Search Results (2,046)

This study investigates the design, microstructure, and performance profile of a novel composite coating combining a high-entropy alloy (HEA) matrix with cermet reinforcement. A 50wt.%CoCrFeMnNi_0.8V–50wt.% Cr₃C₂-Ni₈₀Cr₂₀ powder mixture was successfully deposited onto steel substrates via high-velocity oxy-fuel (HVOF) thermal spraying. Microstructural analysis revealed a highly dense, well-bonded coating architecture (450–500 μm thick) where partially melted, spherical HEA splats were uniformly surrounded by the Cr₃C₂-Ni₈₀Cr₂₀ phase. X-ray diffraction confirmed a complex multiphase evolution consisting of FCC, BCC, and σ-NiCr phases driven by the rapid solidification inherent to the HVOF process. Tribological evaluations via ball-on-disc testing demonstrated that incorporating the Cr₃C₂-Ni₈₀Cr₂₀ reinforcement significantly improves wear resistance compared to the monolithic HEA coating. The composite’s wear behavior is governed by a synergistic mechanism: the ductile HEA matrix accommodates plastic deformation, while the harder carbide particles enhance load-bearing capacity, transitioning from adhesive wear to mild third-body abrasion and protective tribo-oxidation. Conversely, electrochemical testing in a 3.5 wt.% NaCl solution showed that the composite coating exhibits higher corrosion current densities (10.53 × 10⁻⁶ A/cm²) and more active corrosion potentials than the pure HEA matrix. This behavior is attributed to localized micro-galvanic cells forming at the heterogeneous interfaces between the different phases, alongside chloride-induced destabilization of the surface oxide film. Overall, the novel composite coating offers a compelling, sustainable alternative for surface engineering applications requiring a balanced trade-off between mechanical toughness and acceptable environmental durability. This behavior is also verified by the comparison with previous results dealing with monolithic CoCrFeMnNi_0.8V and 75wt.%CoCrFeMnNi_0.8V–25wt.% Cr₃C₂-Ni₈₀Cr₂₀ thermal sprayed coatings, where it is evident that the increase of the reinforcing phase leads to an optimum combination of properties. Full article

To address the engineering challenges of asymmetric large surrounding rock deformation and roadway support failure of deep gob-side entry retaining (GER) in the top-coal roadway, the progressive surrounding rock instability mechanism and fracture spatiotemporal evolution characteristics are revealed via theoretical analysis and universal distinct element code (UDEC) Trigon discrete element simulation. Results show that the top coal first undergoes bed separation and tensile failure, followed by backfill corner crushing and bearing capacity loss, which ultimately induces roadway support failure. Using UDEC simulation and mechanical tests, the influences of top-coal thickness, key block B length, backfill performance, and roadway support mode on roadway support stability are systematically clarified. Results indicate that keeping full top coal within the reinforcement zone, reducing key block B length, adopting a backfill width-to-height ratio of 0.45–0.8, a water–cement ratio of 1.5:1, and combining synergistic anchoring with delayed reinforced support can reduce the risk of roadway support failure. An optimized support scheme for the entry is proposed and field-implemented. Monitoring shows that the backfill has a smooth surface; reinforcement ladder beams and steel mesh have no fracture; coal pillar peak stress reaches 5.95 MPa; coal rib bolt load (178 kN) is significantly higher than that in the backfill section (115 kN); and the backfill adapts well to roof rotation and subsidence. The results support the feasibility of the proposed control scheme under the studied geological and engineering conditions and may provide a useful reference for similar GER projects. Full article

