Archives of Civil and Mechanical Engineering最新文献

The manufacture of thin-walled structures via laser powder bed fusion (L-PBF) is associated with a number of technological challenges, such as control of the melting process, geometric stability, and surface quality. This paper describes the fabrication of inclined thin walls from M300 maraging steel using the L-PBF process. Thin walls were fabricated with thicknesses of 0.2–1.0 mm (in 0.2 mm increments) and inclination angles of 30–90° (in 15° increments). The geometric quality of the as-fabricated samples was analyzed using an optical 3D scanner, and the sample porosity was also examined using X-ray computed tomography and optical microscopy. Finally, the Vickers microhardness and surface roughness of L-PBF-processed inclined thin walls were examined. A geometric analysis revealed that the wall inclination angle relative to the building platform had a significant effect on the reproduction quality. The largest geometric deviations, with high porosity and high surface roughness, were observed for samples built at 30° and 45° angles. Vertical walls (with inclination angle 90°) gave the most precise reproduction of the CAD design and had a uniform microhardness distribution. The surface roughness of the walls was strongly dependent on the inclination angle of the sample relative to the building platform, with a greater wall incination angle resulting in greater wall surface roughness, as defined by the parameters Ra and Rz. These investigations of M300 maraging steel processing using L-PBF contribute to filling the existing research gap in regard to the application of this material for the fabrication of thin-walled structures.

The Al5xxx series is widely utilized across industries due to its high strength and corrosion resistance relative to other aluminium alloy groups. However, high-strength aluminium alloys fabricated via Powder Bed Fusion-Laser Beam of Metals (PBF-LB/M) are prone to solidification cracking and manufacturing defects, such as porosity. Micro-alloying with tantalum (Ta) has emerged as a promising strategy to mitigate these issues, i.e. adding Ta to PBF-LB/M processed Al5254 alloy significantly refined the grain structure, reducing it from > 100 μm to ~ 10 μm. This study evaluates the corrosion resistance of Al5254 and Ta-modified Al5254 processed via PBF-LB/M. Optimized processing parameters and novel chemical compositions were developed to minimize crack areas and porosity. Electrochemical performance was assessed in a 3.5% NaCl solution using linear polarization resistance (LPR) and Tafel extrapolation. Results indicate that Ta addition significantly enhances corrosion resistance by promoting self-passivation and altering the underlying corrosion mechanisms from intergranular corrosion to chemical passivation.

Asphalt pavements are permanently exposed to environmental factors, i.e. de-icing salts, which negatively affect their service properties and consequently shorten their life cycle. In times of increasing environmental awareness, it is necessary to reduce these negative processes and simultaneously prolong the service life of road pavements. In order to achieve this, knowledge of the salt erosion process at the atomic level is required. It is possible only by using computer methods. Therefore, this paper presents the results of quantum chemical calculations at the DFT/B3LYP/6-311 g-dp level. The results clearly show that the formation of the C–Cl chemical bond in the bitumen binder component structures occurs most efficiently in the BbBT molecule, resulting in a reduction of its E_HOMO and E_LUMO. Furthermore, these structural changes also cause a decrease in its E^GAP by approximately 28%. The competitive C–OH bond-forming reaction in the bitumen components occurs via direct uptake of the OH⁻ ion from solution by the previously formed carbocation. The determined energy profiles indicate that this reaction occurs most efficiently in the DOCHN molecule. Considering the fact that this molecule is characterised by a relatively low C–Cl bond formation energy, the obtained results indicate that this molecule is most susceptible to the destructive effects of the salt erosion process.

