Search Results (267)

Based on the research on concrete-filled circular steel tubular columns, the influence of carbon-fiber-reinforced polymers (CFRPs) on the ultimate bearing capacity of concrete-filled steel tubes (CFSTs) was further explored in this paper. Ten different concrete-filled circular CFRP–steel middle long columns were made for an axial compression test, and the influence of the CFRP layers, the concrete strength grades, the steel tube wall thickness, and the slenderness ratio on the ultimate bearing capacity was discussed. Combined with theoretical analysis, the calculation method of ultimate bearing capacity of it was found. The load midspan deflection diagram was obtained by numerical simulation with finite element analysis software ANSYS2021R1, and the test results were compared. The results demonstrate that CFRP layers significantly enhance the ultimate bearing capacity of circular steel tube–CFRP confined concrete columns, with one to three layers increasing the capacity by 42.5%, 69.4%, and 88.4%, respectively, under identical conditions. In comparison, the concrete strength, the steel tube thickness, and the slenderness ratio showed lesser effects (<20% improvement), providing critical support for engineering applications of CFRP-confined circular steel tubular columns. Moreover, the error of ANSYS calculation results is small, which is in line with the test. This is of great significance to verify the correctness of the test of concrete-filled circular CFRP–steel middle long columns. Full article

This study investigates the failure modes and damage extent of reinforced concrete (RC) columns under the combined action of eccentric blast loading and axial compressive loading through experimental tests and numerical simulations. Field blast tests were performed using half-scaled-down models for close-in airburst tests. The effects of charge mass, explosive position, and axial load on the failure modes and damage levels of RC columns under close-range blast loading were investigated. Eight experimental datasets of blast overpressure were obtained, and curve fitting was performed on these data to establish an empirical formula, thereby enhancing the predictive accuracy of blast effect assessment in practical engineering scenarios. The test results indicated that when the explosive position is closer to the column base, the structural failure mode becomes closer to shear failure. To further interpret the experimental data, a detailed finite element model of RC columns was developed. Numerical simulations of RC columns were conducted using the RHT model. The rationality of the model was validated through comparison with experimental data and the SDOF method, with dynamic response analyses performed on cross-sectional dimensions, the longitudinal reinforcement ratio, the scaled distance, the explosion location, and axial compression. An empirical formula was ultimately established to predict the maximum support rotation of RC columns. Studies have shown that when the explosive position is closer to the column base, the structural failure mode approaches shear failure, and axial compression significantly increases the propensity for shear failure. Full article

This paper proposes a joint time–frequency analysis method that combines Rao detector with dynamic sliding thresholds to enhance the detection performance of electric source axial frequency magnetic field signals. For each signal-to-noise ratio (SNR) point, 1000 Monte Carlo simulations were independently conducted, with SNR ranging from 15 dB to −30 dB. The results show that the proposed method maintains high detection rates even at extremely low SNRs, achieving about 90% detection probability at −13 dB, significantly outperforming traditional energy detectors (with a threshold of 2 dB). Under conditions where the detection probability is ≥90% and the false alarm probability is 10⁻³, the SNR threshold for the Rao detector is reduced by 15 dB compared to energy detectors, greatly improving detection performance. Even at lower SNRs (−30 dB), the Rao detector still maintains a certain detection rate, while the detection rate of energy detectors rapidly drops to zero. Further analysis of the impact of different frequencies (1–5 Hz) and CPA distances (45–80 cm) on performance verifies the algorithm’s robustness and practicality in complex non-Gaussian noise environments. This method provides an effective technical solution for low SNR detection of ship axial frequency magnetic fields and has good potential for practical application. Full article