Under complex terrains and extreme environmental conditions such as high wind speeds, prestressed rock anchor foundations for onshore wind turbines are subjected to multiple coupled adverse effects during long-term service, including cyclic wind loading, temperature variation, groundwater intrusion, and rock mass weathering. These factors significantly affect structural performance and service life through corrosion and material degradation processes, while conventional design methods mainly focus on ultimate bearing capacity and lack a systematic consideration of corrosion-induced deterioration mechanisms and long-term performance evolution. Without changing the theoretical framework of current design codes, this study introduces a durability-oriented design concept and explicitly incorporates corrosion effects and material degradation into the analytical system of prestressed rock anchor foundations. First, from the perspective of anchor force evolution, a time-dependent analysis method for long-term prestress loss is established, considering the coupled effects of steel corrosion, material relaxation, and cyclic loading. Second, for the mechanical behavior of group anchor systems, a shear capacity model is proposed that accounts for rock mass strength degradation and grout–rock interface deterioration. Meanwhile, the coupling relationship between foundation void development and groundwater seepage is analyzed, revealing its critical role in the corrosion evolution process. On this basis, a coordinated design method for foundation dimensions and prestress parameters is developed to satisfy both load-bearing capacity and durability requirements. Finite element analysis is further conducted to verify the stress and deformation characteristics of the foundation–rock–anchor system under nonlinear conditions. Engineering case studies demonstrate that the proposed method not only meets bearing capacity requirements, but also effectively suppresses void development, reduces corrosion risk, delays structural performance degradation, and improves long-term service reliability. The findings provide a theoretical basis and engineering reference for the durability design and lifecycle performance optimization of prestressed rock anchor foundations for onshore wind power structures in extreme environments. Furthermore, the study underscores the critical role of advanced anti-corrosion coatings and surface protection systems in mitigating the coupled corrosion-degradation mechanisms, aligning with the scope of this Special Issue on corrosion protection and durability of infrastructure in harsh environments. Full article

To address the insufficient bearing capacity of existing slab culverts under increased fill heights in highway widening projects, a reinforcement method integrating an additional deck slab with a grouted steel pipe pile-supported composite foundation is proposed. A segmented elastic foundation beam model is developed to derive the analytical solution for slab deflection and calculate the load acting on the culvert roof. A three-dimensional finite element model is established in Abaqus, in which the soil is modeled using the Mohr–Coulomb elastoplastic constitutive model to investigate the effects of pile arrangement, pile diameter, pile length, pile spacing, and fill height on reinforcement performance. The results show that culvert displacement and stress decrease with reduced pile spacing and increased pile diameter and pile length, while the best reinforcement performance among the investigated cases is achieved when the piles extend 4 m below the culvert base slab Field tests from the Beijing–Hong Kong–Macao Expressway widening project demonstrate the applicability of the proposed reinforcement method and show that pressure grouting increases the coefficient of subgrade reaction by 7–10%. Based on theoretical and field investigations, recommended reinforcement parameters are proposed for a representative culvert. The proposed method provides an efficient solution for culvert reinforcement in highway widening projects. Full article

This study is focused on the unwrapping contribution of microstructure (mainly expressed in terms of dislocation density) and stress state in the quenched bearing steel 100Cr6. Microstructure as well as residual stress state alterations are developed only as a function of variable infeed rates in the flat plunge grinding (other grinding conditions are kept constant). The study is also dealing with the synergistic contribution of residual stress state and the superimposing elastic external stress developed during bending. It was found that the Barkhausen noise after grinding is mostly a function of the thermal softening, whereas the role of residual stress state is only minor. The growing Barkhausen noise emission at the lower infeed rates is connected with the compressive stress, and the tensile stresses are developed at the higher removal rates only. The study also demonstrates good sensitivity of Barkhausen noise when this emission is descending along the compressive external stresses and the ascending evolution along the tensile stresses when the magnetic field is altering along the direction of exerted stress. On the other hand, this evolution is reversed when the altering magnetic field is altered along the transversal direction. Full article

The structure–activity relationship of three oxyphosphonate inhibitors differing in heteroatom type (C, N, S) was examined to clarify their influence on the pitting corrosion resistance of ferritic–martensitic steel EP-450 in chloride media. Gravimetric tests in 10% FeCl₃, supported by surface microscopy and adsorption analysis, showed that EP-450 is highly susceptible to localized attack, with pits nucleating preferentially at carbide-enriched, chromium-depleted regions. Addition of dimethyl(1-hydroxycyclohexyl)phosphonate reduced the corrosion rate from 49 to 33 mm/year at 2.0 g/L, corresponding to ≈33% protection, while the nitrogen-containing dimethyl[1-(2-ethoxyethyl)-4-hydroxypiperidin-4-yl]phosphonate produced the largest decrease in mass loss, exceeding a 55% reduction under identical conditions. The sulfur-bearing dimethyl(4-hydroxytetrahydro-2H-thiopyran-4-yl)phosphonate afforded an intermediate effect. Adsorption analysis for the cyclohexyl derivative suggested mixed physisorption–chemisorption with limited surface coverage, while heteroatom substitution (N or S) is consistent with a change in adsorption configuration and interfacial packing that can yield a more compact protective layer. The observed inhibition efficiency increased in the sequence C < S < N, which is interpreted empirically in terms of heteroatom-dependent adsorption geometry and film integrity rather than conjugation-driven activation of the P=O group. Full article

