Search Results (3,426)

Gob-side roadways driven along the floor while retaining top coal in thick soft coal seams are prone to instability under strong mining-induced dynamic loading. To clarify the instability mechanism and develop an effective control method, the 1609 return airway of Jiulishan Mine was investigated using field survey, borehole imaging, FLAC3D numerical simulation, industrial testing, and field monitoring. The results show that, under the combined effects of large mining height, insufficient filling of the gob by the caved immediate roof, weak retained top coal, and low coal strength, shear failure planes tend to develop within the narrow coal pillar and extend from the gob-side roof toward the floor. Once the dominant shear plane cuts through the pillar, the overall bearing structure is destroyed, leading to shear slip, asymmetric rib deformation, roof subsidence toward the coal-pillar side, and rib–roof coupled instability. Based on a multi-index evaluation of pillar load-bearing capacity, plastic zone development, stress concentration, roadway deformation, and coal recovery, a 3 m coal pillar was determined as the rational width. A coordinated “narrow coal pillar + cross-rib anchorage” scheme was proposed, and field verification confirmed its effectiveness in controlling roof separation, roadway surface displacement, and internal surrounding-rock damage. Full article

Cementitious materials in the fresh state are commonly regarded as viscoplastic. That is, below a given yield stress, they exhibit solid-like behavior, whereas above this threshold, they behave as fluids. In this context, the shear strength of such materials has traditionally been analyzed from a rheological standpoint, considering them as fluids and using time as the primary state variable. From a structural perspective, however, relatively few studies have treated the material as a solid. With the advent of 3D printing technology, this trend has persisted. Within this framework, the present research aims to evaluate the shear strength of a structural mortar for 3D printing in its solid-like regime, by applying the Mohr–Coulomb failure criterion. Furthermore, in a novel approach, the degree of hydration of Portland cement is proposed as a state variable to replace time, enabling a more comprehensive and objective description of the material’s mechanical evolution. Thus, addressing this gap in the state of the art, a chemo-mechanical coupling is developed. To obtain the necessary data, direct shear, uniaxial compression, and isothermal calorimetry tests are performed. The results indicate that the friction angle remains constant, at approximately 33°, and that cohesion, the parameter governing strength gain, exhibits the same linear rate of increase with hydration in both mechanical tests, indicating an intrinsic relationship within the material. Full article

This study experimentally investigates the structural behavior of hexagonal- and square-shaped composite specimens subjected to vertical compression, vertical tension, and diagonal tension loading. The specimens were fabricated using four- and six-layer alkali-resistant (AR) glass textile reinforcements embedded in a modified cementitious mortar via pull, pour, and roll manufacturing techniques. The mechanical performance of polyvinyl alcohol (PVA) fiber-reinforced composite connectors and steel clamp-type elements was also evaluated at the joints of hexagonal specimens under vertical tension and lateral shear loading. The results show that increasing the number of textile layers significantly enhances structural performance. A 50% increase in textile layers improved load-carrying capacity by up to 56% in compression, 104% in tension, and 216% in diagonal tension. Corresponding increases of approximately 20–42% in ductility and up to 266% in energy dissipation capacity were observed. No failure occurred in the connecting elements, confirming their adequate stiffness, strength, and ductility. In addition, validated three-dimensional finite element models were developed to simulate the response of the hexagonal specimens. Overall, the proposed system demonstrates strong potential for applications such as infill walls, cladding, and sandwich panels due to its favorable strength, ductility, and energy absorption capacity. Full article

The abrupt failure of shear-deficient RC beams may lead to harmful consequences under dynamic loading. The use of Carbon Fiber Reinforced Polymers (CFRP) aims to convert this brittle fracture into a ductile one. However, the complexity of the multiple damage mechanisms makes it difficult to assess their condition using conventional testing methods. In this study, the damage evolution of a shear-critical reference beam and its CFRP-strengthened counterpart was monitored using the acoustic emission (AE) technique. After correcting attenuated AE amplitudes, damage analysis was performed using the Shannon entropy approach based on true source amplitudes. The entropy analysis performed with these corrected data clearly revealed the shear failure in the reference beam through abrupt drops in entropy, indicating damage homogenization. In contrast, the entropy remaining high and dynamically varying over a much longer deflection range in the CFRP-strengthened beam demonstrated that CFRP distributes damage over a wider region and that different damage mechanisms, such as debonding and fiber breakage, in addition to concrete cracking, were simultaneously active. Full article