Rainfall-induced landslide mitigation remains a critical research focus in geotechnical engineering, particularly for safeguarding buildings and infrastructure in unstable terrain. This study investigates the stabilizing performance of slopes reinforced with negative Poisson’s ratio (NPR) anchor cables under rainfall conditions through physical model tests. A scaled geological model of a heavily weathered rock slope is constructed using similarity-based materials, building a comprehensive experimental setup that integrates an artificial rainfall simulation system, a model-scale NPR anchor cable reinforcement system, and a multi-parameter data monitoring system. Real-time measurements of NPR anchor cable axial forces and slope internal stresses were obtained during simulated rainfall events. The experimental results reveal distinct response times and force distributions between upper and lower NPR anchor cables in reaction to rainfall-induced slope deformation, reflecting the temporal and spatial evolution of the slope’s internal sliding surface—including its generation, expansion, and full penetration. Monitoring data on volumetric water content, earth pressure, and pore water pressure within the slope further elucidate the evolution of effective stress in the rock–soil mass under saturation. Comparative analysis of NPR cable forces and effective stress trends demonstrates that NPR anchor cables provide adaptive stress compensation, dynamically counteracting internal stress redistribution in the slope. In addition, the structural characteristics of NPR anchor cables can effectively absorb the energy released by landslides, mitigating large deformations that could endanger adjacent buildings. These findings highlight the potential of NPR anchor cables as an innovative reinforcement strategy for rainfall-triggered landslide prevention, offering practical solutions for slope stabilization near buildings and enhancing the resilience of building-related infrastructure. Full article

Steel fiber-reinforced polymer (FRP) composite bars (SFCBs) combine the ductility of steel reinforcement with the corrosion resistance and high strength of FRP, providing stable secondary stiffness that enhances the seismic resistance and safety of seawater sea–sand concrete structures. However, the seismic performance of SFCB-reinforced seawater sea–sand concrete beam–column joints remains underexplored. This study presents pseudo-static tests on SFCB-reinforced beam–column joints with varying column SFCB longitudinal reinforcement fiber volume ratios (64%, 75%, and 84%), beam reinforcement fiber volume ratios (60.9%, 75%, and 86%), and axial compression ratios (0.1 and 0.2). The results indicate that increasing the axial compression ratio enhances nodal shear capacity and bond strength, limits slip, and reduces crack propagation, but also accelerates bearing capacity degradation. Higher column reinforcement fiber volumes improve crack distribution and ductility, while beam reinforcement volume significantly affects energy dissipation and crack distribution, with moderate volumes (e.g., 75%) yielding optimal seismic performance. These findings provide insights for the seismic design of SFCB-composite-reinforced concrete structures in marine environments. Full article

The global transition toward clean energy has driven the extensive deployment of overhead tower-lines in desserts, where such structures face unique challenges from wind–sand interactions. The current design standards often overlook these combined loads due to oversimplified collision models and inadequate computational frameworks. These gaps are bridged in the present study through the development of a refined impact force model grounded in Hertz contact theory, which captures transient collision mechanics and energy dissipation during sand–structure interactions. Validated against field data from northwest China, the model enables a comprehensive parametric analysis of wind speed (5–60 m/s), sand density (1000–3500 kg/m³), elastic modulus (5–100 GPa), and Poisson’s ratio (0.1–0.4). Our results show that peak impact forces increase by 66.7% (with sand density) and 148% (with elastic modulus), with higher wind speeds amplifying forces nonlinearly, reaching 8 N at 30 m/s. An increased elastic modulus shifts energy dissipation toward elastic rebound, reducing the penetration depth by 28%. The dynamic analysis of a 123.6 m transmission tower under wind–sand coupling loads demonstrated significant structural response amplifications; displacements and axial forces increased by 28% and 41%, respectively, compared to pure wind conditions. These findings reveal the importance of integrating coupling load effects into design codes, particularly for towers in sandstorm-prone regions. The proposed framework provides a robust basis for enhancing structural resilience, offering practical insights for revising safety standards and optimizing maintenance strategies in arid environments. Full article

