Search Results (795)

The seismic design of spatial joints in long-span concrete-filled steel tube (CFST) arch bridges under complex stresses remains a critical challenge in high-intensity seismic zones. This study investigates the seismic performance and failure mechanisms of CFST spatial KT-type joints, using the Pingnan No. 3 Bridge as a case study. Based on similarity theory, four scaled test specimens were designed. The core variable was the axial compression ratio of the main pipe, while the load on the K-branch served as the parametric variable. Quasi-static tests were conducted under constant static loading on the main pipe and K-branches, coupled with low-cycle cyclic loading on the T-branch. Furthermore, nonlinear finite element analysis (FEA) was performed using Abaqus for cross-validation. The results indicate that the primary failure mode of this joint configuration is the shear-punching failure of the main pipe wall at the T-branch intersection. The load–displacement hysteresis curves exhibit a robust “bow-shaped” profile, indicating substantial plastic energy dissipation capacity. Comparative analysis confirms that hollow steel pipe T-branches offer superior ductility in long-span arch bridges compared to concrete-filled alternatives. By extracting shear stress distribution characteristics from the FEA model to precisely locate the neutral axis, this study proposes a theoretical correction to the ultimate load-carrying capacity calculation model. The derived theoretical values demonstrate good agreement with the experimental results. The relative errors between the calculated and experimental bearing capacities of KT783a, KT783, KT700, and KT607 were 1.99%, 0.23%, 2.26%, and 2.45%, respectively, referring to the T-branch out-of-plane bearing capacity predicted by the proposed formula. The proposed theoretical model provides a reliable quantitative basis for the seismic design and local strengthening of similar spatial joints in long-span CFST arch bridges. Full article

Mean atomic bond strain (MABS), based on the globally averaged bond length, has recently emerged as a new strain metric that retains clear physical meaning even as severe atomic neighborhood reconstruction occurs. It has been shown to exhibit a nearly perfect linear relationship with global stress throughout the elastic and plastic deformation in single-crystal face-centered cubic (FCC) metals, contradicting conventional expectations based on nonlinear dislocation activity. Whether this near-linear relationship holds in other materials stands out as an important and intriguing question. In this study, we examine the MABS–stress relationship in representative unary, binary, and ternary metallic glasses (MGs), where neither a crystal structure nor dislocations are present. Large-scale molecular dynamics simulations of uniaxial tensile tests and statistical analysis of millions of atomic bonds are performed. Irrespective of their differing compositions, all the MGs exhibit a persistent near-linear relationship between total MABS (all bonds included) and global stress up to fracture, even in the presence of significant local nonaffine displacements (shear transformation zones and shear bands), with the Pearson correlation coefficient consistently exceeding 0.99. Unlike the nonaffine displacements, the spatial distribution of individual atomic bond strain does not localize under the uniaxial loading. In the MGs containing more than one element, MABS computed for a single bond type may not correlate as linearly with global stress as total MABS. The results demonstrate that the persistent near-linear total MABS–stress relationship over the entire deformation process, recently discovered in single-crystal FCC metals, also applies to MGs despite their vastly different atomic structures. This strengthens the candidacy of total MABS as a universal stress descriptor across materials classes and deformation regimes. With further development and implementation in atomistic simulations and constitutive modeling, the MABS concept has the potential to reshape our understanding of materials mechanics and generate new insights into the design of stronger, tougher, and more thermally and chemically stable materials. Full article

