This study systematically explores the shear-thickening (ST) behavior of silica-based suspensions enhanced with hexagonal-boron-nitride (h-BN) nanoparticles. A series of h-BN/SiO2 shear-thickening fluids (STFs) with varying concentrations was prepared using mechanical stirring and ultrasonication techniques. The structural and interfacial characteristics of the nanoparticles within the STFs were examined through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). Steady-shear rheological analyses demonstrated pronounced shear-thickening effects and distinct flow responses across different h-BN loadings. At an optimal concentration of 0.1

Three-dimensional base isolation systems (3D-BISs) have been increasingly employed owing to their excellent vertical isolation performance relative to conventional horizontal isolation systems. However, their rocking effect in structures with large aspect ratios and insufficient consideration of vertical vibrations in flexible floor slabs still need to be resolved. This study aims to address these issues by developing enhanced analytical models and an optimal design framework for 3D base-isolated structures. First, the effect of rocking on the coupled isolation mechanism of 3D-BISs is investigated via dimensionless modal analyses, and a 3D flexible model is developed and validated to capture the coupled horizontal-rocking response. The modal properties of floor slabs are then derived, enabling accurate prediction of slab vibrations through an integrated frame-slab model combined with the mode superposition method. Additionally, the effect of superstructure uplift on the seismic responses of 3D base-isolated structures is explored. It is demonstrated that the uplift mechanism of the superstructure significantly reduces seismic demands, with the vertical isolation exhibiting superior performance compared to the horizontal isolation. Building on these findings, an optimal design framework is proposed for 3D-BISs, with the objective of minimizing the peak floor accelerations of the superstructure in all directions. A detailed comparative analysis of the optimized results between rocking-restrained and rocking-free designs is presented, so as to provide informed guidance for the preliminary design of 3D base-isolated structures.

Traditional nonlinear energy sinks for broadband vibration suppression are still limited by the demand for additional mass and their sensitivity to input energy. Inerter elements can provide a large equivalent inertial effect under lightweight conditions, whereas multistable structures help improve the adaptability of the system to different excitation levels. To this end, this study proposes an inerter-enhanced tristable nonlinear energy sink (TNESI) and investigates its regulation mechanism and vibration reduction performance for the harmonic response of a linear oscillator. Specifically, a geometric nonlinear model of a four-spring tristable unit is established to analyze the effects of geometric parameters on the potential energy distribution and the evolution of equilibrium branches. An ideal inerter element is then introduced to construct the coupled dynamic equations of the linear oscillator–TNESI system. Subsequently, the steady-state response branches are solved by using the harmonic balance method combined with pseudo-arclength continuation, and the stability of the solutions is determined and verified through linearized eigenvalue analysis and time-domain integration. Furthermore, the effects of excitation amplitude, inertance coefficient, attachment mass, and geometric parameters on the amplitude frequency response, branch evolution, and vibration reduction performance are examined. The results show that the proposed analytical method can accurately characterize the nonlinear steady-state features of the system. The TNESI can effectively improve the system response structure and stability characteristics, and exhibits better vibration mitigation performance and dynamical robustness than the conventional TNES. The present results provide a theoretical basis for the parameter design and performance optimization of multistable broadband vibration control devices.

Phase-transforming cellular materials exhibit hysteresis and programmable steady-state behavior. When the system crosses a potential barrier and undergoes a phase transition, strain energy is rapidly released and redistributed, causing an abrupt change in restoring force and forming a sawtooth hysteresis loop with discontinuities. This feature can be leveraged to design nonlinear energy sink (NES) devices that combine continuous and discrete energy dissipation. This paper investigates nonlinear restoring-force modeling, response formation mechanisms, and targeted energy transfer in multistable hysteretic systems. Specifically, based on the hierarchical phase-transition process triggered by the series connection unit cells, a piecewise implicit equivalent nonlinear model is established to cost-effectively characterize the macroscopic sawtooth hysteresis. Furthermore, the slow-flow equations are derived using the complexification-averaging (CXA) method, and a slow invariant manifold (SIM) is constructed. Lateral stability analysis reveals the geometric roles of fold instability and branch transitions in response formation and energy transfer. Building upon this, sensitivity analyses on coupling stiffness, excitation amplitude, and the number of series-connected bistable units evaluate impacts on energy capture thresholds, dissipation efficiency, and robustness. The study shows that the multi-stable phase-transition modulation characteristics of the system significantly enhance energy dissipation and transfer efficiency across potential barriers through fold instability and branch transition. Moreover, by adjusting the number of series and parallel units, the system can optimize its energy regulation capacity over a broader range of excitation amplitudes. This research provides theoretical support for the design and application of hysteretic multistable structures in passive vibration reduction and wide-frequency energy management.

