Search Results (135)

Hexapod robots are attractive for operation in cluttered and uneven environments, but their walking stability is strongly affected by the coupled effects of leg morphology and foot-end trajectory planning. In many existing designs, leg-segment proportions, reachable workspace, and swing-phase trajectory smoothness are considered separately, which makes it difficult to clarify how structural parameters and motion planning jointly influence locomotion stability. To address this issue, this study presents a spider-leg-inspired hexapod robot with a simplified three-degree-of-freedom leg configuration. Selected functional characteristics of spider legs, including segmented limb structure and compliant distal contact, were abstracted into an engineering-feasible hexapod platform rather than directly reproducing spider anatomy. A parametric workspace analysis was conducted under a fixed total leg length to compare six candidate femur-to-tibia ratios. Based on forward reach, vertical foot-lifting capability, stride potential, and structural compactness, a 4:6 femur-to-tibia ratio was selected. In addition, an eleventh-order Bézier curve was developed for swing-phase foot trajectory planning and compared with a conventional composite cycloid trajectory under identical tripod-gait conditions. Simulation and straight-line walking experiments showed that the Bézier-based trajectory reduced body-attitude fluctuation and produced smoother angular-velocity variation than the composite cycloid trajectory. The results indicate that the proposed structural design and Bézier-based trajectory can improve flat-ground walking stability of the hexapod robot. This work provides a practical reference for biomimetic structural design and gait-trajectory optimization of multi-legged robots, while further validation on more complex terrain remains necessary. Full article

Accurate validation of spaceborne lidar data is fundamental for reliable quantification of aerosol vertical distributions, which strongly influence air quality and climate effects. This study presents a comparative analysis of aerosol profiles from the 532 nm High-Spectral-Resolution Lidar (HSRL) onboard China’s DQ-1 satellite (ACDL) and ground-based observations from the Asian Dust and Aerosol Lidar Observation Network (AD-Net). Using one year of measurements under minimized spatiotemporal mismatches at three representative coastal stations (Matsue, Tokyo, Hedo), we quantify the sources of observational differences. Results show that discrepancies in detection targets (aerosols/clouds) dominate the total variance (>75%), while instrumental differences contribute 10–25%. Horizontal wind speed, particularly its north–south component, correlates more strongly with discrepancies than vertical wind speed, except in high-concentration aerosol layers where vertical motions become influential. Furthermore, larger differences are associated with increased aerosol extinction coefficients (α) and particle depolarization ratios (δ). This work demonstrates that integrated applications of multi-platform lidar data must account for both meteorological controls on aerosol transport and particle microphysical properties. These findings provide a quantitative validation framework for current and future spaceborne HSRL missions and support the integrated application of multi-platform lidar observations in regional aerosol monitoring, air quality assessment, and climate effect research. Full article

Top-heavy industrial towers, which carry large, concentrated masses of equipment at upper levels and feature open lower stories, are vertically irregular by design and tend to amplify seismic displacement and acceleration demands near the tower top. Although tuned mass dampers (TMDs) have been studied extensively for buildings, bridges and chimneys, their application to this particular class of slender industrial towers—where production-equipment vibration tolerance, retrofit accessibility and limited downtime drive the design—has received little dedicated attention. This paper reports a focused numerical investigation of seismic response mitigation for a 101.2 m molten-asphalt granulation tower retrofitted with a single pendulum-type TMD. A three-dimensional coupled finite element (FE) model was constructed in ABAQUS using C3D8R solid elements for the reinforced-concrete shaft and T3D2 truss elements for the embedded reinforcement; modal analysis returned a fundamental frequency of 0.912 Hz and a torsional-to-translational period ratio of 0.65, indicating a translational-mode-dominated response. Elastic time-history analyses under the El Centro and Taft records together with a code-spectrum-compatible synthetic accelerogram show that a pendulum TMD with mass ratio μ = 2.5%, tuning frequency offset Δf = 5% and damping ratio ξ = 10%—installed at the uppermost equipment level guided by the modal-displacement criterion—reduces the peak top displacement, peak top acceleration and peak base shear by roughly 23%, 23% and 22%, respectively, in both principal directions. The controlled top acceleration falls comfortably below the 2.94 m/s² operational tolerance of the on-tower melting equipment. To address the rationality of the chosen TMD parameters, a single-variable parametric sensitivity study spanning μ ∈ [1%, 5%], ξ ∈ [5%, 15%] and Δf ∈ [0%, 10%] is performed on an equivalent reduced model that captures the qualitative parameter-response trends; the chosen baseline values lie inside a stable performance plateau and are shown to be a balanced compromise among the three response measures. The principal contribution of the work is, therefore, (i) a complete TMD retrofit framework—modal-based placement, parameter design, coupled FE assembly and multi-record verification—adapted to top-heavy industrial towers, and (ii) qualitative evidence, supported by a sensitivity scan, with a robust proposed parameter set for small-to-moderate detuning. The study is restricted to elastic time-history analyses under frequent-earthquake-level excitation, three ground-motion records and a fixed-base assumption; nonlinear response, larger record sets and soil–structure interaction effects are explicitly identified as scope limitations and are left for follow-up work. Full article