This study experimentally investigates the mechanical performance of historic brick masonry walls strengthened with three innovative methods: restoration mortar, carbon textile reinforcement, and sprayed polyurea. The research comprises material characterization and structural testing of masonry specimens. Initially, flexural, and compressive strengths of handmade bricks and restoration mortar used for both joining and strengthening were determined. Subsequently, 40 masonry specimens were tested in four groups: unreinforced (control) and three strengthened groups (restoration mortar, restoration mortar with carbon textile and sprayed polyurea). For each group, 20 triplet specimens were subjected to shear strength tests, while 20 four-unit masonry wallets underwent diagonal compression tests following ASTM E519 to evaluate failure loads, shear stresses, deformation capacities, and failure modes. Tensile adhesion tests on polyurea material showed strong bonding without brick spalling. Strengthened walls were compared with control specimens in terms of load capacity, ductility, deformation patterns, and failure behavior. The results indicate that the polyurea-strengthened walls exhibited the highest structural performance together with a significant increase in ductility. This method is advantageous due to its flexibility, ease of application, and minimal intervention on the original masonry. Furthermore, sprayed polyurea enhanced performance under collapsing loads and shear stresses, demonstrating its potential as an innovative strengthening solution for historic masonry structures. Full article

To address the challenges of bedding separation and large deformation in deep gob-side roadways with composite roofs under the influence of stress deviation and weak interlayers, this study takes the 1692(1) rail roadway of Pansan Coal Mine as the research object. By combining numerical simulation, theoretical analysis, and field testing, the study thoroughly investigates the evolution patterns of the plastic zone in the surrounding rock and the mechanisms governing delamination. The results demonstrated that stress deviation induces shear failure of weak interlayers and causes bedding separation at the early excavation stage, which subsequently transforms into tensile failure and leads to coal pillar instability. The principal stress deviation angle determines the expansion direction of the plastic zone, while the thickness and number of weak interlayers are positively correlated with the degree of bedding separation. It is concluded that the coal pillar strength is a critical factor for bedding separation control. Based on these findings, a combined control scheme of “strengthening coal pillars, restraining shear damage, improving coordinated deformation” is proposed. Field engineering practice confirms that this proposed scheme effectively restrains the expansion of the plastic zone and ensures the long-term stability of the roadway. Full article

This study presents a mechanics based analytical framework for predicting the flexural–shear capacity of reinforced concrete (RC) beams strengthened with Engineered Cementitious Composites (ECCs) and a hybrid ECC–GFRP near surface mounted (NSM) system. Building upon previously reported experimental observations, the present work aims to establish rational prediction models capable of capturing the interaction between flexural and shear mechanisms in strengthened beams. The analytical approach integrates sectional analysis for flexural capacity with a modified truss analogy for shear resistance, explicitly incorporating the strain hardening tensile contribution of ECC and the tensile and confinement effects of GFRP reinforcement. An interaction based failure criterion is subsequently employed to identify the governing failure mode under combined flexural shear actions. The proposed model is validated against experimental results obtained from twenty seven beam specimens with varying flexural and shear reinforcement ratios and strengthening configurations. The predicted ultimate loads show good agreement with experimental values, with an average deviation within ±10%. The analytical framework accurately captures the transition between flexural dominated, combined flexural–shear, and diagonal tension failures observed experimentally. Results demonstrate that ECC significantly enhances ductility and shear crack control, while the hybrid ECC–GFRP system provides substantial strength enhancement with a controlled shift in failure mode. Overall, the developed analytical models offer a reliable and computationally efficient tool for predicting the flexural–shear capacity and failure behavior of ECC and hybrid ECC–GFRP-strengthened RC beams, supporting performance based design and practical strengthening applications. Full article

The pursuit of lightweight, high-performance sports equipment drives the development of Al-Li-Mg alloys, yet systematic studies linking a complete processing route, from as-cast to peak-aged condition, to microstructural evolution and mechanical properties remain limited. This work provides the first comprehensive investigation of how a sequential processing route (homogenization, hot rolling, solution treatment, and peak aging) transforms the coarse as-cast structure of an Al-Li-Mg alloy into a refined, recrystallized grain architecture with a uniform dispersion of nanoscale δ′-Al₃Li precipitates. This microstructural transformation leads to a dramatic enhancement in mechanical properties: the peak-aged alloy exhibits increases of approximately 92%, 139%, and 925% in yield strength, ultimate tensile strength, and elongation, respectively, relative to the as-cast condition. The dominant strengthening mechanism is identified as dislocation shearing of coherent δ′-Al₃Li precipitates (average radius ~5 nm, well below the ~25 nm transition threshold for Orowan looping), which enhances strength without compromising ductility, demonstrating the critical role of the processing route in tailoring microstructures and mechanical properties for lightweight sports equipment. Full article