This paper presents experimental and numerical investigations on multistable energy dissipation device, focusing on improving its loading capacity and validating its dynamic performance. A high-strength version of the device was developed using metallic coned disc springs. Extensive experimental validation was conducted regarding the device which confirmed the intended pseudo-yield behavior and consistent energy dissipation capacity. However, the inertia effect of the device's elements was found to become significant at loading rates higher than 2 Hz, affecting its hysteresis curve. Additionally, the snap-through behavior induced sudden changes in the strain states of the NS elements, which may influence the device's fatigue performance. At last, seismic performance of the device was evaluated using response history analysis, which considered its explicit saw-tooth detail. The results demonstrate that the device's seismic performance can be approximated by a simplified flag-shaped hysteresis model that considers its equivalent energy dissipation. These findings contribute to the application of multistable energy dissipation devices in vibration control for civil engineering.

Hybrid simulation is increasingly used in earthquake engineering because it is efficient, flexible, and relatively economical. Nevertheless, it often requires high-performance computing devices with multi-core CPUs and highspeed memory and still involves substantial complexity in loading and controlling the physical substructure. To cope with such challenges, an MLS-OpenSees-RMC Motion Controller hybrid testing platform is proposed, featuring modular hardware to support hybrid simulations with varying structural parameters. An interruptionresilient communication interface is developed between OpenSees and the RMC75E controller. This mechanism enables the use of high-fidelity numerical substructures, reduces PC hardware requirements, and improves platform reliability. The communication test results show that, under the USB connection, the single-register and multi-register access times of the MLS-OpenSees-RMC platform are reduced by 96.3% and 94.3%, respectively, compared with the MATLAB middleware solution. In addition, the inner-loop displacement tracking error of the MLS-OpenSees-RMC generally remains within 5%, while the relative errors in the maximum displacement under outer-loop control are 12.75% and 0.39%, respectively. During the execution of hybrid simulation on a portable laptop (12th Gen Intel Core i5-12500H), a timeout zone is observed near the end of the displacement time history, but the system remains uninterrupted. Finally, the seismic performance of a steel frame is simulated. At the LS level, only limited plasticity develops at the end of the physical substructure, without the formation of a clear plastic hinge, and structural continuity is maintained. At the CP level, plastic hinges progressively form and local instability becomes evident, confirming the structural behavior associated with the two performance levels.

Fatigue damage poses a severe threat to the structural integrity and operational safety of engineering structures in military, aerospace, and transportation fields, which urgently demands high-performance vibration isolation systems and reliable analysis methods. Traditional vibration isolators fail to balance low-frequency isolation and high-amplitude stability, suffering from an inherent trade-off among vibration isolation effect, damping efficiency and displacement control. This study concentrates on exploring the combined vibration isolation and damping performance of viscoelastic (VE) material and silicone oil, and a two-stage nonlinear vibration isolation and damping device (TNVID) is designed as a dedicated experimental platform to reveal the synergistic mechanism of the two materials. By virtue of the synergistic energy dissipation effect of the VE material and silicone oil, the system achieves a two-stage vibration reduction mechanism: efficient low-amplitude vibration isolation through fluid-spring coupling and enhanced limiting and energy dissipation under high-amplitude impacts by activating the VE cylinder. Systematic tests under variable frequencies and amplitudes verify its outstanding nonlinear stiffness, damping and impact resistance. A two-stage fractional-order derivative model considering the synergistic effect is proposed to characterize its static and dynamic mechanical behaviors. A refined numerical method is further developed to accurately predict its dynamic and impact responses, which can effectively capture the continuous evolution of stiffness, damping and restoring force. This work provides a solid theoretical and numerical foundation for the engineering application of the VE-silicone oil composite in complex vibration and impact environments.