Steel moment-resisting frames exhibiting vertical geometric irregularities, particularly those with setback configurations, experience increased seismic demands due to stiffness discontinuities and complex dynamic interactions. These conditions present significant challenges for conventional vibration control strategies. This study introduces a performance-based optimization framework that utilizes the Circle-Inspired Optimization Algorithm (CIOA) to enhance the design of tuned liquid dampers (TLDs) in irregular steel structures. Structural responses are simulated in OpenSees, with a rheological model based on the Housner method employed to accurately capture fluid–structure interaction. Seismic performance is evaluated using a suite of real subduction-type ground motions, selected to represent the seismic hazard level of Armenia, Colombia, in accordance with the Conditional Scenario Spectra (CSS) methodology and the National Seismic Risk Model for Colombia. The optimization process considers the mean response across multiple ground-motion records to ensure robustness against seismic variability. Multiple time-domain objective functions are examined, including peak interstory drift, maximum displacement, and peak acceleration. The results indicate that objective functions related to interstory drift and displacement provide the most effective, stable, and consistent reductions in seismic demand across all scenarios, while acceleration-based objectives display greater sensitivity to record-to-record variability. These outcomes underscore the importance of objective function selection in determining both optimization stability and control effectiveness. The CIOA demonstrates rapid convergence, numerical robustness, and reliable performance, confirming its suitability as a computationally efficient and resilient optimization tool for the design of passive control systems in irregular steel structures exposed to high seismic hazard. Full article

Land subsidence and coseismic deformation can interact in groundwater-stressed sedimentary basins, yet basin-scale identification of event-timed vertical offsets in InSAR products requires explicit control of referencing and processing effects. This study evaluates whether the 27 September 2021 Arkalochori earthquake (Mw 6.0; central Crete) produced detectable coseismic vertical offsets within the Messara Basin by applying a reproducible screening workflow to Copernicus European Ground Motion Service (EGMS) Level-3 Vertical time series, from two processing generations (EGMS 2015–2021 and EGMS 2018–2022). An event-centered step metric (stepEQ), defined as the difference between post-event and pre-event mean displacements over a fixed acquisition window, is evaluated across three fixed spatial masks (MESSARA, R15060, R8750) together with a dispersion-based precision proxy (σstep) and a cross-generation sensitivity diagnostic (ΔstepEQ). A supplementary 2 + 2 subset sensitivity analysis indicates that the adopted fixed 3 + 3 estimator is stable at the basin scale, with sensitivity concentrated mainly in threshold-adjacent cases. Results indicate that Arkalochori-related offsets are not expressed as a basin-wide step across Messara; instead, non-background responses form a spatially limited and coherent subset concentrated where the basin intersects the near-source footprint. In EGMS 2018–2022, the higher vertical offset class (C2; |stepEQ| > 40 mm) is exclusively subsidence-direction and is enriched toward the screening center (up to ~19% within the radii mask R8750 m) but remains sparse at the basin scale mask (MESSARA mask) (~1%). Step-dominated points co-locate with strongly subsiding mean vertical velocity regimes and are hosted almost entirely by post-Alpine basin deposits, indicating strong material and background-deformation conditioning of step detectability. Cross-generation comparison shows basin-scale stability of background behavior but localized near-source sensitivity, supporting use of ΔstepEQ as a Quality Control (QC) lens for threshold-adjacent interpretations. The workflow provides a transparent, transferable approach for prioritizing candidate coseismic-step locations in EGMS time series. Results are interpreted as screening-level evidence in the derived vertical signal using event timing, spatial coherence, and QC diagnostics. Full article