While the longitudinal pre-embedded holes in a reinforced concrete column have a variety of beneficial functions during the whole life of the building, they have certain negative influences on the mechanical properties of the column. To investigate the influences of longitudinally pre-embedded holes on the mechanical properties of reinforced concrete (RC) columns, numerical simulations were conducted using the finite element software ABAQUS 2021 to analyze the effects of various parameters, including hole diameter, concrete strength, stirrup ratio, and slenderness ratio, on the mechanical behavior of RC columns under axial pressure. The results show that the presence of longitudinally pre-embedded holes reduces the load-bearing capacity of the columns. Furthermore, when the hole diameter exceeds 75 mm and the concrete strength is over C35, the failure mode of the columns shifts from axial compression failure to shear failure at the bending section of the pre-embedded hole. Increasing the stirrup ratio effectively enhances the ductility and load-bearing capacity and avoids brittle failure, whereas the influence of slenderness ratio variations on the column’s bearing capacity is negligible. These results provide a theoretical basis for the safe design of longitudinally pre-embedded hole columns in green buildings, effectively balancing the requirements between structural lightweight design and load-bearing performance. Full article

Engineering Cementitious Composites (ECC) has gained significant attention in civil engineering due to its excellent tensile strength, crack width control capability, and remarkable ductility. This study examines the influence of the ECC strength and reinforcement on the flexural behavior of ECC slabs through four-point flexural tests. The results demonstrate that ECC is well suited for flexural applications. During flexural tests, the fibers within the ECC provide a bridging effect, allowing the ECC in the tensile zone to sustain a load while developing a dense network of fine microcracks at failure. This characteristic significantly enhances the crack resistance of ECC slabs. Despite the relatively low flexural capacity of unreinforced ECC slabs, they achieve 59.2% of the capacity of reinforced ECC slabs with a reinforcement ratio of 1.02%, demonstrating the potential for using unreinforced ECC in low-load-bearing applications. Further findings reveal that high-strength ECC (HSECC) not only improves the flexural capacity of unreinforced ECC slabs but also maintains excellent ductility, enabling a better balance between the load-bearing capacity and deformation ability. However, while reinforcement enhances both the flexural capacity and energy absorption, an excessively high reinforcement ratio significantly compromises ductility. Additionally, this study proposes a simplified calculation method for the flexural capacity of ECC slabs based on the axial force and moment equilibrium, providing theoretical support for their design and application. Due to their excellent flexural behavior, ECC slabs exhibit significant potential for use in flexural components such as bridge deck slabs and link slabs in simply supported beam bridges. With continued research and optimization, their application in engineering practice is expected to become more widespread, thereby improving the cracking resistance and durability of concrete structures. Full article

Seismic resilience is a critical concern in the development of prefabricated concrete structures. This study investigates the seismic performance of prestressed prefabricated concrete frames with mechanically connected steel bars through both experiment and finite element simulations using ABAQUS. The research aimed to evaluate the influence of prestressed and mechanical connections on structural stiffness, energy dissipation and failure mechanisms, and a restoring force model was developed based on the experimental and numerical results to provide a theoretical basis for seismic design. The parametric analysis based on the verified numerical model shows that the pretension can significantly enhance the bearing capacity, stiffness and deformation recovery ability of the prefabricated concrete frames. The peak load increased by 30.8%, the initial stiffness improved by 17.4%, the ductility coefficient reached 2.82, the residual deformation rate reduced by 40.7%, the emergence and development of cracks delayed, and the crack width reduced. Improving the effective prestress in a certain range can improve the bearing capacity and initial stiffness of the frame. Increasing the strength of concrete and the ratio of the longitudinal reinforcement of beam and column can effectively enhance the bearing capacity of the frame. With the increase of axial compression ratio in a certain range, the bearing capacity and initial stiffness of the frame increase significantly, but the ductility decreases. Based on the hysteresis curve and skeleton curve tested, the skeleton curve model and stiffness degradation law of the prestressed prefabricated concrete frames reinforced with mechanical connection steel bars were fitted, and the restoring force model was established. The predicted value was in good agreement with the experimental value, illustrating the validity of the model developed. These results offer valuable insights for optimizing the seismic design of prefabricated concrete frames, ensuring a balance between strength, stiffness, and ductility in earthquake-resistant structures. Full article