A validation study has been done to provide evidence on the reliability of Reynolds-averaged simulations for supersonic ejectors operating in the single-choked condition. The existing works show that the simulation accuracy for a given turbulence model strongly depends on ejector geometry and the working conditions. In addition, the performance of different turbulence models is usually presented by comparing the results without discussing the origins of their failures. Part 1 of the present work highlights the importance of properly modeling the turbulence response to the varying shear intensity that characterizes the ejector flow-field. The key elements related to this point have been analyzed for commonly used eddy viscosity models and for a new $K-\epsilon$ model. The models described in Part 1 are tested here on two complementary test cases. A free jet with detailed turbulence measurements in the initial region is used to provide information on the models’ behavior, data which could hardly be obtained directly for ejectors. The simulation of a supersonic ejector is then presented, comparing the results with the measured velocity and pressure distributions. The assessed validity of the new eddy viscosity model is exploited to give insightful considerations on ejector flow-field development. Full article

Joints, as inherent weak structural planes within rock masses, interact with bedding planes and govern the stability of layered rock slopes. Numerical models incorporating different levels of joint persistency and bedding dip angles were developed, followed by direct shear simulations under varying normal stresses. The coupled effects of multiple factors on mechanical response and failure mechanisms were systematically analyzed. The results show that shear strength increases with normal stress and decreases with joint persistency, exhibiting pronounced anisotropy. Microcrack evolution exhibits three distinct stages: elastic, initiation, and coalescence. The synergistic evolution of shear cracks along bedding planes and tensile cracks within the matrix primarily drives macroscopic failure. In contrast, tensile cracks along bedding planes and shear cracks within the matrix play a secondary role. The final failure is dominated by the concentration, expansion, and coalescence of shear microcracks, which penetrate bedding planes and form continuous failure zones. The bedding dip angle controls the geometric orientation of microcracks, normal stress governs the failure mode, and joint persistency affects the continuity of the failure path. The combined effects of these three factors determine the ultimate failure pattern and engineering stability of layered rock masses. These findings provide new insights into how joint persistence governs the shear behavior and failure characteristics of layered rock masses, offering both theoretical and technical support for engineering practices such as slope stability analysis. Full article

To investigate the static behavior of UT-type assembled semi-rigid joints and the effects of bolt pretension loss, two representative joint configurations, UT250 × 150 and UT400 × 200, were studied by combining full-scale tests with refined finite element analysis using ABAQUS. Pure bending, bending-shear, and constant-axial-force-coupled loading conditions were considered, with particular attention paid to the effects of single-bolt and multiple-bolt pretension loss on moment capacity, initial rotational stiffness (K_y), interface slip, and the failure mode of the joints. The results show that the UT-type joint mainly fails through concentrated plastic yielding in the joint zone, and its ultimate moment (M_u) is 12.3–18.7% higher than that of a conventional bolted-welded joint, satisfying the design principle of “strong joint and weak member”. Loss of pretension in a single bolt has only a limited influence on the yield moment (M_y) and ultimate moment (M_u), with a maximum reduction of 8.0% in the ultimate moment (M_u) under negative pure bending; however, it causes clear degradation in the initial rotational stiffness (K_y), and pretension loss in the upper bolt produces a greater stiffness reduction than loss in a single lower bolt, with a maximum reduction of 33.43%. Multiple-bolt pretension loss exhibits a pronounced coupling effect. Simultaneous loss in lower bolts on the same side is the most unfavorable case, leading to a maximum stiffness reduction of 67.78% (coupling coefficient of 1.17), whereas diagonal loss is relatively controllable and generally keeps the stiffness reduction within 7%. When the axial compression ratio does not exceed 0.3, the mechanical response of the joint remains relatively stable, and the adverse effect of pretension loss can be alleviated to a certain extent; further increases in the axial compression ratio accelerate the degradation of both stiffness and load-carrying capacity. The present study provides a useful reference for the design optimization, construction quality control, and in-service maintenance of UT-type semi-rigid joints. Full article

This in vitro study evaluated and compared the shear bond strength (SBS) of three restorative materials bonded to dentin: a glass hybrid ionomer (EQUIA Forte HT), a resin-modified glass ionomer (RIVA Light Cure), and a nanofilled composite resin (Filtek Z350 XT). Additionally, their modes of failure were assessed. Thirty extracted human teeth were prepared and randomly assigned to three groups (n = 10) by restorative material: Group 1: Filtek Z350 XT; Group 2: EQUIA Forte HT; Group 3: RIVA Light Cure. All materials were applied following manufacturer instructions. SBS testing used a universal testing machine, applying a load at the tooth–restoration interface at 1 mm/min until failure. SBS values were recorded in megapascals (MPa). Failure modes were examined under a stereomicroscope at 40× magnification. A one-way ANOVA compared mean SBS among groups, with post hoc tests for pairwise group comparisons. Results: Filtek Z350 XT had the highest mean SBS (21 MPa), followed by RIVA Light Cure (7.5 MPa) and EQUIA Forte HT (7.2 MPa). One-way ANOVA indicated a statistically significant difference in SBS (p < 0.05). Post hoc analysis showed Filtek Z350 XT had significantly higher SBS than the glass ionomer-based materials, while EQUIA Forte HT and RIVA Light Cure did not differ significantly. Conclusions: Filtek Z350 XT demonstrated significantly higher shear bond strength to dentin than the glass ionomer-based materials. No significant SBS difference was found between the resin-modified and hybrid glass ionomers. Full article

