mitigating the hardening nonlinearity without compromising high-frequency performance. The constructed bionic QZS isolation system with the BCS outperforms the initial QZS system in terms of resonance frequency, peak transmissibility, and isolation frequency band. Moreover, the proposed BCS has the prospect of emerging as a usual platform without modifying the current isolation elements. The intrinsic amplification effect and design logic can offer heuristic insights for future research.

This work aims to identify ways to achieve dynamic performances of a novel double‐layer vibration isolation system (DL‐VIS) capable of achieving multi‐directional isolation and extreme environmental adaptability. A forward modeling approach applicable to complex systems has been developed and analyses of nonlinear dynamic characteristics under different working conditions are performed. First, by integrating with constitutive models in terms of individual elastic elements and the connective relationships within the structure, multidirectional constitutive models for isolation devices are established. Further, the decomposition of linear and nonlinear stiffness components in different directions is performed using the Taylor expansion method. Subsequently, the dynamic response under sinusoidal sweep frequency loading is obtained using the related stiffnesses in the dynamic model and adopting the extended harmonic balance method. The effects of stiffness, damping, and a nonlinear stiffness gradient on the DL‐VIS response are thoroughly evaluated. Finally, the vibration isolation performance and nonlinear dynamics under different working conditions are examined, and the proposed dynamic model is experimentally validated. The results indicate that the response of DL‐VIS varies significantly under different working conditions, particularly under overload conditions. The nonlinear characteristics lead to wide‐band instability near the natural frequency and excellent vibration attenuation performance in multiple directions. The theoretical model agrees well with the experimental results in the nonresonant region and near the first resonant peak, which proves the prediction accuracy in the low‐frequency range. These findings provide robust theoretical and technical support for the design and performance optimization of isolation systems.

Recently, there has been increased research interest in the bio-inspired linkage isolators. This paper presents a general six-bar linkage prototype mechanism that is applicable to axisymmetric four- to six-bar linkage isolation systems. First, the mechanical modeling of the presented structure is studied. Then, the dynamics of the nonlinear system, which incorporates damping-coupled velocity-displacement-dependent (VDD damping) terms, are investigated via the discrete incremental harmonic balance method. This method offers a unified and straightforward approach for deriving periodic responses of VDD damping nonlinear systems, encompassing both super- and sub-harmonic resonances, and is particularly suitable for the examined linkage systems. Furthermore, the paper evaluates the impact of VDD damping on isolation performance. Employing VDD damping types with larger absolute values of the VDD term slope is recommended to enhance isolation performance. This process involves adjusting the structural parameters of the system, including the rod length and the angle between the rods. Additionally, a smaller coefficient of VDD damping is preferred within the isolation frequency range to improve high-frequency isolation. However, ensuring that this value does not result in a “snap-back” phenomenon that affects the minimum isolation frequency is crucial for the vibration isolator design. The conclusions drawn from this study provide valuable insights for the design of linkage isolation systems in engineering applications.

The advancement of base isolation systems over recent years has been significant, enhancing the performance of structures under seismic conditions. A particularly effective system is the multi-stage friction pendulum, which offers a variety of effective pendula for energy dissipation. However, conducting nonlinear analyses of these structures using finite element analysis is computationally expensive and time-consuming due to the multiple sources of nonlinearity involved. This limitation poses a significant challenge for developing large-scale systems for post-earthquake rapid assessment. Accordingly, this research aims to address this challenge by developing a block-based physics-informed neural network (PINN) model as an alternative to finite element models for rapidly estimating the inelastic response of base-isolated structures. By embedding the governing physics into the neural network, the PINN model mitigates the data dependency issues associated with traditional artificial intelligence techniques and provides physically consistent predictions. Additionally, incorporating long short-term memory networks enhances the model's predictive capabilities. The proposed technique operates in similar to general finite element models where it infers results specific to the structures it was trained on. This capability is crucial for applications requiring rapid post-earthquake assessment, making it suitable for integration into smart city infrastructure where fast earthquake damage detection systems are needed. The study demonstrates the effectiveness of the PINN model, showing superior performance compared to traditional data-driven models and partially informed PINNs, thereby offering a viable solution for overcoming the limitations of finite element analysis in rapid seismic response estimation.