Road-railway combined steel truss bridges are increasingly adopted in urban infrastructure due to their structural efficiency and versatility. This study proposes a three-level multi-scale finite element framework to investigate the safety reserve and progressive failure mechanism of a four-span (80 + 120 + 120 + 80 m) continuous steel truss bridge carrying both highway and railway traffic. At the macro level, a beam element model was established in Midas/Civil to determine the most unfavorable loading configurations, yielding a minimum buckling load factor of 31.0 under dead load and a maximum vertical displacement of 175 mm at mid-span under combined traffic loading. At the meso level, a mixed beam–shell element model incorporating geometric and material nonlinearities was developed in ABAQUS, revealing an ultimate load factor of 6.61 with distinct progressive failure characteristics: initial yielding occurs near the intermediate pier supports, where deformation is constrained, while final instability develops at Joint A17 due to its lower relative stiffness. At the micro level, a refined solid-shell submodel of the critical joint, driven by displacement boundary conditions extracted from the global model, was constructed to capture the local failure mechanism. The results demonstrate that the governing failure mode is shear buckling of the gusset plate, induced by a vertical displacement differential of approximately 30 mm between the web members on opposite sides of the joint arising from differential stiffness. The stress analysis further reveals pronounced stress concentrations in the splice plates adjacent to the more flexible web member, confirming the asymmetric load distribution mechanism. Based on these findings, strengthening measures including increased gusset plate thickness at pier-top joints, optimized chord sections, and the use of higher-strength steel in critical regions are recommended. Full article

During underground mining, the stability of in-seam gas drainage boreholes is jointly affected by multiple factors, including the in situ stress state and borehole structure. Borehole instability can reduce gas drainage efficiency and increase underground safety risks. Among these factors, confining pressure plays a decisive role in the damage evolution of the coal surrounding the borehole. To clarify the damage evolution characteristics of the coal surrounding the borehole under different confining pressure conditions, conventional triaxial graded cyclic loading–unloading numerical simulations were conducted on borehole-containing specimens using PFC2D software (version 6.0). The effects of confining pressure on acoustic emission (AE) ringing counts, microcrack propagation, crack angle distribution, damage evolution, and failure characteristics were systematically analyzed. The results show that, under graded cyclic loading–unloading, the peak AE ringing count of the borehole-containing specimens first increases and then decreases with increasing confining pressure, whereas the cumulative ringing count continues to increase. The spatial distribution of microcracks gradually evolves from dispersed development to concentration around the borehole, and the crack propagation path changes from single-path dominance to coordinated multi-path propagation. The angular distribution of tensile cracks exhibits a non-monotonic evolution pattern, namely, dispersion, concentration, and weakening, with increasing confining pressure, whereas the distributions of shear cracks and total cracks show a gradually broadened unimodal pattern with enhanced connectivity between angular intervals. At the final failure stage, both the tensile damage ratio and the shear damage ratio increase with increasing confining pressure, and their difference increases from 0.24% to 0.90%, indicating that increasing confining pressure further strengthens the dominant role of shear damage. The failure mode gradually evolves from tensile–shear mixed failure toward relatively shear-dominated failure. The results provide a theoretical basis for analyzing borehole instability and failure characteristics under different confining pressure conditions, as well as for optimizing grouting-based borehole protection parameters. Full article