Strut defects are prone to occur in additively manufactured lattice structures and can significantly degrade their mechanical performance, while non-destructive testing of such periodically complex architectures remains challenging. This study proposes a laser ultrasonic inspection method based on zero-group-velocity (ZGV) Lamb wave features to detect strut defects in single-layer lattice structures. A numerical framework combining dispersion analysis, single-frequency response analysis, and transient spectral analysis is established to clarify the formation and evolution of ZGV modes in intact and defective structures. The results show that the intact lattice supports a distinct S0-ZGV mode, whereas a strut defect not only shifts the initial ZGV frequency but also induces a defect-related feature-guided-wave (FGW) branch and the corresponding FGW-ZGV mode. Intact and defective regions exhibit markedly different localized responses at the ZGV frequencies, which form the basis of the proposed detection method. By extracting the spectral energy near the ZGV frequencies, a defect index (DI) is constructed for point-by-point defect detection. Numerical results further show stable and distinguishable DI between defective and intact regions for different defect severities. Laser ultrasonic experiments on additively manufactured Ti-6Al-4V lattice specimens verify that defective and intact regions possess different local ZGV resonance frequencies, and that both reference-frequency strategies based on S0-ZGV and FGW-ZGV can achieve effective defect visualization. These results demonstrate that the proposed method provides an effective approach for non-contact defect detection in complex lattice structures.

We investigate the rheological behavior of nanosilica/PEG200-based shear thickening fluids (STFs), focusing on their temperature-dependent characteristics over the range of 5-50 degrees C. Results show that increasing temperature significantly reduces both the peak viscosity and shear stress while raising the critical shear rate. At 5 degrees C, the STF transitions into a gel-like state. Mechanistic analysis confirms that solvent viscosity is not the dominant factor; instead, interparticle interactions and temperature-induced evolution of the solvation layer are identified as the key mechanisms. This work quantitatively reveals how solvation layer thickness varies with temperature: a thicker layer at low temperatures promotes the formation of stable force chains, leading to high friction and shear stress, whereas a thinner layer at high temperatures allows hydrodynamic clusters to dominate, resulting in a weaker stress response. The peak viscosity follows the Arrhenius model. These findings elucidate the temperature-dependent link between macroscopic properties and microstructure in STFs, providing a theoretical basis for designing STFs for use in varying thermal environments.

Resilient cities require effective prioritization of critical infrastructures under budget and resource constraints to minimize environmental, economic, and social impacts of disasters. This study develops a methodology to evaluate physical and functional interdependencies and cascading effects among infrastructures, including building clusters, transportation, water supply, power, and communication systems. The methodology integrates deep learning-driven building damage assessment, agent-based path planning, hydraulic analysis, and probabilistic modeling for debris distribution, ignition, road damage, and pipeline failure, as well as physics-to-function mapping for power and communication systems. Monte Carlo simulations are employed to quantify the impacts of dynamic and uncertain environments induced by cascading failures on firefighting responses. Furthermore, a management perspective spanning time, space, economy, social psychology, and recovery efficiency is developed to support urban resilience enhancement and emergency response decision-making. Findings indicate that pre-earthquake strategies should focus on cost-effective reinforcement of key components such as communication base stations and substations, improved fire station layout, and enhanced public evacuation training. As earthquake moment magnitude increases from 7.5 to 8.0, urban firefighting emergency response system failure shifts from resource limitations to cascading system collapse. Post-earthquake response should follow a time-prioritized and rapid recovery approach. For strong earthquakes, emphasis should be placed on power system bypass restoration and maintaining water supply, whereas for great earthquakes, priority should shift toward emergency communication substitution and large-scale road clearance.

Wind-induced vibrations pose significant risks to the safety and serviceability of long-span bridges. However, the rarity of extreme wind events and sensor failures during such events often result in sparse monitoring datasets, impeding the reliability of predictive models. This study introduces SMOGN-GRU, a novel predictive framework that integrates statistical data augmentation and deep regression learning to address small-sample challenges in structural health monitoring (SHM) of bridges. The framework combines the Synthetic Minority Over-sampling technique with Gaussian Noise (SMOGN) to augment sparse wind and vibration datasets, and a Gated Recurrent Unit (GRU) network to learn complex nonlinear relationships and forecast bridge responses. Applied to the Hardanger Bridge in Norway, the framework demonstrates strong performance in predicting both vertical and torsional accelerations under critical windstorms. Comparative ablation studies against alternative data augmentation and regression methods confirm the superiority of the proposed framework in enhancing prediction accuracy and data sparsity mitigation. The results underscore the framework’s potential to improve safety assessments and operational decisions in SHM, particularly for scenarios where real-time data is limited or incomplete. SMOGN-GRU thus offers a robust and practical tool for advancing predictive analytics in bridge structures under challenging data conditions.