Beam–column joints in reinforced concrete frames are subjected to complex forces and are prone to damage under seismic actions. This paper proposes a method to strengthen beam–column joints using angle steel and split bolts. The hysteretic performance of the strengthened components is investigated through test and finite element numerical simulation. The influencing parameters, including concrete strength grade, axial compression ratio, stirrup characteristic value, angle steel leg length, and angle steel leg thickness, are analyzed. The results show that angle steel can simultaneously enhance the strength and stiffness of the strengthened joints. With an increase in concrete strength grade, the load-carrying capacity of the strengthened components continuously increases. However, when the axial compression ratio exceeds 0.6, the load-carrying capacity of the strengthened components significantly decreases. The size of the stirrup characteristic value has little influence on the shear resistance of the strengthened joints. The leg length and leg thickness of the angle steel have certain effects on the strengthening effectiveness. The method of outward movement of plastic hinges can effectively improve the seismic performance of bi-directionally loaded spatial joints. Full article

The finite-element model was developed using ABAQUS to investigate the hysteretic properties of space joints. This study examined the effects of axial compression ratio, T-plate stiffness, column wall thickness, and bolt-preload on the joint’s hysteretic behavior. The model was verified by comparing the failure modes, hysteresis curves, and skeleton curves of the specimens with the test results of the relevant literature, ensuring the reliability of the research. The results reveal three primary failure modes: beam flange buckling, T-plate buckling, and column-wall buckling; increasing the thickness of the T-plate web or column wall significantly enhances joint stiffness and mitigates brittle failure. Specifically, the stiffness of T-plate 1 has a substantial impact on joint performance, and it is recommended that its web thickness be no less than 18 mm. In contrast, variations in the thickness of T-plate 2 have negligible effects on seismic performance. Increasing the column wall thickness improves the bearing capacity and stiffness of the joint, with a recommended minimum thickness of 12 mm, which should not be less than the flange thickness of the steel beam. While an increase in the axial compression ratio reduces the bearing capacity and stiffness, it enhances the energy dissipation capacity and ductility of the joint. Notably, variations in bolt-preload were found to have minimal influence on joint performance. These findings provide valuable insights for optimizing the design of unilateral bolted joints in steel structures to improve seismic resilience. Full article

To reveal the confinement mechanism of high-strength rectangular spiral stirrups (HRSSs) on fiber-reinforced concrete, this study designed and conducted axial compression tests on 20 HRSS-confined fiber-reinforced concrete columns. The effects of stirrup spacing, stirrup strength, and concrete strength on the strength and ductility of the columns were analyzed. The experimental results demonstrate that HRSS can significantly improve the performance of fiber-reinforced concrete. The peak strength of concrete exhibited a maximum increase of 2.033 times, and the ductility ratio achieved a maximum increase of 2.588 times. Furthermore, the application of densely spaced high-strength spiral hoops to confine the core concrete not only effectively enhances its compressive strength but also markedly improves its deformability. Based on the stress distribution across the cross-section of HRSS-confined fiber-reinforced concrete columns, this paper proposes a method for delineating the effective confinement area, establishes calculation models for effective lateral confinement stress, effective confinement coefficient, peak stress, and peak strain, and develops a stress-strain constitutive relationship suitable for HRSS-confined fiber-reinforced concrete columns. Full article