High-translucency zirconia (HTZ) has superior esthetic properties, but its unreliable resin bonding limits minimally invasive anterior restorations. An in situ surface modification was developed to synthesize CaZrO₃ particulates on pre-sintered HTZ for enhanced bonding durability. HTZ specimens were randomized into control (Zr-c) and calcium-modified (Zr-Ca) groups; Zr-Ca was treated with NaF/HCl mixture, calcium chloride glycerol solution, NaOH incubation (80 °C, 2 h), and sintering. Surface characteristics were characterized by SEM/EDS, AFM, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and FTIR. Flexural strength was tested via three-point bending; shear bond strength (SBS) was evaluated immediately and after 5000 thermocycles with resin cements (with/without 10-MDP). Zr-Ca showed uniform surface particulates, increased roughness, enhanced wettability, and surface Ca; XRD/FTIR/XPS confirmed CaZrO₃ and Ca-O-P species (after MDP). Zr-Ca with 10-MDP-containing resin adhesive had significantly higher SBS before/after aging (predominantly mixed failures), with flexural strength within clinical limits. In situ CaZrO₃ formation on HTZ strengthens MDP-mediated resin bonding and thermocycling resistance while preserving mechanical integrity, providing a feasible strategy for durable adhesion. Full article

There are many factors that affect the shear capacity of FRP (fiber-reinforced polymer)-strengthened reinforced concrete (RC) beams, and traditional capacity models based on empirical or semi-empirical formulas often suffer from insufficient accuracy. To enhance the predictive accuracy and generalization ability of the shear capacity of FRP-strengthened RC beams, this study proposes an interpretable machine learning model based on the Jaya-CNN-LSTM model. A comprehensive database consisting of 315 test data on shear capacity of FRP-strengthened RC beams, encompassing various FRP reinforcement modes, has been established. Key feature parameters for predicting the shear capacity of FRP-strengthened RC beams are selected through Pearson correlation coefficient analysis. Based on the Jaya algorithm, the hyperparameters of the ensemble CNN-LSTM prediction model are adaptively optimized. A comparative analysis is conducted between the proposed method, other machine learning models, and existing empirical formulas to evaluate the proposed model’s efficacy. The results demonstrate that the proposed model outperforms other machine learning models and empirical formulas in terms of prediction accuracy and stability. Furthermore, the machine learning-based predictions align more closely with experimental values than those derived from empirical formulas. Additionally, the SHAP method is utilized to quantify the critical parameters’ impact on predicting the shear capacity of FRP-strengthened RC beams. The results reveal that there is an explicit mapping relationship between key features such as shear-span ratio, concrete strength, and yield strength of stirrups and the shear capacity of FRP-strengthened RC beams, providing technical support for practical applications. Full article

The long-term stability of rock–concrete composites largely depends on the mechanical properties and durability of the rock–concrete interface. This study investigated the coupling effect of interfacial roughness and acid sulfate corrosion on sandstone–concrete composites by using uniaxial compression tests combined with acoustic emission (AE) monitoring. The results showed that corrosion continuously reduces the mechanical properties of the specimens with peak strength and elastic modulus, exhibiting a two-stage evolution: rapid degradation in the early stage followed by a slow decline in the later stage. After 60 days of corrosion, the peak strength for composites with JRC = 5, JRC = 10, and JRC = 15 interfaces decreased by 46.59%, 44.34%, and 50.43%, respectively. The elastic modulus exhibited the same pattern of variation, and the decreasing rate was 68.90%, 66.96%, and 76.46% for the JRC = 5, JRC = 10, and JRC = 15 groups. Acoustic emission activities appeared earlier and were more significant after corrosion. With the effect of corrosion, the fracture mode evolved from tensile-dominated cracks to mixed tensile–shear cracks with a stronger shear component. Fractal analysis of AE energy revealed that the Hurst exponent decreased from 0.842–0.864 in the natural state to 0.503–0.567 after 60 days of immersion, whereas the fractal dimension increased from 1.136–1.182 to 1.433–1.497, indicating a decrease in the persistence and increase in complexity of the acoustic emission energy release process. Overall, the moderately rough interface (JRC = 10) achieved a better balance between initial strengthening and long-term corrosion resistance. These findings provide experimental support for evaluating the durability of sandstone–concrete composites in acidic sulfate environments. Full article