Locally resonant metamaterials are engineered structures that use resonance within specific resonant elements to create band gaps, effectively blocking wave transmission. This makes them particularly promising for vibration isolation applications. Low-frequency vibration isolation has long posed challenges across various engineering sectors. Recently, notable progress has been made in employing locally resonant metamaterials for low-frequency vibration isolation. This review offers a comprehensive overview of their applications, including foundational theoretical models, methods for solving dispersion relations, techniques for broadening and tuning band gaps based on underlying mechanisms, and strategies for structural and band gap design. It also explores the current status of cross-disciplinary applications in civil engineering. Furthermore, the paper provides insights into how localized resonant metamaterials can evolve toward low-frequency broadband and smart tunable solutions, which may inspire advancements in mechanical and aerospace engineering. Beyond these fields, the proposed metamaterial-structured multi-hazard resilient city provides crucial guidance for the innovative development of civil engineering.

Despite the increasing application of three-dimensional (3D) seismic base isolators to protect structures from earthquake damage, critical dynamic behaviors of 3D base-isolated structures (3D-BISs), such as coupled horizontal-rocking motion and vertical response propagation from the ground through columns to floor slabs, remain inadequately understood. In light of this, full-scale shaking table tests were performed on two structures (aspect ratio > 3): one equipped with multi-dimensional earthquake isolation and mitigation devices (MEIMDs) and its base-fixed counterpart. The test results demonstrated that for a 3D-BIS with a large aspect ratio, the rocking effect was particularly pronounced in the fundamental mode, exhibiting a significant height dependence in its influence on the horizontal acceleration and displacement responses of the superstructure. Owing to slab flexibility, the MEIMD was found to be more effective in suppressing vertical response propagation from columns to slabs than from the ground to columns. However, as the MEIMD barely altered the modal periods of the floor slabs, an inherent vertical acceleration amplification factor from columns to slabs (e.g., 1.15-1.54 in this study) was observed for the 3D-BIS. Furthermore, a simplified analytical model was developed and validated against the test data; this model was subsequently employed to investigate the effects of rocking suppression measures and vertical long-period components of ground motions on the dynamic response of the test structures. These findings provide valuable insights for the response control design of 3D-BISs.

In structural vibration control utilizing active mass dampers (AMD), conventional model-based control algorithms rely heavily on the precise mathematical representation of the controlled plant. However, in practical engineering applications, uncertainties in structural parameters and environmental disturbances often hinder accurate modeling, leading to performance degradation. To address these challenges, this paper proposes a novel model free control strategy integrating a parallel coupled virtual object (PCVO), model predictive control (MPC), and fuzzy controller. A PCVO is introduced between the true structure and the AMD to establish a designable model, eliminating the need for an explicit structural model. A fuzzy controller adaptively updates the PCVO parameters in real time based on the displacement error between the PCVO and the true structure and its derivative, ensuring the PCVO accurately tracks the true structural response. The MPC algorithm then utilizes the PCVO to solve for the optimal control force under actuator saturation. Numerical simulations on a three degree of freedom structure show that the PCVO-MPC achieves performance comparable to LQR and MPC. Specifically, the inter-story drift and absolute acceleration peak reduction rates reach 33.07% and 43.98%, while the maximum RMS reduction rates for displacement and absolute acceleration reach 38.62% and 44.91%, respectively. Furthermore, the strategy maintains stable effectiveness under measurement noise, where the maximum reduction rates for inter-story drift and absolute acceleration peak are 33.47% and 45.33%, and the maximum reduction rates for displacement RMS and absolute acceleration RMS are 34.61% and 43.62% respectively, ensuring control reliability.

The horizontal interaction between footpads and lunar soil directly affects the mobility and operational safety of legged robots, yet existing studies have predominantly focused on vertical footpad–soil interaction. This study establishes a mechanical model for horizontal footpad–lunar soil interaction by incorporating a composite failure surface consisting of a logarithmic spiral and a straight line, while accounting for soil deformation, velocity-dependent inertial effects, and bottom friction induced by vertical loads. Controlled dragging experiments using CAS-1 lunar soil simulant were conducted over different footpad sizes and dragging velocities. The model achieved an average prediction error of 7.19%, demonstrating its ability to predict horizontal resistance under varying geometric and loading conditions. Supplementary DEM simulations under lunar low-gravity and high-vacuum conditions reproduced the predicted curved-to-linear soil failure pattern and the corresponding resistance trend, providing particle-scale support for the assumed interaction mechanism. By extending footpad–regolith interaction modeling from predominantly vertical loading to horizontal motion and explicitly incorporating the composite failure geometry and velocity-dependent resistance, this study provides a mechanics-based description of horizontal footpad resistance and a theoretical basis for the design and control of legged lunar robots.