This study investigates the influence of vertical separation between the girder and bearings under bidirectional seismic excitations on the failure modes of shear keys. A continuum dynamic model for a two-span girder bridge was established and solved using the transient wave eigenfunction expansion method. The dynamic response of structural vertical separation and horizontal collision under bidirectional seismic excitations was systematically analyzed. The results indicate that the vertical seismic component induces separation at the girder–bearing interface, which significantly alters both the magnitude and contact location of the horizontal collision force on the shear keys. This phenomenon is most pronounced when the predominant period of the ground motion approaches the structure’s vertical natural period, drastically amplifying the girder’s horizontal seismic response. Consequently, the failure mode of shear keys exhibits an evolutionary sequence: with increasing seismic amplitude, it transitions from flat shear to inclined shear, and ultimately to flexural failure. Crucially, this dynamic coupling effect simultaneously amplifies the horizontal collision force and reduces the shear keys’ load-bearing capacity. Under the most unfavorable collision conditions, the limit of the horizontal collision force can reach up to 5.12 times greater than its design bearing capacity. This study reveals that neglecting vertical seismic excitation severely underestimates the actual failure risk of shear keys, underscoring the critical need to consider this coupling effect in the seismic design and performance evaluation of bridges in high-intensity zones. Full article

Myriapods achieve remarkable obstacle-crossing capability through inter-segment pitch adjustment and coordinated anterior–posterior propulsion, providing valuable biomimetic inspiration for engineering design. Articulated tracked vehicles, connecting front and rear units via pitch mechanisms, exhibit functional similarity to myriapod body segments. This study develops a comprehensive dynamic model for articulated tracked vehicle pitch motion to reveal its biomimetic connection with myriapod locomotion. A quadratic-function-based non-uniform track–ground contact pressure distribution method with zero-gradient boundary conditions is proposed, effectively eliminating the non-physical negative pressure issue inherent in traditional assumptions. Systematic analyses reveal that the front unit provides primary traction under pitch-up conditions, forming a front-pulling-rear driving mode, while the rear unit dominates under pitch-down and acceleration conditions, forming a rear-pushing-front driving mode. Through pitch attitude adjustment, the maximum surmountable vertical-wall height increased from 263 to 593 mm, representing a 125.45% improvement. This traction distribution pattern closely matches the anterior-guidance and posterior-propulsion mechanism observed in myriapod locomotion. This study quantitatively validates the functional analogy between articulated tracked vehicle pitch dynamics and myriapod inter-segment coordination, providing theoretical foundations for bio-inspired tracked vehicle design. Full article

In the last decades, satellite remote sensing has played a key role in Earth Observation, as an effective monitoring tool applied to geo-hazard identification and mitigation. In particular, the differential synthetic aperture radar interferometry technique provides incomparable information on ground movements related to volcanic unrest, co-eruptive deformation, and volcano flank motion. In this work, ground deformation data derived from Sentinel-1 satellites were analyzed over the Cumbre Vieja volcano, located in the southern part of La Palma Island, Canary archipelago. The volcano started to erupt on 19 September 2021, after a seismic swarm. The eruption buried hundreds of buildings and properties, causing severe economic losses. Analyzing the vertical ground displacement of the volcano in the year preceding the eruption, the results show that ground deformation can be considered a precursor of the eruption, which allows us to identify the phases of the magmatic ascent up to the opening of the eruptive vent. Interestingly, after a subsidence phase lasting 4 months, the ground displacement rate reverted and an uplift was observed, lasting 9 months, marking an uplift on the Cumbre Vieja volcano related to volcanic activity. This can be interpreted as the effect of the magma rising from the deeper chamber (15–25 km) to an intermediate stagnation zone (5 km) that provided a measurable anticipation of the eruption by 9 months. In the future, regular monitoring of Cumbre Vieja could adopt uplift detection as an indicator for shallow magma activity and as a possible eruption precursor. Full article