Ground failure during major seismic events associated with soil liquefaction can lead to major structural damage to both the columns and the bridge upper deck due to large seismic-induced displacements in the support foundation. Liquefaction-driven ground motion incoherence during the dynamic event and permanent soil deformations are key variables in the observed damage. This paper summarizes a numerical study of an alternative bridge foundation design proposed to reduce support displacements and bearing capacity failure during and after an earthquake, as well as relative settlement associated with partial loss of bearing capacity when the bridge column is founded on a potential liquefiable layer. Three-dimensional numerical models were developed using FLAC^3D. The seismic environment was characterized by a uniform hazard spectrum, UHS, for intraplate and interplate earthquakes, as presented in the current construction Mexico City regulations. Initially, a one-dimensional analysis was performed using SHAKE to evaluate liquefaction susceptibility. Results show that the structured cell foundation reduces excess pore-pressure generation by up to 42% compared to shallow foundations and 25% compared to pile systems. This improvement is associated with (i) restriction of cyclic shear strain, (ii) modification of deformation patterns, (iii) partial confinement of pore-pressure development within the enclosed soil mass, and (iv) preservation of effective stresses during shaking. Additionally, the system reduces shear strain localization and decreases acceleration transmitted to the superstructure by up to 14–33%. The findings demonstrate that structured confinement systems can significantly influence the mechanisms governing liquefaction, offering a promising alternative for bridge foundations in seismic regions. Full article

Evaluation of fiber–matrix interfacial properties is essential for understanding composite performance and exploring the feasibility of real-time diagnostic approaches. In this study, the interfacial behavior between glass fiber and epoxy resin was examined using acoustic emission (AE) features obtained during microdroplet pull-out tests. Four AE features (amplitude, energy, rise time, and Fast Fourier transform peak frequency) were used as input variables to Random Forest models for both regression and classification tasks, targeting interfacial shear strength estimation and failure mode identification (interfacial debonding vs. fiber fracture). In regression analysis, energy and amplitude showed stronger associations with interfacial shear strength, although overall regression performance remained limited. In classification analysis, amplitude alone provided the most stable discrimination between fiber fracture and interfacial debonding, while combining multiple features offered only a marginal additional benefit due to feature redundancy. These results suggest that intensity-related AE parameters are closely associated with interfacial debonding behavior and failure modes. Overall, this exploratory study indicates that AE-based machine learning can serve as a supplementary tool for indirect and trend-level assessment of fiber–matrix interfacial behavior, with potential relevance to real-time monitoring applications. Full article

Dynamic vibration absorbers (DVAs) serve as critical passive control devices. However, their conventional designs are characterized by high directional sensitivity and large additional mass, failing to meet the rigorous demands of modern equipment for multi-directional coupled vibration suppression and lightweighting. To address these challenges, this study establishes an isotropic dynamic model of coupling spring and shell stiffnesses. This model shows that the isotropy degrades with the lightweight design due to a failure mode of shear deformation. Then, by constraining the shear stiffness, a collaborative design framework integrating topology optimization and parameter optimization is constructed to lighten the DVA. Using a 50 Hz DVA as a case study, prototype designs, simulations, and experiments are conducted. The results indicate that the isotropic natural frequencies agree well with the design targets. The shell mass is reduced by 79.8% compared to the conventional rigid shell design. Moreover, in vibration reduction simulations under the same total mass, the optimized absorber further reduces the vibration response by 7.4 dB compared to the rigid shell design. Full article

Aiming to address the shortcomings of traditional large-span light-steel trusses, such as low bearing capacity and inconvenient on-site assembly, this paper proposes a novel cap-shaped chord light-steel truss. It consists of top and bottom cap-shaped chords with uniformly pre-drilled pilot holes and longitudinal stiffeners on both webs, and square/rectangular tubular web members, all connected by self-tapping screws. The novelty lies in the proposed splice geometry, the pilot-hole arrangement for screw connections, and the full-scale 18 m validation. Full-scale bending tests and finite element analyses were conducted on two 18 m span cap-shaped chord light-steel truss specimens subjected to uniformly node-distributed loading. The bearing capacity, stiffness, and failure modes of two specimens were analyzed and compared. Testing results indicate that the usage of edge-curled chord members effectively enhances both the bearing capacity and stiffness of the truss. The main failure mode observed for both specimens was local buckling of the upper chord in the mid-span. No deformation or shear failure occurred for the self-tapping screws at the chord-splice joints, and none of the web members exhibited significant deformation either. This demonstrates that the load-bearing behavior of the truss specimens is primarily governed by the compressive bearing capacity of the upper chord and its splices. The proposed light-steel truss offers advantages including a high degree of standardization, improved load-bearing capacity, and convenient installation. Full article