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A novel precast concrete (PC) shear wall system connected to steel columns with friction bearing devices (FBDs) was recently proposed and experimentally validated, owning excellent ductility and sufficient energy dissipation capacity. However, almost no researches have been conducted to model the behaviors of the novel PC shear wall system. This paper presents a simulation technique developed with OpenSees models and validated against experimental results. The numerical model demonstrates good accuracy in predicting load-bearing capacity, cumulative energy dissipation, and FBD behavior, with a maximum error in peak load of no more than 7.9% compared to experimental results. Parametric analyses further investigated the effects of key variables, including the axial load ratio, column-to-wall stiffness ratio, bolt slot length, friction force threshold, and number of FBDs, on the seismic performance of the novel PC shear walls. Increasing the axial load ratio significantly enhances the peak load and intensifies the pinching effect of hysteresis curves, while its impact on cumulative energy dissipation and initial stiffness is negligible. It also delays the locking displacement of FBDs. Raising the stiffness ratio improves the peak load and initial stiffness but has limited influence on energy dissipation and damping. Extending the slot length of FBDs markedly delays the locking displacement and enhances energy dissipation capacity, whereas its effect on peak load and initial stiffness is minimal. Increasing the friction threshold of FBDs substantially improves energy dissipation performance but offers only modest gains in peak bearing capacity, with initial stiffness showing notable improvement only at lower threshold levels. Employing more FBDs comprehensively enhances the structural bearing capacity, energy dissipation, and stiffness. Notably, across all parametric variations, the locking displacement of FBDs remains consistent and is unaffected by changes in the stiffness ratio, friction threshold, or the number of FBDs. Collectively, these findings offer a systematic parametric foundation for the performance-based design of such new structural systems.

Human-induced vibrations present a critical serviceability and safety challenge for lightweight footbridges in scenic areas. Recent studies have proposed a crowd flow control strategy using fixed obstacles to mitigate such vibrations, yet its effectiveness remains limited. To address this, the present study proposes a more efficient “stationary pedestrian” strategy, which involves designating specific zones on the bridge deck for static occupancy. This strategy intervenes at the vibration source by integrating crowd flow control with the inherent biomechanical damping of the human body. The social force model was employed to simulate crowd flow. A pedestrian-stationary pedestrian-structure coupled model and a finite element model of the footbridge were established. A comparative analysis of the vibration mitigation performance of both strategies was conducted across varying crowd densities. The results show that fixed obstacles, acting through geometric constraints, achieved vibration reduction rates of 11.2%, 14.4%, and 16.4% at the 1/4, 1/2, and 3/4 bridge spans, respectively. In contrast, the stationary pedestrian strategy enhanced these rates to 14.8%, 18%, and 19.7% at the corresponding locations. The 3/4-span layout proved most effective, regulating approximately 70% of the crowd flow velocity. This study represents a paradigm shift from conventional passive structural damping to active source control via crowd management. The core of the proposed strategy lies in the synergy between crowd flow control and human biomechanical damping, effectively reducing structural vibrations without physical modifications. This method thus offers a promising and potentially low-cost solution for mitigating vibrations in existing footbridges.

Weathering has a significant effect on the engineering properties of rocks, therefore the aim of this paper is to investigate the compressive properties, crack evolution trends and damage precursors of granite before and after weathering. For this purpose, uniaxial compression tests and Brazilian splitting tests were carried out with the help of acoustic emission, scanning electron microscopy and nuclear magnetic resonance equipment to complement the study. The results show that: after weathering, the porosity of the rock increases, the cementation between the mineral particles is weakened, and some minerals have been transformed into clay minerals; the fresh rock mainly exhibits axial cleavage damage, while the weathered rock mainly undergoes shear damage; the microscopic failures and internal damages of the rock during the damage process after weathering are reduced, and the degree of the damage is lowered; the signals of the tensile cracks with a high AF and the signals of the more shear The tensile crack signals with high AF values and more shear crack signals can be taken as the basis for determining the damage of the rock samples. The RA/AF values are used as the indicators of the damage of the rocks, and the dispersion of the RA/AF values in a certain time series is used to predict the damage of the rocks, and the use of the coefficient of variation to characterise the dispersion achieves a better effect. This study can provide a reference for understanding the changes in mechanical properties of granite before and after weathering and damage prediction.