To improve deformation compatibility in the negative-moment regions of continuous steel–ultra-high-performance concrete (UHPC) composite girders, this study investigates a controlled-slip bolted shear connector in which bolt-hole clearance is intentionally used as a deformation-release parameter. A three-dimensional nonlinear push-out finite element model was developed in ABAQUS and validated against reported high-strength bolted connector tests. Parametric analyses were then conducted to clarify the effects of bolt-hole clearance, bolt preload, and interface friction on the load–slip response, local UHPC bearing damage, and bolt stress state. The results show that increasing the radial clearance from 0.1 mm to 2.0 mm increases the peak slip from 6.51 mm to 9.17 mm, whereas the peak resistance remains within 661.79–693.86 kN. Bolt preload mainly changes the initial frictional restraint and slip initiation, but has limited influence on the ultimate resistance. Damage and stress distributions further indicate that larger clearance delays UHPC hole-wall bearing damage, while increasing the bending–shear demand on the bolt shank. The results indicate that reserved bolt-hole clearance can be used to increase connector slip capacity while maintaining a comparable shear-resistance level within the investigated parameter range. Full article

To address the challenges of low bearing capacity in Northeast China’s paddy-field soft foundations and the limitations of summer power line construction, a standardized design method for a novel prefabricated modular steel temporary bridge is proposed. Based on the Winkler elastic foundation beam theory, the operating characteristics of rigid short beams and the subgrade reaction distribution under heavy loads were analyzed. On this basis, combined with in situ static load tests and finite element analysis (FEA), the mechanical performance of the temporary bridge under the static loads of crawler-type and six-wheel construction machinery was investigated. The results indicate that when the bridge deck is subjected to a 25-ton construction vehicle, the maximum stress and displacement in the mid-span condition remain well below the material yield strength and the allowable limits stipulated in the Specifications for Design of Highway Steel Bridges (JTG D64-2015). Furthermore, the temporary bridge structure maintains excellent operational stability under a 100-ton extreme construction load and eccentric loading conditions. This study elucidates the mechanical behavior of the temporary bridge, providing a scientific theoretical basis and engineering reference for the design of temporary transit structures in complex environments such as soft paddy field foundations. Full article

This paper presents a code-based static verification of the FA125 hydraulic drilling rig mast under its governing design load combination. Unlike the previously published dynamic investigation of the same platform, the present work establishes the baseline static load path, identifies the governing structural members, evaluates the local stress state in the mast-to-support connection plates, and computes the effective safety coefficients. The mixed finite element model integrates the lattice mast, the support frame, and the base assembly, utilizing beam elements for the slender load-bearing members and shell elements for the localized plate-type connection regions. The governing load combination encompasses structural self-weight, maximum hook load (14.90 kN), and the reactive torque transmitted by the drilling head (0.50 kNm). The maximum mast-top displacement was limited to 4.75 mm. The critical beam elements were located within the lateral base-support region, developing peak compressive and tensile stresses of 70.08 MPa and 69.21 MPa, respectively. The highest localized shell-level von Mises stress (23.62 MPa) was concentrated within the mast-to-support interface connection plates. The results mathematically confirm that the existing FA125 steel structure satisfies the active design criteria, providing a distinct static reference map required for subsequent structural optimization, lightweighting, and selective material substitution. Full article

Precast concrete (PC) structures are increasingly adopted in building construction for their sustainable construction advantages. However, theoretical models for seismic design of precast concrete walls with concrete-filled steel tubular (CFST) elements remain limited. The lack of such models hinders the performance-based seismic design and resilience assessment of these hybrid structures. This study investigates the seismic mechanism and develops a restoring force model for precast concrete superposed shear walls with CFST end columns (PCSSWEC). A refined three-dimensional finite element model was established using ABAQUS and validated against quasi-static cyclic test results of three full-scale specimens. The four-stage loading mechanism—elastic, wall cracking, elastoplastic yielding, and ultimate failure—was revealed, with the precast–postcast concrete interface identified as the primary weak link governing post-peak strength degradation. Comprehensive parametric studies examined the influence of shear span ratio (λ = 0.75–3.25), axial compression ratio (n_a = 0.1–0.6), steel tube width-to-thickness ratio (B/t = 20–80), and concrete strength (C30–C60) on seismic performance. Results indicate that intermediate walls (λ = 1.75–2.25) exhibit optimal ductility, and a steel tube with B/t = 40–60 provides a balanced combination of strength and deformation capacity. A tri-linear backbone curve model with explicit formulae for equivalent stiffness and load capacity was developed, along with modified Clough-based hysteretic rules incorporating stiffness degradation through a common yield-point approach. Validation against experimental and numerical results demonstrates reliable model performance for primary structural parameters: lateral load bearing capacity and ultimate drift ratio are predicted within ±10%, while yield load and ductility predictions show larger scatter due to inherent challenges in cyclic behavior characterization. The proposed restoring force model provides a practical tool for performance-based seismic design and resilience assessment of precast concrete buildings. Full article