The behavior of shield tunnel lining structures is known to be influenced by segmental joints. Most studies conducted in this area use simplified models, which may not properly simulate the behavior of the segmental joints. This study utilizes a full-reinforced concrete segment model to rigorously investigate the seismic behavior of joints in a segmental tunnel lining, explicitly accounting for segment–segment contact, interaction, and joint bolts. Specifically, a comprehensive full dynamic analysis of a two-dimensional (2D) lining–soil model, incorporating nonlinear constitutive models for both concrete (CDPM) and soil (Mohr–Coulomb), was conducted to investigate the effects of joint bolt type, seismic intensity, and vertical excitation component on the seismic response. The lining–soil model was excited using three ground motions. The results indicate that the joint rotation is significantly influenced by the amplitude and frequency content of ground motions, which has implications for the watertightness of the gasketed joint. In particular, including the vertical component of the excitations was found to increase the diametral deformation by at least 150% and tended to increase other structural responses. Moreover, the bolt tension increased significantly by over 400% with only a 150% increase in seismic intensity, highlighting the strong nonlinear sensitivity. However, due to the inherent constraints of the 2D plane-strain assumption, the influence of the bolt type remains inconclusive. Full article

This study addresses a critical gap in seismic design by quantifying how plan asymmetry and multiple earthquake sequences interact to affect the nonlinear reaction of reinforced concrete (RC)-framed models. While earthquake-resistant design provisions have evolved, most current codes are based on single-event assumptions and simplified symmetry considerations, overlooking the cumulative effects of repeated ground motions observed in recent international studies. In this research, symmetrical and asymmetrical low-rise RC buildings are analyzed through nonlinear dynamic simulations, with both single- and multiple-event ground excitations considered for comparison. The analyses incorporate three-dimensional ground motions in horizontal and vertical orientations, while explicitly modeling the nonlinear inelastic response of RC sections under severe seismic demands. The evaluation of elastoplastic findings relies on normalized indices, by considering a simple dimensionless parameter to quantify the physical symmetry or asymmetry of the RC models. Results show that increasing plan asymmetry amplifies inter-story drift, torsional rotations, and plastic hinge concentrations, particularly under successive earthquake sequences. These findings indicate that existing design provisions may underestimate the vulnerability of irregular RC buildings. This work is among the first to integrate plan asymmetry and multi-event seismic loading into a unified evaluation framework, offering a novel tool for refining earthquake-resistant design standards. Full article

On 18 March 2025, a moderate earthquake with moment magnitude Mw 4.2 struck the Basilicata region in Southern Italy. The event occurred at 09:01:25 UTC with an epicentre located approximately 4 km northeast of the city of Potenza (PZ). The earthquake was clearly felt across the urban area and followed by a sequence of low-magnitude aftershocks. A few hours after the main shock, researchers from the University of Basilicata installed a temporary structural monitoring network to check the structural conditions of several buildings located in Potenza. This installation enabled the acquisition of accelerometric recordings of several aftershocks, providing a valuable dataset for preliminary observations on structural seismic response. The monitoring campaign focused on two adjacent twin buildings with similar geometry and structural layout but different seismic design strategies: one conventionally fixed at the base and the other equipped with seismic base isolation made by rubber bearings. Comparative analyses revealed distinct differences in dynamic response. The results highlight the need for refined regulatory tools to address near-epicentral conditions, particularly potential dynamic interactions among the vertical ground-motion component, the vertical vibration frequencies of the superstructure, and floor-system resonance. While not critical for ultimate limit states, these effects may influence comfort and performance in operational and damage limit states. Full article

With the advancement of Light Detection and Ranging (LiDAR) technology and computer science, LiDAR–Inertial Simultaneous Localization and Mapping (SLAM) has become essential in autonomous driving, robotic navigation, and 3D reconstruction. However, dynamic objects such as pedestrians and vehicles, with complex terrain conditions, pose serious challenges to existing SLAM systems. These factors introduce artifacts into the acquired point clouds and result in significant vertical drift in SLAM trajectories. To address these challenges, this study focuses on controlling vertical drift errors in LiDAR–Inertial SLAM systems operating in dynamic environments. The research focuses on three key aspects: ground point segmentation, dynamic artifact removal, and vertical drift optimization. In order to improve the robustness of ground point segmentation operations, this study proposes a method based on a concentric sector model. This method divides point clouds into concentric regions and fits flat surfaces within each region to accurately extract ground points. To mitigate the impact of dynamic objects on map quality, this study proposes a removal algorithm that combines multi-frame residual analysis with curvature-based filtering. Specifically, the algorithm tracks residual changes in non-ground points across consecutive frames to detect inconsistencies caused by motion, while curvature features are used to further distinguish moving objects from static structures. This combined approach enables effective identification and removal of dynamic artifacts, resulting in a reduction in vertical drift. Full article