This study investigates the effect of various debonding conditions on the dynamic vibrational behavior of GFRP-reinforced steel structures through numerical simulations alongside experimental tests for a selected group of debonding conditions. Intact and debonded samples were analyzed in a variety of sizes ranging from 5% to 90% of the bonded area, considering four debonding configuration. The first six natural frequencies obtained numerically were used in quantitative statistical analysis and validated against a group of experimental results. The results revealed that natural frequencies constantly declined as the debonding size expands, with the drop becoming significant beyond 25%. Smaller debonding sizes (5% and 10%) exerted a minimal influence on the first two vibration modes (mode 1–2), which makes the early detection difficult using lower order modes. In contrast, higher modes (modes 4–6) exhibited significant reduction in frequency of vibration even for smaller debonding sizes, indicating higher sensitivity to localized stiffness loss. Among the configurations, longitudinal debonding produced the most significant, whereas centrally positioned transverse debonding exhibited a minor effect. The accuracy of the generated statistical models in identifying relevant parameters demonstrated a high coefficient of determination (R²) ranging from 95.7%, to 99.6% for the first six modes. The numerical results were also close to the experimental measurements with ≤ 10% error for the analyzed debonding scenarios. The research advances the assessment of debonding in GFRP-steel structures by quantifying the combined impact of debonding size and configurations on modal response and demonstrating the effectiveness of GFRP in improving the structural performance across vibration modes, in addition to its potential application for corrosion resistance.

To minimize the influence of particle morphology and fragmentation on the strength and deformation evolution of coarse-grained soils, spherical glass beads were employed in isotropic consolidation and conventional triaxial compression tests. These experiments aimed to investigate the effects of particle size, mass ratio, and confining pressure. The results indicate that during shear processes, the void ratio gradually decreases with increasing confining pressure. Under identical confining pressures, the compaction capacity varies significantly among specimens with different mass ratios. Specifically, the compaction capacities of the void ratios (e_cap) in the 1:1 and 4:1 mass ratios are notably higher than that of the 1:4 mass ratio. Based on the strength parameters and deformation characteristics (q, ε_r, ε_v) of the specimens with mass ratios of 1:1, 4:1, and 1:4, it is evident that a well-balanced combination of coarse and fine particles with better interlocking (1:1 and 4:1) demonstrates higher shear strength and more uniform deformation. Conversely, the 1:4 mass ratio exhibits inferior stability. This phenomenon may be attributed to the complexity of particle arrangement and the evolution of pore structure. Accordingly, a fractal model incorporating correlations between pore-size and particle-size distributions was employed to investigate the underlying mechanisms of the specimen. The results indicate that specimens exhibiting minor variations in D_c (the consolidation-state fractal dimension) and D_cap (the compaction-induced fractal dimension) demonstrate superior structural stability, whereas D_0.25 displays pronounced variation amplitudes and a marked tendency for slippage occurrence. The results establish the fractal dimensions (D_c, D_cap) as indicators of structural stability, providing theoretical and practical guidance for optimizing fill material design in geotechnical engineering.

The paper presents an original design solution for a semi-active torsional damper filled with granular material. The main working element of the damper is the so-called Vacuum Packed Particles—a loose granular material placed in a sealed space where partial vacuum is created (activating the jamming mechanism). Internal pressure changes allow for the real-time, controlled modification of the device’s dissipative properties. Experimental investigations of the damper filled with rubber grains are presented. A mathematical model was applied to describe the experimental data, enabling the capture of damage and fatigue phenomena occurring in the damper. Based on the identified mathematical model, numerical simulations for standard operational damper conditions were conducted.

Composite beam-and-block floor systems are widely used in residential and public buildings, yet their design is still governed by conservative assumptions that neglect the composite action between ceramic infill blocks and structural concrete. This study presents full-scale laboratory tests on four composite ribbed floor models with varying block–concrete interaction and with or without transverse ties. The results show that composite action significantly improves structural performance. In particular, the presence of both block–concrete cooperation and transverse ties increased the bending capacity by approximately 20% and extended the linear range of moment–deflection and strain relationships by about 15% compared to non-composite models. Moreover, the stabilization of the neutral axis at the block–concrete interface confirmed the beneficial effect of composite action on stiffness. These findings highlight hidden reserves in both ultimate and serviceability limit states and provide experimental evidence that challenges current design simplifications. Incorporating composite action into design practice could lead to more economical and reliable slab solutions, with transverse ties playing a crucial role in ensuring structural efficiency.