In this study, we investigate the bearing capacity characteristics and controlling mechanisms of coastal beach sand in Quanzhou Bay, Fujian Province, China. The results provide support for coastal engineering construction and vehicle trafficability assessment in beach areas, while field sampling, laboratory static plate load tests, and data-based modeling were conducted to examine the effects of moisture content, particle size distribution, and relative density on the bearing behavior of beach sand. In total, 52 groups of static load tests were performed, with the results showing that relative density is the dominant controllable factor affecting the bearing capacity of coastal beach sand. When the relative density increased from 40% to 65%, the ultimate load increased by 80%, and the deformation modulus increased by 139.9%. The optimal relative density range was approximately 52–65%, and the improved particle size distribution enhanced bearing performance. The ultimate load of well-graded sand was 60% higher than that of poorly graded sand, and moisture content showed a threshold effect, with the best mechanical performance occurring at a moisture content of about 7%, whereas excessive moisture content significantly reduced the bearing capacity. Under natural conditions, the proportional limit load of medium-dense coastal beach sand in Quanzhou Bay was approximately 200 kPa, the ultimate load was 250 kPa, and the characteristic value of bearing capacity was 125 kPa, while the dominant failure mode was general shear failure. A semi-empirical bearing capacity model was also developed; its average relative error was 10.35%, indicating that it has both physical meaning and engineering applicability. The findings provide a reference for foundation design evaluation in Quanzhou Bay and similar coastal beach areas. Full article

To investigate the dynamic response and damage mechanisms of reinforced concrete (RC) shear walls subjected to the combined action of contact explosions and axial compression, three contact explosion tests were conducted on RC shear walls with a constant axial compression ratio of 0.15 and different charge masses. A self-balancing axial loading device was designed to maintain a continuous and stable axial force during the blast tests. Finite element models were subsequently established using LS-DYNA. The fluid structure interaction (FSI) method was adopted, and the numerical models were validated in terms of crater dimensions and failure modes. Based on the validated model, a numerical parametric study was further conducted to examine the influence of axial compression ratios ranging from 0 to 0.4. The results indicate that the axial compression ratio has a non-monotonic effect on the local damage dimensions of RC shear walls. The wall exhibited a relatively smaller crater area and a more favourable local damage response when the axial compression ratio was approximately 0.2. As the charge mass increased, the failure mode progressively changed from cratering and spalling to perforation and punching shear failure. Based on the experimental and numerical results, empirical relationships were proposed to correlate the crater diameters on the front and rear faces with the charge mass and axial compression ratio. These relationships enable the rapid estimation of local damage dimensions using a limited number of input parameters. Full article

The addition of sulfoaluminate cement (SAC) to ultra-high-performance concrete (UHPC) enables sustainable high-speed construction due to the high 7-day strength without thermal curing. The fast hydration of SAC, however, endangers the admixture efficacy, which may compromise the structural integrity of the infrastructure components. This study investigates the effect of the physical form of polycarboxylate ether (PCE) superplasticizers on the performance of UHPC with the incorporation of SAC in ambient conditions. A paired experimental design of 32 mixtures compared liquid superplasticizers (LSPs) and powder superplasticizers (PSPs) in various binder compositions (OPC/SAC of 1/4–4/1) and water-to-binder ratios (0.18–0.21) at a constant dosage of admixtures of 1% except where w/b 0.18 (1.5% superplasticizers and 1% retarders were used). Findings indicate that LSPs enhance workability and compressive strength by 45% and 10.03%, respectively. The underlying mechanism is explained by comprehensive microstructural characterization through the use of Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) spectroscopy. SEM study showed a 23% decrease in porosity, and XRD patterns showed the increased formation of amorphous C-S-H gel for LSPs. The higher levels of Al³⁺ incorporated into the gel structure (C-A-S-H) of the liquid forms was also verified by FTIR spectra. Mechanically, the research reveals one of the kinetic mismatches, where the rate of SAC hydration is greater than the rate of powder dissolution, which leads to a failure to fully disperse and shear-controlled failures. LSPs, in contrast, make it possible to disperse particles immediately, so the matrices become more dense and shift to axial failure. These results provide practical guidelines to infrastructure engineers to use liquid superplasticizer in SAC-based systems in order to achieve sustainability and reliability in terms of performance in precast and fast-track construction projects. Full article