Quenched and tempered (Q+T) bolt steels are widely used in key load-bearing structures such as bridges, wind power equipment, pressure vessels and engineering machinery, but they are susceptible to hydrogen-induced cracking under applied stress during service. In this study, a bolt steel was subjected to Q+T heat treatment, including quenching at 850, 900, 950, 1000 and 1050 °C, followed by tempering at 500 °C. Microstructural characterization, hydrogen permeation tests, and slow strain rate tensile tests were conducted to investigate the effects of quenching temperature on microstructural evolution, hydrogen diffusion behavior and resistance to hydrogen-assisted cracking. As the quenching temperature increased from 850 °C to 1050 °C, the prior austenite grains, packets and blocks were gradually coarsened, the fraction of high-angle grain boundaries decreased from 64.7% to 54.2%, and although partial dissolution of primary carbides may occur during austenitizing, the number/area fraction and size of carbides observed in the final tempered martensitic microstructure increased after the subsequent tempering treatment. Meanwhile, the Nb/Ti-rich precipitates changed only slightly, and the dislocation density increased. The effective hydrogen diffusion coefficient, D_eff, increased with increasing quenching temperature, mainly because grain coarsening significantly reduced the high-angle grain boundary area and weakened the hydrogen-trapping effect of grain boundaries. This dominant effect masked the diffusion-retarding effects caused by increased dislocation density and coarser carbides. With increasing quenching temperature, the strength loss ratio increased from 7.3% to 12.0%, and the plasticity loss ratio increased from 10.0% to 13.6%, indicating enhanced hydrogen-assisted cracking susceptibility. The fracture morphology gradually changed from deep dimples to flat dimples and flattened ductile–brittle mixed features, while the crack propagation path became straighter. A higher quenching temperature weakened the blocking effect of grain boundaries on crack propagation and reduced the resistance of the quenched and tempered bolt steel to hydrogen-assisted cracking. Full article

The steel–concrete interface in steel–concrete composite structures is susceptible to interfacial void defects during both casting and service, posing a significant threat to structural load-bearing capacity. For early-stage micro-voids exceeding 2 mm in height, signal variations are weak and exhibit response characteristics similar to dense states, leading to feature ambiguity when using conventional criteria based on time-domain amplitude and attenuation or frequency-domain peak values and resulting in a high risk of missed detections. To address this limitation for early warning purposes, this study proposes a high-sensitivity identification method integrating an impact elastic wave response feature system with a feature-attention gated multi-layer perceptron (Feature-attention MLP). Based on full-scale model experiments from an engineering project, the temporal and spectral evolution patterns of impact elastic wave responses under varying dense conditions were analyzed. A comprehensive feature system, including time-domain statistical descriptors, spectral peaks, and sub-band energy distributions, was constructed, with Random Forest used for feature importance ranking and Top-K selection. An MLP classifier was then developed for automatic discrimination of dense states. A feature-level attention gating mechanism was introduced to enable adaptive weighting across feature dimensions, enhancing sensitive features while suppressing noise and structural variability. The final lightweight classifier contains 4052 trainable parameters, enabling rapid execution with an average CPU inference time of approximately 1.24 ms per sample. The average CPU inference time was approximately 1.24 ms per sample. Under the original train–validation split, the recall-prioritized operating point achieved a Void recall of 0.978 and a weighted F1-score of 0.780, accompanied by a non-negligible false-positive screening burden. Stratified five-fold internal validation yielded a balanced accuracy of 0.682 ± 0.021 and a Void recall of 0.845 ± 0.035 under the inner-validation-optimized threshold. These results demonstrate the preliminary potential of the proposed lightweight framework for engineering-oriented micro-void screening under the investigated full-scale conditions. Full article