To address the issues of sealing leakage and airflow-induced vibration in high-speed turbomachinery, a conical straight-tooth annular clearance sealed hybrid aerostatic/aerodynamic bearing is investigated. A three-dimensional CFD model is established to study the effects of radial clearance height, inlet pressure, rotor speed, and eccentricity on pressure distribution, velocity distribution, and leakage rate. The results show that leakage exhibits a strong positive nonlinear correlation with clearance height and inlet pressure, following a power-law or polynomial relationship, while rotor speed and eccentricity exert negligible effects (less than 5%). The underlying mechanisms are identified as the kinetic energy diversion caused by circumferential shear and the mutual cancelation of throttling and backflow effects. Increasing the gap height enhances leakage by expanding the hydraulic diameter and strengthening vortex disturbance; increasing inlet pressure promotes leakage by elevating the driving force and intensifying local flow separation. Full article

Although fault-controlled instability of underground excavation has been widely studied, systematic analyses of how key fault geometric and mechanical parameters affect surrounding-rock behavior in deep hard-rock mine roadways remain limited. This study takes a deep roadway as the engineering background and uses numerical simulation to investigate the effects of fault thickness, fault dip angle, fault mechanical properties, and contact parameters on the initial deformation state, post-excavation deformation, and plastic-zone evolution of surrounding rock. The results indicate that the surrounding rock is already in a non-uniform initial state controlled by fault disturbance prior to excavation. Increasing fault thickness expands the initial high-deformation zone; fault dip angle mainly changes the spatial distribution pattern of the initial deformation field; and increasing either the fault mechanical parameters or the contact parameters reduces deformation concentration in the vicinity of the fault. After roadway excavation, deformation is mainly concentrated in the fault–roadway intersection zone, and roof deformation along the roadway axis shows distinct local peaks and an asymmetric distribution. The maximum roof deformation continues to increase with the increase of fault thickness (the deformation increases by 218% from 1 m to 5 m), and smaller fault dip angle conditions are prone to local large deformation. In contrast, higher fault mechanical parameters and contact parameters can both effectively suppress roof deformation, with the contact parameters exerting more significant control (as the contact parameter increased from C1 to C5, the maximum roof deformation decreased by approximately 75%). The plastic zone mainly develops at the fault–roadway intersection and is dominated by shear plasticity, accompanied by tensile plasticity. Increasing fault thickness significantly enlarges the plastic-zone volume and strengthens the shear-dominated failure characteristic; fault dip angle mainly controls the propagation direction and morphology of the plastic zone; and increasing the fault mechanical parameters and contact parameters both help reduce the extent of the plastic zone. These findings can provide a theoretical basis for zoned support design and differentiated stability control of roadways crossing faults in deep metal mines. Full article

Polyurethane cement (PUC) is a high-performance composite that combines the high toughness of polymers with the durability of cementitious materials, showing potential in the field of structural strengthening. However, when used alone, its crack confinement capability is limited. To investigate the strengthening effect of wire mesh–polyurethane cement (WM-PUC) composite on the shear performance of damaged reinforced concrete (RC) beams, static loading tests were conducted on four RC beams. All strengthened beams were preloaded to induce initial damage and subsequently retrofitted on the sides using the two composite materials. Their shear performance was evaluated through single-point monotonic loading. The failure modes, load–displacement curves, shear capacity, and crack development patterns of the strengthened beams were analyzed in detail. The experimental results indicated that after strengthening with PUC and WM-PUC, the shear capacity of the damaged beams was effectively enhanced. The ultimate loads of the damaged beams strengthened with PUC and WM-PUC were 360 kN and 390 kN, respectively, representing increases of 12.5% and 21.88% compared to the unstrengthened beam. Compared to the PUC-strengthened beam, the ultimate load of the WM-PUC-strengthened beam increased by 8.3%, indicating that the incorporation of wire mesh further enhanced the strengthening effectiveness of the polyurethane cement composite. In terms of crack control, WM-PUC strengthening was more effective than PUC strengthening in restraining the initiation and propagation of diagonal cracks. The findings demonstrate that WM-PUC composite exhibits favorable applicability for the shear strengthening of damaged RC beams, with overall performance superior to that of PUC-only strengthening, thereby providing a technical reference for high-performance shear strengthening of existing concrete structures. Full article