Designing long-span cable-stayed bridges in high seismic hazard zones presents significant challenges due to their flexible structural systems, the influence of multi-support excitation, and the need to control large displacements while limiting seismic demands on critical components. These difficulties are further amplified in regions with complex geology and for bridges required to maintain high levels of post-earthquake serviceability. This study develops a low-damage seismic design approach for long-span cable-stayed bridges and demonstrates its application in the New Panama Canal Bridge. Probabilistic seismic hazard assessment and site response analyses are performed to generate spatially varying ground motions at the pylons and side piers. The pylons adopt a reinforced concrete configuration with embedded steel stiffeners for anchorage, forming a composite zone capable of efficiently transferring concentrated stay-cable forces. The lightweight main girder consists of a lattice-type steel framework connected to a high-strength reinforced concrete deck slab, providing both rigidity and structural efficiency. A coordinated girder–pylon restraint system—comprising vertical bearings, fuse-type restrainers, and viscous dampers—ensures controlled stiffness and effective energy dissipation. Nonlinear seismic analyses show that displacements of the girder remain well controlled under the Safety Evaluation Earthquake, and the dampers and bearings exhibit stable hysteretic behaviours. Cable tensions remain within 500–850 MPa, meeting minimal-damage performance criteria. Overall, the results demonstrate that low-damage seismic performance targets are achievable and that the proposed design approach enhances structural control and seismic resilience in long-span cable-stayed bridges. Full article

The southern Korean Peninsula faces complex seismic challenges due to the concentration of critical infrastructure and the region’s unique intraplate tectonic environment. In this study, over 300 strong-motion records from 10 moderate-magnitude earthquakes were analyzed using data from 10 representative seismic stations. Acceleration response spectra, normalized by peak ground acceleration, were generated and systematically compared with international and domestic seismic design standards, including USNRC Regulatory Guide 1.60 and KBC 2016. The observed spectra frequently exceeded existing code requirements in the mid-to-high-frequency range critical for local infrastructure, indicating potential vulnerabilities in applying generic global standards to Korean conditions. Analysis of vertical-to-horizontal spectral ratios further revealed pronounced frequency dependence and amplification effects, especially in sedimentary basin sites. These findings underscore the importance of accounting for site-specific geological and seismic characteristics in the seismic design of critical infrastructure in Korea. The results advocate for the development of regionally calibrated, risk-informed seismic design frameworks and provide essential empirical data to support safer, more resilient infrastructure amid moderate but potentially hazardous earthquake activity. Full article

Pitching requires effective transfer of ground reaction force (GRF), and structural breakdown of the medial longitudinal arch (MLA) may influence glenohumeral internal rotation (IR) deficits. This study investigated whether changes in foot morphology of the stride leg and soft tissue characteristics are associated with loss of IR during repeated pitching. Fifteen male college pitchers completed 60 pitches in a simulated game. IR range of motion (IRROM) was assessed before and after pitching. The navicular height, mechanical properties of the abductor hallucis (AbH) and plantar fascia, and GRF were measured at multiple time points. Correlation analysis and a linear mixed model were used to identify predictors of IRROM change. The mean change in shoulder IRROM during pitching was −21.9° ± 8.4°. IRROM and navicular height decreased significantly over time. The AbH elasticity increased throughout the pitching sequence. Greater reductions in IRROM appeared related to a higher vertical GRF (p = 0.021) and increased AbH elasticity (p = 0.046). Vertical GRF was unrelated to fastball velocity (p = 0.260), whereas anteroposterior GRF correlated with fastball velocity (p = 0.038). Morphological and mechanical changes in the stride leg, particularly within the support of the MLA, can influence IRROM. Reducing vertical GRF and stress on the AbH may help preserve the IRROM without compromising performance. Full article