Glued-in rod (GIR) connections are widely used in timber composite structures owing to their high load-bearing capacity, high stiffness, and concealed configuration. However, their shear behavior and design methodology under lateral loading remain insufficiently understood. In this study, monotonic shear tests were conducted to clarify the shear failure characteristics and load-transfer mechanisms of steel-to-timber GIR connections. The effects of rod diameter, anchorage length, timber strength grade, and rod orientation relative to the timber grain on the shear performance of the connections were systematically investigated. Self-tapping screw (STS) connections were also tested to compare the shear capacity, deformation behavior, and failure modes of the glued-in rod connections. Based on Johansen’s yield theory and the observed failure modes, shear capacities, and load–slip curves, the shear capacity prediction method and the main influencing factors were evaluated. The results indicate that steel-to-timber GIR connections primarily exhibit a combined failure mode involving timber embedment crushing and rod bending deformation or shear fracture under monotonic shear loading. Shear capacity increases markedly with increasing rod diameter. For the 12 mm rods examined in this study, anchorage length has a limited effect on shear capacity once it exceeds approximately 10d. Connections with rods oriented parallel to the grain demonstrate higher load-carrying capacity and deformation capacity than those with rods perpendicular to the timber grain. Furthermore, the prediction accuracy of the Eurocode 5-based calculation method varies with rod diameter: the calculated capacities agree well with the experimental values for small-diameter rods (10 mm and 12 mm), whereas the predictions for larger-diameter rods (14 mm and 16 mm) are conservative. Full article

To overcome the inherent drawbacks of cast-in-place reinforced concrete bracing—such as long construction periods and difficult demolition—as well as the relatively high construction cost of steel structure bracing, while fully incorporating the respective technical advantages of these two traditional support systems, this paper proposes a novel hybrid prefabricated reinforced concrete (RC)–steel structure foundation pit bracing system. In order to investigate the overall bearing capacity variation in the standard components of this structure under complex external forces in foundation pits, a numerical model was established using the finite element software ABAQUS. The study examines the trend of the axial compressive bearing capacity of a single standard beam segment as the steel thickness of its external stiffening sleeve varies, as well as the effects of eccentric loading, oblique loading, and the presence or absence of auxiliary supports on the structural bearing capacity of multi-segment beam assemblies. The numerical analysis results show that the bearing capacity of a single beam segment exhibits a strong correlation with the variation in sleeve thickness, and a fitting curve of compressive strength as a function of thickness was derived. For the multi-segment assembly, an increase of 1 mm in the load eccentricity in the Y and Z directions reduces the ultimate peak load by approximately 20.95 kN and 23.94 kN, respectively; in the XY and XZ planes, an increase of 1° in the eccentric angle of the oblique load reduces the peak ultimate bearing capacity by about 6.02 kN and 9.67 kN, respectively. Auxiliary supports have a relatively minor influence on the structural bearing capacity. This research thoroughly explores the bearing capacity of the prefabricated steel–concrete composite and steel structure foundation pit bracing under complex working loads, providing strong support for engineering design and demonstrating broad application prospects. Full article

Rapid-repair mortars require high early-age strength, dimensional stability, and reliable substrate bond simultaneously, yet conventional alkali-activated materials (AAMs) have only partially met these requirements, and AAM feedstock base itself is contracting as blast furnace slag and fly ash availability declines under steel and power sector decarbonization. Thus, in this study, the systematic production of a one-part, rapid hardening repair mortar based on calcined clay (CC) and basic oxygen furnace slag (BOFS) is presented for the first time. Concurrently, a direct comparison of three distinct modifier families is conducted within this underutilized binding system. These modifiers consist of a soluble anion-active accelerator (sodium fluoride, NF), an Fe- and Na-bearing mineral residue (red mud, RM), and a reactive oxide (calcined alumina, CAL). Finally, the mechanistic connections between the modifier-induced phases and the macroscale mortar properties are analyzed and evaluated according to ASTM C928, ASTM C1600, and EN 1504-3 standards. The precursors were activated using solid sodium metasilicate, and the setting behavior, compressive strength development, drying shrinkage, substrate bond strength, and microstructural properties were determined for each mortar system. The results indicate that all formulations satisfied the R2 strength class for rapid hardening repair mortars as per ASTM C928 and the incorporation of NF markedly promoted the early-age reactions, reducing the setting time by up to 73% and increasing the 3 h compressive strength by up to 81% (12.8 MPa at 3 h) compared to the control mortar. Furthermore, RM, CAL, and NF effectively mitigated the drying shrinkage of the control mortar from approximately 4252 µƐ down to 162 µƐ. The bond strength of the repair mortars substantially improved through the addition of CAL and NF, fulfilling the R3 and R4 structural repair mortar requirements specified in EN 1504-3. Full article