In this paper, a tristable viscoelastic isolation system with stochastic excitation under both displacement and velocity delayed feedback control is considered. Firstly, the theoretical expressions of the mean first-passage time (MFPT) to measure the activated escape between different potential wells are derived. Induced nonlinear transition dynamics due to the noise and time delays are mainly discussed. It is found that the delay-induced behaviours affect the transitions between the equilibrium points of the system, the corresponding phenomenon of the delay-enhanced stability is observed. In this respect, the existence of the maxima of the MFPT1 and the MFPT2 is found in one period. Meanwhile, the MFPT1 and the MFPT2 show the monotonic behaviour with the increase of the noise intensity. Additionally, the stationary probability density of the amplitude and the stationary mean amplitude are derived. The influence regimes of the system parameters on both stationary probability density of the amplitude and the stationary mean amplitude are explored. This paper establishes the relationship between system parameters and dynamical properties of the tristable viscoelastic isolation system. This provides a fundamental guidance for the optimization of the viscoelastic isolation by utilizing the technique of delayed feedback control.

Inter-storey seismic isolation is increasingly gaining attention. One of the main related issues is the need to limit the relative displacement between substructure and superstructure, while maintaining a good seismic performance of the superstructure. As shown in some studies, fluid viscous dampers (FVDs) mounted in isolation systems are effective in reducing isolator deflection but can be harmful by amplifying inter-storey drifts and floor accelerations. Additionally, the effectiveness of FVDs for inter-storey applications was investigated only recently, and specific approaches for their optimisation and performance evaluation are missing. Therefore, this paper proposes a method for the optimal multi-objective design of FVDs, based on the definition of appropriate surrogate response models, which allows for rationally comparing the FVD effects for a wide range of dampers and structures. In particular, the optimal FVD parameters are provided in a dimensionless form, so that they can be predicted by design equations of general validity within the range of the structures analysed. This method is applied to a stock of regular structures with various vibration periods of superstructure, isolation and substructure, examining a linear and a non-linear isolation system and a set of natural records, in order to comprehensively assess the effects of FVDs and their non-linearity on the seismic performance of these structures. Finally, prediction models of optimal FVD parameters are provided based on the results obtained and are applied to three case studies as an example.

It is thought that structural control systems developed for structures exposed to earthquake warnings may have an important place in the future as well as today. Among these, base isolation systems offer effective and practical solutions by damping earthquake-induced vibrations at the ısolatıon level. However, due to the lack of self-adaptation feature against some near- or far-field earthquakes, semi-active and active control systems have been proposed by some researchers. These systems, which use an external power source, also need a control algorithm in order to take action in the event of an earthquake. In other words, in order for the control system to adapt to any earthquake and act as a vibration damper, a passive device, energy to activate the device and a control algorithm are needed. This review covers important studies on passive, semi-active, hybrid and active control systems recommended for the protection of structures against vibrations caused by earthquakes. The advantages and disadvantages of the studies on these control systems compared to each other have been determined. As a result of the study, some inferences were made about what kind of control system would be recommended in the future, taking into account the deficiencies in the literature.

The third-generation instrument era is approaching, and the Einstein Telescope (ET) giant interferometer is becoming a reality, with the potential to be installed at an underground site where seismic noise is about 100 times lower than at the surface. Moreover, new available technologies and the experience acquired from operating advanced detectors are key to further extending the detection bandwidth down to 2–3 Hz, with the possibility of suspending a cryogenic payload. The New Generation of Super-Attenuator (NGSA) is an R&D project aimed at the improvement of vibration isolation performance for thirrd-generation detectors of gravitational waves, assuming that the present mechanical system adopted for the advanced VIRGO interferometer (second generation) is compliant with a third-generation detector. In this paper, we report the preliminary results obtained from a simulation activity devoted to the characterization of a mechanical system based on a multi-stage pendulum and a double-inverted pendulum in a nested configuration (NIP). The final outcomes provide guidelines for the construction of a reduced-scale prototype to be assembled and tested in the “PLANET” laboratory at INFN Naples, where the multi-stage pendulum—equipped with a new magnetic anti-spring (nMAS)—will be hung from the NIP structure.