Background: This study aims to evaluate how surgical timing and the radiological characteristics of fragment blocks can affect the effectiveness of ligamentotaxis, in restoring the spinal canal area, and local kyphosis in adults with traumatic thoracolumbar A3 burst fractures without neurological impairment treated with percutaneous short-segment fixation. Methods: A retrospective observational study was conducted between January 2016 and December 2022 on neurologically intact adult patients with a single A3 thoracolumbar fracture. Data collected included demographics, injury mechanism, fracture level, and clinical and surgical details. Radiological assessments included spinal canal area, local kyphotic angle, anterior and posterior vertebral heights, and fragment block measurements. Results: Out of 101 treated patients, 9 met the criteria with a mean age of 52.22 years. Most fractures were at L1 (88.89%). All patients had moderate-to-severe pain (NRS 6.22 ± 1.09) at baseline. Five patients (55.55%) underwent surgery within 72 h, with a mean surgical time of 109.22 min. SCA and LKA values improved significantly in all patients post-surgery. Early surgical intervention (<72 h) correlated with greater improvements in spinal canal area (p = 0.016) and local kyphotic angle (p = 0.004). A significant association was found between spinal canal area improvement and the percentage ratio of fragment height to “normal” vertebral height (rho = 0.682; p = 0.043). Conclusions: Early (<72 h) short-segment percutaneous fixation is recommended for adults with high functional demands and moderate-to-severe axial pain due to single traumatic A3N0M0 thoracolumbar fracture. This “upfront” approach is associated with enhanced indirect decompression and better local kyphotic angle restoration. Considering the fragment morphology could also be important in surgical planning. Full article

To investigate the influence of circulation distribution on axial-flow pump performance, this study integrates numerical simulation and theoretical analysis methods, establishing a simulation framework based on MATLAB and CFX. By adjusting the circulation distribution function from the hub to the tip of the impeller, various design models were constructed. Three-dimensional parametric modeling of the blades was achieved through MATLAB programming, generating key parameters such as blade profile coordinates. Subsequently, the geometric data were imported into CFX to establish a full-flow passage numerical model. The simulation employed the RANS equations with the k-ε turbulence model to analyze flow field characteristics and hydraulic performance under different circulation schemes. Numerical results indicate that under identical circulation distributions, the head–flow curve exhibits a monotonically decreasing trend, while the efficiency curve demonstrates a distinct single-peak characteristic. Notably, under specific design conditions, variations in design parameters can shift the best efficiency point while simultaneously improving efficiency. Cavitation performance analysis reveals that as the hub-to-tip ratio increases, the velocity circulation initially rises rapidly before gradually stabilizing. This distribution pattern effectively optimizes the pressure gradient at the impeller outlet, thereby significantly enhancing cavitation resistance across a wide operational range. The proposed circulation control methodology provides critical theoretical support and engineering guidance for the hydrodynamic optimization of low-head axial flow pumps. Full article

Object Detection (OD) in Remote Sensing Imagery (RSI) encounters significant challenges such as multi-scale variation, high aspect ratios, and densely distributed objects. These challenges often result in misalignments among Bounding Box (BBox) representation, Label Assignment (LA) strategies, and regression loss functions. To address these limitations, this study proposes a novel detection framework, the Gaussian Detection (GaussianDet) Framework, that integrates probabilistic modeling with dynamic sample assignment to achieve more precise OD. The core design of this framework is inspired by the theory of geometric symmetry. Specifically, the radial symmetry of a two-dimensional Gaussian distribution is employed to capture the rotational and scale-invariant properties of Remote Sensing (RS) objects. By leveraging the axial symmetry of elliptical geometry, the proposed Gaussian Elliptical Intersection over Union (GEIoU) enables rotation-aligned matching, while Omni-dimensional Adaptive Assignment (ODAA) introduces dynamic symmetric constraints to optimize the spatial distribution of training samples. Specifically, a Flexible Bounding Box (FBBox) representation based on a 2D Gaussian distribution is introduced to more accurately characterize the shape, aspect ratio, and orientation of objects. In addition, the GEIoU is designed as a scale-invariant similarity metric to align regression loss with detection accuracy. To further enhance sample quality and feature learning, the ODAA strategy adaptively selects positive samples based on object scale and geometric constraints. Experimental results on the High-Resolution Ship Collection 2016 (HRSC2016) and University of Chinese Academy of Sciences–Aerial Object Detection (UCAS-AOD) datasets demonstrate that GaussianDet achieves mean Average Precision (mAP) scores of 90.53% and 96.24%, respectively. These results significantly outperform existing Oriented Object Detection (OOD) methods, thereby validating the effectiveness of the proposed approach and providing a solid theoretical foundation for future research in Remote Sensing Object Detection (RSOD). Full article